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. |
| Molecular Weight | 372.48 |
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 | Penicillin G is generally considered safe in pregnancy; crosses placenta but no evidence of teratogenicity in humans. Use only if clearly needed. |
| 2nd trimester | Safe; no known fetal risk. Used for infections like syphilis and group B streptococcus prophylaxis. |
| 3rd trimester | Safe; no known fetal risk. Used for intrapartum prophylaxis for group B streptococcus. |
Clinical note
Comprehensive clinical and safety monograph for PFIZERPEN-A (PFIZERPEN-A).
| Placental transfer | Crosses placenta; fetal serum levels can reach 30-50% of maternal levels. |
| Breastfeeding | Penicillin G is excreted into breast milk in small amounts (0.5-2% of maternal dose); not expected to cause adverse effects in nursing infants. Compatible with breastfeeding. |
■ 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 |
History of severe hypersensitivity (e.g., anaphylaxis) to penicillinsHistory of severe hypersensitivity to beta-lactam antibiotics (e.g., cephalosporins, carbapenems)
| 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. |
| Food/Dietary | No significant food interactions; may be taken with or without food. Avoid alcohol to reduce risk of disulfiram-like reaction (rare). |
Loading safety data…
| Lactation Rating |
| L1 - Safe |
| 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. |
| 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. |
| Clinical Pearls | Administration with penicillin skin testing recommended prior to therapy; monitor for immediate hypersensitivity reactions; adjust dose in renal impairment (CrCl <10 mL/min) to q12h; preferred for neurosyphilis due to high CNS penetration; use with probenecid to increase serum levels; check for cross-reactivity in patients with cephalosporin allergy; reconstitute with sterile water for injection; avoid IM injection in neonates due to risk of sterile abscess; maintain adequate hydration to prevent crystalluria with high doses. |
| Patient Advice | Complete the full course of therapy even if you feel better. · Report any skin rash, hives, difficulty breathing, or swelling immediately. · Take with food if gastrointestinal upset occurs. · Avoid alcohol while on treatment. · Inform your doctor if you have kidney disease or are pregnant. · Store oral suspension in refrigerator; discard after 14 days. · Do not skip doses; take at evenly spaced intervals. |