Carcinogenesis

In carcinogenicity studies, mice and rats were given naratriptan by oral gavage for 104 weeks. There was no evidence of an increase in tumors related to naratriptan administration in mice receiving up to 200 mg/kg/day. That dose was associated with a plasma (AUC) exposure that was 110 times the exposure in humans receiving the MRDD of 5 mg. Two rat studies were conducted, one using a standard diet and the other a nitrite-supplemented- diet (naratriptan can be nitrosated in vitro to form a mutagenic product that has been detected in the stomachs of rats fed a high-nitrite diet). Doses of 5, 20, and 90 mg/kg were associated with AUC exposures that in the standard-diet study were 7, 40, and 236 times, respectively, and in the nitrite-supplemented-diet study were 7, 29, and 180 times, respectively, the exposure in humans at the MRDD. In both studies, there was an increase in the incidence of thyroid follicular hyperplasia in high-dose males and females and in thyroid follicular adenomas in high-dose males. In the standard-diet study only, there was also an increase in the incidence of benign c-cell adenomas in the thyroid of high-dose males and females. The exposures achieved at the no-effect dose for thyroid tumors were 40 (standard diet) and 29 (nitrite-supplemented diet) times the exposure achieved in humans at the MRDD. In the nitrite-supplemented diet study only, the incidence of benign lymphocytic thymoma was increased in all treated groups of females. It was not determined if the nitrosated product is systemically absorbed. However, no changes were seen in the stomachs of rats in that study.

Mutagenesis

Naratriptan was not mutagenic when tested in in vitro gene mutation (Ames and mouse lymphoma tk) assays. Naratriptan was also negative in the in vitro human lymphocyte assay and the in vivo mouse micronucleus assay. Naratriptan can be nitrosated in vitro to form a mutagenic product (WHO nitrosation assay) that has been detected in the stomachs of rats fed a nitrite-supplemented diet.

Impairment of Fertility

In a reproductive toxicity study in which male and female rats were administered naratriptan orally prior to and throughout the mating period (10, 60, 170, or 340 mg/kg/day; plasma exposures [AUC] approximately 11, 70, 230, and 470 times, respectively, the human exposure at the MRDD), there was a drug-related decrease in the number of females exhibiting normal estrous cycles at doses of 170 mg/kg/day or greater and an increase in preimplantation loss at 60 mg/kg/day or greater. In high-dose males, testicular/epididymal atrophy accompanied by spermatozoa depletion reduced mating success and may have contributed to the observed preimplantation loss. The exposures achieved at the no-effect doses for preimplantation loss, anestrus, and testicular effects were approximately 11, 70, and 230 times, respectively, the exposures in humans at the MRDD.

In a study in which rats were dosed orally with naratriptan (10, 60, or 340 mg/kg/day) for 6 months, changes in the female reproductive tract including atrophic or cystic ovaries and anestrus were seen at the high dose. The exposure at the no-effect dose of 60 mg/kg was approximately 85 times that in humans at the MRDD.