Fourteen-Day and Thirteen-Week Studies:
Dietary concentrations of furosemide used in the 14-day studies for rats and mice ranged up to 46,000 ppm. Two of five male and 3/5 female rats that received 46,000 ppm furosemide died before the end of the studies. Rats that received 15,300 or 46,000 ppm lost weight over the course of the studies. The final mean body weights of rats that received 1,700 or 5,100 ppm were 12% or 23% lower than that of controls for males and 8% or 16% lower for females. Nephrosis was dose related in rats. All five male and 1/5 female mice that received 46,000 ppm furosemide died before the end of the 14-day studies. Male mice that received 15,300 ppm and female mice that received 46,000 ppm lost weight. The final mean body weights of male mice that received 1,700 or 5,100 ppm were 16% or 14% lower than that of controls. The final mean body weight of females that received 15,300 ppm was 13% lower than that of controls. Slight dilatation of the renal cortical tubules and/or nephrosis were dose related in mice.
Dietary concentrations of furosemide used in the 13-week studies were 0 and 625-10,000 ppm for male rats and 0 and 938-15,000 ppm for female rats and male mice. Concentrations for female mice were 0 and 1,250-20,000 ppm. None of the rats died before the end of the studies. The final mean body weights of male rats that received 2,500, 5,000, or 10,000 ppm furosemide were 11%, 22%, or 44% lower than that of controls. The final mean body weights of female rats that received 3,750, 7,500, or 15,000 ppm were 18%, 26%, or 35% lower than that of controls. Minimal-to-mild nephrosis occurred in the two highest dose groups of male and female rats. Mineralization of minimal to mild severity was observed at the renal corticomedullary junction in dosed male rats receiving 625 ppm or more; the severity and incidence of the mineralization increased with increased dose. No compound-related deaths occurred in mice. The final mean body weights of male mice that received 3,750, 7,500, or 15,000 were 12%, 22%, or 17% lower than that of controls. Final mean body weights of dosed and control female mice were comparable. Compound-related lesions in mice induced minimal-to-mild nephrosis.
Because of the lower body weights and the kidney lesions in the 13-week studies, doses selected for the 2-year studies were 0, 350, or 700 ppm furosemide in the diet for groups of 50 F344/N rats of each sex. Groups of 50 B6C3F1 mice of each sex were fed diets containing 0, 700, or 1,400 ppm furosemide for 104 weeks.
Body Weight and Survival in the Two-Year Studies:
Mean body weights of dosed and control rats were comparable throughout the studies. No significant differences in survival were observed between any groups of rats of either sex (final survival--male: control, 17/50; low dose, 17/50; high dose, 20/50; female: 35/50; 31/50; 34/50). The final survival of all groups of male rats was low, reflecting the large number of moribund animals killed after week 91. Survival at week 90 was 35/50, 28/50, and 34/50. Mean body weights of high dose male mice were up to 17% lower than those of controls, and mean body weights of low dose male mice were about 5%-10% lower than those of controls after week 31. Mean body weights of high dose female mice were up to 22% lower than those of controls. Mean body weights of low dose female mice were 5%-13% lower than those of controls after week 82. The survival of the high dose group of female mice was significantly lower than that of controls after week 99 (final survival--male: 31/50; 24/50; 26/50; female: 36/50; 29/50; 18/50). Feed consumption by dosed rats was similar to that by controls. The estimated average amount of furosemide consumed per day was approximately 14-16 or 29-31 mg/kg for low dose or high dose rats. Feed consumption by dosed mice was approximately 5%-7% greater than that by controls. The average amount of furosemide consumed per day was approximately 91-99 or 191-214 mg/kg for low dose or high dose mice.
Nonneoplastic and Neoplastic Effects in the Two-Year Studies:
Nephropathy occurred at similar incidences in all groups of rats, but the severity was greater in dosed male rats. Tubular cell hyperplasia was observed in 4/50 control, 2/50 low dose, and 4/50 high dose male rats. Tubular cell adenomas of the kidney occurred in 1/50 control, 3/50 low dose, and 1/50 high dose male rats. Tubular cell adenocarcinomas were seen in a fourth low dose male rat and in a second high dose male rat (adenomas or adenocarcinomas, combined: control, 1/50; low dose, 4/50; high dose, 2/50). The historical incidence of renal tubular cell adenomas or adenocarcinomas (combined) in untreated male F344/N rats is 9/1,928 (0.5%), and the highest incidence observed in controls is 3/50.
Malignant meningiomas of the brain occurred in 3/50 low dose male rats; none was observed in other groups. The historical incidence of meningiomas in untreated male F344/N rats is 2/1,928 (0.1%).
C-Cell adenomas of the thyroid gland in female rats occurred with a positive trend; the incidence in the high dose group was not statistically greater than that in the controls (4/50; 6/50; 11/50). A C-cell carcinoma occurred in another low dose female rat. The incidence of adenomas of the anterior pituitary gland in low dose male rats was marginally greater than that in controls (4/50; 11/50; 8/50). Neither of these marginal increases was considered to be chemically related.
Malignant mixed tumors (adenocarcinoma, type C) of the mammary gland occurred in dosed female mice (0/50; 1/50; 5/48). One mammary gland acinar cell carcinoma occurred in a second low dose female mouse. The historical incidence of all malignant mammary gland neoplasms in untreated female B6C3F1 mice is 40/2,040 (2%).
Compound-related nonneoplastic lesions of the kidney in mice included nephropathy and dilatation of the renal pelvis for males and females and tubular cysts, suppurative inflammation, and epithelial hyperplasia of the renal pelvis for males. Kidney lesions may have contributed to the low survival of high dose female mice.
Mucosal epithelial hyperplasia and submucosal chronic focal inflammation of the urinary bladder were observed at increased incidences in dosed male mice. Suppurative inflammation of the prostate was observed at an increased incidence in high dose male mice. Fighting may have contributed to urogenital lesions in male mice. Suppurative inflammation of the ovary or uterus was observed at an increased incidence in high dose female mice. Hematopoiesis was observed at increased incidences in the spleen and liver of dosed male and high dose female mice and in the adrenal cortex of high dose female mice.
Furosemide was not mutagenic in S. typhimurium strains TA98, TA100, TA1535, or TA1537 when tested with or without exogenous metabolic activation. In the mouse lymphoma assay for trifluorothymidine (Tft) resistance, furosemide produced an equivocal response in the absence of metabolic activation and a positive response in the presence of activation. Furosemide induced sister chromatid exchanges and chromosomal aberrations in CHO cells in both the presence and absence of exogenous metabolic activation.
The data, documents, and pathology materials from the 2-year studies of furosemide have been audited. The audit findings show that the conduct of the studies is documented adequately and support the data and results given in this Technical Report.
Under the conditions of these 2-year feed studies, there was equivocal evidence of carcinogenic activity of furosemide for male F344/N rats, as shown by marginal increases in uncommon tubular cell neoplasms of the kidney and meningiomas of the brain. There was no evidence of carcinogenic activity of furosemide for female F344/N rats fed diets containing 350 or 700 ppm furosemide for 2 years. There was no evidence of carcinogenic activity for male B6C3F1 mice fed diets containing 700 or 1,400 ppm furosemide for 2 years. There was some evidence of carcinogenic activity of furosemide for female mice, as shown by an increase in malignant tumors of the mammary gland.
Nephropathy was more severe in the kidney of male rats and of male and female mice fed diets containing furosemide than in controls.