PFIZERPEN-AS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PFIZERPEN-AS (PFIZERPEN-AS).
PFIZERPEN-AS (penicillin G procaine) inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidation and transglycosylation, leading to cell lysis.
| Metabolism | Hepatic metabolism (minor); primarily renal elimination via glomerular filtration and tubular secretion (unchanged drug). |
| Excretion | Primarily renal (60-80% as unchanged drug via tubular secretion and glomerular filtration); minor biliary/fecal elimination (10-20%) |
| Half-life | 0.5-1 hour in healthy adults; prolonged to 2.5-10 hours in renal impairment (CrCl <10 mL/min). Clinically relevant for dosing interval adjustment in renal dysfunction. |
| Protein binding | 50-65% primarily to serum albumin |
| Volume of Distribution | 0.3-0.4 L/kg; low Vd indicating limited extravascular distribution. Increased in neonates, pregnancy, and inflammatory states. |
| Bioavailability | IM: 70-100%; Oral: 30-60% (variable due to gastric acid degradation). IV: 100% |
| Onset of Action | IM: 15-30 minutes; IV: immediate (<5 minutes). Oral: 30-60 minutes (peak serum levels at 1-2 hours). |
| Duration of Action | 4-6 hours for IM/IV; 6-8 hours for oral. Duration may be extended in renal failure. Bactericidal effect persists briefly after serum levels fall below MIC due to post-antibiotic effect (1-2 hours). |
| Molecular Weight | 356.37 |
250-500 mg orally every 6-8 hours for moderate infections; 500 mg to 2 g intravenously every 4-6 hours for severe infections.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 10-50 mL/min: administer every 8-12 hours; CrCl <10 mL/min: administer every 12-18 hours; hemodialysis: supplement dose after dialysis. |
| Liver impairment | No dosage adjustment required for mild to moderate hepatic impairment; caution in severe impairment due to potential accumulation. |
| Pediatric use | Children >12 years: same as adult; children 1 month to 12 years: 25-50 mg/kg/day orally divided every 6-8 hours; intravenous: 100-200 mg/kg/day divided every 4-6 hours; neonates: 50 mg/kg per dose intramuscularly or intravenously every 12 hours for first week of life, then every 8 hours. |
| Geriatric use | Use lowest effective dose; monitor renal function and adjust based on CrCl; increased risk of neurotoxicity (seizures) with high doses. |
| 1st trimester | Generally considered safe; penicillin crosses placenta but no evidence of teratogenicity in humans. |
| 2nd trimester | Safe for use when indicated; treat infections to avoid maternal/fetal complications. |
| 3rd trimester | Safe; no known adverse fetal effects. |
Clinical note
Comprehensive clinical and safety monograph for PFIZERPEN-AS (PFIZERPEN-AS).
| Placental transfer | Crosses placenta; achieves therapeutic levels in fetal circulation. |
| Breastfeeding | Penicillin G enters breast milk in low concentrations; unlikely to cause adverse effects in nursing infants. Compatible with breastfeeding; monitor for rash or diarrhea. |
| Lactation Rating |
■ FDA Black Box Warning
Severe and occasionally fatal hypersensitivity (anaphylactic) reactions have been reported. Some patients have a history of penicillin hypersensitivity but others have had no prior history. Emergency measures including epinephrine, corticosteroids, and airway management must be immediately available.
| Serious Effects |
Hypersensitivity to penicillinsHistory of severe allergic reaction (e.g., anaphylaxis) to beta-lactam antibiotics
| Precautions | Severe hypersensitivity reactions including anaphylaxis, CNS toxicity (e.g., seizures) with high doses or renal impairment, Local reactions (e.g., procaine-induced neuropsychiatric reactions), Risk of C. difficile-associated diarrhea, Renal impairment: dose adjustment may be required, Superinfection with prolonged use |
| Food/Dietary | No clinically significant food interactions. However, patients on prolonged therapy should maintain adequate hydration. No dietary restrictions required. |
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| Teratogenic Risk | Pfizerpen-AS (penicillin G procaine) is classified as FDA pregnancy category B. Animal studies have not demonstrated teratogenic effects. In humans, penicillins are generally considered safe during pregnancy with no established risk of congenital anomalies. First trimester: No evidence of increased malformations. Second/third trimesters: No known fetal harm. However, use only if clearly needed. |
| Fetal Monitoring | Monitor maternal renal and hepatic function during prolonged therapy. Observe for signs of hypersensitivity reactions. In neonates, monitor for gastrointestinal disturbances. No specific fetal monitoring required; routine prenatal care suffices. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies have not shown impaired fertility. Penicillin antibiotics are not associated with reproductive toxicity. |
| Clinical Pearls | PFIZERPEN-AS (aqueous penicillin G procaine) is a long-acting intramuscular formulation; avoid intravenous administration. Always confirm absence of penicillin allergy before administration; obtain culture and sensitivity prior to initiation for confirmed bacterial infections. Monitor for procaine reactions (psychomotor agitation, seizures) and anaphylaxis. Do not use for neurosyphilis; use aqueous crystalline penicillin G instead. In renal impairment (CrCl <10 mL/min), dosing interval may be extended to 24 hours. |
| Patient Advice | This medication is given as a deep intramuscular injection, usually into the buttock or thigh; do not massage the injection site. · Report any signs of allergic reaction (rash, hives, difficulty breathing, swelling of lips/face) immediately. · Complete the full course even if you feel better; inform your doctor if you have a history of penicillin allergy. · Possible injection site pain, tenderness, or redness may occur. Seek medical attention if severe pain, swelling, or drainage develops. · Avoid driving or operating machinery if you experience dizziness, confusion, or seizure-like symptoms (procaine reaction). |