Year of Publication

2005

Document Type

Dissertation

College

Pharmacy

Department

Pharmaceutical Sciences

First Advisor

Robert P. Rapp

Abstract

The drug-drug interaction involving zidovudine and sulfamethoxazole-trimethoprim was investigated using an in vitro culture system, an in vivo mouse model, and a clinical trial in HIV-infected patients. We hypothesized that combination exposure causes immune cell populations in the bone marrow to undergo apoptotic cell death, and that the toxicity would affect the host response to an infectious stimulus. Mice were dosed with zidovudine, sulfamethoxazole-trimethoprim, the combination of both drugs, or vehicle only control via oral gavage. Focusing on B-lineage cells in the bone marrow, we determined that cells of the rapidly cycling, early pre-B cell subset are targeted, as well as pro-B cells earlier in development. This toxicity was found to be cell cycle dependent, with an increase in percentage of cells in the S/G2/M phases of the cycle. In vitro experiments using the drugs in a bone marrow culture system demonstrated that the effect of cytotoxicity with combination exposure is synergistic and concentration-dependent. The mechanism of apoptosis that is induced appears to be caspase-independent. To measure host response in mice, animals treated with zidovudine plus sulfamethoxazole-trimethoprim were infected with Pneumocystis murina pneumonia, and the group that received the combination of agents had a blunted antigen-specific IgG response, possibly due to a decreased number of B cells and activated B cells in the draining lymph nodes of the lungs. A clinical trial was conducted in HIV-infected patients, dividing subjects into groups receiving zidovudine, sulfamethoxazole-trimethoprim, the combination of both, or neither agent. Upon vaccination with the influenza vaccine, the combination treatment group had a blunted humoral response, with reduced antigen-specific serum IgG titers as compared to the control group. We conclude that the drug-drug interaction involving zidovudine and sulfamethoxazole-trimethoprim is clinically-significant, and clinicians must consider this toxicity when treating patients with these agents concurrently.

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