A 22-year-old receives intramuscular benzathine penicillin G 2.4 million units for early syphilis. The property of this formulation that permits single-dose therapy is:
- A Very low solubility producing slow release and detectable serum concentrations for weeks ✓
- B Resistance to degradation by penicillinase allowing prolonged plasma levels
- C Irreversible binding to serum proteins creating a depot reservoir
- D Active uptake and storage within macrophages at the injection site
Correct answer: A. Very low solubility producing slow release and detectable serum concentrations for weeks
Explanation
Benzathine penicillin G is a poorly water-soluble salt of penicillin G with dibenzylethylenediamine. After deep intramuscular injection it dissolves slowly, maintaining low but treponemicidal plasma concentrations for 2 to 4 weeks. This repository property underlies its use in syphilis and rheumatic fever prophylaxis. Treponema pallidum remains exquisitely sensitive rather than the drug being penicillinase resistant, killing option B.
Reference: Katzung Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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