PFIZERPEN G
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PFIZERPEN G (PFIZERPEN G).
Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidase activity and autolysin inhibition.
| Metabolism | Primarily renally eliminated; undergoes tubular secretion with minimal hepatic metabolism. |
| Excretion | Primarily renal excretion via glomerular filtration and tubular secretion; 60-90% of dose excreted unchanged in urine within 6 hours. Biliary excretion accounts for less than 10%. |
| Half-life | Terminal elimination half-life is 30-60 minutes in patients with normal renal function; prolonged to 2-10 hours in renal impairment (CrCl <10 mL/min). |
| Protein binding | Approximately 60-80% bound to serum albumin. |
| Volume of Distribution | 0.2-0.3 L/kg; limited distribution primarily to extracellular fluid; low penetration into CSF unless meninges inflamed (CSF concentrations 5-10% of serum). |
| Bioavailability | Intramuscular: 60-100% (variable) due to slow absorption. Oral: 15-30% (unreliable, therefore not used). |
| Onset of Action | Intravenous: immediate (peak plasma concentration within minutes). Intramuscular: 15-30 minutes. Subcutaneous: 30-60 minutes. |
| Duration of Action | Intravenous: 2-4 hours (bactericidal levels maintained). Intramuscular: 4-6 hours. Sustained release formulations (e.g., procaine penicillin G) may extend to 12-24 hours. |
2-4 million units (1.2-2.4 g) IV every 4-6 hours; maximum 24 million units per day.
| Dosage form | TABLET |
| Renal impairment | GFR 10-50 mL/min: 2-4 million units IV every 6-8 hours; GFR <10 mL/min: 2-4 million units IV every 8-12 hours. |
| Liver impairment | No adjustment required; primarily renally excreted. |
| Pediatric use | Neonates <7 days: 50,000-100,000 units/kg IV every 12 hours; infants and children: 100,000-250,000 units/kg/day IV divided every 4-6 hours. |
| Geriatric use | Dose based on renal function; consider lower initial doses due to age-related decline in GFR. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PFIZERPEN G (PFIZERPEN G).
| Breastfeeding | Penicillin G is excreted into human breast milk in small amounts (M/P ratio approximately 0.1-0.2). Concentrations are low and unlikely to cause adverse effects in the nursing infant. Considered compatible with breastfeeding by the American Academy of Pediatrics. Monitor infant for potential gastrointestinal disturbances or allergic reactions. |
| Teratogenic Risk | Penicillin G (PFIZERPEN G) is classified as FDA Pregnancy Category B. Animal reproduction studies have not demonstrated a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women. Generally considered low risk; use only if clearly needed. No known teratogenic effects in first trimester; second and third trimester use is considered safe. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
["History of immediate-type hypersensitivity (e.g., anaphylaxis, urticaria) to any penicillin","Use of procaine penicillin G in patients with known procaine sensitivity"]
| Precautions | ["Severe hypersensitivity reactions (anaphylaxis, angioedema)","Clostridioides difficile-associated diarrhea (CDAD)","Neurotoxicity with high doses or renal impairment (seizures, myoclonus)","Electrolyte disturbances (sodium or potassium overload with high doses)","Renal impairment requires dose adjustment","Use in neonates requires caution due to immature renal function"] |
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| Fetal Monitoring | No specific routine monitoring required beyond standard obstetric care. Monitor maternal renal function if high doses are used, as excretion is renal. Observe for signs of allergic reaction or anaphylaxis in the mother. Fetal monitoring per standard obstetric indications. |
| Fertility Effects | No known adverse effects on fertility in animal or human studies. Penicillin G is not associated with impairment of reproductive function. |