Dapsone, trimethoprim-sulfamethoxazole, and the acquired immunodeficiency syndrome

Safety of dapsone as Pneumocystis carinii pneumonia prophylaxis in human immunodeficiency virus-infected patients with allergy to trimethoprim/sulfamethoxazole

OBJECTIVE

To assess the safety of dapsone prophylaxis of Pneumocystis carinii pneumonia (PCP) in patients with prior intolerance to trimethoprim/sulfamethoxazole (TMP/SMX).

METHODS

We conducted a retrospective study in the categorical human immunodeficiency virus out-patient program of a university hospital. Patients who had filled prescriptions for dapsone at our pharmacy between January 1991 and April 1994 were evaluated and 75 patients were found eligible for analysis.

RESULTS

The overall incidence of adverse events (AE) in our study cohort was 39%. The most common AEs were anemia (23%) and rash (16%). However, after critical evaluation of each case, only 3 cases of anemia (4%) and 2 cases of rash (3%) were judged to be "likely related" to dapsone. Only 5/75 patients (7%) developed the same intolerance to dapsone as previously experienced on TMP/SMX, and none of these cases was viewed as "likely related" to dapsone. A dapsone regimen of 100 mg qd and a prior episode of PCP were associated with a higher incidence of AEs. Eight cases of PCP occurred in spite of dapsone prophylaxis for an incidence of 7 cases per 1,000 patient-months. Seven of the cases of PCP occurred in patients who were receiving secondary prophylaxis.

CONCLUSIONS

Given the low incidence of AEs judged to be "likely related" to dapsone, this drug is a reasonable choice for PCP prophylaxis in patients with prior AEs to TMP/SMX.

Pneumocystis carinii, an opportunist in immunocompromised patients

Pneumocystis carinii has been recognized as a cause of pneumonia in immunocompromised patients for over 40 years. Until the 1980s, Pneumocystis pneumonia (pneumocystosis) was most often seen in patients undergoing chemotherapy for malignancy or transplantation. Infection could be prevented by trimethoprim-sulfamethoxazole prophylaxis; thus, it was an uncommon clinical problem. With the onset of the AIDS epidemic, Pneumocystis pneumonia has become a major problem in the United States because it develops in approximately 80% of patients with AIDS and because almost two-thirds of patients have adverse reactions to anti-Pneumocystis drugs. Thus, physicians and laboratories in any community may be called upon to diagnose and provide care for patients with Pneumocystis pneumonia. The classification of the organism is currently controversial, but it is either a protozoan or a fungus. P. carinii appears to be acquired during childhood by inhalation and does not cause clinical disease in healthy persons but remains latent. If the person becomes immunosuppressed, the latent infection may become activated and lead to clinical disease. Damage of type I pneumocytes by Pneumocystis organisms leads to the foamy alveolar exudate which is characteristic of the disease. Diagnosis is established by morphologic demonstration of Pneumocystis organisms in material from the lungs. Current efforts to find better anti-Pneumocystis drugs should provide more effective therapy and prophylaxis.

Dapsone in low doses prevents Pneumocystis carinii pneumonia in the rat model

Less toxic drugs are needed for the prophylaxis and treatment of Pneumocystis carinii pneumonia (PCP) in patients with AIDS. Rats immunosuppressed with cortisone were given dapsone, chlorproguanil (CPG) and chlorcycloguanil (CCG), alone or in combination, in the diet and the P. carinii attack rate was compared with that of untreated controls. Dapsone alone at doses of 25 and 5 mg/kg/day was 100% effective in preventing PCP. The efficacy of CPG and CCG, however, could not be properly assessed because of the lack of acceptance of the diet by the animals. Even so, as a result of the findings with dapsone in this study, and because of its pharmacokinetics and minimum inhibitory concentration for P. carinii in vitro, a clinical trial of reduced dosage of dapsone given prophylactically to human beings is suggested. Such a trial may show a decrease in the toxicity of the drug that usually accompanies its long-term administration but retention of its efficacy.

Comparison of dosages, intervals, and drugs in the prevention of Pneumocystis carinii pneumonia

The efficacies of trimethoprim (TMP)-sulfamethoxazole (SMZ), TMP-dapsone, dapsone, and pentamidine were compared for the prevention of Pneumocystis carinii pneumonia in the corticosteroid-treated-rat model. While 11 (73%) of 15 untreated control animals had P. carinii pneumonia after 10 weeks of immunosuppression, none of the animals given 125 mg of dapsone per kg daily, weekly, biweekly, or monthly had evidence of infection. Of the 10 rats given a single dose of dapsone 23 and 50 days after immunosuppression was started, 5 (50%) had P. carinii pneumonia. When three drugs were given separately to groups of 10 rats in single doses biweekly, P. carinii pneumonia occurred in 40% of those treated with TMP-SMZ and in none of those treated with TMP-dapsone; although only 2 of those treated with pentamidine survived for evaluation, both had P. carinii pneumonia. The experiments showed that dapsone is highly effective in chemoprophylaxis for P. carinii pneumonia when given at monthly intervals or more frequently and that dapsone and TMP-dapsone are more effective than is TMP-SMZ when given at biweekly intervals. It seems reasonable to expect that biweekly doses of dapsone or TMP-dapsone would provide an effective and reasonably safe chemoprophylaxis regimen for patients at high risk for P. carinii pneumonia, and studies to test such a scheme are justifiable. Biweekly doses are preferred over monthly doses to allow for occasional inadvertent omission of doses expected from patients.