Variables influencing penicillin treatment outcome in streptococcal tonsillopharyngitis.

OBJECTIVE To examine whether penicillin treatment success for group A beta-hemolytic streptococcal tonsillopharyngitis is influenced by patient age, number of days ill prior to initiation of treatment, number of prior episodes, season, total dosage (milligrams per kilogram), and frequency of administration (2 vs 3 times daily). METHODS Four hundred seventy-eight children, adolescents, and young adults aged 2 to 21 years with acute symptoms compatible with the clinical diagnosis of group A beta-hemolytic streptococcal tonsillopharyngitis and a positive streptococcus rapid antigen detection test result were enrolled (intent-to-treat group). Patients were randomly assigned to receive penicillin V potassium, 250 mg 3 times daily (n = 239) or 500 mg 2 times daily (n = 239). Randomization was independent of patient body weight and treatment was for 10 days with both regimens. Follow-up examinations occurred, and cultures were obtained at 14 to 21 days after the initiation of antibiotic therapy; those with group A beta-hemolytic streptococcus isolated from a throat culture and who returned for follow-up were assessed for outcome (n = 359). RESULTS Using a logistic regression analysis with a stepwise variable selection, we found the major variables associated with penicillin treatment success to be the number of days ill prior to initiation of treatment (P = .001; odds ratio, 1.55 [95% confidence interval, 1.2-2.1]) and the age of the child when infected (P = .004; odds ratio, 1.14 [95% confidence interval, 1.05-1.25]). The number of prior episodes within the preceding year, the season, the total daily penicillin dose (range, 8-76 mg/kg), and 2 vs 3 times daily dosing did not significantly alter treatment outcome. CONCLUSION Treatment after 2 days of illness and of adolescent patients increases penicillin treatment success for group A beta-hemolytic streptococcal tonsillopharyngitis.