NIEHS Technical Report on the Subchronic Toxicity Study of 3'-Azido-3'-dioxythymidine (AZT) and Pyrazinamide Combinations (CASRNs 30516-87-1 and 98-96-4) Administered by Gavage to Swiss (CD-1®) Mice (NIEHS AIDS Therapeutics Toxicity Report 7)
Report Date: April 2002
Male and female Swiss CD-1® mice were dosed orally with AZT alone (200 or 400 mg/kg per day), pyrazinamide alone (300, 1,500, or 3,000 mg/kg per day), or combinations of AZT and pyrazinamide. The doses of AZT were equivalent to 2 and 4 times the therapeutic dose in humans, based on body surface area, and the doses of pyrazinamide were 2, 10, and 20 times the therapeutic dose for experimental tuberculosis in mice (Freireich et al., 1966; Grosset et al., 1992; PDR, 1999). Male mice (10 per group) were dosed from day 5 until the day prior to sacrifice on day 25 or 26. Females were divided into two groups designated female-A mice and female-B mice. The female-A mice (20 per group) were dosed from day 0 to the day of sacrifice. They were cohabited with treated males on days 9 to 13 to test for effects of treatment on mating behavior, fertilization, and implantation, and caesarean sections were performed on days 28 to 32. Female-B mice (20 per group) were cohabited with untreated males on days 0 to 4. Sperm-positive female-B mice were dosed during organogenesis on days 6 to 15 of presumed gestation and sacrificed on day 4 of lactation. A summary of the most significant toxicological parameters is presented in Table 1.
Administration of AZT alone to male mice resulted in a mild dose-related anemia accompanied histopathologically by hematopoietic cell proliferation in the spleen. Administration of pyrazinamide alone to male mice did not produce significant alterations in hematology parameters, and histopathological alterations were limited to minor degrees of hepatocellular glycogen depletion and hematopoietic cell proliferation in the spleen. Administration of combinations of AZT and pyrazinamide to male mice resulted in exacerbation of the anemia produced by AZT alone. Combination therapy in male mice also resulted in diminished leukocyte, neutrophil, and lymphocyte counts and a treatment-related thrombocytosis. Significant histopathological alterations consisted of bone marrow depletion, hematopoietic cell proliferation in the spleen, atrophy of the splenic red pulp, and hepatocellular glycogen depletion.
Administration of AZT alone to female-A mice resulted in a mild dose-related anemia. Biologically significant alterations were not evident in hematology parameters of female-A mice treated with pyrazinamide alone and histopathological changes were limited to hepatocellular glycogen depletion. Administration of combinations of AZT and pyrazinamide to female-A mice resulted in exacerbation of the anemia induced by AZT alone. Female-A mice receiving combination therapy also developed a treatment-related leukopenia, with declines in granulocytes and mononuclear cells. A biologically significant thrombocytosis occurred in female-A mice treated with the highest combination of both drugs. Hepatocellular glycogen depletion was prominent in female-A mice receiving combination therapy and coincided with significant elevations in relative liver weights. The only significant clinical sign detected in female-A mice was pallor documented in a few of the more anemic animals.
Biologically significant declines in body weight were only evident in female mice. Terminal body weights and gravid uterine weights were diminished in female-A mice treated with AZT alone and AZT plus pyrazinamide. Corrected body weights, however, were similar to those of the controls. A slight decline in gestational body weight occurred in female-B mice treated with the highest combination of both drugs. Significant alterations in mortality, clinical chemistry parameters, and necropsy findings were not evident in any treated female groups. Biologically significant alterations in hematology parameters did not occur in any of the female-B treatment groups.
Administration of AZT alone resulted in reproductive toxicity manifested by an increase in the number of resorptions, diminished litter size, and diminished fetal weights per litter. Pyrazinamide alone resulted in a mild increase in the number of resorptions, diminished fetal body weights per litter, and a mild increase in the duration of gestation. Combination therapy resulted in alterations in the above reproductive parameters of far greater magnitude than occurred with either compound alone. Other changes evident subsequent to combination therapy consisted of a decrease in the number of pregnant females that delivered litters, diminished litter size, an increase in the number of stillborn pups, and a decrease in the number of liveborn pups per litter. Combination therapy also resulted in diminished live litter size and an increase in the number of pup deaths during the lactation period. Significant numbers of gross external alterations did not occur following administration of either compound alone or in combination.