Objective: This prospective study was aimed at answering two important questions: 1) Is a biweekly schedule of 1.2 million U intramuscular benzathine penicillin G (BPG) superior to a 4-week one in the prevention of upper respiratory Group A beta-hemolytic streptococcal (GABHS) infections and rheumatic fever (RF) recurrences? 2) Is there a difference in the bioavailability of BPG obtained from different manufacturers?
Methodology: Three hundred sixty rheumatic patients aged 4 to 20 years were randomly assigned to either a biweekly (190 patients) or 4-week (160 patients) BPG prophylactic schedule and were followed-up monthly for 2 years by clinical examination, throat swab culture for GABHS and measurement of antistreptolysin O titer to detect GABHS infection and/or recurrences of RF (according to revised Jones' Criteria). Thereafter, 34 rheumatic subjects, aged 8 to 16 years were randomly assigned to receive a 4-week injection of 1.2 million U of either a locally manufactured BPG brand (22 patients) or an imported one (12 patients). Sera of all patients were tested for penicillin level by plate diffusion method on days 1, 2, 3, 4, 5, 6, 7, 14, 21, and 28 after the intramuscular injection of BPG.
Results: The GABHS infection rate was found to be 0.2% and 0.3% for patients on the biweekly and 4-week BPG schedules, respectively, with no significant differences between them. However, the RF recurrence rate/patient/year for the 4-week schedule patients (0.12) was double that for the biweekly schedule ones (0.06). Estimation of the bioavailability of the two different brands of BPG demonstrated a difference in their pharmacokinetics and a decrease in the serum penicillin concentration below the minimum inhibitory concentration 3 weeks after the injection of either brand.
Conclusion: Although a biweekly schedule may not be superior in preventing upper respiratory GABHS infection, it may play a role in preventing the sequelae of such infections. The short duration of penicillinemia explains the superiority of the 2-week schedule in RF prophylais. The difference in the pharmacokinetics of penicillin brands might contribute to the high recurrence rate of RF reported in Egypt.