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Background: Whether to treat urogenital chlamydia with azithromycin or doxycycline is an ongoing debate, because of tradeoffs between each drug’s respective efficacy, adherence, and cost. To add public health perspective to the clinical debate, we calculated the total costs of azithromycin and doxycycline treatment in women as a function of reported treatment efficacies across variable levels of adherence to doxycycline, estimating direct medical cost to the health care system as the sum of drug and pelvic inflammatory disease (PID) costs.
Methods: We used a simple linear mathematical model to estimate the percent of infections successfully treated and the associated direct medical costs, which includes drug and PID costs, across variable levels of doxycycline adherence. We conducted sensitivity analyses by constructing a Latin Hypercube Sample from varied treatment efficacies and rates of PID from both successful and unsuccessful treatment. We estimated cost-equivalence- the threshold where the lack of adherence to doxycycline is balanced perfectly by the lower efficacy of azithromycin.
Results: Higher levels of doxycycline adherence result in lower direct medical costs, and fewer unsuccessfully treated infections. However, the threshold at which doxycycline is less costly than azithromycin requires at least 98% doxycycline adherence if azithromycin efficacy is 97%, and at least 83% adherence if azithromycin efficacy is 77%.
Conclusions: Tradeoffs between azithromycin and doxycycline efficacy, adherence, and cost interact to affect direct medical costs, with implications for clinical and public health decision-making. If doxycycline has higher efficacy, it would be preferred when high adherence can be guaranteed. However, because 1) adherence to doxycycline is challenging, and 2) azithromycin efficacy may be similar to doxycycline efficacy, azithromycin may often be favored for urogenital chlamydia treatment for both public health and clinical impact.