Therapeutic failure of trimethoprim/sulfamethoxazole in the treatment of Pneumocystis carinii pneumonia

OBJECTIVE: To report a case of failure of treatment of Pneumocystis carinii pneumonia (PCP) with trimethoprim/sulfamethoxazole (TMP/SMX) in a patient with HIV infection, despite an adequate serum SMX concentration. CASE SUMMARY: A 52-year-old white man was treated with TMP/SMX for PCP. After discharge he returned to the hospital with worsening of the PCP despite a serum SMX concentration of 60 μg/mL 18 hours after his last dose of TMP/SMX. DISCUSSION: PCP is one of the most common complications of HIV infection. TMP/SMX is the drug of choice for prophylaxis and treatment. The causes of therapeutic failure with this agent are not well documented. CONCLUSIONS: Alternative therapies to TMP/SMX should be seriously considered if the serum concentrations are therapeutic and the patient is not clinically improved.