PFIZERPEN

Clinical safety rating: caution

Comprehensive clinical and safety monograph for PFIZERPEN (PFIZERPEN).

How it works

Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidation and causing autolysin activation, leading to cell lysis.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for PFIZERPEN (PFIZERPEN).

Breastfeeding	Penicillin G is excreted into breast milk in small amounts (M/P ratio approximately 0.05). It is generally considered compatible with breastfeeding. The low levels in milk are unlikely to cause adverse effects in the infant. Caution only in case of neonatal sensitization or diarrhea.
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.

Warnings & precautions

■ FDA Black Box Warning

No FDA black box warning.

Side Effect Profile

Serious Effects

Absolute Contraindications

["History of immediate hypersensitivity (anaphylaxis, urticaria) to any penicillin","Hypersensitivity to cephalosporins or carbapenems due to cross-reactivity"]

Clinical Precautions

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"]

Clinical Tips & Counseling

Drug interactions

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PFIZERPEN

Clinical safety rating: caution

Comprehensive clinical and safety monograph for PFIZERPEN (PFIZERPEN).

How it works

Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidation and causing autolysin activation, leading to cell lysis.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for PFIZERPEN (PFIZERPEN).

Breastfeeding	Penicillin G is excreted into breast milk in small amounts (M/P ratio approximately 0.05). It is generally considered compatible with breastfeeding. The low levels in milk are unlikely to cause adverse effects in the infant. Caution only in case of neonatal sensitization or diarrhea.
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.

Warnings & precautions

■ FDA Black Box Warning

No FDA black box warning.

Side Effect Profile

Serious Effects

Absolute Contraindications

["History of immediate hypersensitivity (anaphylaxis, urticaria) to any penicillin","Hypersensitivity to cephalosporins or carbapenems due to cross-reactivity"]