PFIZERPEN-A
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PFIZERPEN-A (PFIZERPEN-A).
Penicillin G inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidase activity and activating autolytic enzymes.
| Metabolism | Primarily renal tubular secretion (90% unchanged). Minimal hepatic metabolism. |
| Excretion | Primarily renal (60-70% unchanged via glomerular filtration and tubular secretion); hepatic metabolism minor (<10%); biliary/fecal elimination <10%. |
| Half-life | Terminal elimination half-life: 0.6-0.8 hours in adults with normal renal function; prolonged to 7-10 hours in end-stage renal disease (ESRD). In neonates, half-life ranges 2-4 hours. |
| Protein binding | Approximately 60-65% bound primarily to serum albumin, with minor binding to alpha-1-acid glycoprotein. |
| Volume of Distribution | 0.2-0.3 L/kg; low Vd reflects limited tissue distribution (primarily extracellular fluid). Higher in neonates (0.4-0.5 L/kg). |
| Bioavailability | Oral bioavailability: negligible (<10%) due to acid lability; IM bioavailability: ~80-100% with rapid absorption. |
| Onset of Action | IV bolus: immediate (within minutes); IM injection: 15-30 minutes; oral: not applicable (parenteral only). |
| Duration of Action | Duration of bactericidal levels: 4-6 hours after IM/IV administration; requires frequent dosing (q4-6h) for continuous coverage. Short duration necessitates careful scheduling. |
1-2 million units intramuscularly or intravenously every 4 hours; or continuous intravenous infusion of 20-30 million units per day.
| Dosage form | FOR SUSPENSION |
| Renal impairment | For GFR 10-50 mL/min: administer every 6-8 hours. For GFR <10 mL/min: administer every 12 hours or reduce dose by 50%. |
| Liver impairment | No specific adjustment required; caution in severe hepatic impairment due to potential risk of encephalopathy. |
| Pediatric use | Neonates <7 days: 50,000 units/kg intramuscularly or intravenously every 12 hours. Neonates 7-28 days: 50,000 units/kg every 8 hours. Infants and children: 100,000-250,000 units/kg/day divided every 4-6 hours. |
| Geriatric use | Use with caution; adjust dosing interval based on renal function; monitor for electrolyte disturbances. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PFIZERPEN-A (PFIZERPEN-A).
| Breastfeeding | Penicillin G is excreted into breast milk in low concentrations. The milk-to-plasma ratio is approximately 0.2. Doses up to 1.2 million units daily are considered compatible with breastfeeding. Theoretical risk of alteration of infant gut flora and sensitization. Monitor infant for rash and gastrointestinal disturbances. |
| Teratogenic Risk | Penzicillin G (PFIZERPEN-A) is generally considered low risk in pregnancy. Animal studies have not shown teratogenicity. In humans, no increased risk of major congenital malformations has been observed. Use in the first trimester: no evidence of teratogenic effects. Second and third trimesters: no specific fetal risks, but may cause altered fetal gut flora. High doses near term may increase risk of kernicterus in jaundiced neonates. |
■ FDA Black Box Warning
None listed by FDA for this formulation; however, rapid IV administration may cause severe or fatal anaphylaxis. No specific boxed warning.
| Serious Effects |
Known hypersensitivity to penicillins. Use with caution in patients with history of severe immediate allergy to cephalosporins or carbapenems (possible cross-sensitivity).
| Precautions | Hypersensitivity reactions (anaphylaxis) can occur; skin testing recommended in patients with penicillin allergy history. Neurologic adverse effects (e.g., seizures) with high doses or renal impairment. Electrolyte disturbances with large IV doses (potassium or sodium salt). Prolonged use may lead to superinfection due to Clostridium difficile. |
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| Fetal Monitoring | No specific fetal monitoring required for penicillin G. Monitor maternal renal function in high-dose therapy or prolonged use. For prolonged high-dose therapy, consider monitoring for electrolyte imbalances (sodium and potassium content). |
| Fertility Effects | No known adverse effects on fertility in animal studies or human reports. |