The toxicity of combinations of AZT (200 or 400) mg and clarithromycin (500, 1250, or 2500 mg) was evaluated in Swiss (CD-1) mice treated by oral gavage. Doses of AZT were equivalent to approximately two and four times the therapeutic dose in humans. Doses of clarithromycin were approximately two, four, and 10 times the human therapeutic dose. Male mice (10 to 18/dose group) were dosed from study day 5 until the day prior to sacrifice on study day 25 or 26. Females were divided into two groups designated females-A and females-B. The females-A (20 to 28/group) were dosed from day 0 to sacrifice. They were cohabited with treated males on days 9-13 to test for effects on mating behavior, fertilization, and implantation, and Caesarean sections were performed on days 28-32. The females designated as females-B (approximately 20/group) were cohabited with untreated males on days 0-4. Sperm-positive females-B were dosed during organogenesis on days 6-15 of presumed gestation and sacrificed on day 4 of lactation.
Summarized in Table 1 are the most significant effects of treatment with AZT and clarithromycin. Administration of AZT alone resulted in slight hematopoietic toxicity manifested by mild declines in RBC, HGB, and HCT values. Hematopotetic cell proliferation and increased hemosiderin deposition in the spleen accompanied the mild alterations in erythrocyte parameters.
Administration of clarithromycin alone resulted in toxicity in multiple vital organs including the liver, spleen, bone marrow, kidney, heart, and brain. Other treatment-related lesions occurred in the thymus, lymph nodes, stomach, and salivary gland. Diminished body weights and a 100% mortality rate occurred in male and female-A mice in the highest dose group. Elevated BUN and creatinine levels accompanied the renal lesions and elevated ALP, ALT, AST, and bile acid values accompanied the liver toxicity. Extensive cytoplasmic vacuolization of phagocytic cells occurred in the majority of the tissues with lesions.
Administration of AZT in combination with clarithromycin resulted in severe hematotoxicity in male and female-A mice and the severity of the anemia was far greater than that induced by AZT alone. The anemia contributed to high mortality rates and was accompanied by extensive atrophy of the bone marrow and splenic red pulp. The anemia was characterized as a moderate nonregenerative macrocytic anemia which progressed to a severe microcytic nonregenerative anemia in the higher dose combination groups. Neutrophilia, lymphopenia, reticulocytopenia, and sporadic thrombocytosis were also considered to be treatment-related manifestations of hernatopoietic toxicity. In general, the morphological alterations in other tissues with lesions were similar to those induced by clarithromycin alone, with extensive cytoplasmic vacuolization of phagocytic cells.
Inflammatory lesions in the forestomach and glandular stomach occurred in several mice of both sexes treated with the higher doses of clarithromycin alone or in combination with AZT. In general, the severity of these lesions increased dramatically when complicated by the presence of fungal organisms. The antibacterial action of clarithromycin likely altered the normal flora in the stomach lumen, which subsequently allowed the fungal overgrowth. Chronic dilatation of the stomach with the large volume of thick gavaged material may have predisposed the stomach to the initial inflammatory lesions.
Treatment with AZT alone resulted in reduced live litter size, an increase in the number of resorptions, and a slight decline in total weight per litter. Treatment with clarithromycin alone resulted in diminished fertility with a reduction in the number of litters delivered, diminished litter size, and a decrease in the number of pups surviving. Fertility was further reduced in groups treated with combinations of AZT and clarithromycin (200 or 400 mg of AZT + 1250 or 2500 mg of clarithromycin). Live litter size was reduced and the average number of resorptions per litter was increased in groups treated with 200 or 400 mg of AZT + 500 mg of clarithromycin but not in the group treated with 500 mg of clarithromycin alone, indicating potentiation with the combination treatment. Prominent declines in fetal weight per litter also occurred in groups treated with combinations of AZT and clarithromycin.