Evaluation of the Interaction Between Low Dose Sulfamethoxazole-Trimethoprim and Zidovudine

To determine if the pharmacokinetics of low doses of zidovudine (AZT) (that is, how fast AZT reaches the blood, what concentration of AZT is attained in the blood, and how long AZT remains in the blood) changes from day-to-day in the same patient. Also to determine whether the pharmacokinetics of AZT is changed by sulfamethoxazole/trimethoprim (SMX/TMP) given at the same time or whether the pharmacokinetics of SMX/TMP is altered by AZT therapy. AZT has been effective in treating some patients with AIDS, and SMX/TMP is an antibiotic combination which is useful in preventing or treating Pneumocystis carinii pneumonia (PCP), which is an important cause of disease and death in patients with AIDS. It is important to know how drugs interact in patients because addition of a second drug may change the speed at which a drug is eliminated from the body, and cause increased toxic effects or decreased therapeutic effects. AZT has been effective in treating some patients with AIDS, and SMX/TMP is an antibiotic combination which is useful in preventing or treating Pneumocystis carinii pneumonia (PCP), which is an important cause of disease and death in patients with AIDS. It is important to know how drugs interact in patients because addition of a second drug may change the speed at which a drug is eliminated from the body, and cause increased toxic effects or decreased therapeutic effects. Patients take AZT every 4 hours and/or SMX/TMP every 12 hours by mouth for 4 days as outpatients and then come into the clinical research center for 2 days of studies. On day 5 the final dose of medicine is given orally (SMX/TMP) or by intravenous infusion (AZT). Blood samples are drawn 10-20 times over a period of 12 hours and urine is collected for 36 hours. Concentrations of the drugs in the blood and urine samples are determined. This sequence is repeated twice, so that each patient takes AZT alone, SMX/TMP alone, and the combination of AZT and SMX/TMP over a period of about 3 weeks. Patients may be included in the study if they are asymptomatic, or have been diagnosed with ARC or AIDS, but not if they have PCP or any other severe opportunistic infection.