minocycline (34%), doxycycline hyclate (33%), extended-release minocycline (21%), doxycycline monohydrate (8%), and low-dose extended-release doxycycline (3%).Frequency of Therapeutic Switching
Among women with acne who were started on spironolactone, 14.4% were prescribed a different systemic agent within 1 year. Among women with acne who were started on oral tetracycline-class antibiotics, 13.4% were prescribed a different systemic agent within 1 year (Table 2). When adjusted for age, topical retinoid, and oral contraceptive use, the odds ratio for being prescribed a different systemic agent within one year was 1.07 (95% CI 0.99-1.16) for those prescribed spironolactone when compared with oral tetracycline-class antibiotics and the risk difference was 0.007 (95% CI -0.002-0.017). The number of women needed to treat with an oral tetracycline-class antibiotic instead of spironolactone to prevent one instance of switching was 143 women.
Subgroup and Secondary Analyses
Among adolescent women, the adjusted odds ratio for being prescribed a different systemic agent within one year was 1.58 (95% CI 1.35-1.86) for those prescribed spironolactone when compared with oral tetracycline-class antibiotics and the risk difference was 0.060 (95% CI 0.039-0.080). The number of adolescent women needed to treat with an oral tetracycline-class antibiotic instead of spironolactone to prevent one instance of therapeutic switching was 17 women. Among adult women, the adjusted odds ratio for being prescribed a different systemic agent within one year was 0.94 (95% CI 0.86-1.03) for those prescribed spironolactone when compared with oral tetracycline-class antibiotics and the risk difference was -0.007 (95% CI -0.018-0.004).Compared to spironolactone, doxycycline was the oral tetracycline-class antibiotic that was least likely to be switched. The adjusted odds ratio for being prescribed a 
