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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Probenecid may decrease excretion Serious and occasionally fatal hypersensitivity reactions have been reported.
| Breastfeeding | Compatible with breastfeeding; trace amounts in milk, M/P ratio ~0.04. No adverse effects in infants. |
| 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. |
■ 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 penicillins","History of immediate hypersensitivity to cephalosporins (cross-reactivity risk)"]
| 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)"] |
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| Fertility Effects | No known adverse effects on fertility. |