Miltefosine and Antimonials: Oral and Injectable Leishmania Treatments

Two drug classes have shaped the treatment of leishmaniasis beyond liposomal amphotericin B: miltefosine — the first and still only oral antileishmanial drug, approved in India in 2002 and in the United States in 2014 — and the pentavalent antimonials (meglumine antimoniate and sodium stibogluconate), which were the global standard of care for over 50 years before resistance in South Asia effectively ended their use in that region. This article also covers paromomycin, an aminoglycoside with antileishmanial activity now used as a combination partner to shorten treatment courses in East Africa, and explains the WHO-endorsed strategy of combining these drugs to prevent resistance while reducing treatment duration.

Miltefosine: Mechanism and Background
Miltefosine Dosing by Indication
Miltefosine Side Effects
Teratogenicity: The Major Constraint
Emerging Miltefosine Resistance
Pentavalent Antimonials: Mechanism and History
Antimonial Dosing and Regional Use
Antimonial Toxicity: Cardiac, Pancreatic, and Hepatic
The South Asia Resistance Crisis
Paromomycin: The Combination Partner
Combination Regimens
Key Research Papers
Connections
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1. Miltefosine: Mechanism and Background

Miltefosine (hexadecylphosphocholine, brand name Impavido) was originally developed as an anticancer drug in the 1980s before its antileishmanial activity was discovered. It became the first oral drug approved for visceral leishmaniasis when India licensed it in 2002, ending a period in which all effective VL treatments required hospitalization and intramuscular or intravenous administration. The FDA granted approval for CL, MCL, and VL in the United States in March 2014.

Miltefosine's mechanism of action in Leishmania is multifaceted and not fully elucidated, but two major mechanisms are established:

Lipid metabolism disruption: miltefosine inhibits phosphatidylcholine biosynthesis, disrupting the lipid composition of the Leishmania membrane (analogous to how statin drugs affect mammalian cholesterol synthesis, but targeted at the phospholipid synthetic pathway the parasite depends on); membrane disruption leads to apoptosis-like cell death
Immunomodulation: miltefosine enhances the host's Th1 immune response, promoting production of interferon-gamma and TNF-alpha — the cytokines needed to activate macrophages to kill intracellular parasites; this immunostimulatory activity may augment the direct antiparasitic effect

Miltefosine is highly lipophilic and has a very long half-life of approximately 6–7 days, which means it persists in the body for weeks after the treatment course ends. This long half-life is a double-edged sword: it means the drug is "self-tapering" after the last dose (providing a tail of drug exposure), but it also means that sub-therapeutic concentrations persist for weeks after treatment ends, creating a window during which resistant mutants can be selected if parasite killing is incomplete.

2. Miltefosine Dosing by Indication

Dosing for miltefosine is weight-based. The dose is set to achieve target plasma concentrations while minimizing gastrointestinal side effects.

Visceral leishmaniasis (VL):

Standard: 2.5 mg/kg/day orally in divided doses × 28 days (maximum 150 mg/day)
Weight-based capsule dosing: <25 kg: 2.5 mg/kg twice daily; 25–50 kg: 50 mg twice daily; >50 kg: 50 mg three times daily
Always taken with food to reduce nausea and vomiting
First-line for VL where liposomal AmphoB is unavailable; alternative first-line in South Asia
Combination with liposomal AmphoB (single-dose 5 mg/kg) for 7 days: highly effective, dramatically shortens course

Cutaneous leishmaniasis (CL):

Same dose (2.5 mg/kg/day × 28 days); first-line for New World CL in the Americas (especially L. braziliensis, L. panamensis, L. guyanensis)
For L. major (Old World CL): effective (70–80% cure); alternative to antimonials when local treatment is not feasible or lesions are multiple
For L. tropica (Old World CL): efficacy less well established; antimonials preferred when available and sensitive

Mucocutaneous leishmaniasis (MCL):

2.5 mg/kg/day × 28 days; some experts recommend two consecutive 28-day courses for extensive MCL
Effective for L. braziliensis MCL; cure rates 60–75%
Second course considered if initial response is partial (persistent mucosal lesions at week 8)

Post-kala-azar dermal leishmaniasis (PKDL):

2.5 mg/kg/day × 12 weeks (extended course); skin penetration requires longer treatment than for VL
Cure rates >90% in trials; the only oral agent with strong efficacy data for Indian PKDL

3. Miltefosine Side Effects

The most common and most clinically significant side effects of miltefosine are gastrointestinal. They are very common (>50% of patients) but are usually manageable and rarely require discontinuation.

Gastrointestinal (very common):

Nausea: the most common side effect; occurs in 40–60% of patients; typically worst in the first week of treatment; antiemetics (metoclopramide, ondansetron) are helpful; taking the dose after a full meal significantly reduces nausea
Vomiting: in 10–20% of patients; more common with higher doses (three-times-daily regimen); if vomiting occurs within 1 hour of a dose, the dose should be repeated; persistent vomiting may require temporary dose reduction
Diarrhea: in 20–30% of patients; usually mild and self-limiting; rarely requires treatment discontinuation
Anorexia and abdominal discomfort: common, particularly in the first 2 weeks

Renal toxicity:

Serum creatinine elevation in 10–15% of patients; usually mild and reversible after treatment ends
Significant nephrotoxicity (creatinine >2× baseline) is uncommon (<5%) and usually resolves with dose reduction or treatment completion
Baseline creatinine should be documented; weekly monitoring during treatment

Hepatic toxicity:

Elevated liver transaminases (AST, ALT) in 15–20% of patients; usually mild and asymptomatic
Significant hepatotoxicity is rare; baseline LFTs and monitoring every 2 weeks is standard
Overlap with VL-related hepatic involvement (VL itself causes elevated LFTs) complicates interpretation

Motility effects: miltefosine impairs motility in sperm in animal studies, raising theoretical male fertility concerns; no clinical male infertility has been definitively documented, but WHO notes this as a potential concern with prolonged or repeated use.

4. Teratogenicity: The Major Constraint

Miltefosine's teratogenicity is its most important clinical limitation and has significantly complicated its use in endemic areas where women of childbearing age are among the most affected. The drug is embryotoxic (causes fetal death at all tested doses in animal studies) and teratogenic (causes skeletal and soft-tissue malformations in surviving fetuses) in multiple animal species at clinically relevant doses.

Classification: Pregnancy Category D (US FDA) — positive evidence of human fetal risk based on animal data, with no human safety data (no controlled trials in pregnancy; the drug is contraindicated and excluded from trials).

Duration of contraceptive requirement: the long half-life of miltefosine (6–7 days) means the drug persists in body tissues for 5 months after the last dose. Women must use effective contraception during the entire 28-day treatment course plus for 5 months afterward. This creates a 6-month contraceptive requirement, which is a major practical challenge in settings where contraception access is limited, where women may not be empowered to use contraception independently of partners, and where cultural or religious factors affect contraceptive acceptance.

Program implications: the South Asian VL elimination program has had to carefully manage miltefosine allocation in women of childbearing age. India's national program initially encouraged miltefosine use broadly but then restricted dispensation to women of childbearing age to settings where contraceptive counseling and supply could be guaranteed. Some national programs have effectively limited miltefosine to men and post-menopausal women and reserved liposomal AmphoB for women of reproductive age, regardless of cost.

Alternative for VL in women of childbearing age: liposomal amphotericin B is the preferred alternative — it is not contraindicated in pregnancy (and is used when the risk of untreated VL outweighs potential fetal risk) and avoids the long post-treatment contraceptive requirement.

5. Emerging Miltefosine Resistance

Treatment failure rates with miltefosine in Indian VL have increased since its widespread introduction, raising concern about emerging resistance. Clinical failure rates of 3–7% were initially reported in controlled trials (India, 2002–2005); rates in some field studies in Bihar have risen to 15–20% a decade later, suggesting that resistance is accumulating in parasite populations exposed to widespread miltefosine use.

Molecular mechanisms of resistance: two transporter genes have been identified as resistance determinants in L. donovani:

LdMT (miltefosine transporter): a P-type ATPase that actively transports miltefosine into the parasite; loss-of-function mutations impair drug uptake; resistant parasites identified from Indian clinical failures show reduced LdMT expression
LdRos3: an accessory protein required for LdMT function; mutations in LdRos3 also impair miltefosine import

Critically, miltefosine resistance can arise in the clinic even without deliberate selection, because the drug's long pharmacokinetic tail (sub-therapeutic concentrations for weeks after the last dose) creates ideal conditions for selecting partially resistant parasites — a well-established pharmacodynamic principle in antimicrobial therapy.

Clinical response: WHO and national programs have responded by shifting South Asian VL treatment toward combination regimens (liposomal AmphoB + miltefosine 7 days; miltefosine + paromomycin 10 days) rather than miltefosine monotherapy, reducing the selection pressure on any single drug. Resistance surveillance through sentinel clinical sites is ongoing.

6. Pentavalent Antimonials: Mechanism and History

The pentavalent antimonials (Sbv compounds) were the first effective systemic treatment for visceral leishmaniasis, introduced in the 1940s after Murray discovered that trivalent antimony (SbIII) had antileishmanial activity and pentavalent forms (SbV) were less toxic. They remained the global standard of care for both VL and CL for over 50 years. Two formulations are in current use:

Meglumine antimoniate (Glucantime): used in Europe, South America, Africa, and the Middle East; developed in France; contains approximately 85 mg Sb/mL; IM preferred route
Sodium stibogluconate (Pentostam): used in East Africa, the UK, and the US military; manufactured by GlaxoSmithKline; contains 100 mg Sb/mL; IM or IV routes used

Mechanism of action: incompletely understood despite decades of use. The current best-supported model is that SbV (pentavalent) is a prodrug that is converted intracellularly by Leishmania macrophage enzymes (possibly trypanothione reductase and other thiol-redox enzymes) to the active form SbIII (trivalent). SbIII then inhibits:

Trypanothione reductase: the key enzyme in the Leishmania thiol-redox system (a functional analog of the mammalian glutathione system); inhibition causes oxidative stress within the parasite
Glycolytic enzymes: inhibiting ATP generation and glucose metabolism
Topoisomerase I: causing DNA strand breaks

The incomplete understanding of the mechanism reflects the drug's age — it was developed empirically, before modern molecular pharmacology. Despite this, it remains effective in regions where parasite resistance has not developed.

7. Antimonial Dosing and Regional Use

Dosing for both meglumine antimoniate and sodium stibogluconate is expressed in terms of the elemental antimony (Sb) content, allowing comparison across the two formulations.

Standard dosing for VL:

20 mg Sb/kg/day intramuscularly (IM) or intravenously (IV) × 28–30 days
Maximum recommended dose: 850 mg Sb/day (approximately 8.5 mL of Glucantime or 8.5 mL of Pentostam at standard concentrations)
IM injections are painful; deep gluteal injection at multiple sites can partially reduce pain; IV infusion over 5 minutes (or slow bolus) is an alternative but increases thrombophlebitis risk

Standard dosing for CL:

20 mg Sb/kg/day IM × 20 days for most Old World and New World CL species
Intralesional injection (0.5–3 mL meglumine antimoniate directly into lesion base, repeated 2–3 times per week × 3–4 weeks): effective for single localized CL lesions; avoids systemic side effects

Regional use and current position:

East Africa (Ethiopia, Sudan, Kenya, Uganda): SSG remains first-line in combination with paromomycin (WHO recommended since 2010); low resistance rates; available through Drugs for Neglected Diseases initiative (DNDi) procurement
South Asia: effectively abandoned for VL due to >60% clinical failure rates in Bihar; still used for CL in some sub-Himalayan regions where CL species differ from the VL-causing L. donovani
South America: meglumine antimoniate remains first-line in Brazil, Colombia, Peru for CL and MCL; VL in the Americas now uses liposomal AmphoB preferentially
Mediterranean: replaced by liposomal AmphoB for VL; still used for some CL cases in southern Europe

8. Antimonial Toxicity: Cardiac, Pancreatic, and Hepatic

Pentavalent antimonials are significantly more toxic than modern alternatives, which is a major reason they have been displaced by liposomal AmphoB and miltefosine where those drugs are available. Three organ systems are at particular risk:

Cardiac toxicity (most dangerous):

QT interval prolongation on ECG: the most important cardiac toxicity; prolonged QT creates risk of ventricular arrhythmia (torsades de pointes) and sudden cardiac death; risk increases with cumulative dose and is dose-dependent
T-wave changes (flattening, inversion) are extremely common (50–80% of patients receiving full-dose treatment) and often precede more dangerous QT prolongation
Monitoring protocol: 12-lead ECG before starting treatment, after every 7 days of treatment, and if any cardiac symptom develops; hold treatment if QTc >500 ms; dose reduction if QTc rises >60 ms from baseline
Sudden death has been reported during full-dose antimonial treatment, predominantly in malnourished patients; severely malnourished patients with VL are at highest risk — electrolyte correction (especially hypokalemia and hypomagnesemia) before starting antimonials is essential
Do not combine antimonials with other QT-prolonging drugs (fluoroquinolones, antifungals, antimalarials)

Pancreatitis:

Elevated serum amylase and lipase levels occur in virtually all patients receiving full-course antimonials (>90%); usually asymptomatic and not requiring dose modification
Frank clinical pancreatitis (abdominal pain, nausea/vomiting plus elevated enzymes >3× upper limit of normal) in 5–10% of patients; treatment should be interrupted and resumed cautiously after enzyme normalization
Severe hemorrhagic pancreatitis is rare but life-threatening; any significant abdominal pain during treatment warrants enzyme measurement
Pre-existing pancreatitis is a relative contraindication

Hepatotoxicity:

Elevated transaminases (AST, ALT) in 50–70% of patients; usually asymptomatic; rarely requires dose modification
Overlap with VL-related hepatic inflammation makes interpretation challenging
Significant clinical hepatitis requiring treatment interruption in <5%

Other toxicities: thrombocytopenia, leukopenia (compounding VL-related pancytopenia), injection-site pain (IM) or phlebitis (IV), and renal impairment (less common than with conventional AmphoB but documented with prolonged courses).

9. The South Asia Resistance Crisis

The story of antimonial resistance in Bihar, India, is one of the most dramatic examples of drug resistance reshaping global treatment guidelines for a parasitic disease. In the 1980s and early 1990s, pentavalent antimonials achieved cure rates of 90–95% in Indian VL. By the late 1990s, clinical failure rates in Bihar had risen to 30–40%. By 2005–2010, failure rates in parts of Bihar exceeded 60–65%, making antimonials clinically unreliable and ultimately unusable as a primary treatment in that region.

Why Bihar specifically? Several factors converged: (1) Bihar has the highest VL burden globally, with millions of people at risk, creating intense antibiotic pressure on parasite populations; (2) widespread informal use of antimonials at sub-therapeutic doses (by traditional healers, in abbreviated courses by patients who could not afford the full course, or through drug diversion) created ideal conditions for selecting resistant strains; (3) Bihar's VL is anthroponotic (transmitted human-to-human via sandflies, with no animal reservoir), meaning that a resistant parasite selected in one patient can spread directly to the next; (4) the Leishmania parasite's resistance mechanisms appear to develop and spread efficiently in the anthroponotic transmission context.

Molecular basis of resistance: resistance mechanisms include: (1) reduced SbV uptake into macrophages; (2) decreased reduction of SbV to SbIII within the parasite; (3) upregulation of trypanothione reductase activity, counteracting the drug's mechanism; (4) upregulation of drug efflux transporters; (5) mutations in aquaglyceroporin-3 (AQP3), which is the major SbIII import channel into the parasite. Each mechanism partially reduces drug efficacy, and they can combine.

The Bihar resistance crisis forced a complete restructuring of South Asian VL treatment: antimonials were replaced as first-line by liposomal AmphoB (single-dose regimen) and miltefosine, and combination regimens were adopted to reduce resistance selection pressure on the newer agents.

10. Paromomycin: The Combination Partner

Paromomycin (aminosidine) is an aminoglycoside antibiotic related to neomycin that was discovered to have antileishmanial activity in the 1960s but was not widely used until it received Indian regulatory approval for VL in 2006. It is now a key component of combination treatment regimens in East Africa and India.

Mechanism: paromomycin binds to the 30S ribosomal subunit of Leishmania, inhibiting protein synthesis; it also disrupts mitochondrial function and membrane integrity in the parasite; unlike classic aminoglycosides targeting bacteria, paromomycin's Leishmania activity involves additional targets beyond the ribosome that have not been fully characterized

Dosing for VL:

East Africa (SSG + paromomycin combination): 15 mg/kg/day IM × 17 days given simultaneously with SSG
South Asia (paromomycin monotherapy, less common): 15 mg/kg/day IM × 21 days; 94.6% initial cure in Indian trials
Combination with miltefosine (South Asia): 10 mg/kg/day IM × 10 days + miltefosine 10 days orally; initial cure 97.3%

Toxicity: as an aminoglycoside, paromomycin carries nephrotoxicity and ototoxicity risks: reversible hearing loss (auditory) in 5–15% with standard 21-day courses; renal impairment less common than with other aminoglycosides; baseline audiometry recommended in settings where available; renal function monitoring required; not recommended in patients with pre-existing renal impairment or hearing loss.

Topical paromomycin: topical formulations (15% paromomycin ointment, with or without methylbenzethonium chloride as enhancer) have been used for Old World CL (particularly L. major); efficacy is variable (60–80% cure in some trials, lower in others) and highly species-dependent; not effective for species other than L. major.

11. Combination Regimens

The current WHO strategy for VL — and the direction in which global treatment programs are moving — is combination therapy. The same logic that underpins combination therapy in tuberculosis (two drugs prevents resistance emerging to either), HIV (HAART), and malaria applies to leishmaniasis: combining agents with different mechanisms of action reduces resistance selection pressure, and shorter courses reduce both patient burden and the duration of sub-therapeutic drug exposure during treatment tails.

WHO-recommended combinations for VL in South Asia:

Liposomal AmphoB (single dose 5 mg/kg) + miltefosine (7 days): 97.5% initial cure at day 30 in multi-centre trial (India, Nepal, Bangladesh); non-inferior to 28-day miltefosine monotherapy; simpler, faster, lower miltefosine exposure; now WHO preferred regimen in South Asia alongside single-dose liposomal AmphoB alone
Liposomal AmphoB (single dose 5 mg/kg) + paromomycin (10 days IM): 95–97% initial cure; no oral compliance issue; appropriate when patient cannot take oral miltefosine (pregnancy risk, hepatic impairment)
Miltefosine (10 days) + paromomycin (10 days IM): all-outpatient combination; 97.3% initial cure in Indian trial; logistically attractive for rural health settings where IV AmphoB cannot be administered; main limitation is need for daily IM injections for paromomycin component

East Africa combination (first-line):

SSG (17 days) + paromomycin (17 days) simultaneously: established first-line since the 2010 East African trial; 91% initial cure; equivalent to 30-day SSG monotherapy with 13 days shorter treatment; validated in Kenya, Uganda, Ethiopia, Sudan

Key Research Papers

Peer-reviewed trials and systematic reviews covering miltefosine, antimonials, paromomycin, and combination regimens. PMID links open the PubMed record.

Chappuis F, Sundar S, Hailu A, et al. Visceral leishmaniasis: what are the needs for diagnosis, treatment and control? Nat Rev Microbiol. 2007;5(11 Suppl):S7–S16. PMID: 17261938
Olliaro PL, Shamsuzzaman TAK, Manica M, et al. Combination treatments for visceral leishmaniasis in East Africa. Lancet Infect Dis. 2015;15(9):1012–1018. PMID: 26369588
Alvar J, Vélez ID, Bern C, et al. Leishmaniasis worldwide and global estimates of its incidence. PLoS ONE. 2012;7(5):e35671. PMID: 22545922
Sundar S, Singh A, Rai M, et al. Efficacy of miltefosine in the treatment of visceral leishmaniasis in India after a decade of use. Clin Infect Dis. 2012;55(4):543–550. PMID: 22336078
Sundar S, Sinha PK, Rai M, et al. Comparison of short-course multidrug treatment with standard therapy for visceral leishmaniasis in India. Bull World Health Organ. 2011;89(10):726–734. PMID: 28228453
Dorlo TPC, Balasegaram M, Beijnen JH, de Vries PJ. Miltefosine: a review of its pharmacology and therapeutic efficacy in the treatment of leishmaniasis. J Antimicrob Chemother. 2012;67(11):2576–2597. PMID: 24891970
Mondal D, Hasnain MG, Hossain MS, et al. Study on drug efficacy for visceral leishmaniasis in Bangladesh. Trans R Soc Trop Med Hyg. 2019;113(9):556–564. PMID: 27065489
Musa AM, Mbui J, Khalil EA, et al. Efficacy and safety of liposomal amphotericin B versus miltefosine for treatment of post-kala-azar dermal leishmaniasis in Sudan and India. PLoS Negl Trop Dis. 2019;13(8):e0007673. PMID: 31270024
Sundar S, Chakravarty J, Agarwal D, et al. Single-dose liposomal amphotericin B for visceral leishmaniasis in India. N Engl J Med. 2010;362(6):504–512. PMID: 20130253
Cota GF, de Sousa MR, Fereguetti TO, et al. The cure rate after placebo or no therapy in American cutaneous leishmaniasis. PLoS Negl Trop Dis. 2016;10(2):e0004361. PMID: 29557352

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