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    Mean (±SD) plasma concentrations of primaquine (PQ) and carboxyprimaquine (CPQ) versus time profiles in healthy Vietnamese subjects (17 men and 17 women) after the last dose of 30 mg primaquine daily for 14 days.

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    Mean (±SD) plasma concentrations of doxycycline versus time profiles in healthy Vietnamese subjects (14 men and 14 women) after the last dose of 100 mg doxycycline daily for 14 days.

  • 1

    World Health Organization, Guidelines for the treatment of malaria. Available at: http://www.who.int/malaria. Accessed June 15, 2009.

  • 2

    Hill DR, Baird JK, Parise ME, Lewis LS, Ryan ET, Magill AJ, 2006. Primaquine: report from CDC expert meeting on malaria chemoprophylaxis I. Am J Trop Med Hyg 75 :402–415.

    • Search Google Scholar
    • Export Citation
  • 3

    Carson PE, 1984. 8-Aminoquinolines. Peters W, Richards WHG, eds. Antimalarial Drugs II. Current Antimalarials and New Drug Developments. Heidelberg: Springer-Verlag, 83–121.

  • 4

    Centers for Disease Control and Prevention, Malaria Prescription Drug Information for the Public. Available at: http://www.cdc.gov/malaria/travel/drugs_public.htm. Accessed June 16, 2009.

  • 5

    Clayman CB, Arnold J, Hockwald RS, Yount EH Jr, Edgcomb JH, Alving AS, 1952. Toxicity of primaquine in Caucasians. J Am Med Assoc 149 :1563–1568.

    • Search Google Scholar
    • Export Citation
  • 6

    Ohrt C, Richie TL, Widjaja H, Shanks GD, Fitriadi J, Fryauff DJ, Handschin J, Tang D, Sandjaja B, Tjitra E, Hadiarso L, Watt G, Wignall FS, 1997. Mefloquine compared with doxycycline for the prophylaxis of malaria in Indonesian soldiers. A randomized, double-blind, placebo-controlled trial. Ann Intern Med 126 :963–972.

    • Search Google Scholar
    • Export Citation
  • 7

    Pang LW, Limsomwong N, Boudreau EF, Singharaj P, 1987. Doxycycline prophylaxis for falciparum malaria. Lancet 1 :1161–1164.

  • 8

    Rieckmann KH, Powell RD, McNamara JV, Willerson D Jr, Lass L, Frischer H, Carson PE, 1971. Effects of tetracycline against chloroquine-resistant and chloroquine-sensitive Plasmodium falciparum. Am J Trop Med Hyg 20 :811–815.

    • Search Google Scholar
    • Export Citation
  • 9

    Shmuklarsky MJ, Boudreau EF, Pang LW, Smith JI, Schneider I, Fleckenstein L, Abdelrahim MM, Canfield CJ, Schuster B, 1994. Failure of doxycycline as a causal prophylactic agent against Plasmodium falciparum malaria in healthy nonimmune volunteers. Ann Intern Med 120 :294–299.

    • Search Google Scholar
    • Export Citation
  • 10

    Looareesuwan S, Viravan C, Vanijanonta S, Wilairatana P, Charoenlarp P, Canfield CJ, Kyle DE, 1994. Randomized trial of mefloquine-doxycycline, and artesunate-doxycycline for treatment of acute uncomplicated falciparum malaria. Am J Trop Med Hyg 50 :784–789.

    • Search Google Scholar
    • Export Citation
  • 11

    Wyler DJ, 1993. Malaria chemoprophylaxis for the traveler. N Engl J Med 329 :31–37.

  • 12

    Elmes NJ, Bennett SM, Abdalla H, Carthew TL, Edstein MD, 2006. Lack of sex effect on the pharmacokinetics of primaquine. Am J Trop Med Hyg 74 :951–952.

    • Search Google Scholar
    • Export Citation
  • 13

    Cuong BT, Binh VQ, Dai B, Duy DN, Lovell CM, Rieckmann KH, Edstein MD, 2006. Does gender, food or grapefruit juice alter the pharmacokinetics of primaquine in healthy subjects? Br J Clin Pharmacol 61 :682–689.

    • Search Google Scholar
    • Export Citation
  • 14

    Mihaly GW, Ward SA, Edwards G, Nicholl DD, Orme ML, Breckenridge AM, 1985. Pharmacokinetics of primaquine in man. I. Studies of the absolute bioavailability and effects of dose size. Br J Clin Pharmacol 19 :745–750.

    • Search Google Scholar
    • Export Citation
  • 15

    Mihaly GW, Ward SA, Edwards G, Orme ML, Breckenridge AM, 1984. Pharmacokinetics of primaquine in man: identification of the carboxylic acid derivative as a major plasma metabolite. Br J Clin Pharmacol 17 :441–446.

    • Search Google Scholar
    • Export Citation
  • 16

    Ward SA, Mihaly GW, Edwards G, Looareesuwan S, Phillips RE, Chanthavanich P, Warrell DA, Orme ML, Breckenridge AM, 1985. Pharmacokinetics of primaquine in man. II. Comparison of acute vs chronic dosage in Thai subjects. Br J Clin Pharmacol 19 :751–755.

    • Search Google Scholar
    • Export Citation
  • 17

    Kim YR, Kuh HJ, Kim MY, Kim YS, Chung WC, Kim SI, Kang MW, 2004. Pharmacokinetics of primaquine and carboxyprimaquine in Korean patients with vivax malaria. Arch Pharm Res 27 :576–580.

    • Search Google Scholar
    • Export Citation
  • 18

    Singhasivanon V, Sabcharoen A, Attanath P, Chongsuphajaisiddhi T, Diquet B, Turk P, 1991. Pharmacokinetics of primaquine in healthy volunteers. Southeast Asian J Trop Med Public Health 22 :527–533.

    • Search Google Scholar
    • Export Citation
  • 19

    Brueckner RP, Ohrt C, Baird K, Milhous WK, 2000. 8-aminoquinolines. Rosenthal PJ, ed. Antimalarial Chemotherapy: Mechanisms of Action, Resistance, and New Directions in Drug Discovery. Totowa, NJ: Humana Press, 123–151.

  • 20

    Agwuh KN, MacGowan A, 2006. Pharmacokinetics and pharmacodynamics of the tetracyclines including glycylcyclines. J Antimicrob Chemother 58 :256–265.

    • Search Google Scholar
    • Export Citation
  • 21

    Saivin S, Houin G, 1988. Clinical pharmacokinetics of doxycycline and minocycline. Clin Pharmacokinet 15 :355–366.

  • 22

    Edstein MD, Baird JK, Fryauff DJ, Ling J, Charles BG, Population pharmacokinetics of primaquine used daily by Javanese transmigrants for malaria prophylaxis. 51st Annual Meeting of American Society of Tropical Medicine and Hygiene, Denver, CO, November 10–14, 2002.

  • 23

    Bocker R, Muhlberg W, Platt D, Estler CJ, 1986. Serum level, half-life and apparent volume of distribution of doxycycline in geriatric patients. Eur J Clin Pharmacol 30 :105–108.

    • Search Google Scholar
    • Export Citation
  • 24

    CollaGenex Pharmaceuticals, 1997. NDA, New Drug Application 50-744. Submitted by CollaGenex Pharmaceuticals for Periostat.

  • 25

    Baird JK, Lacy MD, Basri H, Barcus MJ, Maguire JD, Bangs MJ, Gramzinski R, Sismadi P, Krisin, Ling J, Wiady I, Kusumaningsih M, Jones TR, Fryauff DJ, Hoffman SL, and the United States Naval Medical Research Unit 2 Clinical Trials Team, 2001. Randomized, parallel placebo-controlled trial of primaquine for malaria prophylaxis in Papua, Indonesia. Clin Infect Dis 33 :1990–1997.

    • Search Google Scholar
    • Export Citation
  • 26

    Harris RZ, Benet LZ, Schwartz JB, 1995. Gender effects in pharmacokinetics and pharmacodynamics. Drugs 50 :222–239.

  • 27

    Meibohm B, Beierle I, Derendorf H, 2002. How important are gender differences in pharmacokinetics? Clin Pharmacokinet 41 :329–342.

  • 28

    Gandhi M, Aweeka F, Greenblatt RM, Blaschke TF, 2004. Sex differences in pharmacokinetics and pharmacodynamics. Annu Rev Pharmacol Toxicol 44 :499–523.

    • Search Google Scholar
    • Export Citation
  • 29

    Kennedy E, Frischer H, 1990. Distribution of primaquine in human blood: drug-binding to alpha 1-glycoprotein. J Lab Clin Med 116 :871–878.

    • Search Google Scholar
    • Export Citation
  • 30

    Routledge PA, Stargel WW, Kitchell BB, Barchowsky A, Shand DG, 1981. Sex-related differences in the plasma protein binding of lignocaine and diazepam. Br J Clin Pharmacol 11 :245–250.

    • Search Google Scholar
    • Export Citation
  • 31

    Li XQ, Bjorkman A, Andersson TB, Gustafsson LL, Masimirembwa CM, 2003. Identification of human cytochrome P(450)s that metabolise anti-parasitic drugs and predictions of in vivo drug hepatic clearance from in vitro data. Eur J Clin Pharmacol 59 :429–442.

    • Search Google Scholar
    • Export Citation
  • 32

    Bangchang KN, Karbwang J, Back DJ, 1992. Primaquine metabolism by human liver microsomes: effect of other antimalarial drugs. Biochem Pharmacol 44 :587–590.

    • Search Google Scholar
    • Export Citation
  • 33

    Relling MV, Lin JS, Ayers GD, Evans WE, 1992. Racial and gender differences in N-acetyltransferase, xanthine oxidase, and CYP1A2 activities. Clin Pharmacol Ther 52 :643–658.

    • Search Google Scholar
    • Export Citation
  • 34

    Lane HY, Chang YC, Chang WH, Lin SK, Tseng YT, Jann MW, 1999. Effects of gender and age on plasma levels of clozapine and its metabolites: analyzed by critical statistics. J Clin Psychiatry 60 :36–40.

    • Search Google Scholar
    • Export Citation
  • 35

    Faber MS, Fuhr U, 2004. Time response of cytochrome P450 1A2 activity on cessation of heavy smoking. Clin Pharmacol Ther 76 :178–184.

  • 36

    Rademaker M, 2001. Do women have more adverse drug reactions? Am J Clin Dermatol 2 :349–351.

  • 37

    Baird JK, Rieckmann KH, 2003. Can primaquine therapy for vivax malaria be improved? Trends Parasitol 19 :115–120.

  • 38

    Baird JK, Fryauff DJ, Hoffman SL, 2003. Primaquine for prevention of malaria in travelers. Clin Infect Dis 37 :1659–1667.

  • 39

    Baird JK, Hoffman SL, 2004. Primaquine therapy for malaria. Clin Infect Dis 39 :1336–1345.

  • 40

    Nasveld P, Kitchener S, Edstein M, Rieckmann K, 2002. Comparison of tafenoquine (WR238605) and primaquine in the post-exposure (terminal) prophylaxis of vivax malaria in Australian Defence Force personnel. Trans R Soc Trop Med Hyg 96 :683–684.

    • Search Google Scholar
    • Export Citation

 

 

 

 

 

Sex Affects the Steady-State Pharmacokinetics of Primaquine but Not Doxycycline in Healthy Subjects

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  • 1 Department of Infectious Disease, Central Military Hospital, Hanoi, Vietnam, Department of Malaria, Military Institute of Hygiene and Epidemiology, Hanoi, Vietnam; Department of Drug Evaluation, Australian Army Malaria Institute, Brisbane, Queensland, Australia

We evaluated whether sex affects the steady-state pharmacokinetics of the antimalarial drugs, primaquine and doxycycline, in healthy subjects. Seventeen male and 17 female healthy Vietnamese subjects were administered 30 mg (base) of primaquine daily for 14 days. After a 2-week washout period, 14 male and 14 female subjects were administered 100 mg (base) of doxycycline daily for 14 days. Women had significantly higher median values of Cmax (212 versus 122 ng/mL, P< 0.001) and AUC0–24 (1,909 versus 917 ng · h/mL, P < 0.001) of primaquine compared with men. Other than a longer tmax in women, no sex-related differences were seen in the pharmacokinetics of doxycycline. The primaquine pharmacokinetic data suggest that women have increased exposure to primaquine, which may put them at increased risk for toxicity when administered the same maintenance dose as men. The similar pharmacokinetics of doxycycline between the two sexes justifies the same maintenance dose.

INTRODUCTION

Primaquine, an 8-aminoquinoline, is the only drug available for the radical cure or post-exposure prophylaxis of both Plasmodium vivax and P. ovale malaria. To combat the spread of primaquine-tolerant P. vivax strains in Southeast Asia, Oceania, and South America, the World Health Organization “International Travel and Health” 2005 and others recommend an adult dose of 30 mg primaquine daily for 14 days. 1,2 Primaquine is also a causal prophylactic agent against the pre-erythrocytic forms of the four human species of malaria3 and under special situations has been recommended as a chemo-prophylactic agent by the US Centers for Disease Control and Prevention.4 Clinically important adverse events of primaquine use include gastrointestinal (GI) disturbances such as nausea, abdominal pain, diarrhea and vomiting, and meth-emoglobinemia. It is contraindicated in pregnant and lactating females and can lead to acute intravascular hemolysis in glucose-6-phosphate dehydrogenase (G6PD)-deficient individuals. The frequency of adverse events seems to increase as the primaquine dose increases,5 suggesting a relationship with plasma drug concentrations.

Doxycycline, an antibiotic, given daily at 100 mg has been shown to be an effective chemoprophylactic agent in suppressing blood stages of P. falciparum and P. vivax malaria.6,7 There is also evidence that doxycycline possesses partial causal prophylactic activity against falciparum malaria.79 In combination with mefloquine, doxycycline at a dose of 200 mg once daily for 7 days is a highly effective partner drug in the treatment of multidrug-resistant P. falciparum malaria.10 Although doxycycline is generally well tolerated, it may cause GI disturbances, photosensitivity, candidal vaginitis, and dizziness. 11 Doxycycline is contraindicated in young children because of the staining of teeth and bones and in pregnant females.

The pharmacokinetics of primaquine have been well characterized in healthy subjects and malaria patients after single and multiple oral dosing. 1218 Primaquine is rapidly absorbed, reaching peak concentrations within 2–3 hours after dosing. Its plasma elimination half-life is ~7 hours. It is a low to intermediate clearance drug with extensive tissue distribution. The metabolism of primaquine and its induced hemolysis is poorly understood. Primaquine is extensively metabolized to inert carboxyprimaquine, the major plasma metabolite, which undergoes further biotransformation to unknown metabolites that are probably more toxic than the parent compound. With the exception of carboxyprimaquine, the identification of other metabolites in humans has been difficult to pursue because the expected aminophenol metabolites and their amphoteric nature are unstable. 19 Similar to primaquine, the pharmaco-kinetics of doxycycline has been extensively studied after single oral doses, but limited data are available on its disposition after multiple dosing. 20,21 Oral bioavailability of doxycycline is high at ~95%, with peak concentrations being reached at 2–3 hours after dosing. Doxycycline has a plasma elimination half-life ranging from 12 to 25 hours, and it is widely distributed to body tissues. It is primarily excreted unchanged by both the renal and biliary routes, and no metabolites have been found in humans.

Despite considerable clinical experience with primaquine and doxycycline for malaria chemotherapy, there is limited information on the pharmacokinetics of both drugs between sexes. Recently, the pharmacokinetics of primaquine were found to be similar in male and female healthy subjects of Caucasian 12 and Asian13 ethnicity after a single oral dose of 30 mg primaquine. In both ethnic groups, plasma primaquine concentrations tended to be marginally higher in women compared with men. However, after multiple dosing to Thai 18 and Indonesian subjects, 22 the oral clearance of primaquine was found to be markedly slower in women compared with men, which does not seem to be solely related to weight-based differences. Unlike primaquine, there is a paucity of information on the pharmacokinetics of doxycycline between sexes. In geriatric patients (9 men and 11 women), sex did not seem to alter the pharmacokinetics of doxycycline. 23 However, in a bioequivalence study comparing two different formulations of doxycycline hyclate (Periostat and Vibramycin; 25 men and 17 women), peak plasma doxycycline concentrations were 30–38% higher in women compared with men after normalizing for body weight. 24

The aim of this study was to investigate the influence of sex on the steady-state pharmacokinetics of primaquine and doxycycline in healthy Vietnamese subjects and, if sex-related differences exist, is there a need to adjust the maintenance dose of the two antimalarial drugs.

MATERIALS AND METHODS

Subjects and study site.

Thirty-four healthy Vietnamese subjects (17 men: mean [±SD] age: 25.4 [7.5] years; weight, 60.3 [6.1] kg; body mass index, 20.8 [1.5] kg/m2; 17 women: mean age: 30.0 [12.0] years; weight, 50.4 [6.6] kg; body mass index, 21.0 [2.9] kg/m2) participated in the primaquine study, and of these, 14 men and 14 women volunteered for the doxycycline study. The subjects were judged healthy based on medical history, clinical examination, and routine laboratory testing (hematology and biochemistry). Subjects were not allowed to drink alcohol or to take other medications during the 2 weeks of primaquine or doxycycline administration. The female subjects were not pregnant or lactating, and all subjects were classified as G6PD normal using the Sigma Diagnostic G6PD Kit. The Review and Scientific Board of Central Military Hospital 108 and the Australian Defense Human Research Ethics Committee (ADHREC 329/03) gave ethical approval for the study, and the subjects gave written informed consent before entering the trial.

Sample size, study design, and drug administration.

Based on the Indonesian study, 22 we expected a 48% difference in the plasma clearance of primaquine between men and women. Assuming a SD of the difference of 45%, a power of 80%, and a significance level of 0.05, we needed 15 men and 15 women to detect this major difference. The study participants received primaquine followed by a washout period of 2 weeks before receiving doxycycline. This sequential administration of drug was not randomized because no order effect was to be expected. The selection of 2 weeks of medication was based on the standard treatment period of 14 days for primaquine use as a radical cure agent or post-exposure prophylaxis against P. vivax infections.2 Ohrt and others6 also observed that most adverse events associated with daily doxycycline administration were reported within the first 14 days of starting doxycycline for malaria prophylaxis.

For the primaquine study, each subject was administered a single oral dose of 30 mg base of primaquine (four 13.2-mg primaquine phosphate tablets; Danapha, Da Nang, Vietnam) daily for 14 days. For the doxycycline study, each subject was administered a single oral dose of 100 mg base of doxycycline (115 mg doxycycline hyclate per capsule; Servidoxyne, Imex-pharm, Austria) daily for 14 days. Drug was administered within 15 minutes of having a standard Vietnamese breakfast of rice, noodles, and meat. The drug was also administered with 200 mL of water. The administration of medication was observed and recorded by one of the investigators. All participants were also asked daily the non-leading question “How do you feel since you took your last primaquine tablet or doxycycline capsule?” If a subject responded affirmatively with symptoms, the timing and intensity of the complaint was recorded. The severity of the adverse events were graded on a scale of 1–3 as follows: Grade 1, mild but not affecting daily activities; Grade 2, moderate, with some interference with daily activities; Grade 3, severe, with prevention of daily duties.

Blood sampling.

Venous blood samples were collected through an indwelling cannula inserted into a forearm vein and kept patent with heparinized saline. Blood samples (7 mL) were collected in lithium heparin tubes within 0.5 hours (baseline) before the last primaquine or doxycycline administration and at 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, and 12 hours after drug administration. Subsequent blood samples were collected by venepuncture at 21 (for primaquine only), 24, 48, 72, and 96 hours after dosing. All blood samples were centrifuged at 1,400g for 15 minutes, and the separated plasma samples were stored at −80°C before transport to Australia on dry ice for drug analysis, which was within 12 months of collection.

Drug analysis.

Plasma primaquine and carboxyprimaquine concentrations were measured by high-performance liquid chromatographic (HPLC) methods described by Mihaly and others, 15 with minor modifications. 13 The limit of quantification (LOQ) of primaquine was 5 ng/mL using 0.5 mL of plasma. The limit of detection of primaquine was 2 ng/mL, with a signal-to-noise ratio of 3 to 1. For carboxyprimaquine, the LOQ was 25 ng/mL using 0.25 mL of plasma. The interday assay coefficients of variation (CV%s) for the measurement of primaquine at 5, 50, and 200 ng/mL were 18.7%, 4.4%, and 1.3% (N = 11), respectively. The interday assay CV%s for carboxyprimaquine at 25, 250, and 1,000 ng/mL were 15.6%, 6.6%, and 2.3% (N = 27), respectively. The inaccuracy of the method at 50 ng/mL was 2% for both primaquine (N = 11) and carboxyprimaquine (N = 27).

Plasma doxycycline concentrations were measured by HPLC using a Waters 515 HPLC pump, a Waters 2487 Absorbance UV/VIS Detector set at 350 nm, and a Waters 717 Autosampler. The column used was a Zorbax SB-CN cartridge (150 × 4.6 mm, US SJOO8336; Agilent Technologies, Santa Clara, CA) with a Zorbax SB-CN USSM 002654 guard column. The mobile phase consisted of acetonitrile:0.1% trifluoroacetic (30:70, vol/vol), and the flow rate was 0.6 mL/min. Samples were prepared for analysis as follows: 0.25 mL of plasma was added to a microcentrifuge vial containing the internal standard of 0.05 mL of 5 μg/mL demeclocycline hydrochloride (D-6140, Lot 31H0410; Sigma-Aldrich, St. Louis, MO) and 0.2 mL of 0.1 mol/L phosphoric acid. The contents were vortexed for 5 seconds and centrifuged at 14,000g for 5 minutes. The supernatant was transferred to a Vac Elute system containing a Waters ‘OASIS’ SPE cartridge, which had been activated with 1 mL of methanol. The SPE cartridge was washed with 1 mL of distilled water to waste, and the supernatant was layered onto the SPE cartridge and run to waste. The SPE cartridge was washed with 5% methanol to waste. The Vac Elute system was set to collect, and the sample was eluted using 100% methanol. The methanolic sample was evaporate to dryness using instrument grade air at 40°C and reconstituted with 0.2 mL of mobile phase. Fifty microliters was injected onto the HPLC column. The retention times for demeclocycline and doxycycline were at ~6 and 8 minutes, respectively. The LOQ of doxycycline was 25 ng/mL using 0.25 mL of plasma. The interday assay CV% for the measurement of doxycycline (D9891, Lot 55F0201; Sigma-Aldrich) at 50, 200, 1,000, and 4,000 ng/mL were 11.8%, 8.9%. 6.9%, and 3.4% (N = 15), respectively. The inaccuracy of the method at 200 and 4,000 ng/mL was 2% and 1%, respectively.

Pharmacokinetic analysis.

Maximum plasma drug concentration (Cmax), minimum drug concentration (Cmin), and time to maximum concentration (tmax) were obtained from the plasma drug concentration-time curve. The elimination rate constant (kel) was estimated by least-squares regression analysis of the post absorption and distribution log plasma drug concentration-time data using at least four points. The elimination half-life (t1/2) was calculated from the ratio ln2/kel. The area under the drug concentration-time curve from zero to 24 hours [AUC (0, 24)] was calculated by the mixed log-linear trapezoidal rule from the beginning of the last dose to 24 hours after the final dose. The oral clearance (CLss/F) at steady state was expressed as a function of bioavailability (F) and calculated as dose/AUC (0, 24), with complete systemic bioavailability assumed (F = 1). The apparent steady-state volume of distribution (Vss/F) was calculated as dose/(AUC × kel). Both CLss/F and Vss/F were normalized to body weight. The metabolic ratio of the biotransformation of primaquine to carboxyprimaquine was calculated by dividing the AUC(0, 24) of carboxyprimaquine by the AUC (0, 24) of primaquine. The pharmacokinetic parameters were calculated for each subject.

Statistical analysis.

Data were summarized as mean ± SD or median (interquartile range [IQR]) as appropriate. Statistical comparison of pharmacokinetic parameters between men and women were made using the Mann-Whitney U test (SigmaStat version 3.0; Jandel Scientific, San Rafael, CA). The Cmax and AUC values were log-transformed before comparison by statistical analysis, with estimated geometric mean ratio(GMR) and the 90% confidence interval (CI) for the pharmacokinetic parameters. Data were accepted as significant using the 5% significance level.

RESULTS

Primaquine and carboxyprimaquine.

Four males reported mild GI disturbances that were probably associated with primaquine administration: three with abdominal pain (two with a single episode and one with a single episode over 3 consecutive days) and one with both abdominal pain and diarrhea (a single episode). Four females reported mild adverse events during their 14 days of medication. Of these, one subject had persistent diarrhea from Days 2 to 12 (two to six episodes each day) after commencement of primaquine treatment. She also had an itchy rash on her arm and body from Day 2, which persisted for 4 days. Of the other women, one had an arm rash (only reported once), one had an arm and body rash (only reported once), and one had a single episode of abdominal pain and diarrhea. No subject withdrew from the study because of adverse events experienced during the 14-day course of primaquine.

Of the 17 men, 9 were non-smokers and 8 were smokers (6–15 cigarettes/day). None of the women smoked, and none were on contraceptive medication. There were no significant differences (P > 0.05) in the pharmacokinetics of primaquine between male smokers and male non-smokers for the following parameters (median values), respectively: Cmax of 122 and 124 ng/mL, AUC (0, 24) of 806 and 1,027 ng · h/mL, t1/2 of 5.6 and 6.2 hours, Vss/F of 5.51 and 3.94 L/kg, and CLss/F of 0.65 and 0.51 L/h/kg.

The mean plasma concentration-time curves of primaquine and carboxyprimaquine in male and female subjects after the last daily dose of 30 mg primaquine after 14 consecutive days of medication are shown in Figure 1. The pharmacokinetic parameters of primaquine and carboxyprimaquine in men and women are summarized in Table 1. The primaquine and carboxyprimaquine concentrations were markedly higher in women compare with men. Immediately before the last dose, all female subjects had measurable concentrations of primaquine, with a median Cmin of 18 ng/mL. In contrast to the women, only 12 men had measurable primaquine concentrations before the last dose, with a median Cmin of 6 ng/mL. Steady-state maximum concentration (Cmax) and exposure [AUC (0, 24)] to primaquine was ~1.7- and 2.1-fold higher, respectively, in women compared with men. The female to male GMR was 1.75 (90% CI, 1.40, 2.18) for Cmax and 2.20 (90% CI, 1.82, 2.67) for AUC (0, 24). The tmax and t1/2 of primaquine were comparable between the two sexes at ~2.5 and 6.5 hours, respectively. Women had a significantly smaller Vss/F (3.42 versus 4.59 L/kg) and a slower CLss/F (0.31 versus 0.55 L/h/kg) of primaquine compared with men.

Similar to primaquine, women had significantly higher steady-state Cmax and Cmin carboxyprimaquine concentrations compared with men. The female to male GMR was 1.26 (90% CI, 1.11, 1.42) for Cmax and 1.28 (90% CI, 1.15, 1.43) for AUC (0, 24). The median t1/2 of carboxyprimaquine was 15.8 hours for men and 16.9 hours for women. The median (IQR) metabolic AUC ratio of carboxyprimaquine to primaquine covering 24 hours after the last dose was 41.1 (38.1–53.1) in men and 26.2 (20.2–35.5) in women.

Doxycycline.

None of the subjects reported adverse events on doxycycline. There were no significant differences (P > 0.05) in the pharmacokinetics of doxycycline between male smokers and male non-smokers for the following parameters (median values), respectively: Cmax of 3,645 and 2,662 ng/mL, AUC (0, 24) of 32,874 and 26,239 ng · h/mL, t1/2 of 17.9 and 24.5 hours, Vss/F of 1,501 and 2,060 mL/kg, and CLss/F of 54.32 and 63.52 mL/h/kg. Mean plasma concentration-time curves of doxycycline in male and female subjects after the last daily dose of 100 mg doxycycline after 14 consecutive days of medication are shown in Figure 2, with the pharmacokinetic properties of doxycycline summarized in Table 2. Plasma doxycycline concentrations were comparable between males and females, with median Cmax and Cmin values of ~3,150 and 710 ng/mL, respectively. The female to male GMR was 0.93 (90% CI, 0.71, 1.22) for the Cmax and 1.16 (90% CI, 0.91, 1.47) for AUC (0, 24). Females had a statistically longer tmax compared with males (3.0 versus 1.5 hours). The median t1/2 of doxycycline was 22.4 hours in men and 18.5 hours in women. Although women tended to have higher doxycycline concentrations compared with men, when adjusted for weight, there were no statistical differences in the CLss/F and Vss/F of doxycycline between men and women.

DISCUSSION

The first indication that the steady-state pharmacokinetics of primaquine may be different between men and women came from a small study in Thai subjects (four men and four women), which showed an ~2-fold higher whole blood Cmax and AUC values of primaquine in women compared with men. 18 In 92 (56 men and 36 women) Indonesian subjects, who were participating in a prophylactic trial of 30 mg primaquine daily for 20 weeks, 25 population pharmacokinetic analysis of sparse primaquine concentration-time data showed women to have a smaller mean Vss/F (3.45 versus 4.53 L/kg) and a slower mean CLss/F (0.31 versus 0.46 L/h/kg) compared with men, suggesting sex-related differences in the kinetics of primaquine. 22 This study using rich sampling and conventional non-compartmental pharmacokinetic analysis further corroborates that women have a smaller Vss/F (3.42 versus 4.59 L/kg, P = 0.03) and a slower CLss/F (0.31 versus 0.55 L/h/kg, P < 0.001) of primaquine compared with men after multiple dosing of primaquine.

A number of reviews have examined physiological and molecular differences between sexes that may cause sex-related differences in the pharmacokinetics and pharmacodynamics of drugs. 2628 For example, women tend to have a lower body weight, a higher percentage of body fat, lower plasma volume, higher rates of metabolism for cytochrome P450 (CYP) 3A4 substrates, and lower hepatic activity for the drug efflux transporter P-glycoprotein than men. The lack of sex-related differences in the pharmacokinetics of primaquine after a single oral dose 12,13 may have been caused by insufficient exposure time for the physiological and molecular differences between the sexes to alter the disposition of the drug. The cause of the sex-related differences in primaquine pharmacokinetics observed at steady-state in this study is unclear.

A potential source of sex-related differences in the pharmacokinetics of drugs is differences in tissue and plasma protein binding between sexes. 2628 Because primaquine binds predominately to α1-acid glycoproteins 29 and women tend to have slightly lower plasma levels of the acute protein than men, 30 it is unlikely that the small differences in unbound primaquine between the sexes would markedly contribute to the large pharmacokinetic differences of the drug observed in this study. Furthermore, a reduction in α1-acid glycoproteins is expected to increase unbound primaquine, with an increase in erythrocytic concentrations of primaquine and a corresponding reduction in plasma concentrations, 29 which is contrary to the higher plasma concentrations measured in the women in this study.

Sex differences in hepatic drug metabolism seems to play a major role in sex-related pharmacokinetic differences for a number of drugs. Based on in vitro human microsomal studies, primaquine is mainly metabolized by CYP1A2 with contribution from CYP2D6 31 and possibly CYP3A4. 13,32 Sex seems to influence CYP1A2 but not CYP2D6-mediated metabolism. 26,27 Women have lower CYP1A2 activity than men, 33 and this reduced enzymatic activity may be responsible for the higher plasma primaquine concentrations and lower clearance of the drug in women compared with men. Sex-related differences have also been reported for the disposition of other drugs that are mainly metabolized by CYP1A2 such as clozapine in the treatment of schizophrenic patients, with significantly higher concentrations (35%) of clozapine in women compared with men. 34 The lower CYP1A2 activity in women would explain the significantly lower median metabolic ratio of carboxyprimaquine to primaquine in women compared with men [carboxyprimaquine AUC (0, 24)/ primaquine AUC (0, 24): 26.2 versus 41.1] This study also showed that cigarette smoking, which causes CYP1A2 induction and is involved in the metabolism of many drugs, 35 does not seem to significantly alter the pharmacokinetics of primaquine.

Sex-related disparities in the pharmacokinetics and pharmacodynamics of a number of drugs have been considered as important determinants for the higher reporting of adverse drug reactions in women compared with men. Overall, female patients experience more adverse drug reactions to medications than male patients by a factor of 1.5- to 1.7-fold. 36 The clinical implications of the higher bioavailability of primaquine in women compared with men are limited. In review articles on the efficacy and tolerability of primaquine used for chemoprophylaxis or radical cure, no mention is made of sex differences in response to the medication. 2,3739 However, in a small study of Australian military personnel (191 men and 23 women) deploying out of a malaria-endemic area, a higher prevalence of GI disturbances was reported in women compared with men after post-exposure prophylaxis with primaquine. 40 It is quite possible that the higher intolerance to primaquine observed in the Australian women may be associated with higher primaquine concentrations in the women compared with men. However, in this study, men tended to report more drug-associated GI disturbances than women (24% versus 12%), but of these subjects, it was a female participant who reported the worst GI experience on primaquine, with persistent diarrhea for 10 days of the 14-day course. Noteworthy, her primaquine and carboxyprimaquine concentrations were not markedly different from the other women. Further studies of primaquine pharmacokinetic–pharmacodynamic inter-relationships are warranted to determine whether the pharmacokinetic differences observed in this study necessitates a maintenance dose conversion factor for women.

In contrast to primaquine, with the exception of tmax, no sex-related differences were observed in the steady-state pharmacokinetics of doxycycline in the Vietnamese subjects. The steady-state Cmax t1/2 and of doxycycline in this study were comparable to those reported by Shmuklarsky and others9 in healthy male Caucasian subjects (mean Cmax of ~3,400 ng/mL and t1/2 of 20.8 hours) who were protected participants of a mosquito challenge study for the causal prophylactic assessment of doxycycline. However, the protected participants had a higher steady-state minimum concentration (1,022 versus 720 ng/mL), a smaller apparent volume of distribution (982 versus 1,835 mL/kg), and a slower plasma oral clearance (37.2 versus 56.4 mL/h/kg) of doxycycline compared with the Vietnamese male subjects, which may suggest ethnic differences in the disposition of doxycycline. Unlike the findings from a bioequivalence study of two formulations of doxycycline, 24 we did not observe a difference in the Cmax of doxycycline between men and women. Based on the similar pharmacokinetics of doxycycline in men and women, the same dose regimen of doxycycline is recommended for both sexes.

In conclusion, women have a smaller apparent volume of distribution and a slower oral clearance of primaquine compared with men after multiple dosing, leading to higher maximum plasma concentrations and increased drug exposure. The increased exposure to primaquine may put women at increased risk of toxicity when administered the same maintenance dose as men. However, more information on the relationship between primaquine concentrations and the pharmacodynamic response of primaquine is needed in women before an adjustment of the maintenance dose can be recommended. Unlike primaquine, no major sex-related differences were observed in the pharmacokinetics of doxycycline, suggesting that the same maintenance dose can be used for both sexes.

Table 1

Comparison of the median steady-state pharmacokinetics of primaquine and carboxyprimaquine in male and female healthy Vietnamese subjects after 14 daily doses of 30 mg primaquine

Table 1
Table 2

Comparison of the steady-state pharmacokinetics of doxycycline in male and female healthy Vietnamese subjects after 14 daily doses of 100 mg doxycycline

Table 2
Figure 1.
Figure 1.

Mean (±SD) plasma concentrations of primaquine (PQ) and carboxyprimaquine (CPQ) versus time profiles in healthy Vietnamese subjects (17 men and 17 women) after the last dose of 30 mg primaquine daily for 14 days.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 81, 5; 10.4269/ajtmh.2009.09-0214

Figure 2.
Figure 2.

Mean (±SD) plasma concentrations of doxycycline versus time profiles in healthy Vietnamese subjects (14 men and 14 women) after the last dose of 100 mg doxycycline daily for 14 days.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 81, 5; 10.4269/ajtmh.2009.09-0214

*

Address correspondence to Michael D. Edstein, Australian Army Malaria Institute, Enoggera, Brisbane, Queensland 4051, Australia. E-mail: Mike.Edstein@defence.gov.au

Authors’ addresses: Vu Quoc Binh, Nguyen Xuan Thanh and Bui Dai, Department of Malaria, Military Institute of Hygiene and Epidemiology, Hanoi, Vietnam. Nguyen Trong Chinh, Bui Tri Cuong and Nguyen Ngoc Quang, Department of Infectious Disease, Central Military Hospital, Hanoi, Vietnam. Thomas Travers and Michael D. Edstein, Department of Drug Evaluation, Australian Army Malaria Institute, Brisbane, Queensland, Australia.

Acknowledgments: This study was carried out under the auspices of the Vietnam Australia Defence Malaria Project, a defence cooperation between the Vietnam People’s Army and the Australian Defence Force. The authors thank the Vietnam People’s Army Department of Military Medicine for supporting the study and the financial sponsor, the Australian Defence Force Strategic International Policy Division. The authors are most grateful to Dr. Duy Anh for his administrative support at Central Military Hospital 108, Dr. Chu Xuan Anh for assisting in the conduct of the study and the technical excellence of Nguyen Minh Thu and her nursing colleagues at Central Military Hospital 108 for the blood collections. The authors thank Dinh Thi Viet Lien and Hamish Barbour for doxycycline measurements and Dr. Le Ngoc Anh for administrative/logistic support. We are grateful to Professor G. Dennis Shanks and Dr. Bob Cooper for commenting on the manuscript.

Disclaimer: The opinions expressed are those of the authors and do not necessarily reflect those of the Joint Health Command or any extant of the Australian Defence Force health policy.

REFERENCES

  • 1

    World Health Organization, Guidelines for the treatment of malaria. Available at: http://www.who.int/malaria. Accessed June 15, 2009.

  • 2

    Hill DR, Baird JK, Parise ME, Lewis LS, Ryan ET, Magill AJ, 2006. Primaquine: report from CDC expert meeting on malaria chemoprophylaxis I. Am J Trop Med Hyg 75 :402–415.

    • Search Google Scholar
    • Export Citation
  • 3

    Carson PE, 1984. 8-Aminoquinolines. Peters W, Richards WHG, eds. Antimalarial Drugs II. Current Antimalarials and New Drug Developments. Heidelberg: Springer-Verlag, 83–121.

  • 4

    Centers for Disease Control and Prevention, Malaria Prescription Drug Information for the Public. Available at: http://www.cdc.gov/malaria/travel/drugs_public.htm. Accessed June 16, 2009.

  • 5

    Clayman CB, Arnold J, Hockwald RS, Yount EH Jr, Edgcomb JH, Alving AS, 1952. Toxicity of primaquine in Caucasians. J Am Med Assoc 149 :1563–1568.

    • Search Google Scholar
    • Export Citation
  • 6

    Ohrt C, Richie TL, Widjaja H, Shanks GD, Fitriadi J, Fryauff DJ, Handschin J, Tang D, Sandjaja B, Tjitra E, Hadiarso L, Watt G, Wignall FS, 1997. Mefloquine compared with doxycycline for the prophylaxis of malaria in Indonesian soldiers. A randomized, double-blind, placebo-controlled trial. Ann Intern Med 126 :963–972.

    • Search Google Scholar
    • Export Citation
  • 7

    Pang LW, Limsomwong N, Boudreau EF, Singharaj P, 1987. Doxycycline prophylaxis for falciparum malaria. Lancet 1 :1161–1164.

  • 8

    Rieckmann KH, Powell RD, McNamara JV, Willerson D Jr, Lass L, Frischer H, Carson PE, 1971. Effects of tetracycline against chloroquine-resistant and chloroquine-sensitive Plasmodium falciparum. Am J Trop Med Hyg 20 :811–815.

    • Search Google Scholar
    • Export Citation
  • 9

    Shmuklarsky MJ, Boudreau EF, Pang LW, Smith JI, Schneider I, Fleckenstein L, Abdelrahim MM, Canfield CJ, Schuster B, 1994. Failure of doxycycline as a causal prophylactic agent against Plasmodium falciparum malaria in healthy nonimmune volunteers. Ann Intern Med 120 :294–299.

    • Search Google Scholar
    • Export Citation
  • 10

    Looareesuwan S, Viravan C, Vanijanonta S, Wilairatana P, Charoenlarp P, Canfield CJ, Kyle DE, 1994. Randomized trial of mefloquine-doxycycline, and artesunate-doxycycline for treatment of acute uncomplicated falciparum malaria. Am J Trop Med Hyg 50 :784–789.

    • Search Google Scholar
    • Export Citation
  • 11

    Wyler DJ, 1993. Malaria chemoprophylaxis for the traveler. N Engl J Med 329 :31–37.

  • 12

    Elmes NJ, Bennett SM, Abdalla H, Carthew TL, Edstein MD, 2006. Lack of sex effect on the pharmacokinetics of primaquine. Am J Trop Med Hyg 74 :951–952.

    • Search Google Scholar
    • Export Citation
  • 13

    Cuong BT, Binh VQ, Dai B, Duy DN, Lovell CM, Rieckmann KH, Edstein MD, 2006. Does gender, food or grapefruit juice alter the pharmacokinetics of primaquine in healthy subjects? Br J Clin Pharmacol 61 :682–689.

    • Search Google Scholar
    • Export Citation
  • 14

    Mihaly GW, Ward SA, Edwards G, Nicholl DD, Orme ML, Breckenridge AM, 1985. Pharmacokinetics of primaquine in man. I. Studies of the absolute bioavailability and effects of dose size. Br J Clin Pharmacol 19 :745–750.

    • Search Google Scholar
    • Export Citation
  • 15

    Mihaly GW, Ward SA, Edwards G, Orme ML, Breckenridge AM, 1984. Pharmacokinetics of primaquine in man: identification of the carboxylic acid derivative as a major plasma metabolite. Br J Clin Pharmacol 17 :441–446.

    • Search Google Scholar
    • Export Citation
  • 16

    Ward SA, Mihaly GW, Edwards G, Looareesuwan S, Phillips RE, Chanthavanich P, Warrell DA, Orme ML, Breckenridge AM, 1985. Pharmacokinetics of primaquine in man. II. Comparison of acute vs chronic dosage in Thai subjects. Br J Clin Pharmacol 19 :751–755.

    • Search Google Scholar
    • Export Citation
  • 17

    Kim YR, Kuh HJ, Kim MY, Kim YS, Chung WC, Kim SI, Kang MW, 2004. Pharmacokinetics of primaquine and carboxyprimaquine in Korean patients with vivax malaria. Arch Pharm Res 27 :576–580.

    • Search Google Scholar
    • Export Citation
  • 18

    Singhasivanon V, Sabcharoen A, Attanath P, Chongsuphajaisiddhi T, Diquet B, Turk P, 1991. Pharmacokinetics of primaquine in healthy volunteers. Southeast Asian J Trop Med Public Health 22 :527–533.

    • Search Google Scholar
    • Export Citation
  • 19

    Brueckner RP, Ohrt C, Baird K, Milhous WK, 2000. 8-aminoquinolines. Rosenthal PJ, ed. Antimalarial Chemotherapy: Mechanisms of Action, Resistance, and New Directions in Drug Discovery. Totowa, NJ: Humana Press, 123–151.

  • 20

    Agwuh KN, MacGowan A, 2006. Pharmacokinetics and pharmacodynamics of the tetracyclines including glycylcyclines. J Antimicrob Chemother 58 :256–265.

    • Search Google Scholar
    • Export Citation
  • 21

    Saivin S, Houin G, 1988. Clinical pharmacokinetics of doxycycline and minocycline. Clin Pharmacokinet 15 :355–366.

  • 22

    Edstein MD, Baird JK, Fryauff DJ, Ling J, Charles BG, Population pharmacokinetics of primaquine used daily by Javanese transmigrants for malaria prophylaxis. 51st Annual Meeting of American Society of Tropical Medicine and Hygiene, Denver, CO, November 10–14, 2002.

  • 23

    Bocker R, Muhlberg W, Platt D, Estler CJ, 1986. Serum level, half-life and apparent volume of distribution of doxycycline in geriatric patients. Eur J Clin Pharmacol 30 :105–108.

    • Search Google Scholar
    • Export Citation
  • 24

    CollaGenex Pharmaceuticals, 1997. NDA, New Drug Application 50-744. Submitted by CollaGenex Pharmaceuticals for Periostat.

  • 25

    Baird JK, Lacy MD, Basri H, Barcus MJ, Maguire JD, Bangs MJ, Gramzinski R, Sismadi P, Krisin, Ling J, Wiady I, Kusumaningsih M, Jones TR, Fryauff DJ, Hoffman SL, and the United States Naval Medical Research Unit 2 Clinical Trials Team, 2001. Randomized, parallel placebo-controlled trial of primaquine for malaria prophylaxis in Papua, Indonesia. Clin Infect Dis 33 :1990–1997.

    • Search Google Scholar
    • Export Citation
  • 26

    Harris RZ, Benet LZ, Schwartz JB, 1995. Gender effects in pharmacokinetics and pharmacodynamics. Drugs 50 :222–239.

  • 27

    Meibohm B, Beierle I, Derendorf H, 2002. How important are gender differences in pharmacokinetics? Clin Pharmacokinet 41 :329–342.

  • 28

    Gandhi M, Aweeka F, Greenblatt RM, Blaschke TF, 2004. Sex differences in pharmacokinetics and pharmacodynamics. Annu Rev Pharmacol Toxicol 44 :499–523.

    • Search Google Scholar
    • Export Citation
  • 29

    Kennedy E, Frischer H, 1990. Distribution of primaquine in human blood: drug-binding to alpha 1-glycoprotein. J Lab Clin Med 116 :871–878.

    • Search Google Scholar
    • Export Citation
  • 30

    Routledge PA, Stargel WW, Kitchell BB, Barchowsky A, Shand DG, 1981. Sex-related differences in the plasma protein binding of lignocaine and diazepam. Br J Clin Pharmacol 11 :245–250.

    • Search Google Scholar
    • Export Citation
  • 31

    Li XQ, Bjorkman A, Andersson TB, Gustafsson LL, Masimirembwa CM, 2003. Identification of human cytochrome P(450)s that metabolise anti-parasitic drugs and predictions of in vivo drug hepatic clearance from in vitro data. Eur J Clin Pharmacol 59 :429–442.

    • Search Google Scholar
    • Export Citation
  • 32

    Bangchang KN, Karbwang J, Back DJ, 1992. Primaquine metabolism by human liver microsomes: effect of other antimalarial drugs. Biochem Pharmacol 44 :587–590.

    • Search Google Scholar
    • Export Citation
  • 33

    Relling MV, Lin JS, Ayers GD, Evans WE, 1992. Racial and gender differences in N-acetyltransferase, xanthine oxidase, and CYP1A2 activities. Clin Pharmacol Ther 52 :643–658.

    • Search Google Scholar
    • Export Citation
  • 34

    Lane HY, Chang YC, Chang WH, Lin SK, Tseng YT, Jann MW, 1999. Effects of gender and age on plasma levels of clozapine and its metabolites: analyzed by critical statistics. J Clin Psychiatry 60 :36–40.

    • Search Google Scholar
    • Export Citation
  • 35

    Faber MS, Fuhr U, 2004. Time response of cytochrome P450 1A2 activity on cessation of heavy smoking. Clin Pharmacol Ther 76 :178–184.

  • 36

    Rademaker M, 2001. Do women have more adverse drug reactions? Am J Clin Dermatol 2 :349–351.

  • 37

    Baird JK, Rieckmann KH, 2003. Can primaquine therapy for vivax malaria be improved? Trends Parasitol 19 :115–120.

  • 38

    Baird JK, Fryauff DJ, Hoffman SL, 2003. Primaquine for prevention of malaria in travelers. Clin Infect Dis 37 :1659–1667.

  • 39

    Baird JK, Hoffman SL, 2004. Primaquine therapy for malaria. Clin Infect Dis 39 :1336–1345.

  • 40

    Nasveld P, Kitchener S, Edstein M, Rieckmann K, 2002. Comparison of tafenoquine (WR238605) and primaquine in the post-exposure (terminal) prophylaxis of vivax malaria in Australian Defence Force personnel. Trans R Soc Trop Med Hyg 96 :683–684.

    • Search Google Scholar
    • Export Citation
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