Objective: To assess the incremental cost-effectiveness of 3 Pneumocystis carinii pneumonia (PCP) prophylaxis strategies in patients with Wegener's granulomatosis (WG) receiving immunosuppressive therapies: 1) no prophylaxis; 2) trimethoprim/sulfamethoxazole (TMP/SMX) 160 mg/800 mg 3 times a week, which is discontinued if patients experience an adverse drug reaction (ADR); and 3) TMP/SMX 160 mg/800 mg 3 times a week, which is replaced by monthly aerosolized pentamidine (300 mg) if patients experience an ADR.
Methods: A Markov state-transition model was developed to follow a hypothetical cohort of WG patients over their lifetimes starting from the time of initial exposure to the immunosuppressive therapy. The effect of PCP prophylaxis on life expectancy, quality-adjusted life expectancy, average discounted lifetime cost (ADLC), and incremental cost-effectiveness was estimated based on data obtained from a literature review. Direct medical costs were examined from a societal perspective, and costs and benefits were discounted at 3% annually.
Results: No prophylaxis resulted in a life expectancy of 13.36 quality-adjusted life years (QALY) at an ADLC of $4,538. In comparison, prophylaxis with TMP/ SMX alone increased the QALY to 13.54 and was cost saving, with an ADLC of $3,304. The addition of pentamidine in patients who had an ADR to TMP/SMX resulted in 13.61 QALY, with an ADLC of $7,428. Compared with TMP/SMX alone, TMP/SMX followed by pentamidine increased the QALY by 0.07 at an incremental cost of $58,037 per QALY. Both TMP/SMX alone and TMP/SMX followed by pentamidine prophylaxis strategies dominated the no prophylaxis strategy until the incidence of PCP fell below 0.2% and 2.25%, respectively. Institution of pentamidine therapy for patients with a TMP/SMX ADR increased quality-adjusted life expectancy compared with that with TMP/ SMX alone until the incidence of PCP rose above 7.5%.
Conclusion: Prophylaxis using TMP/SMX alone increased life expectancy and reduced cost for patients with WG receiving immunosuppressive therapy. Replacing TMP/SMX with monthly aerosolized pentamidine in cases of ADR further increased life expectancy, although at an increased cost.