PENICILLIN G POTASSIUM
Clinical safety rating: safe
Human studies have proved safety
Bactericidal: inhibits transpeptidases (penicillin-binding proteins) involved in bacterial cell wall synthesis, leading to cell lysis.
| Metabolism | Mainly renally excreted unchanged (60-90%); minimal hepatic metabolism. |
| Excretion | Renal (60-90% as unchanged drug via tubular secretion and glomerular filtration); biliary (minor, <10%); fecal (minimal, <5%). |
| Half-life | 0.5-1 hour in normal renal function; prolonged to 3-10 hours in anuria/end-stage renal disease. |
| Protein binding | Approximately 60% bound primarily to serum albumin. |
| Volume of Distribution | 0.3-0.4 L/kg; low distribution consistent with limited tissue penetration and high water solubility. |
| Bioavailability | IM: 60-70%; IV: 100%; Oral: not administered due to acid lability. |
| Onset of Action | IV: Immediate; IM: 15-30 minutes. |
| Duration of Action | IV: 4-6 hours; IM: 6-8 hours. Short duration due to rapid renal clearance. |
| Molecular Weight | 372.48 |
1-4 million units IV every 4-6 hours; maximum 24 million units/day
| Dosage form | TABLET |
| Renal impairment | GFR 30-60 mL/min: give 75% of usual dose every 4-6 hours; GFR 10-30 mL/min: give 50% of usual dose every 4-6 hours; GFR <10 mL/min: give 25% of usual dose every 4-6 hours or 100% of usual dose every 8-12 hours |
| Liver impairment | No adjustment required for Child-Pugh A, B, or C; primarily renally excreted |
| Pediatric use | Neonates <7 days: 50,000 units/kg IV every 12 hours; Neonates 7-28 days: 75,000 units/kg IV every 8 hours; Children: 100,000-250,000 units/kg/day IV divided every 4-6 hours (maximum 24 million units/day) |
| Geriatric use | Initiate at lower end of dosing range; monitor renal function and adjust based on creatinine clearance; typical dose: 1-2 million units IV every 4-6 hours |
| 1st trimester | Penicillin G potassium is generally considered safe in the first trimester. Animal studies have not shown fetal harm, and it is a first-line treatment for syphilis and group B streptococcus. Crosses placenta but no teratogenicity. |
| 2nd trimester | Safe in second trimester. Used for infections such as syphilis and group B streptococcus. Fetal ototoxicity not associated with penicillins. |
| 3rd trimester | Safe in third trimester. Used intrapartum for group B streptococcus prophylaxis. No known adverse fetal effects. |
Clinical note
Probenecid may decrease excretion Serious and occasionally fatal hypersensitivity reactions have been reported.
| Placental transfer | Penicillin G crosses the placenta rapidly, achieving fetal serum concentrations similar to maternal levels. Used therapeutically to treat fetal infections such as syphilis. |
| Breastfeeding | Penicillin G potassium is excreted into breast milk in small amounts. Generally considered compatible with breastfeeding. May alter infant gut flora or cause allergic sensitization, but no adverse effects reported. Use caution in infants with penicillin allergy. |
■ FDA Black Box Warning
Rapid IV administration may cause life-threatening arrhythmias or cardiac arrest due to potassium toxicity. Use with caution in patients with renal impairment.
| Common Effects | Diarrhea |
| Serious Effects |
Hypersensitivity to penicillinsAnaphylactic reaction to any beta-lactam antibiotic
| Precautions | Hypersensitivity reactions (anaphylaxis, urticaria, serum sickness-like reactions), Renal impairment: dose adjustment required, Electrolyte disturbances: hyperkalemia, especially with high doses or renal impairment, CNS toxicity: seizures, especially with high doses or renal impairment (due to penicillin) |
| Food/Dietary | No specific food interactions. Avoid alcohol consumption during treatment as it may reduce therapeutic efficacy. |
Loading safety data…
| Lactation Rating | L1 (Safe) |
| Teratogenic Risk | No teratogenic effects documented in first trimester; safe in all trimesters. Crosses placenta but no fetal harm. |
| Fetal Monitoring | No specific monitoring required beyond standard clinical observation. Monitor for allergic reactions. |
| Fertility Effects | No known adverse effects on fertility. |
| Clinical Pearls | Administer IV only; avoid intra-arterial or intramuscular injection due to risk of necrosis. Contains potassium (1.7 mEq per million units); monitor serum potassium in renal impairment. Perform rapid IV infusion over 15-30 minutes; avoid continuous infusion due to instability in solution. Check for penicillin allergy history before administration; cross-reactivity with cephalosporins is low but possible. Use within 24 hours when reconstituted; discard unused portions due to rapid degradation. |
| Patient Advice | Report any signs of allergic reaction immediately, such as rash, itching, or difficulty breathing. · Complete the full course of therapy even if you feel better. · Inform your doctor if you have kidney problems or a high potassium level. · This medication is given intravenously (into a vein) and must be administered by a healthcare professional. · Do not mix this medication with alcoholic beverages. |