Warnings for Furadantin
Included as part of the "PRECAUTIONS" Section
Precautions for Furadantin
Hypersensitivity Reactions
Serious and occasionally fatal hypersensitivity (anaphylactic) reactions have been reported in patients receiving FURADANTIN [see ADVERSE REACTIONS]. If signs and symptoms of a hypersensitivity reaction occurs, immediately discontinue FURADANTIN and initiate appropriate medications and/or supportive care. FURADANTIN is contraindicated in patients with known hypersensitivity to nitrofurantoin.
Pulmonary Reactions
Acute, subacute, or chronic pulmonary reactions have been reported in patients treated with FURADANTIN. If these reactions occur, discontinue FURADANTIN and take appropriate measures. Reports have cited pulmonary reactions as a contributing cause of death.
Chronic pulmonary reactions (diffuse interstitial pneumonitis or pulmonary fibrosis, or both) can develop insidiously. These reactions occur generally in patients receiving therapy for six months or longer. Close monitoring of the pulmonary condition of patients receiving long-term therapy is warranted and requires that the benefits of therapy be weighed against potential risks [see ADVERSE REACTIONS].
Hepatotoxicity
Hepatic reactions, including hepatitis, cholestatic jaundice, chronic active hepatitis, and hepatic necrosis, has occurred. Fatalities have been reported. The onset of chronic active hepatitis may be insidious. Monitor patients periodically for changes in biochemical tests that would indicate liver injury. If hepatitis occurs, discontinue FURADANTIN immediately, and take appropriate measures.
Neuropathy
Peripheral neuropathy, which may become severe or irreversible, has occurred. Fatalities have been reported. Conditions such as renal impairment (creatinine clearance under 60 mL per minute or clinically significant elevated serum creatinine), anemia, diabetes mellitus, electrolyte imbalance, vitamin B deficiency, and debilitating disease may enhance the occurrence of peripheral neuropathy. Monitor patients receiving long-term therapy periodically for changes in renal function.
Optic neuritis has been reported with nitrofurantoin formulations [see ADVERSE REACTIONS].
Hemolytic Anemia
Cases of hemolytic anemia of the primaquine-sensitivity type have been induced by nitrofurantoin. Hemolysis appears to be linked to a glucose-6-phosphate dehydrogenase deficiency in the red blood cells of the affected patients. This deficiency is found in 10 percent of Blacks and a small percentage of ethnic groups of Mediterranean and Near-Eastern origin. If hemolysis occurs, discontinue FURADANTIN immediately; hemolysis ceases when the drug is withdrawn.
Clostridioides Difficile-Associated Diarrhea
Clostridioides difficile-associated Diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including FURADANTIN, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of C. difficile.
C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antibacterial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibacterial use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.
If CDAD is suspected or confirmed, ongoing antibacterial use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibacterial treatment of C. difficile, and institute surgical evaluation as clinically indicated.
Persistence Or Reappearance Of Bacteriuria
Nitrofurantoin lacks the broader tissue distribution of other therapeutic agents approved for urinary tract infections. Consequently, many patients who are treated with FURADANTIN are predisposed to persistence or reappearance of bacteriuria. If persistence or reappearance of bacteriuria occurs with symptoms of urinary tract infection, after treatment with FURADANTIN, other therapeutic agents with broader tissue distribution should be selected. In considering the use of FURADANTIN, lower eradication rates should be balanced against the increased potential for systemic toxicity and for the development of antibacterial resistance when agents with broader tissue distribution are utilized.
Nonclinical Toxicology
Carcinogenesis, Mutagenesis, Impairment Of Fertility
Carcinogenesis
Nitrofurantoin was not carcinogenic when fed to female Holtzman rats for 44.5 weeks or to female Sprague-Dawley rats for 75 weeks. Two chronic rodent bioassays utilizing male and female Sprague-Dawley rats and two chronic bioassays in Swiss mice and in BDF1 mice revealed no evidence of carcinogenicity.
Nitrofurantoin presented evidence of carcinogenic activity in female B6C3F1 mice as shown by increased incidences of tubular adenomas, benign mixed tumors, and granulosa cell tumors of the ovary. In male F344/N rats, there were increased incidences of uncommon kidney tubular cell neoplasms, osteosarcomas of the bone, and neoplasms of the subcutaneous tissue.
The significance of carcinogenicity findings relative to the therapeutic use of nitrofurantoin in humans is unknown.
Mutagenesis
Nitrofurantoin has been shown to induce point mutations in certain strains of Salmonella typhimurium and forward mutations in L5178Y mouse lymphoma cells. Nitrofurantoin induced increased numbers of sister chromatid exchanges and chromosomal aberrations in Chinese hamster ovary cells but not in human cells in culture. Results of the sex-linked recessive lethal assay in Drosophila were negative after administration of nitrofurantoin by feeding or by injection. Nitrofurantoin did not induce heritable mutation in the rodent models examined.
The significance of mutagenicity findings relative to the therapeutic use of nitrofurantoin in humans is unknown.
Impairment Of Fertility
The administration of high doses of nitrofurantoin to rats causes temporary spermatogenic arrest; this is reversible on discontinuing the drug.
Use In Specific Populations
Pregnancy
Risk Summary
Nitrofurantoin is contraindicated in pregnant women at term (38 weeks to 42 weeks gestation), during labor and delivery, or when the onset of labor is imminent because of the possibility of hemolytic anemia in the infant (see Clinical Considerations).
Published epidemiological studies, including cohort studies and case control studies, have reported inconsistent findings related to nitrofurantoin use during the first trimester and risk of major birth defects. These studies cannot definitively establish the presence or absence of risk due to several methodological limitations. The limited number of epidemiological studies available have not identified drug-associated risks of major birth defects, miscarriage or other adverse maternal or fetal outcomes.
In animal reproduction studies, no fetotoxicity was observed when nitrofurantoin was administered orally to pregnant rats and rabbits, during organogenesis, at up to 6 times the recommended human dose (see Data).
The 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
Fetal/Neonatal Adverse Reactions
Nitrofurantoin is not recommended in pregnant women at term (38 weeks to 42 weeks gestation), during labor and delivery, or when the onset of labor is imminent because of the possibility of hemolytic anemia due to immature erythrocyte enzyme systems (glutathione instability) [see CONTRAINDICATIONS and WARNINGS AND PRECAUTIONS].
Data
Animal Data
Several reproduction studies have been performed in rabbits and rats at doses up to six times the human dose and have revealed no harm to the fetus due to nitrofurantoin. In a single published study conducted in mice at 68 times the human dose (based on mg/kg administered to the dam), growth retardation and a low incidence of minor and common malformations were observed. However, at 25 times the human dose, fetal malformations were not observed.
Nitrofurantoin has been shown in one published transplacental carcinogenicity study to induce lung papillary adenomas in the F1 generation mice at doses 19 times the human dose on a mg/kg basis. The relationship of this finding to potential human carcinogenesis is presently unknown.
Lactation
Risk Summary
Nitrofurantoin is present in human breast milk following oral administration. There are insufficient data on the effect of nitrofurantoin on milk production.
Infants less than one month of age or who have glucose-6-phosphate dehydrogenase (G6PD) deficiency are at risk for hemolytic anemia from FURADANTIN exposure. Therefore, breastfeeding is not recommended in these infants.
In a breastfed infant over the age of one month and with normal G6PD, the developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for FURADANTIN and any potential adverse effects on the breastfed infant from FURADANTIN or from the underlying maternal condition. Monitor these infants for vomiting, diarrhea, and rash.
Females And Males Of Reproductive Potential
Infertility
Male
Based on findings from a fertility study conducted in 36 healthy male volunteers and an animal fertility study, nitrofurantoin may reversibly decrease spermatogenesis [see Nonclinical Toxicology]. Nitrofurantoin doses of 10 mg/kg/day or greater in healthy human males may produce a slight to moderate spermatogenic arrest with a decrease in sperm count. The effect on fertility is unknown.
Pediatric Use
FURADANTIN is contraindicated in pediatric patients younger than 1 month of age because of the possibility of hemolytic anemia due to immature erythrocyte enzyme systems (glutathione instability). [see CONTRAINDICATIONS and WARNINGS AND PRECAUTIONS].
The safety and effectiveness of FURADANTIN in pediatric patients aged 1 month of age and older for the treatment of urinary tract infections have been established.