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| ABSTRACT |
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Nearly coincident with the 100th anniversary of the original clinical descriptions of visceral leishmaniasis (VL) (kala-azar) (by Leishman and Donovan in 1903), the status of this disseminated intracellular protozoal infection was upgraded. Regrettably, the upgrade was to that of a "most neglected" disease,1 a sobering promotion for kala-azar from its traditional position as simply a "neglected" disease. The new designation is not particularly surprising, however, since except for endemic regions in southern Europe, kala-azar remains for the most part firmly embedded in high-level poverty. Approximately 90% of the estimated 500,000 new annual cases of visceral disease occur in rural areas of India, Nepal, Bangladesh, Sudan, and Brazil in some of the worlds poorest regions (Figure 1
). Predictably, then, practical advances in prevention and control and in diagnosis and proper treatment remain difficult to develop and/or implement in the countries where such advances are needed most. In this way, VL is not different from other infectious diseases similarly trapped by poverty.
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| TREATMENT IN 1990 |
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| TREATMENT IN 2004 |
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| PARENTERAL AGENTS: CURRENT STATUS AND NEW DEVELOPMENTS |
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Second, Sb use in Mediterranean kala-azar has also decreased considerably, not because of drug resistance, but because of increasing deployment of the highly effective and efficient lipid formulations of amphotericin B. Clinicians in southern Europe have tested and primarily use liposomal amphotericin B (AmBisome®; Gilead Sciences, Foster City, CA);7,8 however, amphotericin B cholesteryl sulfate (Amphotec® [AmphocilTM]; InterMune Corp., Burlingame, CA) and amphotericin B lipid complex (Abelcet®; Enzon Pharmaceuticals, Bridgewater, NJ) are also available and likely just as effective.4,5 The remarkable cost of these agents limits their application even in southern Europe; nevertheless, AmBisome has replaced Sb in Italy8 and use in other Mediterranean countries has increased predictably as well.
The one recent positive development in the use of Sb in VL relates to thorough testing of a particular generic preparation (Sodium Stibogluconate Injection; Albert David, Ltd., Calcutta, India) provided via the International Dispensary Association (Amsterdam, The Netherlands).9 In a series of comparative studies carried out in Kenya, Ethiopia, and Sudan, generic Sb was safe, well-tolerated, and as effective as Pentostam at a fraction (1/8) of the cost of the latter per treatment course (approximately US $22 versus US $180200).9 Other generic forms of Sb, manufactured and used in India, China, and Brazil, have not been well-tested in other countries.
Amphotericin B deoxycholate.
Since resistance to Sb has not yet meaningfully surfaced in other regions, virtually all of the published experience with amphotericin B has been generated in India (Bihar State).4,5 In short, amphotericin B is effective, but arduous treatment with drawbacks that include well-known adverse reactions and toxicity, the requirement for infusions, prolonged duration of therapy (up to 30 days, Table 2
) and comparatively high overall cost of treatment. Nevertheless, in Bihar, amphotericin B is currently first-line parenteral therapy, and regularly induces long-term cure rates
95%.4,5,10
Lipid formulations of amphotericin B.
The physicochemical nature of these agents enables preferential uptake by tissue macrophages in the liver, spleen, and bone marrow, the cells and organs targeted in VL (Figure 3
). These well-tolerated drugs are remarkably active in kala-azar and effective in children and adults in all endemic regions and under diverse field conditions. Provided that sufficient doses are given, cure rates of approximately 95% are nearly routine in patients treated with AmBisome, Abelcet, or Amphotec, including those who receive short-course regimens.4,5
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Findings in a tri-continental AmBisome study have suggested regional variations in clinical and parasitologic responsiveness in patients with VL: total doses required for 100% cure were low in India (6 mg/kg, Leishmania donovani), higher in Kenya (14 mg/kg, L. donovani), and highest in Brazil (> 20 mg/kg, L. chagasi).12 Similarly high total doses of AmBisome (1820 mg/kg) are also needed in the Mediterranean region (L. infantum [identical to L. chagasi]).2,7,8 Why Brazilian and Mediterranean kala-azar require higher-dose therapy is not clear, but this may reflect the infecting species and/or the primary population targeted (young children). Alternatively, Indian kala-azar, which develops primarily in adults and older children, may simply be more treatment-responsive in general.
Abelcet and Amphotec have also been tested in VL with similar success: Abelcet thoroughly in India but not elsewhere5,11 and Amphotec in limited studies in Brazil and Italy.13,14 Recent preliminary data from India also indicate that Amphotec induces high-level cure rates in Bihar State as well (Table 2
).11
The particular usefulness of the lipid formulations in VL, however, lies in the non-toxic, macrophage-targeted delivery of sufficient amphotericin B to induce high cure rates after relatively few doses. Thus, when used at 35 mg/kg (or even up to 1015 mg/kg) per infusion, these agents have made clinically appealing short-course regimens a reality.4 Cure rates of 90100%, which depend upon the total doses of the preparation administered,4 can be achieved by once a day infusions for five days in India11,15 or by six or seven infusions given over a 710-day period in Brazil and southern Europe (Table 2
).7,8,13,14 Using AmBisome, which seems best-suited pharmacologically for ultra-short-course therapy, the treatment duration can apparently be compressed still further: to a single day in India in adults and children (one infusion of 5 or 7.5 mg/kg)16,17 and to two days in children in Greece (two infusions of 10 mg/kg each)18 (Table 3
). In both instances, the total dose of AmBisome, which would have been administered over a 5- or 10-day period in India or Greece, respectively, was given in one or two infusions.
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Paromyomycin. This aminoglycoside (identical to aminosidine) was tested alone and in combination with Sb in kala-azar patients in Kenya, India, and Sudan in the early 1990s.4 More recently, paromyomycin given by itself for 21 days demonstrated good activity in India (approximately 95% cure), including in patients who had failed prior Sb treatment.19 International efforts have successfully resurrected a newly manufactured preparation that is now being tested in India (once a day intramuscular injections of 15 mg/kg for 21 days). Assuming that its high-level efficacy and low rate of adverse reactions are redocumented, the one drawback of paromyomycin (prolonged treatment duration) should be satisfactorily balanced by its proposed cost to be capped at US $45.2 Since the 21-day schedule for this drug is also attractive compared with the 2830 days for Sb or amphotericin B, paromyomycin has the potential to replace amphotericin B (and residual Sb use) in India, and, if tested successfully elsewhere, could replace Sb in other regions as well.
| ORAL AGENTS: CURRENT STATUS |
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Hexadecylphosphocholine (miltefosine) is a membrane-activating alkylphospholipid originally developed as an antineoplastic agent. Initial testing in kala-azar patients, which was based upon solid experimental antileishmanial activity, demonstrated gastrointestinal toxicity but also obvious clinical and parasitologic effects. Succeeding trials, performed in a region of high-level Sb resistance (Bihar State), showed satisfactory safety, tolerable adverse reactions, and efficacy in both adults and children, about one-third of whom had failed Sb treatment.4 Miltefosine given for 28 days at a dose of 50 mg once or twice a day (depending on a body weight < 25 kg or
25 kg, respectively) induced cure rates of approximately 9095% (range = 87100%). In a large, randomized phase III trial, long-term cure rates were 94% after 28 days of miltefosine therapy (n = 299) versus 97% after amphotericin B treatment (15 alternate-day infusions of 1 mg/kg) (n = 99).20
Miltefosine commonly induces anorexia, nausea, vomiting (approximately 60%) and diarrhea (approximately 20%); however, these reactions are typically brief and usually resolve as treatment of VL continues.4,20 Renal insufficiency and increases in levels of hepatic transaminases are much less frequent and reversible once use of the drug is discontinued. Miltefosine is teratogenic in animals and cannot be used in pregnant women. The drug should also not be used in women of child-bearing age unless a pregnancy test result is negative and adequate contraception can be assured during and for two months after treatment.
One obvious benefit of an active oral agent is treatment outside the hospital. However, the key question of how miltefosine would fare clinically in the unsupervised outpatient setting was necessarily left open, since the trials leading to registration were all performed in carefully selected and monitored inpatient subjects. To generate this important information (e.g., compliance, efficacy of self-administered drug), nearly 1,200 adults and children were enrolled in a recently completed phase IV study in India. After up to three initial in-hospital days for treatment and observation, subjects then completed 28 days of treatment as outpatients. These results will clearly be a relevant guide to the proper use, efficacy, and future clinical impact of this agent in the field.
Since Indian kala-azar may be more treatment-responsive in general, it is important to point out that miltefosine has not yet been tested in VL in other regions. However, studies are now being extended to Nepal and are planned in Brazil, Kenya, and Sudan. In a recently initiated trial in Ethiopia, patients coinfected with human immunodeficiency virus (HIV) are being specifically included because, other than compassionate use in southern Europe, miltefosine has not been tested in acquired immunodeficiency syndrome-related VL. In addition, concern about possible resistance developing in the future has prompted the suggestion to test miltefosine now in combination with a second agent in an effort to protect its current high-level efficacy.2
| COST OF TREATMENT |
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In direct contrast, since > 90% of cases of kala-azar arise in regions where bare-bones national health expenditures are as little as $510 annually per capita, the only truly affordable treatment would be one distributed at essentially no charge. The only drug that even comes close to this likely unattainable goal is generic Sb (approximately $22 per treatment course in an adult).4 This $22 figure, however, does not include hospitalization and medical care, which still mount up, even in regions such as India with hospital per diem charges of only approximately $2. Assuming Sb therapy was still an option in India, these latter expenses come to approximately $359 for 30 days of treatment in Bihar State.4
Largely by default, then, a total cost (drug plus hospitalization) of approximately $375400 per treatment course has been an unofficial benchmark in kala-azar in poor regions. For comparison (reviewed by Murray;4 see Table 3
), estimated costs in India for selected regimens in Table 2
for a 25-kg adult include amphotericin B, 30-day treatment (drug = $49, total = $417); AmBisome, 2 mg/kg/day for five days (drug = $800, total = $872); and Abelcet, 2 mg/kg/day for five 5 days (drug = $875, total = $947). To bring the total expense of the latter two short-course regimens into line with that of amphotericin B (the current benchmark in Bihar State), the cost of AmBisome and Abelcet would need to be subsidized or substantially reduced (by approximately 60%).11 Since neither subsidy nor price reduction have materialized, a cost-neutral regimen (total cost equal to that of amphotericin B treatment) of single-dose AmBisome (5 mg/kg) was tested in India and appeared to perform well (91% cure).16 However, when considered together with the 90% cure rate in a follow-up study (a single dose of 7.5 mg/kg that was not cost-neutral; Table 3
),17 there may well be some trade-off for the high-level efficiency of single-infusion treatment, namely, apparently somewhat lower efficacy (versus > 95% cure expected with conventional amphotericin therapy).
In contrast to the preceding obstacles, price-capping (paromomycin) and eliminating most if not all in-patient care (miltefosine) should further strengthen the appeal of these already appealing agents. Estimated total per patient costs in India (paromyomycin, drug = $45 [projected], total = $285; miltefosine, drug = $100 [proposed], total = $160)4 should be well below those of amphotericin B deoxycholate and Sb (used outside of Bihar).6
| TREATMENT IN T CELL-IMPAIRED OR-DEFICIENT PATIENTS |
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Most of the subjects in the preceding trials were not receiving highly active antiretroviral therapy (HAART) at the time the studies were carried out. Satisfactory increases in CD4 cell counts, especially to > 200 cells/mm3, likely enhance responsiveness to antileishmanial chemotherapy and are important in preventing relapse. However, while HAART has reduced the overall frequency of VL as an opportunistic infection in southern Europe, it is not entirely clear how well the initial response to antileishmanial treatment is influenced by the extent of HIV suppression, and symptomatic relapse may also occur despite HAART.
A variety of agents, administered as infrequently as once every 24 weeks (e.g., Sb, pentamidine, Abelcet, and others) appear capable of reducing post-treatment relapse in coinfected patients.22,23 Nevertheless, there is no consensus about the regular use of long-term maintenance therapy even in patients clearly at risk for relapse, for example, HAART recipients in whom CD4 cell counts do not increase to and/or stay above 200 cells/mm3. It is worth pointing out, however, that in some HIV-coinfected patients with quite low CD4 cell counts, persistent visceral infection (documented before and/ or after antileishmanial treatment) may be entirely subclinical and remain curiously asymptomatic for extended periods. Such observations, coupled with other factors (decreasing numbers of coinfected patients [at least in Europe] and absence of firm guidance from a large controlled study) will likely continue to frustrate any consensus about optimal post-treatment management in HIV-associated VL.
| IMMUNOCHEMOTHERAPY AND OTHER EXPERIMENTAL TREATMENTS |
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Abundant experimental evidence (and supportive clinical observations) indicate that multiple T cell- and macrophage-activating cytokines likely interdigitate to mediate host defense in visceral infection.4,5 Two of these cytokines, interferon-
(IFN-
) and granulocyte-macrophage colony-stimulating factor, graduated nearly 10 years ago to limited clinical testing in combination with Sb (Table 1
).4,5 Since symptomatic VL can be viewed simplistically as a failure in macrophage activation, IFN-
was used as an adjunct to Sb to directly stimulate tissue macrophages and trigger intracellular leishmanicidal mechanisms4,5 (Figure 4
). The hope was that such a combination, active experimentally, could improve outcome by accelerating the kinetics of parasite killing, reducing the duration of chemotherapy and/or by enhancing overall efficacy. However, results with Sb plus IFN-
in Brazil, Kenya, and India were mixed, and additional studies have not been pursued. Granulocyte-macrophage colony-stimulating factor also enhances macrophage antileishmanial activity, and readily mobilizes and delivers myelomonocytic cells to infected tissue foci.5 It was given by Brazilian investigators to ameliorate the leukopenia of kala-azar, and in a single study, this effect appeared to reduce secondary, complicating infections.25
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-inducing regulatory cytokine that drives the curative Th1 cell-type response, 2) more proximal T cell-antigen-presenting (dendritic) cell events including T cell costimulation via CD40 ligand:CD40 and CD28:B7, and 3) macrophage intracellular signaling mechanisms. An entirely separate approach to immunoenhancement in experimental visceral infection, targeting suppressive down-regulating cytokines such as IL-10 for inhibition, has also proven effective alone and in combination with Sb or amphotericin B.4 Experimental efforts specifically directed at developing chemotherapy also continue in laboratories around the world, and the state of this research has recently been reviewed elsewhere.26 Current approaches include modifying existing drugs, identifying novel compounds (including those rationally selected with validated parasite targets), and improving drug delivery systems by targeting parasitized macrophages. Work directed at heated amphotericin B deoxycholate (heated-induced aggregates are phagocytized by tissue macrophages26) and at manipulating Sb to produce an orally-active form27 are both of particular interest.
Received May 20, 2004. Accepted for publication May 26, 2004.
Acknowledgment: Space constraints did not permit many relevant references to be included; however, these references can be found in recent reviews.2,4,5,26 I am particularly grateful to colleagues who generously shared their slides and photographs.
Financial support: This study was supported by National Institutes of Health research grant AI-16963. The American Committee on Clinical Tropical Medicine and Travelers Health (ACCTMTH) assisted with publication expenses.
Authors address: Henry W. Murray, Department of Medicine, Weill Medical College of Cornell University, Box 136, 1300 York Avenue, New York, NY 10021, Telephone: 212-746-6330, Fax: 212-746-6332, E-mail: hwmurray{at}med.cornell.edu.
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