PFIZERPEN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PFIZERPEN (PFIZERPEN).
Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidation and causing autolysin activation, leading to cell lysis.
| Metabolism | Primarily eliminated unchanged by renal tubular secretion; minor hepatic metabolism to penicilloic acid. |
| Excretion | Primarily renal tubular secretion (60-90% unchanged) and glomerular filtration; about 10% biliary/fecal. In neonates, renal clearance is reduced. |
| Half-life | Terminal elimination half-life: ~0.5-1 hour (adults with normal renal function); prolongs to 7-10 hours in end-stage renal disease. Clinical context: short half-life requires frequent dosing (q4-6h) or continuous infusion for severe infections. |
| Protein binding | ~60-65% bound to serum albumin (mainly); to a lesser extent to other proteins. |
| Volume of Distribution | Vd: ~0.18-0.3 L/kg in adults (low, consistent with limited tissue distribution; remains largely in extracellular fluid). Clinical meaning: low Vd indicates poor penetration into cells and CNS (except with inflamed meninges). |
| Bioavailability | Oral: 15-30% (unreliable due to gastric acid degradation). IM aqueous: >90%. IM procaine: slow release, effective levels for 12-24h. IV: 100%. |
| Onset of Action | IM: rapid (15-30 min) for susceptible organisms. IV: immediate. Oral: 30-60 min (but not preferred due to acid lability). |
| Duration of Action | IM (aqueous): 2-4 hours for susceptible bacteria. IV: 2-4 hours. Procaine salt: 12-24 hours. Benzathine salt: 2-4 weeks. Clinical note: depends on formulation and renal function. |
| Molecular Weight | 356.37 |
250-500 mg orally every 6 hours or 1-2 g intravenously every 4-6 hours.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 10-50 mL/min: same dose every 8-12 hours; CrCl <10 mL/min: same dose every 12-24 hours. |
| Liver impairment | No adjustment required for mild to moderate impairment (Child-Pugh A/B). Severe impairment (Child-Pugh C): caution, monitor for adverse effects. |
| Pediatric use | 25-50 mg/kg/day orally divided every 6-8 hours; maximum 2 g/day. For severe infections: 100-400 mg/kg/day IV divided every 4-6 hours. |
| Geriatric use | Initiate at lower end of dosing range; monitor renal function and adjust dose accordingly. |
| 1st trimester | Penicillin G is generally considered safe; use only if clearly needed. |
| 2nd trimester | Safe; no known risk of fetal harm. |
| 3rd trimester | Safe; no known risk of fetal harm. |
Clinical note
Comprehensive clinical and safety monograph for PFIZERPEN (PFIZERPEN).
| Placental transfer | Penicillin G crosses the placenta; achieves therapeutic levels in fetal circulation. |
| Breastfeeding | Penicillin G is excreted into breast milk in small amounts; unlikely to cause adverse effects in nursing infants. |
| Lactation Rating | L1 |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Hypersensitivity to penicillinsHypersensitivity to beta-lactam antibiotics
| Precautions | Serious hypersensitivity reactions (anaphylaxis) can occur, especially with prior penicillin allergy, Use with caution in patients with renal impairment, as accumulation may occur, Clostridium difficile-associated diarrhea (CDAD) reported with nearly all antibacterial agents, Prolonged use may lead to superinfection |
| Food/Dietary | No significant food interactions. Administer injection on an empty stomach for rapid absorption if given orally, but parenteral route preferred. |
| Clinical Pearls |
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| Teratogenic Risk | Penicillin G (PFIZERPEN) is generally considered low risk during pregnancy. Animal studies have not shown teratogenic effects. In humans, first-trimester exposure is not associated with an increased risk of major congenital malformations. However, as with all drugs, use only if clearly needed. No known fetal risks in any trimester. |
| Fetal Monitoring | Monitor for allergic reactions, including anaphylaxis, in the mother. No specific fetal monitoring required. For prolonged therapy, monitor maternal renal function and serum electrolytes (risk of sodium overload). |
| Fertility Effects | No adverse effects on fertility have been reported in animal studies or human data. Penicillin G is not known to impair fertility. |
| PFIZERPEN (penicillin G) is primarily used for streptococcal, pneumococcal, and meningococcal infections. It is inactivated by gastric acid, so administer IV or IM for systemic infections. Monitor for hypersensitivity reactions, especially in patients with history of penicillin allergy. Do not use for staphylococcal infections due to resistance. For syphilis, benzathine penicillin G is preferred. In renal impairment, dose adjustment may be needed. |
| Patient Advice | Complete the full course even if you feel better. · Report any rash, itching, or difficulty breathing immediately. · This medication is given by injection; do not take orally unless specified. · Avoid alcohol during treatment as it may increase side effects. · Inform your doctor if you have kidney disease or allergies. |