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 episod es, season, total dosage (milligrams per kilogram), and frequency of admini stration (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 diagno sis of group A beta-hemolytic streptococcal tonsillopharyngitis and a posit ive streptococcus rapid antigen detection test result were enrolled (intent -to-treat group). Patients were randomly assigned to receive penicillin V p otassium, 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 cult ure and who returned for follow-up were assessed for outcome (n = 359). Results: Using a logistic regression analysis with a stepwise variable sele ction, we found the major variables associated with penicillin treatment su ccess to be the number of days ill prior to initiation of treatment (P =.00 1; 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 seas on, the total daily penicillin dose (range, 8-76 mg/kg), and 2 vs 3 times d aily dosing did not significantly alter treatment outcome. Conclusion: Treatment after 2 days of illness and of adolescent patients in creases penicillin treatment success for group A beta-hemolytic streptococc al tonsillopharyngitis.