Amoxicillin and penicillin G dosing in pediatric community-acquired pneumococcal pneumonia in the era of conjugate pneumococcal vaccines.

Background: Parenteral penicillin G (PENG) and oral amoxicillin (AMOX) are recommended as treatment for pediatric community-acquired pneumonia (CAP). With recent epidemiologic penicillin susceptibility data for Streptococcus pneumoniae, the most common etiology of CAP, the objective of this study was to evaluate optimal dosing regimens of PENG and AMOX based on population pharmacokinetics linked to current susceptibility data.

Methods: Using NONMEM v7.3, Monte Carlo simulations (N = 10,000) were conducted for AMOX 15 mg/kg/dose PO every 8 h (standard-dose), AMOX 45 mg/kg/dose PO every 12 h (high-dose), and PENG 62,500 units/kg/day IV every 6 h using six virtual subjects with ages spanning 3 months to 15 years old. The probability of target attainment (PTA) was determined for both serum and epithelial lining fluid (ELF) to achieve free drug concentrations above the minimum inhibitory concentration (%fT>MIC) across the population of pneumococci for 30%-50% of the dosing interval.

Results: In 2018, all 21 (100%) pneumococcal isolates were susceptible to both PENG and AMOX based on Clinical and Laboratory Standards Institute (CLSI; MIC at 2 mg/L) breakpoints, and 15 of 21 (71%) were susceptible based on EUCAST (MIC at 0.5 mg/L) breakpoints. As compared to CLSI, EUCAST breakpoints consistently achieved higher PTA for all antibiotic regimens. At 50% fT>MIC in the serum at the susceptible MICs, standard-dose AMOX achieved >4% PTA (CLSI) and >86% PTA (EUCAST); high-dose AMOX achieved >73% PTA (CLSI) and >99% PTA (EUCAST); and PENG achieved 0% PTA (using CLSI) and 100% PTA (using EUCAST). Standard-dose AMOX, high-dose AMOX, and PENG achieved >71%, >93%, and 100% PTA, respectively, in the serum at 30%-50% fT>MIC when each patient was stochastically linked to an MIC based on the frequency distribution of national susceptibility data. The PTA was consistently lower in ELF as compared with serum for all regimens.

Conclusion: Based on the recent rates of resistance, antibiotic doses evaluated provide appropriate exposure for pediatric CAP based on the serum and ELF data associated with predicted clinical and microbiologic success for pneumococcus. High-dose AMOX may still be required to treat pediatric CAP, especially if using CLSI breakpoints. Ongoing surveillance for resistance is essential.