. Breast milk concentrations range from 0.015—0.37 mcg/ml with a milk:plasma ratio of 0.02—0.13. Penicillins may cause diarrhea, candidiasis, and skin rash in the breast-feeding infant. The infant should be observed for potential effects. Consider the benefits of breast-feeding, the risk of potential infant drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding infant experiences an adverse effect related to a maternally administered drug, healthcare providers are encouraged to report the adverse effect to the FDA.
MECHANISM OF ACTION
Mechanism of Action: Penicillin G Procaine is a beta-lactam antibiotic. It is mainly bactericidal in action. It inhibits the third and final stage of bacterial cell wall synthesis by preferentially binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall. Penicillin-binding proteins are responsible for several different steps in the synthesis of the cell wall and are found in quantities of several hundred to several thousand molecules per bacterial cell. Penicillin-binding proteins vary among different bacterial species. Thus, the intrinsic activity of penicillin G, as well as the other penicillins, against a particular organism depends on its ability to gain access to and bind with the necessary PBP. Like all beta-lactam antibiotics, penicillin G's ability to interfere with PBP-mediated cell wall synthesis ultimately leads to cell lysis. Lysis is mediated by bacterial cell wall autolytic enzymes (i.e., autolysins). The relationship between PBPs and autolysins is unclear, but it is possible that the beta-lactam antibiotic interferes with an autolysin inhibitor.
PHARMACOKINETICS
Procaine penicillin G is administered by intramuscular injection. Approximately 60% of penicillin G is bound to albumin. Penicillin G is rapidly eliminated via renal tubular excretion. A dose of 300,000 units of penicillin G procaine contains 120 mg of procaine. When large doses of penicillin G procaine are administered (e.g., 4.8 million units) procaine may reach toxic serum concentrations (see Dosage section for Maximum Dosage Limits).
Intramuscular Route
Following intramuscular administration, a tissue depot is created at the site of IM injection and active drug is slowly released into the systemic circulation. Penicillin G serum concentrations are lower but more prolonged with penicillin G procaine compared to aqueous penicillin G administration. Compared with penicillin G benzathine, however, penicillin G procaine reaches higher serum concentrations but has less prolonged drug levels. When high, sustained serum concentrations are required, aqueous penicillin G, administered either IM or IV, should be used. IM administration of penicillin G procaine, results in penicillin serum concentrations which peak within 4 hours and slowly decrease over the next 15—20 hours. Penicillin serum concentrations are detected for up to 5—7 days post administration. |
