Benznidazole

Description

Benznidazole Tablets contain benznidazole, a nitroimidazole antimicrobial. The chemical name of benznidazole is N-benzyl-2-(2-nitro-1H-imidazol-1-yl) acetamide. The empirical formula is C₁₂H₁₂N₄O₃ and the molecular weight is 260.246 g/mol. The structural formula is:

 

Figure 1: Benznidazole Structure

Benznidazole is a yellowish, practically crystalline powder that is practically insoluble in water, sparingly soluble in acetone and ethanol, and slightly soluble in methanol.

Benznidazole Tablets are white round tablets each containing 12.5 mg or 100 mg of benznidazole, for oral use. The 100 mg white tablets are round and functionally scored twice as a cross on both sides debossed with “E” on one side of each quarter portion. The 12.5 mg white tablets are round and unscored debossed with “E” on one side.

The inactive ingredients are as follows: magnesium stearate, NF; microcrystalline cellulose, NF; monohydrate lactose, NF; pre-gelatinized corn starch, NF; and sodium croscarmellose, NF.

Indications

Benznidazole Tablets are indicated in pediatric patients 2 to 12 years of age for the treatment of Chagas disease (American trypanosomiasis) caused by Trypanosoma cruzi.

This indication is approved under accelerated approval based on the number of treated patients who became Immunoglobulin G (IgG) antibody negative against the recombinant antigens of T. cruzi [see Clinical Studies]. Continued approval for this indication may be contingent upon verification and description of clinical benefit in confirmatory trials.

Dosage And Administration

Important Administration Instructions

• Benznidazole Tablets (12.5 mg and 100 mg) are for oral use and may be taken with or without food [see CLINICAL PHARMACOLOGY].
• Benznidazole Tablets are dosed by body weight (kg) [see Recommended Dosage In Pediatric Patients (2 To 12 Years Of Age)].
• Benznidazole Tablets 100 mg are functionally scored tablets which can be split into one-half (50 mg) or one-quarter (25 mg) at the scored lines to provide doses less than 100 mg [see Instructions for Use].
• Benznidazole Tablets 12.5 mg and 100 mg can be made into slurry as an alternative method of administration [see Preparation Of Slurry As An Alternative Method Of Administration].

Recommended Dosage In Pediatric Patients (2 To 12 Years Of Age)

The total daily dose for pediatric patients 2 to 12 years of age is 5 mg/kg to 8 mg/kg orally administered in two divided doses separated by approximately 12 hours, for a duration of 60 days (see Table 1).

Table 1: Recommended Dosage of Benznidazole Tablets in Pediatric Patients (2 to 12 Years of Age)

Body Weight Range (kg)	Dose (mg)	Number of Benznidazole Tablets 12.5 mg	Number of Benznidazole Tablets 100mg	Duration and Frequency of Therapy
Less than 15 kg	50 mg	4 tablets	½ tablet	Administered twice daily approximately 12 hours apart for 60 days.
15 kg to less than 20 kg	62.5 mg	5 tablets
20 kg to less than 30 kg	75 mg	6 tablets	¾ tablet
30 kg to less than 40 kg	100 mg		1 tablet
40 kg to less than 60 kg	150 mg		1 ½ tablets
Greater than or equal to 60 kg	200 mg		2 tablets

Assessment Prior To Initiating Benznidazole Tablets

Obtain a pregnancy test in females of reproductive potential prior to therapy with Benznidazole Tablets [see Use In Specific Populations].

Preparation Of Slurry As An Alternative Method Of Administration

Preparation Of Slurry Using Benznidazole Tablets 12.5 mg For The Pediatric Population With Body Weight Less Than 30 kg

Benznidazole Tablets 12.5 mg may be made into slurry in a specified volume of water for the pediatric population with body weight less than 30 kg (see Table 2). The 12.5 mg tablet slurry is prepared by the following method:

Table 2: Preparation and Administration of Slurry Using Benznidazole Tablets 12.5 mg for the Pediatric Population with Body Weight of Less than 30 kg

Place the prescribed dose of Benznidazole Tablets 12.5 mg into a cup. Add the specified volume of water per number of 12.5 mg tablets as shown below.
Body Weight Range (kg)	Dose (mg)	Number of Benznidazole Tablets 12.5 mg	Quantity of Water for Preparing the Slurry
Less than 15 kg	100 mg	4 tablets	40 mL
15 kg to less than 20 kg	62.5 mg	5 tablets	50 mL
20 kg to less than 30 kg	75 mg	6 tablets	60 mL
Allow the tablets to disintegrate in the cup over a period of approximately 1-2 minutes. Shake the contents of the cup gently to mix. Drink the contents of the cup (slurry of tablets with water) immediately. Rinse the cup with an additional 10 mL of water and drink the whole amount.

Preparation Of Slurry Using Benznidazole Tablets 100 mg For The Pediatric Population With Body Weight (30 kg Or Greater)

Benznidazole Tablets 100 mg may be made into a slurry in a specified volume of water for the pediatric population with body weight of 30 kg or greater (see Table 3). The 100 mg tablet slurry is prepared as follows:

Table 3: Preparation and Administration of Slurry Using Benznidazole Tablets 100 mg for the Pediatric Population with Body Weight 30 kg or greater

Place the prescribed dose of Benznidazole Tablets 100 mg tablets into a cup. Add the specified volume of water per number of 100 mg tablets as shown below.
Body Weight Range (kg)	Dose (mg)	Number of Benznidazole Tablets 100 mg	Quantity of Water for Preparing the Slurry
30 kg to less than 40 kg	100 mg	1 tablet	80 mL
40 kg to less than 60 kg	150 mg	1 ½ tablets	120 mL
Greater than or equal to 60 kg	200 mg	2 tablets	160 mL
Allow the tablet(s) to disintegrate in the cup over a period of approximately 1-2 minutes. Shake the contents of the cup gently to mix. Drink the contents of the cup (slurry of tablet(s) with water) immediately. Rinse the cup by adding 80 mL of water and drink the whole amount. Repeat this rinse with 80 mL of water and drink again.

How Supplied

Dosage Forms And Strengths

Benznidazole Tablets are available as 100 mg and 12.5 mg tablets.

The 100 mg white tablets are round and functionally scored twice as a cross on both sides, debossed with “E” on one side of each quarter portion.

The 12.5 mg white tablets are round and unscored, debossed with “E” on one side.

Benznidazole Tablets (12.5 mg or 100 mg) are supplied as follows:

• 100 mg white tablets, round and functionally scored twice as a cross on both sides. Each tablet is about 10 mm in diameter debossed with “E” on one side of each quarter portion.
• 12.5 mg white tablets, round and unscored. Each tablet is about 5 mm in diameter debossed with “E” on one side.

Benznidazole Tablets 100 mg are available in bottles of 100 tablets (NDC 0642-7464-10).

Benznidazole Tablets 12.5 mg are available in bottles of 100 tablets (NDC 0642-7463-12).

Storage And Handling

Store at controlled room temperature 20°C to 25°C (68°F to 77°F); excursions permitted to 15°C to 30°C (59°F to 86°F) [See USP Controlled Room Temperature]. Keep bottle tightly closed and protect from moisture.

REFERENCES

1. Sosa Estani S, et al., 1998, Efficacy of Chemotherapy with Benznidazole in Children in the Indeterminate Phase of Chagas’ Disease. Am J Trop Med Hyg 59: 526-529.

2. de Andrade, Ana Lucia S. Sgambatti, et al., 1996, Randomised Trial of Efficacy of Benznidazole in Treatment of Early Trypanosoma cruzi Infection. Lancet 348: 1407-1413.

3. Altcheh, Jaime, et al., 2014, Population Pharmacokinetic Study of Benznidazole in Pediatric Chagas Disease Suggests Efficacy Despite Lower Plasma Concentrations than in Adults. PLoS Negl Trop Dis 8:e2907.

4. García-Bournissen, F, S Moroni, ME Marson, et al., 2015, Limited Infant Exposure to Benznidazole Through Breast Milk During Maternal Treatment for Chagas Disease. Arch Dis Child 100:90-94.

Manufactured by: Laboratorios Liconsa S.A., Guadalajara, Spain. Revised: Aug 2017

Side Effects

The following serious and otherwise important adverse reactions are discussed in greater detail in other sections of labeling:

• Potential for Genotoxicity, Carcinogenicity, and Mutagenicity [see WARNINGS AND PRECAUTIONS]
• Hypersensitivity Skin Reactions [see WARNINGS AND PRECAUTIONS]
• Central and Peripheral Nervous System Effects [see WARNINGS AND PRECAUTIONS]
• Hematological Manifestations of Bone Marrow Depression [see WARNINGS AND PRECAUTIONS]

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.

Benznidazole was evaluated in two randomized, double-blind, placebo-controlled trials (Tril 1¹ and Trial 2²) and one uncontrolled trial (Trial 3³).

Trial 1 was conducted in pediatric patients 6 to 12 years of age with chronic indeterminate Chagas disease in Argentina. The chronic indeterminate form includes patients with serologic evidence of T. cruzi infection without symptoms of cardiac or gastrointestinal disease. A total of 106 patients were randomized to receive either benznidazole (5 mg/kg/day twice daily for 60 days; N= 55) or placebo (N=51) and followed for 4 years.

Trial 2 was conducted in pediatric patients 7 to 12 years of age with chronic indeterminate Chagas disease in Brazil. A total of 129 patients were randomized to receive either benznidazole (7.5 mg/kg/day twice daily for 60 days; N = 64) or placebo (N = 65) and followed for 3 years.

Trial 3 was an uncontrolled study in pediatric patients 2 to 12 years of age with chronic indeterminate Chagas disease. A total of 37 pediatric patients with Chagas disease were enrolled in this safety and pharmacokinetics study. Patients were treated with benznidazole 5 to 8 mg/kg/day twice daily for 60 days.

Adverse Reactions Leading To Discontinuation

In Trial 1, benznidazole was discontinued due to an adverse reaction in 5/55 (9%) patients. Some patients had more than one adverse reaction resulting in treatment discontinuation. The adverse reactions included abdominal pain, nausea, vomiting, rash, decreased appetite, headache, and transaminases increased.

Common Adverse Reactions In Pediatric Patients

The most frequently reported adverse reactions in pediatric patients treated with benznidazole in Trial 1 were abdominal pain (25%), rash (16%), decreased weight (13%), and headache (7%). Table 4 lists adverse reactions occurring at a rate of 1% or greater in pediatric patients with Chagas disease aged 6 to 12 years of age in Trial 1.

Table 4: Adverse Reactions Occurring in Pediatric Patients with Chagas Disease aged 6 to 12 Years in Trial 1

Body System	Adverse Reaction	Benznidazole (N=55) N (%)	Placebo (N=51) N (%)
Gastrointestinal	Abdominal pain	14 (25)	4 (8)
	Weight decreased	7 (13)	1 (2)
	Nausea	3 (5)	1 (2)
	Vomiting	3 (5)	0
	Diarrhea	2 (4)	0
	Decreased appetite	3 (5)	0
Skin and subcutaneous tissue	Rash	9 (16)	0
Metabolism/Laboratory	Transaminases increased	3 (5)	0
Nervous system Disorders	Dizziness	2 (4)	2 (4)
	Peripheral neuropathy	1 (2)	0
	Tremor	1 (2)	0

In Trial 2, skin lesions were reported in 7 of 64 (11%) pediatric patients treated with benznidazole and in 2 of 65 patients receiving placebo. Adverse reactions reported in fewer than 5% of benznidazole-treated patients included nausea, anorexia, headache, abdominal pain and arthralgia.

In a subset of 19 pediatric patients 2 to 6 years of age treated with benznidazole in Trial 3, 6 patients (32%) had the following adverse reactions: rash, leukopenia, urticaria, eosinophilia, decreased appetite, and neutropenia. These adverse reactions were similar to those observed in the overall population of 37 patients.

Postmarketing Experience

The following adverse reactions have been identified during the use of other formulations of benznidazole outside of the United States. Because these reactions are reported from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Table 5: Adverse Reactions Reported in the Published Literature

Body System	Adverse Reactions
Dermatological	Maculo-papular cutaneous eruptions Erythematous plaques Rash, generalized Rash, erythematous Pruritic rash Blistering eruptions Peeling skin Exfoliative dermatitis Toxic epidermal necrolysis AGEP Erythema multiforme Drug reaction with eosinophilia and systemic symptoms
Neurological (central and peripheral nervous system)	Paresthesia Hypoesthesia Headaches Insomnia Convulsions Inability to concentrate Amnesia, temporary Disorientation, temporary
Gastrointestinal	Epigastric pain Dry mouth Ageusia
Hepatobiliary disorders	Hepatitis Toxic hepatitis
Skeletal Muscle	Myalgia Musculoskeletal pain Migratory arthritis
General / Constitutional Symptoms	Fever Asthenia Fatigue
Lymphatic	Generalized edema Eyelid edema Edema in the extremities Lymphadenopathy
Bone Marrow	Thrombocytopenia Granulocytopenia Agranulocytosis
Metabolism / Laboratory	Elevation of alkaline phosphatase Elevation of bilirubin

Drug Interaction

Disulfiram

Psychotic reactions have been reported in patients who are concurrently taking disulfiram and nitroimidazole agents (structurally related to benznidazole, but not with benznidazole). Benznidazole Tablets should not be given to patients who have taken disulfiram within the last two weeks [see CONTRAINDICATIONS].

Alcohol And Products Containing Propylene Glycol

Abdominal cramps, nausea, vomiting, headaches, and flushing may occur if alcoholic beverages or products containing propylene glycol are consumed during or following therapy with nitroimidazole agents which are structurally related to benznidazole. Although no similar reactions have been reported with benznidazole, discontinue alcoholic beverage or products containing propylene glycol during and for at least 3 days after therapy with Benznidazole Tablets [see CONTRAINDICATIONS]

Warnings

Included as part of the “PRECAUTIONS” Section

PRECAUTIONS

Potential For Genotoxicity And Carcinogenicity

Genotoxicity

Genotoxicity of benznidazole has been demonstrated in humans, in vitro in several bacterial species and mammalian cell systems, and in vivo in rodents [see Nonclinical Toxicology].

A study evaluating the cytogenetic effect of benznidazole in pediatric patients ranging from 11 months to 11 years of age (the safety and effectiveness of Benznidazole Tablets in patients less than 2 years old has not been established) with Chagas disease demonstrated a two-fold increase in chromosomal aberrations. In pediatric patients with Chagas disease who were treated with benznidazole, the median incidence of micronucleated interphase lymphocytes in 20 patients increased 2 fold compared to pre-dose values. In the same study, the mean incidence of chromosomal aberrations in 10 patients also increased 2 fold compared to pre-dose values.

Carcinogenicity

Carcinogenicity has been observed in mice and rats treated chronically with nitroimidazole agents which are structurally similar to benznidazole. Similar data have not been reported for benznidazole [see Nonclinical Toxicology]. It is not known whether benznidazole is associated with carcinogenicity in humans.

Embryo-Fetal Toxicity

Based on findings from animal studies, Benznidazole Tablets can cause fetal harm when administered to a pregnant woman. In animal reproduction studies, benznidazole administered orally to pregnant rats and rabbits during organogenesis was associated with fetal malformations at doses approximately 1-3 times the maximum recommended human dose (MRHD) in rats (anasarca, anophthalmia, and/or microphthalmia) and doses approximately 0.3-1 times the MRHD in rabbits (ventricular septal defect). In rats, reduced maternal weights and smaller litter sizes occurred at a dose approximately 3 times the MRHD. In rabbits, reduced maternal weight gain, and abortions in 2/20 females occurred at a dose approximately equal to the MHRD [see Use In Specific Populations]. Advise pregnant women of the potential risk to a fetus. Pregnancy testing is recommended for females of reproductive potential [see DOSAGE AND ADMINISTRATION]. Advise females of reproductive potential to use effective contraception during treatment with Benznidazole Tablets and for 5 days after the last dose [see Use In Specific Populations and CLINICAL PHARMACOLOGY].

Hypersensitivity Skin Reactions

Serious skin and subcutaneous disorders including acute generalized exanthematous pustulosis (AGEP), toxic epidermal necrolysis (TEN), erythema multiforme, and eosinophilic drug reaction have been reported with benznidazole. Discontinue treatment at the first evidence of these serious cutaneous reactions [see ADVERSE REACTIONS].

Extensive skin reactions, such as rash (maculopapular, pruritic macules, eczema, pustules, erythematous, generalized, and allergic dermatitis, exfoliative dermatitis) have also been reported. Most cases occurred after approximately 10 days of treatment with benznidazole. Most rashes resolved with treatment discontinuation.

In case of skin reactions presenting with additional symptoms or signs of systemic involvement such as lymphadenopathy, fever and/or purpura, discontinuation of treatment is recommended.

Central And Peripheral Nervous System Effects

Treatment with Benznidazole Tablets can cause paresthesia or symptoms of peripheral neuropathy that may take several months to resolve. Headache and dizziness have been reported. In cases where neurological symptoms occur, immediate discontinuation of treatment is recommended. In most cases, symptoms occur late in the course of treatment.

Hematological Manifestations Of Bone Marrow Depression

There have been reports of hematological manifestations of bone marrow depression, such as neutropenia, thrombocytopenia, anemia and leukopenia, which resolved after treatment discontinuation [see ADVERSE REACTIONS]. Patients with hematological manifestations of bone marrow depression must take Benznidazole Tablets only under strict medical supervision. Monitor complete blood count. Total and differential leukocyte counts are recommended before, during and after therapy.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment Of Fertility

Carcinogenicity

Long-term carcinogenicity studies for benznidazole have not been performed.

Nitroimidazoles, which have similar chemical structures to benznidazole have been reported to be carcinogenic in mice and rats.

Genetic Toxicity

Genotoxicity of benznidazole has been demonstrated in vitro in several bacterial species and mammalian cell systems and in vivo in mammals.

Benznidazole was mutagenic in several strains of S. typhimurium (TA 100, 102 1535, 1537, 1538, 97, 98 99 53 and UTH8414), E.coli, and K. pneumoniae.

Benznidazole was genotoxic in several in vitro mammalian cell assays including a chromosome aberration assay in human lymphocytes and in sister chromatid exchange assays in human lymphocytes and in Human Hep G2 cells

In vivo, benznidazole was shown to be positive for genotoxicity in a mouse bone marrow micronucleus assay, in mouse and human red blood cell micronucleus assays, in a mouse abnormal sperm head assay and in a human peripheral blood lymphocyte assay. However in other micronucleus studies in mice and rats, oral doses of benznidazole did not cause a significant increase in the frequency of chromosomal aberrations in bone marrow cells or micronuclei in peripheral blood cells.

Impairment Of Fertility

In a 6-month, chronic repeated-dosing study with Wistar rats, benznidazole was shown to produce dose-dependent testicular and epididymal atrophy at a dose of 30 mg/kg/day (approximately equivalent to 0.6 times the MRHD based on whole body surface area comparisons). Aspermia was also evident in affected rats, but fertility was not assessed in this study. The NOAEL value in this study was considered to be 10 mg/kg/day (5 mg/kg twice daily) in males which is approximately 0.2-times the MRHD based on body surface area comparison. In other literature reports, benznidazole has been shown to cause testicular atrophy and inhibit spermatogenesis in pubertal and adult rats and mice^5-7 .

In a female fertility study, oral (gavage) administration of benznidazole to female Wistar rats twice daily for a 2-week pre-mating period, during mating, and through day 7 of gestation was associated with transient lower body weight gain and food consumption. There was no benznidazole-related effect on mating performance or fertility and no adverse macroscopic or reproductive organ weight changes. However, benznidazole reproductive performance was associated with a higher post-implantation loss with lower live litter size at a dose of 150 mg/kg/day (equivalent to approximately 3 times the MRHD based on whole body surface area comparisons). The NOAEL value for this study was considered to be 50 mg/kg/day which is approximately equivalent to the MRHD based on whole body surface area comparison.

Use In Specific Populations

Pregnancy

Risk Summary

Based on findings from animal studies, Benznidazole Tablets may cause fetal harm when administered to a pregnant woman. Published postmarketing reports on benznidazole use during pregnancy are insufficient to inform a drug-associated risk of adverse pregnancy-related outcomes. There are risks to the fetus associated with Chagas Disease (see Clinical Considerations). In animal reproduction studies, benznidazole administered orally to pregnant rats and rabbits during organogenesis was associated with fetal malformations at doses approximately 1-3 times the MRHD in rats (anasarca, anophthalmia, and/or microphthalmia) and doses approximately 0.3-1.0 times the MRHD in rabbits (ventricular septal defect) (see Data). Advise pregnant women of the potential risk to a fetus.

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 2-4% and 15-20%, 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 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 Benznidazole Tablets.

Acute symptomatic Chagas disease is rare in pregnant women; however, symptoms may be serious or life-threatening. There have been reports of pregnant women with life-threatening symptoms associated with acute Chagas disease who were treated with benznidazole. If a pregnant women presents with acute symptomatic Chagas disease, the risks versus benefits of treatment with Benznidazole Tablets to the mother and the fetus should be evaluated on a case-by-case basis.

Data

Animal Data

In an embryo-fetal toxicity study in pregnant rats, an oral dose of benznidazole of 150 mg/kg/day during organogenesis (days 6-17 of gestation) was associated with maternal weight loss, reduced fetal weights, and smaller litter sizes. Benznidazole was also associated with a low incidence of fetal malformations including anasarca in one fetus at a dose of 50 mg/kg/day and anasarca and eye abnormalities (anophthalmia and microphthalmia) in 5 fetuses in 5 litters at a high dose of 150 mg/kg/day (approximately equivalent to 1 and 3 times, respectively, the MRHD based on whole body surface area comparisons). The No Observed Adverse Effect Level (NOAEL) dose for maternal toxicity in this study, 50 mg/kg/day, is approximately equal to the MRHD based on body surface area comparisons. The NOAEL dose for fetal toxicity was 15 mg/kg/day which is approximately equivalent to 0.3 times the MRHD based on whole body surface area comparisons.

In an embryo-fetal study in pregnant rabbits, oral (gavage) administration of benznidazole during organogenesis (days 6 to 19 of gestation) at a high dose of 25 mg/kg/day was associated with maternal toxicity including reduced weight gain and food consumption and abortions in 2/20 females. Benznidazole was also associated with a low incidence of fetal abnormalities including ventricular septal defect in 2 fetuses in 2 litters at a dose of 7.5 mg/kg/day and in 1 fetus at a dose of 25 mg/kg/day (approximately equivalent to 0.3 and 1 times respectively the MRHD based on whole body surface area comparisons). The NOAEL values for maternal and fetal toxicity in this study were 7.5 and 2.5 mg/kg/day respectively, which are respectively equivalent to approximately 0.3 and 0.1 times the MRHD based on body surface area comparisons.

In a pre-postnatal study in rats, first generation (F₁) pups born to dams administered 15, 50, and 75 mg/kg/day benznidazole demonstrated normal pre-weaning behavior, physical and functional development, neurological findings, and reproductive parameters. However, cesarean section data for the pregnant first generation (F₁) females in the high-dose group included significantly higher pre-implantation loss and significantly lower mean values for corpora lutea counts, number of implantations, and number of live embryos. Also small testes and/or epididymides were observed in 1/20 and 2/20 first generation males in the mid-and high-dose groups respectively, and two of the affected animals failed to mate or induce pregnancy. However, the mean values for mating performance, fertility index, testes weight, testes and epididymides sperm counts, and epididymal sperm motility and progression were not altered in any of the F₁ males in benznidazole treatment groups. The number of live second generation (F₂) fetuses born to F₁ dams was reduced in the high-dose group. The NOAEL value was considered to be 50 mg/kg/day which is approximately equal to the MRHD based on body surface area comparisons.

Lactation

Risk Summary

Limited published literature based on breast milk sampling reports that benznidazole is present in human milk at infant doses of 5.5 to 17% of the maternal weight-adjusted dosage and a milk/plasma ratio ranging between 0.32.79. There are no reports of adverse effects on the breastfed infant and no information on the effects of benznidazole on milk production. Because of the potential for serious adverse reactions, and transmission of Chagas disease, advise patients that breastfeeding is not recommended during treatment with Benznidazole Tablets.

Females And Males Of Reproductive Potential

Pregnancy Testing

Pregnancy testing is recommended for females of reproductive potential.

Contraception

Females

Benznidazole Tablets can cause fetal harm when administered to a pregnant woman [see Pregnancy]. Advise females of reproductive potential to use effective contraception during treatment with Benznidazole Tablets and for 5 days after the final dose.

Infertility

Males

Based on findings in rodents, Benznidazole Tablets may impair fertility in males of reproductive potential. It is not known whether effects on fertility are reversible [see Nonclinical Toxicology].

Pediatric Use

The safety and effectiveness of Benznidazole Tablets have been established in pediatric patients 2 to 12 years of age for the treatment of Chagas disease. Use in pediatric patients 2 to 12 years of age was established in two adequate and well-controlled trials in pediatric patients 6 to 12 years old with additional safety and pharmacokinetic data from pediatric patients 2 to 6 years of age. [see DOSAGE AND ADMINISTRATION , ADVERSE REACTIONS , Clinical Studies].

Safety and effectiveness in pediatric patients below the age of 2 years and above the age of 12 years have not been established.

Hepatic Impairment

Use of Benznidazole Tablets has not been evaluated in patients with hepatic impairment.

Renal Impairment

Use of Benznidazole Tablets has not been evaluated in patients with renal impairment.

REFERENCES

5. Bernacchi, AS, CR de Castro, EG de Toranzo, and JA Castro, 1986, Effects of Nifurtimox or Benznidazole Administration on Rat Testes: Ultrastructural Observations and Biochemical Studies, Exp Mol Pathol 45: 245-256.

6. Vieira, CL, TL Lamano-Carvalho, AL Favaretto, MM Valenca, J Antunes-Rodridgues, and AA Barreira, 1989, Testes Alterations in Pubertal Benznidazole-treated Rats, Braz J Med Biol Res, 22: 695-698.

7. Navarro, ML and R Nagel, 1990, Abnormal Sperm Induced in Mice by Oral Administration of Antichagasic Drugs, Comunicaciones Biologicas, 8: 251-258.

Overdose

No Information Provided

Contradiction

Hypersensitivity

Benznidazole Tablets are contraindicated in patients with a history of hypersensitivity reaction to benznidazole or other nitroimidazole derivatives. Reactions have included severe skin and soft tissue reactions [see ADVERSE REACTIONS].

Disulfiram

Benznidazole Tablets are contraindicated in patients who have taken disulfiram within the last two weeks. Psychotic reactions may occur in patients who are using benznidazole and disulfiram concurrently [see DRUG INTERACTIONS].

Alcohol And Products Containing Propylene Glycol

Consumption of alcoholic beverages or products containing propylene glycol is contraindicated in patients during and for at least 3 days after therapy with Benznidazole Tablets. A disulfiram-like reaction (abdominal cramps, nausea, vomiting, headaches, and flushing) may occur due to the interaction between alcohol or propylene glycol and benznidazole [see DRUG INTERACTIONS].

Clinical Pharmacology

Mechanism Of Action

Benznidazole is a nitroimidazole antimicrobial drug [see Microbiology].

Pharmacodynamics

The pharmacodynamics of benznidazole is unknown.

Pharmacokinetics

Absorption

The absorption of benznidazole from three different 100 mg benznidazole preparations was comparable when administered as a single dose under fasting conditions in adult healthy volunteers (Table 6).

Table 6: Summary of Benznidazole Pharmacokinetic (PK) Parameters Following a Single Oral Dose of 100 mg Benznidazole Administered Under Fasting Conditions in Adult Healthy Volunteers

	Preparations for 100 mg Benznidazole Oral Dose
	One Benznidazole 100 mg Tablets Taken Whole	Slurry prepared with one Benznidazole 100 mg Tablet	Slurry prepared with eight Benznidazole12.5 mg Tablets
Parameter	Mean (SD)	Mean (SD)	Mean (SD)
Cmax (mg/L)	2.4 (0.5)	2.4 (0.4)	2.4 (0.4)
Tmaxa (h)	2 (1 – 4)	2 (0.5 – 4)	2 (1 – 4.5)
AUC (mg*h/L)	43.5 (9.0)	41.8 (9.6)	44.1 (11.8)
aTmax is presented as median (range)

Effect of Food

Benznidazole Cmax and AUC were not affected by the administration of Benznidazole 100 mg tablet with a high-fat, high-caloric meal (approximately 1034 total kcal, 67 kcal from fat, 42 kcal from carbohydrates, 59 kcal from protein) compared with fasted conditions in adult healthy volunteers. Serum concentrations of benznidazole reached peak levels at 3.2 hours (1-10 hours) after administration of Benznidazole Tablets 100 mg tablet after a high-fat, high-caloric meal, and at 2.0 hours (0.5-4 hours) in fasted conditions [see DOSAGE AND ADMINISTRATION].

Distribution

Protein binding is reported to be approximately 44 to 60 %.

Elimination

The elimination half-life of benznidazole is approximately 13 hours in healthy volunteers following single dose.

Metabolism

Benznidazole metabolism pathway is unknown.

Excretion

Benznidazole and unknown metabolites are reported to be excreted in the urine and feces.

Specific Populations

The effect of sex, race, renal impairment, or hepatic impairment on the pharmacokinetics of benznidazole is unknown.

Drug Interaction Studies

In vitro studies showed that benznidazole is a P-gp substrate and does not notably induce Cytochrome P450 enzymes 1A2, 2B6, and 3A4 at concentrations up to 100 uM.

Microbiology

Mechanism Of Action

Benznidazole inhibits the synthesis of DNA, RNA, and proteins within the T. cruzi parasite. Studies suggest that benznidazole is reduced by a Type I nitroreductase (NTR) enzyme of T. cruzi producing a series of short-lived intermediates that may promote damage to several macromolecules including DNA. In mammalian cells, however, benznidazole is metabolized by reduction of the nitro group to an amino group by a Type II NTR enzyme. The precise mechanism of action is not known.

Antimicrobial Activity

Benznidazole is active against all three stages, trypomastigotes, amastigotes, and epimastigotes, of T. cruzi. However, the sensitivity of T. cruzi strains to benznidazole, from different geographic regions, may vary.

Resistance

Studies in vitro and in mice infected with T. cruzi suggest a potential for development of resistance to benznidazole.

The mechanisms of drug resistance appear to be multifactorial. These mechanisms include decreased activity due to a mutation in the nitroreductase (TcNTR) gene. Other mechanisms include higher efflux activity due to over expression of TcPGP₁ and TcPGP₂ genes that encode p-glycoprotein as well as TcABCG1 genes that encode ATP-binding cassette transporters. Also, some studies reported overexpression of other genes TcFeSOD-A and TcCyP19 that encode superoxide dismutase and cyclophilin, respectively, which have diverse biological function and may help parasite survival. However, the clinical relevance of these findings is not known.

Animal Toxicology And/Or Pharmacology

Single oral-dose toxicity studies in rats have established that benznidazole causes ultrastructural changes in the adrenal cortex, colon, esophagus, ovaries, and testis ^{5, 8-11}In these tissues, the changes were associated with the presence of nitro reductase activity, the production of reactive metabolites, and/or covalent binding of metabolites.

Neurotoxicity including brain axonal degeneration and Purkinje cell degeneration was observed with repeated-oral dosing in dogs without adverse changes in peripheral nerves^12-14. Neurological signs included: apathy, hypertonia, hyperreflexia, ataxia, loss of balance, oscillatory movements of the trunk and head, strong contractions of the back and leg muscles, opisthotonus and nystagmus. Neurotoxicity was not observed in other test species, including mouse, rat, guinea pig, and rabbit.

Clinical Studies

The safety and effectiveness of benznidazole for the treatment of Chagas disease in patients 6 to 12 years of age was established in two adequate and well-controlled trials (Trial 1 and Trial 2) as described below.

Trial 1 was a randomized, double-blind, placebo-controlled trial in children 6 to 12 years of age with chronic indeterminate Chagas disease conducted in Argentina. The chronic indeterminate form of Chagas disease includes patients with serologic evidence of T. cruzi infection without symptoms of cardiac or gastrointestinal disease. A total of 106 patients were randomized to receive either benznidazole (5 mg/kg/day for 60 days) or placebo and followed for 4 years. Patients with at least two positive conventional serologic tests for antibodies to T. cruzi were included in the study. The conventional serologic tests used include indirect hemagglutination assay (IHA), immunofluorescence antibody assay (IFA), and/or enzyme linked immunosorbent assay (ELISA) and were based on the detection of antibodies against T. cruzi parasites.

Trial 2 was a randomized, double-blind, placebo-controlled trial in pediatric patients 7 to 12 years of age with chronic indeterminate Chagas disease conducted in Brazil. A total of 129 patients were randomized to receive either benznidazole (7.5 mg/kg/day for 60 days) or placebo and followed for 3 years. Patients with three positive conventional serologic tests for antibodies to T. cruzi were included in the study. The conventional serologic tests include IHA, IFA, and/or ELISA and were based on the detection of antibodies against T. cruzi parasites.

Both trials measured antibodies by conventional and nonconventional assays. The nonconventional assays include F29-ELISA and AT-chemiluminescence-ELISA that are based on detection of anti-T. cruzi IgG antibodies against the recombinant antigens, F29 and AT from the flagella of T. cruzi parasites. Benznidazole treatment resulted in a significantly higher percentage of seronegative patients by a nonconventional assay. Results at the end of follow-up are reported in the following table.

Table 7. Nonconventional ELISA^a Serologic Status at End-of-Follow-Up (mITT population^b)

	Benznidazole	Placebo	Difference (95% CI)c
Trial 1	N=40	N=37
Seronegative	24 (60.0)	5 (13.5)	46.5 (24.5, 64.4)
Seropositive	15	29
Missing	1	3
Trial 2	N=64	N=65
Seronegative	35 (54.7)	3 (4.6)	50.1 (35.8, 63.4)
Seropositive	23	51
Missing	6	11
aEnzyme-linked immunosorbent assay (F29 ELISA in Study Trial 1 and AT chemiluminescence-ELISA in Trial 2); the F29 and AT antigens represent antigens from the flagella of T. cruzi parasites. bModified intent to treat (mITT) population includes subjects who are positive for the assay at baseline; cExact confidence intervals presented.

In Trial 1 using conventional ELISA, 4 of 53 (7.5%) benznidazole subjects and 2 of 50 (4.0%) placebo subjects seroconverted to negative by the end of follow-up (difference 3.5, 95% CI (-7.0, 14.9)). In Trial 2 using conventional ELISA, 4 of 64 (6.3%) of benznidazole subjects and 0 of 65 placebo subjects seroconverted to negative by the end of follow-up (difference 6.3, 95% CI (0.3, 15.2)).

REFERENCES

5. Bernacchi, AS, CR de Castro, EG de Toranzo, and JA Castro, 1986, Effects of Nifurtimox or Benznidazole Administration on Rat Testes: Ultrastructural Observations and Biochemical Studies, Exp Mol Pathol 45: 245-256.

8. de Castro, RC, EG Diaz de Toranzo, and JA Castro, 1992, Benznidazole-induced Ultrastructural Alterations in Rat Adrenal Cortex: Mechanistic Studies, Toxicology, 74: 223-232.

9. Diaz, EG, RC de Castro, M Montalto de Mecca, and JA Castro, 2000, Benznidazole-induced Ultrastructural and Biochemical Alterations in Rat Colon, Acta Pharmacol Sin, 21: 961-966.

10. de Castro, RC, M Montalto de Mecca, SL Fanelli, EC de Ferreyra, EG Diaz, and JA Castro, 2003, Benznidazole-induced Ultrastructural and Biochemical Alterations in Rat Esophagus, Toxicology, 191: 189198.

11. de Castro, CR, EGD de Toranzo, AS Bernacchi, M Carbone, and JA Castro, 1989, Ultrastructural Alterations in Ovaries from Nifurtimox or Benznidazole-treated Rats: Their Relation to Ovarian Nitroreductive Biotransformation of Both Drugs, Exp Mol Pathol, 50: 385-397.

12. Scharer, K, 1972, Selective Purkinje Cell Damage in Dogs after Oral Administration of High Doses of Nitroimidazole Derivatives, Verhandlungen der Deutschen Gesellschaft fur Pathologie, 56: 407-10.

13. Flores-Vieira, CLL and AA Barreira, 1997a, Experimental Benznidazole Encephalopathy: I. Clinical-Neurological Alterations, J Neurol Sci, 150: 3-11.

14. Flores-Vieira, CLL, L Chimelli, RMF Fernandez, and AA Barreira, 1997b, Experimental Benznidazole Encephalopathy: II. Electroencephalographic and Morphological Alterations, J Neurol Sci, 150:13-25.