Nifurtimox

Risk Summary

Based on animal studies, nifurtimox may cause fetal harm when administered to a pregnant woman. Published postmarketing reports on nifurtimox use during pregnancy are insufficient to inform a drug-associated risk of birth defects and miscarriage. There are risks to the fetus associated with Chagas disease.

Nifurtimox administered orally to pregnant mice, rats, and rabbits during organogenesis was associated with reduced fetal body weights in mice, reduced maternal and fetal body weights in rats, and abortions, reduced maternal weight gain, and reduced numbers of live fetuses in rabbits when nifurtimox was administered orally during organogenesis at doses approximately equal to the MRHD in rodents and 2-times the MRHD in rabbits. An increased incidence of a fetal skeletal malformation (fusion of caudal vertebral bodies) occurred in rabbits at nifurtimox doses approximately 0.2 times the MRHD. In a pre-postnatal study, maternal body weights and fetal body weights of first generation offspring were reduced at doses approximately equal to or 0.5 times the MRHD, respectively, and several male offspring in the nifurtimox treatment groups exhibited slightly small testes at doses ≥0.2 times the MRHD (see Data). Advise pregnant women of the potential risk to a fetus.

There is a pregnancy safety study for nifurtimox. If nifurtimox is administered during pregnancy, or if a patient becomes pregnant while receiving nifurtimox or within six months following the last dose of nifurtimox, healthcare providers should report nifurtimox exposure.

The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.

Clinical Considerations

Disease-associated Maternal and/or Embryo/Fetal Risk

Published data from case-control and observational studies on chronic Chagas disease during pregnancy are inconsistent in their findings. Some studies showed an increased risk of pregnancy loss, prematurity and neonatal mortality in pregnant women who have chronic Chagas disease while other studies did not demonstrate these findings. Chronic Chagas disease is usually not immediately life-threatening. Since pregnancy findings are inconsistent, treatment of chronic Chagas disease during pregnancy is not recommended due to risk of embryo-fetal toxicity from nifurtimox.

Acute symptomatic Chagas disease is rare in pregnant women; however, symptoms may be serious or life-threatening. If a pregnant woman presents with acute symptomatic Chagas disease, the risks versus benefits of treatment with nifurtimox to the mother and the fetus should be evaluated on a case-by-case basis.

Data

Animal Data

In preliminary embryo-fetal studies, pregnant mice and rats were administered 20, 50, and 125 mg/kg/day nifurtimox during the period of organogenesis [gestation day (GD) 6 to GD 15 for both species]. Maternal body weights were significantly reduced in the 50 and 125 mg/kg/day dose groups in rats, but not in mice. No fetal malformations were reported for either species, but mean fetal weights were significantly reduced in the 125 mg/kg/day dose group in mice and in the 50 and 125 mg/kg/day dose groups in rats. No maternal toxicity was observed in mice at 125 mg/kg/day or in rats at 20 mg/kg/day (respectively approximately equal to or 0.3-times the MRHD based on body surface area comparison). No adverse fetal effects were observed in mice at a dose of 50 mg/kg/day or in rats at a dose of 20 mg/kg/day (respectively equivalent to 0.4-times or 0.3-times the MRHD based on body surface area comparison).

In pregnant rabbits administered 5, 15, and 60 mg/kg/day nifurtimox during the period of organogenesis (GD 6 to GD 20), the high dose was associated with maternal toxicity including reduced body weights and food consumption, and abortions in 8/20 high-dose dams. The mean number of live fetuses/litter and the percent of live fetuses per total implantations per group were significantly lower in the mid- and high-dose groups compared to the control group. Nifurtimox administration was associated with increased fetal and litter incidences of a skeletal malformation (fusion of caudal vertebral bodies) in fetuses in the low-dose group receiving 5 mg/kg/day (approximately equivalent to 0.2-times the MRHD based on body surface area comparison). No maternal toxicity was observed at 15 mg/kg/day which is approximately equivalent to 0.5 times the MRHD based on body surface area comparison.

In a pre-postnatal study, pregnant female rats were administered 15, 30, and 60 mg/kg/day nifurtimox during organogenesis and lactation [GD 6 to lactation day (LD) 21]. Maternal findings included reduced maternal body weights in high-dose dams during gestation and to a lesser degree during lactation. In first-generation offspring, body weights were significantly reduced in males and females in the high-dose group during the lactation and post-lactation periods. Physical development, neurological function, and reproduction of first-generation offspring were not substantially changed in the nifurtimox treatment groups, but 5–20% of male offspring in all the nifurtimox treatment groups exhibited slightly small testes. No adverse maternal effects or fetal effects on first-generation female offspring occurred at 30 mg/kg/day, and no adverse fetal effects on the development of male offspring occurred at 15 mg/kg/day (respectively approximately 0.5- and 0.2-times the MRHD based on body surface area comparison).

Risk Summary

Published literature demonstrates that nifurtimox is present in human breast milk with an estimated infant daily dose of less than 15% of the recommended daily dose for pediatric patients with Chagas disease. There were no reports of adverse effects on the small number of infants who were breastfed by mothers taking nifurtimox. There is no information on the effects of nifurtimox on milk production. Monitor infants exposed to nifurtimox through breast milk for vomiting, rash, decreased appetite, pyrexia and irritability.

The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for nifurtimox and any potential adverse effects on the breastfed infant from nifurtimox or from the underlying maternal condition.

Carcinogenicity

Adequate long-term carcinogenicity studies for nifurtimox have not been performed. Nitrofurans, which have similar chemical structures to nifurtimox have been reported to be carcinogenic in mice and rats.

Genetic Toxicity

The genotoxicity of nifurtimox has been demonstrated in vitro in several bacterial species and mammalian cell systems and in vivo in mammals.

Nifurtimox was mutagenic in strains of S. typhimurium (TA 98, 100, and 1537) in an Ames assay.

Nifurtimox was genotoxic in human lymphocytes in an in vitro micronucleus assay.

In vivo, nifurtimox was shown to be positive for genotoxicity in a mouse micronucleus assay, a mouse sister-chromatid exchange assay, and a human chromosome aberration assay. However, in a sister-chromatid exchange study in humans, oral doses of nifurtimox did not cause a significant increase in the frequency of sister-chromatid exchange in blood lymphocytes.

Impairment of Fertility

In a study examining the effects of nifurtimox on testicular morphology, male mice fed 0.08% or 0.16% nifurtimox in animal feed for 14 weeks experienced dose-dependent testicular toxicity including complete inhibition of spermatogenesis with the highest dose, evidence of arrested mitosis, signs of pyknosis, and no mature sperm. However, interstitial cells were unchanged, and fibrosis and inflammatory infiltrates were not observed. Nine weeks after the end of nifurtimox exposure, all testicular effects were almost entirely reversed.

In a male and female fertility study in rats, nifurtimox was administered in dietary feed at doses of 150 ppm (equivalent to 7–15 mg/kg), 300 ppm (equivalent to 15–30 mg/kg/day), and 600 ppm (equivalent to 30–60 mg/kg/day) for 10 weeks before mating. Male fertility was completely inhibited in rats administered 30–60 mg/kg/day nifurtimox, but female fertility was not affected for the same dosing regimen. In a recovery study, 11 weeks after the end of dosing, fertility was still inhibited in 75% of male rats administered nifurtimox for 32 weeks indicating a lack of complete reversibility. The nifurtimox dose in male rats that was not associated with inhibition of fertility was considered to be ≤30 mg/kg/day which is approximately equivalent to 0.5 times the MRHD for fertile males based on body surface area comparison.

• Potential for Genotoxicity, Carcinogenicity, and Mutagenicity
• Worsening of Neurological and Psychiatric Conditions
• Hypersensitivity
• Decreased Appetite and Weight Loss
• Porphyria

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The safety data described below reflect exposure to nifurtimox in one prospective, randomized, double-blind trial (Trial 1). 330 pediatric patients with serologic evidence of T. cruzi infection and without Chagas disease-related cardiac or gastrointestinal symptoms were randomly assigned in a 2:1 fashion to a 60-day (n=219) or a 30-day (n=111) nifurtimox treatment regimen and were followed up for one year after end of treatment. Nifurtimox was administered three times a day with food using a body weight-based dosing. The median treatment duration was 61 days for subjects in the 60-day regimen. The majority (86.7%) of the study population was ≥2 to <18 years of age at randomization.

Discontinuation of nifurtimox due to adverse reactions occurred in 14 of 330 (4.2%) patients overall, 12 of 219 (5.5%) patients in the 60-day arm, and 2 of 111 (1.8%) patients in the 30-day arm. Adverse reactions were reported for 213 of 330 (64.5%) patients. The proportion of patients with adverse reactions was higher in the 60-day regimen (67.1%) compared with the 30-day regimen (59.5%). Most patients with adverse reactions had mild (76.5%) or moderate (22.0%) reactions.

The most frequently reported adverse reactions in patients treated with nifurtimox for 60 days were vomiting (14.6%), abdominal pain (13.2%), headache (12.8%), decreased appetite (10.5%), nausea (8.2%), pyrexia (7.3%), rash (5.5%).

Adverse reactions occurring in ≥1% of nifurtimox-treated patients are shown in the following table.

Adverse Reactions Reported in (≥1%) Pediatric Patients with Chagas Disease in Trial 1 Treated with Nifurtimox for 60 days:

^a Abdominal pain includes abdominal pain and abdominal pain upper
^b Rash includes rash, rash macular, rash maculo-papular, rash morbilliform, and rash papular.

Other adverse reactions occurring in 0.1% to less than 1% of patients treated with nifurtimox for 60 days included asthenia, vertigo, arthralgia, myalgia, paresthesia, tremor, irritability, anxiety, pruritus, fatigue, somnolence, seizure, syncope, neutropenia, leukopenia.

Postmarketing Experience

The following safety data were derived during postmarketing surveillance of nifurtimox from outside the United States, including literature data for all age groups (pediatric and adult populations). Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Postmarketing Adverse Reactions Reported in Pediatric and Adult Populations Treated with Nifurtimox: