Penicillin G is a broad-spectrum beta-lactam antibiotic administered parenterally. It is the treatment of choice for syphilis, meningococcal meningitis, and infective endocarditis.
Also known as: Benzylpenicillin, Penicilina Benzatina
Penicillin + uricosuric: penicillin levels increased ~2x via blockade of renal tubular secretion.
Probenecid blocks renal tubular secretion of penicillin via OAT1/OAT3 transporters, increasing serum levels ~2x and prolonging half-life from 30 min to ~6 h. Historically, this interaction was used intentionally (pre-antibiotic era) to prolong penicillin action. Currently, the combination is rare, but may be considered in: (1) neurosyphilis (when IV ceftriaxone is unavailable), (2) enterococcal endocarditis (combination therapy).
Penicillin + uricosuric: penicillin levels ~2x via tubular secretion blockade.
Probenecid blocks renal tubular secretion of penicillin, increasing serum levels and prolonging half-life. Historically used intentionally to prolong penicillin action. Currently, concomitant use is rare.
Serum penicillin levels (if available), clinical response.
If intentional coadministration (syphilis, endocarditis): reduce penicillin dose. If unintentional: no adjustment required — just monitor.
DailyMed/FDA (NIH/NLM) — approved Penicillin G label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9e58122f-5c75-4905-a774-d3a4dae4ff8c
Alkaline foods inactivate penicillin G by hydrolysis. Increase interval between food and medication.
Administer 1 h before or 2 h after meals. Avoid acidic fruit juices (may precipitate).
Renal excretion >80% — accumulation in renal impairment. Risk of neurotoxicity (seizures) with unadjusted doses.
Adjust interval to eGFR: eGFR 10-50: q6-8h; eGFR <10: q12-16h. Haemodialysis removes ~40%.
DailyMed/FDA (NIH/NLM) — approved Penicillin G label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9e58122f-5c75-4905-a774-d3a4dae4ff8c
Category B: safe in pregnancy. Penicillins are the drugs of choice in pregnancy (syphilis, listeriosis).
All trimesters. Safe.
Excreted in small amounts in breast milk. Safe during breastfeeding.
No evidence of effects on fertility.
DailyMed/FDA (NIH/NLM) — approved Penicillin G label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9e58122f-5c75-4905-a774-d3a4dae4ff8c
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Bactericidal: inhibits peptidoglycan synthesis in bacterial cell wall. Activity against streptococci, meningococci, Treponema pallidum, anaerobes (except Bacteroides).
Binds to PBPs (penicillin-binding proteins), preventing peptidoglycan cross-linking. Results in osmotic bacterial lysis.
Inactivated by gastric acid — IV/IM administration. Wide distribution (CSF, synovial fluid, bone), but poor CSF penetration without meningeal inflammation.
Not hepatically metabolised — renally excreted by tubular secretion (>80% in 6 h). Probenecid blocks tubular secretion.
30 minutes (IV). Approximately 6-12 h with probenecid.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
