INTRODUCTION
Chagas disease (CD) or American trypanosomiasis is a potentially life-threatening zoonosis with the flagellate protozoan Trypanosoma cruzi as its etiological agent. An estimated eight million people in Latin America are infected with this parasite,1 and 100 million living in endemic areas (i.e., 25% of the total population in Latin America) are at risk of infection.2 Human infection also occurs in nonendemic areas because of growing international immigration and nonvectorial transmission routes such as blood transfusion, organ transplantation, and congenital infection.3 In addition, orally transmitted CD has been detected in endemic areas such as the Brazilian Amazon because of food carrying T. cruzi that originated from sylvatic triatomines.4
Trypanosoma cruzi has four developmental stages: the replicative epimastigote and amastigote stages, and the infective nonreplicative metacyclic and bloodstream trypomastigote stages. Infection begins when metacyclic trypomastigotes in the excreta of reduviid insects penetrate the bite wound; after entering the host cell, they transform into amastigotes that after several cycles of binary division in the cytoplasm differentiate into bloodstream trypomastigotes.5 When released from the host cell on rupture of the cell membrane, the bloodstream trypomastigotes infect neighboring cells and, owing to their dissemination throughout the blood, cells at other locations in the body. Amastigotes can also infect cells. Innate and acquired immune responses are critical for the control of T. cruzi and involve macrophages, natural killer cells, natural killer T cells, T and B lymphocytes, and the production of pro-inflammatory Th-1 cytokines such as interferon-γ (IFN-γ), tumor necrosis-α, and interleukin-12.6
CD has two clinical phases. The short acute phase is mainly oligosymptomatic but sometimes involves flulike symptoms and is defined by patent parasitemia. The chronic phase is characterized by fluctuating parasitemia, although most patients remain asymptomatic after several months and even decades, characterizing the indeterminate form of CD. Approximately 30–40% develop clinical symptoms characteristic of this phase, with the majority experiencing different levels of cardiac and/or digestive tract pathologies7,8 (cardiac and digestive forms of CD), which might be attributable to autoimmunity initiated by molecular mimetization.9
A drawback of the studies assessing the efficacy of BZ in the chronic phase of CD is the lack of a marker to define cure. Current recommendations rely on the switch of serology from positive to negative; however, this may take many years, precluding its use in clinical trials. Detection of T. cruzi DNA in peripheral blood allows having a rapid result, but it cannot be used to define cure. Trypanosoma cruzi DNA only serves as a tool to identify treatment failure because a negative result does not mean absence of infection. Moreover, long prospective studies to assess the value of a persistent negative polymerase chain reaction (PCR) after treatment are lacking.
CD treatment has been explored using two approaches: development of a preventive vaccine and identification of new effective drugs. Currently, no vaccines for CD are available or undergoing clinical tests. The present treatment of CD, used for > 40 years, is based on the nitroheterocyclic compounds nifurtimox (NFX; 3-methyl-4-[5′-nitrofurfurylideneamine]tetrahydro-4H-1,4-tiazine-1,1-dioxide; Bayer 2502; Bayer, Leverkusen, Germany) and benznidazole (BZ; N-benzyl-2-nitroimidazole acetamide; RO7-1051; Laboratório Farmacêutico do Estado de Pernambuco (LAFEPE), Recife, Brazil and Laboratorio ELEA, Ciudad Autónoma de Buenos Aires, Argentina), which have trypanocidal activity against all parasitic forms. Because of the side effects, which can interrupt the therapeutic protocol,10 and limited cure efficacy (acute phase, 50–80%; chronic phase, 8–20%), they are considered far from ideal.11–16 In addition to the CD phase, other factors influencing the cure efficacy of both drugs include the treatment period, dose, age and immune system of patient, and geographical patient origin.11 Moreover, the existence of T. cruzi strains naturally resistant to both drugs may partly explain the low cure rates detected in treated chagasic patients.17
According to the World Health Organization (WHO), the ideal drug for CD treatment should have the following characteristics: parasitological cure during the acute and chronic phases, efficacy in one dose or a few doses, low cost, absence of side effects or teratogenic effects, and no induction of resistance. However, no drug meets all these requirements then new, more effective, and better-tolerated compounds are urgently needed.
In the present review, we analyze the current data regarding the development of new drugs for CD and discuss current treatments, clinical trials, and the testing of new compounds. In addition, we review the pharmacokinetics and biodistribution of BZ.
METHODS
We searched the Medline database for articles published in English from 1952 to 2017 using the terms “Chagas disease”, “benznidazole”, and “nifurtimox”. Ongoing and completed clinical trials were queried at ClinicalTrials.gov. Google was used for additional queries of specific references freely available on the internet.
Current drugs used for the treatment of Chagas disease.
Nifurtimox.
NFX was the first drug used for CD treatment. Packchanian18 was the first to experimentally demonstrate that nitrofurans were promising for CD treatment. Later, Brener19 used nitrofurazone to cure chronically infected mice. Although important results were reported regarding treatment with nitrofurazone,20–23 the unfavorable side effects and toxicity ceased its use. Clinical trials with NFX started in 1965 in South America, and the results differed based on the disease phase, treatment duration, patient age, and geographical area, with the best results obtained during the acute phase in children and patients with a recent infection (8–10 mg/kg/day for 60–90 days)10,11; negative xenodiagnosis was achieved in 88–100% of acute phase patients who completed the treatment schedule. The treatment effectiveness in adult patients with chronic disease was low, with a cure rate of 7–8% in the chronic indeterminate phase; however, in children < 14-years old in the chronic asymptomatic phase, the cure rate was significantly higher, reaching up to 85.7%.11,24 Table 1 describes the studies in which NFX was used to treat CD.
Summary of the studies in which nifurtimox was used to treat Chagas disease
| Reference no. | Year | Country | No. of patients | Age (years)* | Treatment protocol | Follow-up* | Results at the end of the study |
|---|---|---|---|---|---|---|---|
| 25 | 1977 | Argentina | 42 | Not shown | 8–10 mg/kg 60–120 days | ≥ 12 months | 27/29 negative XD |
| 25 | 1977 | Chile | 15 | Not shown | 8–10 mg/kg 60–120 days | ≥ 12 months | 12/14 negative XD |
| 25 | 1977 | Brazil | 52 | Not shown | 8–10 mg/kg 60–120 days | ≥ 12 months | 35/44 negative XD |
| 26 | 1990 | Brazil | 50 | Not shown | 10–15 mg/kg 60–120 days | 2 years | 50% negative XD, 6% negative serology |
| 27 | 1990 | Argentina | 39 | < 17 | 8–10 mg/kg 60 days | 139 months | 11–14% negative serology, 15% negative XD |
| 28 | 1997 | Brazil | 27 | Not shown | 5 mg/kg 30 days | 1 year | 100% positive serology, 8/83 positive XD |
| 29 | 1998 | Chile | 28 | < 10 | 7 mg/kg 60 days | 6 months | 100% negative XD, 35.8% negative PCR |
| 30 | 2000 | Argentina | 32 | 13–52 | 5–8 mg/kg 60 days | 14 years (8–23) | 100% positive serology, 100% negative XD |
| 31 | 2000 | Brazil | 28 | Adults | 10 mg/kg 60 days | 10 years | 100% positive serology, 100% positive PCR |
| 32 | 2001 | Chile | 66 | Children | Not shown | 3 years | 34/36 positive serology, 100% negative XD and PCR |
| 33 | 2002 | Brazil | 10 | 38 (25–48) | 8–9 mg/kg 60 days | 303 months | 100% positive serology, 9/10 positive XD |
| 34 | 2003 | Chile | 99 | Children | 10 mg/kg 30 days | 3 years | 100% negative XD, 100% negative PCR |
| 24 | 2004 | Argentina | 7 | < 14 | 12–15 mg/kg 45–60 days | 21 years (median) | 6/7 negative serology |
| 35 | 2013 | Chile | 21 | 38 (23–50) | 6 mg/kg 60 days | 13 months | Four patients positive PCR† |
| 36 | 2013 | Switzerland | 37 | 44 (22–59) | 10 mg/kg 30–60 days | 4 years | 100% positive serology, one patient positive PCR |
PCR = polymerase chain reaction; XD = xenodiagnosis.
The data are expressed as mean except where noted otherwise. In some instances, the range is shown in parentheses.
PCR was performed in both the patient’s blood and fecal samples of Triatoma infestans nymphs.
The most frequent side effects are anorexia, weight loss, paresthesia, drowsiness or psychic excitability, and gastrointestinal symptoms such as nausea, vomiting, and occasional intestinal cramps. Treatment with NFX, even at low doses, has more intense side effects than BZ; a high number of treatment attempts were interrupted because of severe digestive intolerance.28 Incomplete treatment was recently shown to lead to NFX resistance.37
Benznidazole.
Near the end of the 1970s, Grunberg et al.38 showed for the first time that BZ was active against T. cruzi. BZ was shown to have similar efficacy as nitrofurazone in both the acute and chronic phases but with less toxic effects.39 Thereafter, several experimental and clinical CD treatments using BZ were published.40–43 Numerous clinical studies showed that BZ had significant activity during the acute phase (all parasitological and conventional serological tests had up to 80% negative results).14,44 Although several reports have demonstrated its effectiveness, the major limitation of BZ is the low cure rate during the chronic phase. In 2002, Cançado15 observed cure in 76% of patients with acute phase CD (13–21-year follow-up) and only 8% of patients with chronic phase CD (6–18-year follow-up), supporting previous studies demonstrating the lack of effect during the chronic phase. Table 2 describes the studies in which BZ was used to treat CD.
Summary of the studies in which benznidazole was used to treat Chagas disease
| Reference no. | Year | Country | No. of Patients | Age* | Treatment protocol | Follow-up* | Results at the end of the study |
|---|---|---|---|---|---|---|---|
| 45 | 1994 | Argentina | 131 | 9–66 | 5 mg/kg 30 days | 5–13 years | 21/110 negative serology, 18/18 negative XD |
| 46 | 1996 | Brazil | 64 | 7–12 | 7.5 mg/kg 60 days | 36 months | 37/64 negative serology |
| 28 | 1997 | Brazil | 50 | Not shown | 5 mg/kg 30 days | 12 months | 24/26 negative XD |
| 47 | 1998 | Argentina | 106 | 6–12 | 5 mg/kg 60 days | 48 months | 27/44 negative serology, 40/42 negative XD |
| 30 | 2000 | Argentina | 36 | 13–52 | 5 mg/kg 30 days | 14 (8–23) years | 100% positive serology, 100% negative XD |
| 31 | 2000 | Brazil | 17 | Adults | 10 mg/kg 60 days | 10 years | 100% positive serology, 100% positive PCR |
| 48 | 2000 | Argentina | 130 | 33 (10–79) | 4–8 mg/kg 45–60 days | 80 months | 3/130 negative serology, 3/46 negative PCR |
| 15 | 2002 | Brazil | 113 | 9–69 | 5–10 mg/kg 40–60 days | 6–18 | 9/113 negative serology |
| 24 | 2004 | Argentina | 64 | < 14 | 5 mg/kg 30 days | 13 years (median) | 23/37 negative serology |
| 49 | 2006 | Argentina | 283 | 39 (30–50) | 5 mg/kg 30 days | 9.8 years | 32/218 negative serology |
| 50 | 2006 | Brazil | 27 | 49 (23–88) | 5 mg/kg 60 days | 24 months | 24/27 negative blood culture |
| 51 | 2007 | Argentina | 27 | 17–46 | 5 mg/kg 45–60 days | 20.6 years | 9/27 negative serology, 100% negative XD |
| 52 | 2009 | Honduras | 232 | < 12 | 5–7.5 mg/kg 60 days | 36 months | 215/232 negative serology |
| 52 | 2009 | Guatemala | 124 | < 15 | 5–7.5 mg/kg 60 days | 18 months | 18/31 negative serology |
| 52 | 2009 | Bolivia (Entre Ríos) | 1,409 | < 15 | 5–7.5 mg/kg 60 days | 60 months | 42/1007 negative serology |
| 52 | 2009 | Bolivia (Sucre) | 1,040 | < 18 | 5–7.5 mg/kg 60 days | 9–27 months | 0 negative serology |
| 53 | 2014 | Spain | 26 | 40 | 300 mg/day 60 days | 10 months | 100% positive serology, 16/17 sustained negative PCR |
| 54 | 2015 | Colombia, El Salvador, Brazil, Argentina | 1,431 | 55 (44–61) | 300 mg/day 40–80 days | 7 years | 59.5% PCR+ after treatment |
PCR = polymerase chain reaction; XD = xenodiagnosis.
The data are expressed as mean values except where noted otherwise. In some instances, the range is shown in parentheses.
Drug efficacy is dependent on the susceptibility of different T. cruzi strains to the compound.41,55,56 The existence of strains that are naturally resistant to BZ and NFX has been previously described and poses a major challenge to the development of new anti-T. cruzi drugs.56 Geographical differences of T. cruzi strain might affect cure efficacy because of parasite genetic variability. More than 80% of CD patients in the acute or chronic phase from Chile, Argentina, and Southern Brazil (state of Rio Grande do Sul) treated with NFX showed a high percentage of cure based on xenodiagnosis and serology.28 By contrast, only 40% of cure was detected in the treated patients with CD from Brazilian states of São Paulo, Minas Gerais, Bahia, and Goiás.
Patient age is also an important factor for BZ efficacy. In children with CD aged 6–12 years, treated with BZ for 60 days had a cure efficacy of approximately 56%46 and 62%,47 similar to children aged 6–12 years with an indeterminate CD phase in Argentina,47 in which negative seroconversion was observed in 62% of the treated group.
According to current recommendations for CD treatment from the I Latin American Guidelines for the Diagnosis and Treatment of Chagas Heart Disease,57 BZ chemotherapy is indicated for children, acute cases (congenital transmission included), laboratory accidents, and reactivation (pharmacologically immunosuppressed and human immunodeficiency virus (HIV)-infected patients). In adult patients with an indeterminate phase or established chronic chagasic cardiomyopathy, indications for parasite treatment remain controversial.57 However, in the largest recent study49 to show that BZ treatment slows the development and progression of cardiomyopathy in adults with chronic infection,49,51 566 adults with chronic infection but without advanced heart disease were chosen to receive BZ or no treatment. Significantly fewer treated patients showed disease progression or electrocardiographic (ECG) abnormalities despite seroconversion in only 15% of these patients (median follow-up, 9.8 years).49
A recent retrospective study has shown that treatment with BZ prevents the occurrence of ECG alterations and decreases serological immunofluorescence titers in patients with chronic CD.58
The most frequent adverse effects observed with BZ are skin manifestations, paresthesia, peripheral neuropathy, anorexia, and weight loss; decreased bone marrow, thrombocytopenic purpura, and agranulocytosis are the most severe manifestations.10,59 Side effects have led to treatment interruption in approximately 12–13% of patients.18,30,49 However, other studies have found higher levels of treatment interruption, in 25%60 and 41.5%61 of patients. These differences might be attributable to the treatment duration (30 days in the former and 60 days in the latter studies).
Mechanisms of action of nifurtimox and benznidazole.
Figure 1 shows the mechanism of action of NFX, BZ, and other trypanocidal drugs.
Schematic representation of the mode of action of the major drugs with trypanocidal activity. The green boxes represent drugs currently used for treatment, the yellow boxes represent drugs in clinical trials, and the red boxes represent experimental drugs. (A) Bisphosphonates inhibit farnesyl pyrophosphate synthase, which reduces the levels of sterols and other essential poly-isoprenoids compounds, affecting cell viability. (B) Nifurtimox (NFX) and benznidazole (BZ) are reduced by the parasite nitroreductase, resulting in the production of reactive oxygen species (ROS), which directly damage the cells of the parasite. Trypanothione reductase helps relieve the oxidative stress, and inhibitors of this enzyme, such as thioridazine and sulfoximine buthionine (SB), increase the amount of ROS in the intracellular space. (C) The ergosterol biosynthetic pathway is essential for parasite survival. Blocking this pathway leads to loss of cell viability via depletion of essential sterols and accumulation of toxic intermediates. Ergosterol inhibitors and fenarimol analogues target lanosterol C14 demethylase, and amiodarone and dronedarone partially inhibit oxidosqualene cyclase. Phospholipid inhibitors block sterol synthesis, inhibit de novo phospholipid synthesis via Greenberg’s pathway, and inhibit signal transduction enzymes such as phosphatidylinositol phospholipase C. (D) Amiodarone and dronedarone release Ca2+ from mitochondria and acidocalcisomes (ACs), which increases Ca2+ levels in the cytoplasmic space and compromises cell survival. (E) Cruzipain (CZ) is typically located in the Golgi apparatus, flagellar pocket, and glycosomes and is an essential cysteine protease involved in parasite differentiation, cell invasion, multiplication, and immune evasion. Inhibitors of cruzipain alter the Golgi apparatus, owing to the accumulation of unprocessed cruzipain precursors. This figure appears in color at www.ajtmh.org.
Citation: The American Journal of Tropical Medicine and Hygiene 97, 5; 10.4269/ajtmh.16-0761
The mechanisms of action of BZ and NFX are not entirely clear. BZ reportedly acts via reductive stress involving covalent modification of macromolecules such as DNA, proteins, and lipids.62 In addition, BZ and its metabolites can affect the trypanothione metabolism of T. cruzi.63 BZ also improves phagocytosis,64 increases trypanosomal death through IFN-γ induction,64 and inhibits T. cruzi NADH-fumarate reductase.65
The reduction of NFX to a nitro anion radical followed by the autoxidation of this radical produces highly toxic oxygen metabolites.62 Its deficient metabolic detoxification mechanisms for oxygen render T. cruzi highly susceptible to partial reduction products of oxygen, particularly hydrogen peroxide; therefore, it is more sensitive to oxidation than the vertebrate cells.62,66
Previous studies suggest that the nitroheterocyclic compounds BZ and NFX are prodrugs and require activation by nitroreductases for cytotoxic activity.67 Interestingly, the deletion of copies of genes encoding two different nitroreductases, namely, old yellow enzyme (TcOYE, also named prostaglandin synthase)68 and trypanosomal type I nitroreductase (NTR-1),67 has been associated with the resistance of T. cruzi to NFX and BZ in vitro. A functional analysis associated reduced NTR-1 levels in T. cruzi and T. brucei with resistance to nitroheterocyclic compounds, whereas overexpression of this enzyme resulted in hypersensitivity.67 NTR-1 is absent from mammals, is selective, and catalyzes the two-electron reduction of nitroheterocyclic compounds within the parasite, producing toxic metabolites.69 Interestingly, a recent study using a metabolomic analysis showed that the covalent binding of BZ with thiols as well as protein thiols is the major mechanism of BZ toxicity against T. cruzi metabolites.70 Although the mechanism of drug resistance in this parasite remains poorly understood, differences in susceptibility to BZ and NFX between T. cruzi strains17,56,71 and/or the genetic diversity of the host56 might explain, in part, the variations in the efficacies of these antiparasitic drugs.
In addition to its effects on T. cruzi, nitroreductive bioactivation is also responsible for mammalian BZ toxicity because of the interaction between its reactive metabolites and DNA, proteins, lipids, and other relevant cellular components.
Clinical trials and other studies for Chagas disease treatment.
Since the introduction of BZ and NFX, only allopurinol and the azoles itraconazole, fluconazole, ketoconazole, posaconazole (POSA), and ravuconazole (RAVU) have been studied in clinical trials, observational studies, or clinical cases.53,72–76 When designing novel drugs, specific targets of T. cruzi should be identified using cellular and molecular approaches to achieve both high efficacy and low toxicity.77,78 Currently, the main experimental/preclinical approaches for anti-T. cruzi drugs are based on the inhibitors of ergosterol, trypanothione metabolism, cysteine protease, pyrophosphate metabolism, protein and purine synthesis, lysophospholipid analogues (LPAs), and natural drugs.79 Unfortunately, only a few clinical trials for CD treatment are ongoing or were performed recently (Table 3).
Current status of the drugs used to treat Chagas disease
| Drug | Drug development | In vitro assay | In vivo Assay | Phase I studies | Phase II studies | Phase III studies | Phase IV/approved |
|---|---|---|---|---|---|---|---|
| BZ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| NFX | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| POSA | ✓ | ✓ | ✓ | ✓ | ✓ | – | – |
| RAVU | ✓ | ✓ | ✓ | ✓ | ✓ | – | – |
| ITRA | ✓ | ✓ | ✓ | ✓ | ✓ | – | – |
| KETO | ✓ | ✓ | ✓ | ✓ | X | – | – |
| VORI | ✓ | ✓ | ✓ | ✓ | – | – | – |
| ALBA | ✓ | ✓ | ✓ | ✓ | – | – | – |
| DO8701 | ✓ | ✓ | ✓ | – | – | – | – |
| TAK-187 | ✓ | ✓ | ✓ | – | – | – | – |
| K-777 | ✓ | ✓ | ✓ | X | – | – | – |
| FENARI | ✓ | ✓ | ✓ | Planned | – | – | – |
| FEXINI | ✓ | ✓ | ✓ | ✓ | ✓ | – | – |
| MILTEFO | ✓ | ✓ | ✓ | ✓ | – | – | – |
| EDELFO | ✓ | ✓ | – | – | – | – | – |
| ILMOFO | ✓ | ✓ | – | – | – | – | – |
| NANO BZ | ✓ | ✓ | ✓ | – | – | – | – |
| SELENIUM | ✓ | ✓ | ✓ | ✓ | ✓ | In progress | – |
| ALOPU | ✓ | ✓ | ✓ | ✓ | X | – | – |
| AMIO | ✓ | ✓ | ✓ | ✓ | In progress | – | – |
| SCYX-7158 | ✓ | ✓ | ✓ | In progress | – | – | – |
ALBA = albaconazole; ALOPU = allopurinol; AMIO = amiodarone; BZ = benznidazole; EDELFO = edelfosine; FENARI = fenarimol; FEXINI = fexinidazole; ILMOFO = ilmofosine; ITRA = Itraconazole; KETO = ketoconazole; MILTEFO = miltefosine; NANO BZ = benznidazole nanoformulated; NFX = nifurtimox; POSA = posaconazole; RAVU = ravuconazole; SCYX-7158 = oxaborole; VORI = voriconazole; X = interrupted.
Ergosterol biosynthesis inhibitors.
Posaconazole.
POSA (SCH 56592; Schering-Plough Research Institute) is a potent and selective inhibitor of fungal and protozoan CYP51, a cytochrome P-450 family member. It is commercially available for the prophylaxis of invasive fungal infections and treatment of azole-resistant candidiasis.80 POSA also has potent trypanocidal activity in vitro81 and in vivo82,83 against T. cruzi strains naturally resistant to nitrofurans, nitroimidazoles, and conventional antifungal azoles.83 More importantly, POSA was more active than the reference drug, BZ, against drug-resistant T. cruzi strains in murine models of acute and chronic CD.83 However, recent studies have demonstrated an advantage of BZ over POSA. In an in vitro study comparing the activity of nitroheterocyclics with the activity of POSA and RAVU against intracellular T. cruzi amastigotes representing all current discrete typing units (DTUs), the nitroheterocyclics showed broad, but less potent, efficacy against all T. cruzi DTUs tested, whereas POSA and RAVU showed variable activity and were unable to eradicate intracellular infection even after 7 days of continuous compound exposure.84 In an in vivo study, POSA failed as single treatment and in combination with BZ to clear an infection with a BZ-resistant strain and was less effective in curing infections with BZ susceptible strains.85
The success demonstrated with POSA in a patient with chronic CD and systemic lupus erythematosus86 encouraged the initiation of two phase II clinical trials in CD patients (ClinicalTrials.gov Identifiers: NCT01377480 and NCT01162967). One of these clinical trials (CHAGASAZOL) concluded in August 2012 and was an independent study financed by the Spanish Ministry of Health and performed by Vall d’Hebron University Hospital and the International Health Program of the Catalan Health Institute (PROSICS).53 This multicenter, randomized, open-label clinical trial compared BZ (5 mg/kg/day for 60 days) and two schedules of POSA (100 mg/12 hours and 400 mg/12 hours for 60 days) in 78 chronic CD patients. During the follow-up, a greater proportion of patients had treatment failure with POSA than BZ, as measured by positivity with real-time PCR of T. cruzi in peripheral blood. The other study, STOP CHAGAS (ClinicalTrials.gov Identifier: NCT01377480), was completed in 2015. The successful response, which was defined as a negative qualitative PCR value at the day 180 follow-up were the following: POSA (13.3%), Placebo (10%), POSA + BZ (80%) and BZ + Placebo (86.7%); P = 0.69 for POSA versus Placebo; P < 0.0001 for POSA versus POSA + BZ. These data reinforce the idea that BZ monotherapy is superior to POSA either as monotherapy or as combination therapy.87
In addition, POSA is an extremely expensive drug, and its cost can hinder its use in developing countries.88
Ravuconazole.
It is a triazole derivative with potent and broad-spectrum antifungal activity. In murine models of acute CD, RAVU had high parasitological cure activity against nitrofuran/nitroimidazole-susceptible (CL strain) and partially drug-resistant (Y strain) T. cruzi strains, but no curative activity in mice infected with the fully drug-resistant Colombiana strain in a model of chronic CD.89 In a canine model of acute CD, RAVU had potent suppressive, but not curative, activity.90 The short terminal half-life of RAVU in mice (4 hours) and dogs (8.8 hours) may explain these results. The longer half-life in humans (4–8 days) encouraged its use for chemotherapy in human CD. One advantage is the need for less frequent use of RAVU than BZ and NFX.
The major advantages of RAVU include its simpler chemical structure and low price compared with POSA.91 In 2009, the Drugs for Neglected Diseases initiative (DNDi) collaborated with Eisai Co. Ltd., a Japanese pharmaceutical company that discovered E1224, to develop a new chemical entity for CD. E1224 is a prodrug that converts to RAVU, leading to improved drug absorption and bioavailability.76 A phase II randomized, multicenter, placebo-controlled study evaluated the safety and efficacy of three oral E1224 dosing regimens (high dose for 4 or 8 weeks; low dose for 8 weeks) and BZ (5 mg/kg/day) in 231 adult patients with chronic indeterminate CD who were recruited from research centers in Tarija and Cochabamba, Bolivia (ClinicalTrials.gov Identifier: NCT01489228). E1224 showed good safety and was effective in clearing the T. cruzi, but 1 year after treatment, only 8–31% of patients treated with E1224 maintained parasite clearance compared with 81% of BZ-treated patients, demonstrating that E1224 has low parasite eradication rates.76
Itraconazole.
Itraconazole, a synthetic imidazole derivative, has shown good efficacy against T. cruzi both in vitro and in vivo.92 In a blinded study of itraconazole use (6 mg/kg/day for 120 days) in 46 patients with chronic CD from an endemic area of Chile, monitoring for ECG abnormalities and xenodiagnosis or real-time xenodiagnosis quantitative polymerase chain reaction for T. cruzi infection was conducted before treatment and annually for 20 years.93 The control group consisted of 67 patients with chronic indeterminate CD who were followed-up for 4 years, and for ethical reasons, this group was treated after the experimental period. After the 20 years, only 10.86% of the patients had developed ECG abnormalities, and 32.6% had negative xenodiagnosis test results, indicating that itraconazole prevents ECG abnormalities. The major limitation of this study is that xenodiagnosis and PCR are not reliable indicators of cure because they show low sensitivity for T. cruzi detection in chronic CD patients.14
Amiodarone/Dronedarone.
Amiodarone is a class III antiarrhythmic agent frequently used for the treatment of symptomatic patients with the clinical cardiac form of CD. It has direct activity against T. cruzi, both in vitro and in vivo, and potent synergistic activity with POSA.94 In addition to disrupting Ca2+ homeostasis in T. cruzi by inducing Ca2+ release from intracellular stores, specifically the single giant mitochondrion, amiodarone also blocks ergosterol biosynthesis.94 Treatment with amiodarone was associated with clinical improvement in at least one clinical case of human CD.95 An observational study showed that cardioverter-defibrillator implantation plus amiodarone reduced the risk of all-cause mortality and sudden death com