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EFFECTIVE TREATMENT OF UNCOMPLICATED PLASMODIUM FALCIPARUM MALARIA WITH AZITHROMYCIN-QUININE COMBINATIONS: A RANDOMIZED, DOSE-RANGING STUDY

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  • 1 Department of Immunology and Medicine, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand; Kwai River Christian Hospital, Sangkhlaburi, Kanchanaburi, Thailand; Pfizer Inc., New York, New York; Division of Experimental Therapeutics, Walter Reed Army Institute of Research, Silver Spring, Maryland

Azithromycin, the most potent antimalarial macrolide antibiotic, is synergistic with quinine against Plasmodium falciparum in vitro. We assessed combinations of azithromycin and quinine against uncomplicated P. falciparum malaria at the Armed Forces Research Institute of Medical Sciences–Kwai River Clinical Center along the Thailand-Myanmar border, an area with a high prevalence of multidrug-resistant P. falciparum. Four regimens were assessed in an open-label dose-ranging design involving 61 volunteers. All received oral quinine (Q; 30 mg/kg/day divided every 8 hours for 3 days) with oral azithromycin (Az; 500 mg twice a day for 3 days, 500 mg twice a day for 5 days, or 500 mg three times a day for 3 days). A comparator group received quinine and doxycycline (Dx; 100 mg twice a day for 7 days). Study observation was 28 days per protocol. Sixty volunteers completed the study. Seven days of QDx cured 100% of the volunteers. One failure occurred in the lowest QAz regimen (on day 28) and none occurred in either of the two higher Az regimens. Cinchonism occurred in nearly all subjects. Overall, the azithromycin regimens were well tolerated, and no volunteers discontinued therapy. Three- and five-day azithromycin-quinine combination therapy appears safe, well tolerated, and effective in curing drug-resistant P. falciparum malaria. Further evaluation, especially in pediatric and obstetric populations, is warranted.

INTRODUCTION

The emergence of resistance to standard antimalarial drugs by Plasmodium falciparum represents a major public health threat.1,2 Combination antimalarial therapy, usually consisting of a rapid-acting, short half-life antimalarial and more-slowly acting agent with a longer half-life, has been advocated for the treatment of P. falciparum malaria.3

Nowhere is the problem of multidrug-resistant malaria more severe than the border regions of Thailand.4 Traditional long-acting agents, such as chloroquine and sulfadoxine-pyrimethamine, are ineffective or rapidly losing effectiveness in many areas, particularly in southeast Asia.3 Mefloquine resistance has reached critical levels, limiting its use to combination regimens with artemisinins.5,6 The artesunate-mefloquine combination has become the standard therapy in Thailand, but is hampered by lingering concerns of neurotoxicity with repeated doses of artemisinins,7 the neuropsychiatric effects of mefloquine,8 and an increased risk of stillbirth in pregnancy.9 Second-line treatment in Thailand is quinine-tetracycline or quinine-doxycycline combinations, each given for seven days.10 This combination is effective but limited by poor compliance in the outpatient setting,11 and the inability to use this regimen in pregnant women and children less than eight years of age. Quinine monotherapy for seven days, the first-line treatment in early pregnancy in Thailand, is associated with failures in one-third of cases despite supervised treatment, and even higher failures rates in unsupervised settings because of non-adherence secondary to drug side effects.12 New combinations that are safe and effective against drug-resistant P. falciparum in children and pregnant women are clearly needed.

The macrolide antibiotics demonstrate modest antimalarial activity13 and, moreover, are safe in children and pregnant women. Azithromycin (Az), the most potent macrolide anti-malarial with a long half-life (68 hours), demonstrates synergism with quinine (Q) against P. falciparum in vitro, suggesting clinical utility as a combination therapy.14 Here, as a first step in assessing the safety and efficacy of convenient, short course quinine-azithromycin (QAz) combinations against P. falciparum, we conducted a dose-escalation study in adults with uncomplicated P. falciparum malaria in western Thailand.

MATERIALS AND METHODS

Study site.

This study was conducted at the Armed Forces Research Institute of Medical Sciences (AFRIMS) inpatient clinical trials center located at the Kwai River Christian Hospital, Sangkhlaburi District, Kanchanaburi Province, Thailand along the western border with Myanmar. This screened indoor facility allows conducting of malaria treatment trials with little risk of re-infection. This partially forested hill region has low seasonal transmission of P. falciparum, which is generally resistant to chloroquine, sulfadoxine-pyrimethamine, and recently mefloquine.6

Study design.

The trial was an open-label, randomized dose-ranging study conducted at the AFRIMS-Kwai River Christian Hospital Clinical Center from July 1999 to December 2001. The study was reviewed and approved by the Human Subjects Research Review Board, Office of the Surgeon General, Department of the U.S. Army and the Ethical Review Committee for Research in Human Subjects of the Thai Ministry of Public Health. Quinine, doxycycline, and azithromycin are all approved for use in the United States and Thailand.

Dose ranging was performed in a dose-escalation format to identify a well-tolerated dose of quinine-azithromycin with 100% cure, defined as clearance of P. falciparum parasitemia without recrudescence of malaria in a 28-day period. The standard quinine-doxycycline (QDx) regimen used in southeast Asia served as a comparator (Table 1), and these subjects were distributed throughout the study enrollment. A block randomization table of 10 QAz to 2 QDx subjects was generated, and volunteers were randomly assigned by rolling enrollment to the active QAz arm or the comparator. Tolerability and efficacy results were reviewed by an independent medical monitor, and enrollment to a well-tolerated azithro-mycinquinine group with 100% cure was then extended by an additional 10 subjects to improve the power of the study. In the subsequent year’s malaria season, an additional regimen containing a higher daily Az regimen (quinine and azithromycin 500 mg three times a day for three days) was assessed without comparator.

Study population.

Male and non-pregnant female adults (age ≥ 20 years) who came with fever to the outpatient clinic of Kwai River Christian Hospital or the nearby government malaria clinic were routinely screened for malaria, and those diagnosed with P. falciparum were eligible for enrollment. After written informed consent, volunteers underwent a medical history and physical examination, including laboratory testing and electrocardiogram.

Exclusion criteria included 1) a known history of chronic illness, 2) signs or symptoms of severe or complicated P. falciparum malaria15 or hyperparasitemia (> 5% red blood cells infected), or sustained hyperpyrexia (fever > 40°C), 3) significant liver dysfunction (alanine aminotransferase [ALT] > 300 IU/L), 4) known pregnancy or positive urine test result for β-human chorionic gonadotrophin (β-hCG), 5) mixed malaria infection by Giemsa smear, 6) drug therapy for P. falciparum malaria administered in the previous 42 days, or 7) history of allergy to study medicines or concurrent use of drugs with known interactions with study drugs.

Eligible volunteers were then admitted to a closed, screened study ward and assigned sequentially to one of the treatment regimens based on the block randomization schedule. Volunteers withdrawing before trial completion were replaced in the randomization schedule. The first dose of medication was generally given within three hours of a preliminary diagnosis of infection with P. falciparum.

Study drugs.

Quinine sulfate (lot no. 4172 895, 325-mg capsules; Zenith Goldline Pharmaceuticals, Miami, FL) was given in doses of 30 mg/kg divided every 8 hours. Quinine and doxycycline hyclate (lot no. 41949, 100 mg; Qualitest Pharamaceuticals, Huntsville, AL) were provided by Walter Reed Army Medical Center (Washington, DC). Azithromycin tablets (lot no. 9HP083A, 250 mg) were produced and provided by Pfizer Inc (New York, NY). All antimalarial medications were administered under supervision with meals or snack. Acetaminophen and dimenhydrinate were provided, as needed, for symptoms of fever/headache/myalgias and nausea/dizziness, respectively. Other medications or intravenous fluids were provided only as prescribed by a physician.

Clinical and laboratory evaluation.

After enrollment, signs and symptoms of the malaria, medication history, and adverse events (AEs) were recorded daily. Routine physical examinations and laboratory tests were performed on a periodic schedule until day 28. Blood smears were obtained twice a day until the malaria cleared, daily for a week, and then weekly or as clinically warranted.

Laboratory evaluation.

Giemsastained malaria thick and thin smears were prepared per standard operating procedures16 and read onsite by an expert microscopist. Two hundred high-power fields were reviewed before a smear was declared negative. Asexual and sexual parasites were generally counted against 200 white blood cells (WBCs); if less than 10 parasites were observed, parasites were counted against 500 WBCs. Smears were then re-read by an off-site microscopist who was blinded to clinical response or the other microscopy assessment. The parasite density was determined by the mean of the non-discrepant values;16 discrepant interpretations were judged by a third referee microscopist whose results were final.

Complete blood counts were determined on a Coulter 890 instrument (Coulter Corp., Miami, FL) and the volunteer’s most recent WBC count served to calculate parasite density. Blood urea nitrogen, creatinine, glucose, ALT, and gamma-glutanyl transferase were measured on a Kodak Ektachem DTSC and DT-60 system (Eastman Kodak Co., Rochester, NY). Urinalysis (Multistix 10 reagent strips; Bayer Diagnostics, Tarrytown, NY) and a urine pregnancy test (Plus-One HCG; Syntron BioResearch, Carlsbad, CA) were performed by the hospital laboratory. A physician on-site interpreted electrocardiograms, which were then over-read for data analysis.

On admission and recrudescence, parasites were collected, processed for cryopreservation, and transported to AFRIMS in Bangkok. Culture and drug sensitivity testing were performed according to standard isotopic methods.17

Clinical and parasitologic efficacy.

The primary study endpoint was cure, which was defined as clearance of asexual parasites without recrudescence within a 28-day period. Secondary endpoints were fever clearance time and parasite clearance time. Parasite clearance time (PCT) was defined as time from the start of treatment until the first negative blood smear for asexual stages, which remained negative for an additional 24 hours. Fever clearance time (FCT) was defined as the time until temperature was ≤ 37.4°C and remained there for at least an additional 48 hours.

Evaluation of safety.

All patients were evaluated daily for the reporting of AEs during treatment that were new in onset or aggravated in severity or frequency after administration of the study drugs. An AE was considered to be drug related if its relationship to treatment was rated definite or probable by a study clinician.

Statistical methods.

This study was designed to identify the QAz regimen(s) with acceptable tolerability and efficacy (cure rates) for further testing. It was not designed to have power to detect specific differences in efficacy among groups. Cure rates were summarized along with 95% confidence intervals (CIs) (exact based on binomial distribution). Overall group (two or more) differences between secondary endpoints of PCT and FCT were compared by a non-parametric method using the Kruskal-Wallis test.

The AEs were reported and tabulated for each tested regimen. Sample sizes were not expected to provide reliable estimates of side effects of low incidence, or to provide statistical power to detect differences in percentages of side effects among treatment groups.

RESULTS

Study population.

Sixty-one volunteers met eligibility requirements and were randomized to one of four treatment groups (Table 1). The demographic and enrollment characteristics among the four groups were similar (Table 2). All but one volunteer (highest QAz dose group), who electively dropped out of the study on day 2 after feeling better, received all medication and remained in the study for 28 days.

Two patients had very low-density (~25 parasites/μL) P. vivax co-infection on admission malaria smear that was detected only by the secondary microscopist after trial completion. The data for these volunteers were included in all subsequent analyses; Plasmodium vivax parasitemia cleared by day 2 of treatment for P. falciparum infection in both cases. Both were treated with primaquine to eradicate P. vivax after study completion.

Clinical and microbiologic efficacy.

Cure rates, FCTs, and PCTs are shown in Table 3. All persons clinically improved within six days. All were cured in the comparator group (QDx for seven days). One volunteer in the Q3Az3 had a P. falciparum recrudescence on day 28, which was confirmed by DNA fingerprinting. There were no failures in either of the higher (≥ 4.5 grams total) Az dose regimens (100% cure rate, 95% CI = 90–100%). There were 3 relapses (5%) of P. vivax malaria, all noted on day 28.

Forty-five of 61 admission parasite isolates grew in culture and underwent in vitro drug sensitivity testing at AFRIMS.18 All isolates were sensitive to quinine (cutoff 50% inhibitory concentration [IC50] > 500 ng/mL), with a geometric mean IC50 of 114 ng/mL (range = 39.2–258 ng/mL). The sole recrudescent isolate (QAz3 arm) had similar drug sensitivities to the initial isolate.

Safety.

All 61 volunteers were included in the safety evaluations (Table 4). The only clinically significant laboratory abnormality was an elevated ALT level observed in four volunteers in equal distribution among the groups. All liver function test abnormalities resolved within 10 days of completion of therapy.

Cinchonism, which was defined in the symptom reporting as tinnitus and/or dizziness, was described in 97% of the volunteers. The three-day quinine regimens with Az were associated with a shortest duration of cinchonism (Table 4). Cinchonism of moderate intensity, i.e., requiring symptomatic medication for control, occurred more frequently in the QDx comparator group. Hearing loss was not reported.

Gastrointestinal side effects were most common in the QDx comparator group and the highest dose of Az (1.5 grams/day for three days). Vomiting was more frequently common in the QDx group compared with any QAz group. New-onset diarrhea, generally mild and not requiring medication, was reported in few QAz and QDx recipients without a dose-dependent trend in azithromycin administration.

Electrocardiographic changes commonly associated with quinine, consisting of significant QTc prolongation (≥ 0.57 seconds), occurred in eight cases without a trend in dose escalation of azithromycin. Additionally, PR prolongation causing first-degree heart block was noted in one patient receiving QAz. All electrocardiographic findings were transient. No dysrhythmias were noted, and no serious AEs were reported.

DISCUSSION

Since the western border of Thailand has some of the most multidrug-resistant strains of P. falciparum malaria described,4 the efficacy of the quinine-azithromycin combinations reported herein is highly encouraging. A recent in vivo study of mefloquine monotherapy in this same population showed a failure rate at 42 days of 46%,6 and artesunate was recently added to the mefloquine regimen as standard therapy in the province.5 Isolates from this region remain sensitive to quinine in vitro.

The combination of quinine and a tetracycline for seven days remains second-line therapy for outpatient treatment of P. falciparum malaria.10,19 This regimen, although effective as observed again in this study, remains hampered by limited applicability to non-pregnant adults and older children, as well as the poor tolerability of quinine for seven days. Funglatta and others11 have estimated field effectiveness of the seven-day quinine-tetracycline regimen at 68–77% due to poor adherence to the regimen, cinchonism associated with quinine therapy, and the length of treatment after symptoms have resolved. Quinine monotherapy (10 mg salt/kg every eight hours) for seven days, which is currently used in Thailand for the treatment of uncomplicated P. falciparum malaria in pregnancy, has a reduced and decreasing efficacy (67%) despite direct-observed therapy in a clinical trial setting.12 Quinine-clindamycin, which was shown to be effective and safe in pregnancy,20 still requires a seven-day regimen of both drugs. Azithromycin should not be used as a single agent for treatment because of its slow onset of action

A short course (three-day) quinine combination regimen, such as still used in sub-Saharan Africa,21,22 would be expected to be effective and have much greater adherence. Tetracycline antibiotics would not be expected to be an ideal partner drug for a three-day quinine regimen because of their pharmacokinetic profile, weak intrinsic antimalarial activity, and lack of synergy with quinine. Azithromycin offers promise as a partner drug because of its enhanced antimalarial activity in vivo,23 additive to synergistic effects in combination with quinine against laboratory strains of P. falciparum,14 and favorable pharmacokinetic profile (t1/2 = 68 hours) whereby a three-day dosing regimen provides sustained drug levels for at least seven days. Since testing for in vitro synergy of quinine with azithromycin on field isolates was not attempted in this study, the role and mechanisms of in vitro synergy in the clinical efficacy remain unclear. Nonetheless, the success of three-day quinine-azithromycin regimens demonstrates their potential as a short-course combination for treatment of P. falciparum malaria, even in southeast Asia where longer courses of quinine are traditionally used.

Azithromycin, which is approved for use in children and has a proven safety record in pregnancy, has intrinsic activity against P. falciparum similar to tetracycline antibiotics.23,24 Despite initial promise as a causal prophylactic agent,25 three field malaria prophylaxis trials2628 with azithromycin (250 mg/day or 1 gram/week) proved less than effective against P. falciparum to warrant further development (70–90%).

The higher doses of azithromycin (1–1.5 grams/day divided twice or three times a day) used in this trial may largely explain the success seen here compared with the prophylaxis studies and limited studies on artemisinin combination treatments.2932 Similar high doses of azithomycin were effective against P. falciparum malaria in India,33 and were reasonably well tolerated.

The azithromycin-quinine regimens were generally well tolerated, even at an azithromycin dose of 1.5 grams/day. No volunteer discontinued therapy because of AEs. The comparator (QDx for seven days) was associated with a longer duration of cinchonism and more vomiting, compared with the azithromycin-containing regimens using a three-day regimen of quinine. In small series, quinine and azithromycin combinations have also been well tolerated when used for the treatment of babesiosis.34

Limitations of this preliminary study as designed are the relative small group sample size and the open-label design, and further study of an effective three-day quinine-azithromycin regimen is warranted before additional recommendations can be made. Since the only failure was seen on day 28, a concern about missing late recrudescences was raised. This has not been reported with previous studies of azithromycin-artemisinin combinations. In this study, volunteers were instructed to return if any fevers occurred in the two-month period after discharge. Two did return but did not have P. falciparum malaria (Miller RS, unpublished data). We believe that a 28-day follow-up for this combination is adequate because of the pharmacokinetics and limited anti-malarial activity of azithromycin.

In summary, quinine (30 mg salt/kg divided three times a day) and azithromycin (≥ 1 gram/day) for three days is effective against multidrug-resistant P. falciparum malaria, and appears to be better tolerated than the seven-day combination of quinine with doxycycline. Since 1.5 grams azithromycin per day is well tolerated and allows a three-day antimalarial combination, we recommend this dose be tested in future treatment studies. Additional azithromycin combination trials with quinine and artesunate combinations are underway. Cost of therapy is an issue in the developing world, but since both drugs have a favorable safety profile in pregnancy and children, the combination of azithromycin and quinine should be further explored in these populations for which new antimalarial regimens are badly needed.

Table 1

Treatment groups

CohortCode*No.†Dose regiment‡Total azithromycin dose (g)
* Q = quinine; Dx = doxycycline; Az = azithromycin.
† Volunteers completing 28-day study.
‡ TID = three times a day; BID = twice a day. All AZ recipients (cohorts 2–4) received quinine sulfate (QS) 30 mg/kg TID for 3 days.
§ Includes 10 additional enrollments for efficacy confirmation.
1Q7Dx710QS 30 mg/kg TID × 7 days + Dx 100 mg BID × 7 days
2Q3Az310QS + AZ 500 mg BID for 3 days3
3Q3Az520§QS + AZ 500 mg BID for 5 days5
4Q3Az4.5203§QS + AZ 500 mg TID for 3 days4.5
Total60
Table 2

Demographic and baseline characteristics*

Q7Dx7 (n = 10)Q3Az3 (n = 10)Q3Az5 (n = 20)Q3Az4.5 (n = 20)
* Data are mean ± SEM, unless otherwise indicated. WBC = white blood cell; RBC = red blood cell. For definitions of other abbreviations, see Table 1.
† One volunteer had rare Plasmodium vivax (Pv) trophozoites under second, blinded microscopic review and was excluded from asexual parasitemia calculations; P. falciparum (Pf) ring forms were estimated at 7,000 parasites/μL.
‡ One volunteer had rare Pv trophozoites under second, blinded microscopic review and was excluded from asexual parasitemia calculations; Pf ring forms were estimated at 17,000 parasites/μl.
Male:female ratio8:26:48:214:6
Age, years (range)35 (21–50)36 (20–56)31 (20–50)35 (20–60)
Parasitemia (parasites/μL)
Admission (geometric mean and range)15,290 ± 17,528 (1,841–140,400)5,782 ± 3,133† (3,568–26,964)21,324 ± 17,528 (636–184,382)6,924 ± 5,274‡ (227–85,500)
Peak (geometric mean and range)18,744 ± 26,213 (1,841–197,370)12,753 ± 7,882 (3,568–70,941)26,423 ± 17,316 (636–295,488)7,720 ± 7,724 (227–131,208)
% fever on admission90909585
Temp. maximum (°C)38.7 ± 0.339.3 ± 0.339.0 ± 0.238.4 ± 0.2
WBC (×103/μL)5.41 ± 0.505.04 ± 0.816.00 ± 0.495.78 ± 0.57
RBC (×106/μL)4.33 ± 0.193.91 ± 0.234.40 ± 0.174.26 ± 0.19
Platelets (×103/μL)92 ± 18126 ± 26104 ± 10125 ± 21
Blood urea nitrogen (mg/dL)13 ± 1.614 ± 1.313 ± 0.713 ± 1.3
Creatinine (mg/dL)1.1 ± 0.051.2 ± 0.051.1 ± 0.031.1 ± 0.05
Alanine aminotransferase (μ/L)43 ± 1338 ± 643 ± 645 ± 11
Table 3

Clinical and parasitologic efficacy of QDx and QAz regimens*

Regimen
Q7Dx7 (n = 10)Q3Az3 (n = 10)Q3Az5 (n = 20)Q3Az4.5 (n = 20)
* CI = confidence interval. For definitions of other abbreviations, see Table 1.
† One P. falciparum recrudescence on day 28.
No. cured109†2020
% (95% CI)100 (69–100)90 (55–100)100 (83–100)100 (83–100)
Plasmodium vivax relapses0120
Fever clearance time (hours ± SEM)52.8 ± 14.052.5 ± 14.041.5 ± 7.149.8 ± 10.1
Parasite clearance time (hours ± SEM)68.8 ± 7.778.9 ± 8.677.7 ± 4.977.7 ± 5.3
Table 4

Number (%) of volunteers with adverse events (AEs) during the 28-day observation study*

Regimen
Q7Dx7 (n = 10)Q3Az3 (n = 10)Q3Az5 (n = 20)Q3Az4.5 (n = 21)†
* GERD = gastroesophageal reflux disease; ALT = alanine aminotransferase; URI = upper respiratory infection. For definitions of other abbreviations, see Table 1.
† Includes one voluntary dropout on day 2 (no AEs reported).
‡ Includes AEs attributable or possibly attributable to drug therapy.
§ Including one volunteer with asymptomatic PR prolongation causing transient first-degree heart block and concurrent QTc prolongation.
Drug-related AE‡
    Tinnitus or dizziness10 (100%)10 (100%)20 (100%)19 (95%)
        Requiring medication5 (50%)3 (30%)3 (15%)3 (15%)
        Duration (mean days)5.23.64.12.3
    Vomiting4 (40%)1 (10%)2 (10%)4 (20%)
    Diarrhea1 (10%)2 (20%)3 (15%)2 (10%)
    GERD/epigastric pain1 (10%)1 (10%)03 (15%)
    Prolonged QTc (≥ 0.57 sec)3 (30%)1 (10%)2 (10%)3 (15%)§
    ALT > 3× upper limits of normal1 (10%)1 (10%)1 (5%)1 (5%)
Other AE, not drug atributable11161723
    Viral URI/rhinitis3198
    Headache5636
    GERD/epigastric pain2313
    Plasmodium vivax relapse0120

*

Address correspondence to R. Scott Miller, Department of Immunology and Medicine, U.S. Army Medical Component, Armed Forces Research Institute of Medical Sciences, 315/6 Rajvithi Rd., Phayathai, Bangkok 10400, Thailand, APO AP, USA 96546. E-mail: robert.s.miller@us.army.mil

Authors’ addresses: R. Scott Miller and Nillawan Buathong, Department of Immunology and Medicine, U.S. Army Medical Component, Armed Forces Research Institute of Medical Sciences, 315/6 Rajvithi Rd., Phayathai, Bangkok 10400, Thailand, APO AP, USA 96546, Telephone: 66-2-644-5775, Fax: 66-2-644-4784, E-mails: robert.s.miller@us.army.mil and nillawanb@afrims.org. Chansuda Wongsrichanalai, National Institute of Public Health/Naval Medical Research Unit No. 2 Laboratory, P.O. Box 131, Phnom Penh, Cambodia, E-mail: chansuda@namru2.med.navy.mil. Philip McDaniel, 10803 SE Cherry Blossom Drive, Portland, OR 97216-3107, E-mail: philmcd@concentric.net. Douglas Walsh, Department of Clinical Trials, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, E-mail: douglas.walsh@us.army.mil. Charles Knirsch, Worldwide Medical Division, Pfizer Inc., New York, NY 10017-5755, E-mail: charles.knirsch@pfizer.com. Colin Ohrt, Division of Experimental Therapeutics, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, Telephone: 301-319-9280, Fax: 301-319-9449, E-mail: colin.ohrt@us.army.mil.

Acknowledgments: We thank Douglas Tang for assistance with statistical design and Harald Noedl for his review of the manuscript. We also thank the staff at Kwai River Christian Hospital, particularly Sabaithip Sriwichai and Panjan Watchara, for providing most of the clinical nursing care, and the dedicated staff of the Malaria Clinic in Sangkhlaburi, Thailand, and the Field Studies and Epidemiology team of the Department of Immunology and Medicine of the Armed Forces Research Institute of Medical Sciences for their support of this trial. This study was presented in part at the 51st Annual Meeting of the American Society of Tropical Medicine and Hygiene, Denver, Colorado, October 10–14, 2002.

Financial support: This study was supported by Pfizer, Inc. and U.S. Army Medical Research and Materiel Command.

Disclosure: Charles Knirsch is an employee of Pfizer, Inc and has equity interest in the company.

Disclaimer: The opinions reflected herein reflect those of the authors and do not necessarily reflect the official views of the U.S. Army or the U.S. Department of Defense.

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Author Notes

Reprint requests: R. Scott Miller, U.S. Army Medical Component, Armed Forces Research Institute of Medical Sciences, APO AP, USA 96546, E-mail: robert.s.miller@us.army.mil.
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