PFIZERPEN VK
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PFIZERPEN VK (PFIZERPEN VK).
Penicillin V binds to penicillin-binding proteins (PBPs) located on the bacterial cell wall, inhibiting transpeptidase activity and disrupting peptidoglycan cross-linking, leading to cell lysis via autolytic enzymes.
| Metabolism | Primarily excreted unchanged in urine via renal tubular secretion; minor hepatic metabolism to inactive metabolites (penicilloic acid). |
| Excretion | Renal: ~60-80% unchanged via tubular secretion; biliary/fecal: minor (hepatic elimination of metabolites). |
| Half-life | Terminal half-life: 30–60 minutes in adults with normal renal function; prolonged in renal impairment (up to 4–10 hours in anuria). |
| Protein binding | ~80% bound, primarily to serum albumin. |
| Volume of Distribution | 0.3–0.5 L/kg (approx. 20–40 L in adults); limited distribution into CNS except with inflamed meninges. |
| Bioavailability | Oral: approximately 60–75% (variable, reduced by food); IM: nearly complete (~100%). |
| Onset of Action | Oral: 30–60 minutes to therapeutic plasma levels; IM: 15–30 minutes; IV: immediate (within minutes). |
| Duration of Action | Approximately 4–6 hours for oral and IM routes; dose-dependent; clinical effect may persist longer at high doses or in renal impairment. |
| Molecular Weight | 388.48 |
250-500 mg orally every 6 hours for mild to moderate infections; 500 mg orally every 6 hours for severe infections. For group A streptococcal pharyngitis: 250 mg orally 3 times daily or 500 mg twice daily for 10 days.
| Dosage form | FOR SOLUTION |
| Renal impairment | CrCl >30 mL/min: no adjustment. CrCl 10-30 mL/min: administer every 8-12 hours. CrCl <10 mL/min: administer every 12-18 hours. For anuria: avoid use or reduce dose to 250 mg every 12 hours. |
| Liver impairment | No specific Child-Pugh based adjustments required; monitor for hepatic adverse effects. No dose modification recommended in hepatic impairment. |
| Pediatric use | Children >12 years: adult dosing. Infants and children <12 years: 25-50 mg/kg/day orally divided every 6-8 hours; maximum 3 g/day. For group A streptococcal pharyngitis: 25-50 mg/kg/day divided every 12 hours for 10 days. |
| Geriatric use | No specific dose adjustment; use with caution due to age-related renal decline. Monitor renal function and adjust based on CrCl. Increased risk of adverse effects (e.g., seizures with high doses). |
| 1st trimester | Generally considered safe; use only if clearly needed. No known teratogenic effects in humans. |
| 2nd trimester | Safe; used for infection treatment during pregnancy. |
| 3rd trimester | Safe; no known adverse fetal effects. |
Clinical note
Comprehensive clinical and safety monograph for PFIZERPEN VK (PFIZERPEN VK).
| Placental transfer | Penicillin V crosses the placenta to a limited extent; fetal serum concentrations are about 10-50% of maternal levels. |
| Breastfeeding | Penicillin V potassium is excreted into breast milk in low concentrations (<0.1% of maternal dose). Generally considered compatible with breastfeeding; monitor for rash or diarrhea in the infant. |
| Lactation Rating |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Hypersensitivity to penicillinsHistory of severe immediate hypersensitivity reaction (e.g., anaphylaxis) to beta-lactam antibiotics
| Precautions | Serious hypersensitivity reactions (anaphylaxis) may occur, especially in patients with penicillin allergy, Use caution in renal impairment (CrCl <10 mL/min) due to risk of neurotoxicity with high doses, Pseudomembranous colitis associated with C. difficile may occur, Prolonged use may predispose to superinfection, Assess renal function periodically in prolonged therapy |
| Food/Dietary | Avoid taking with food, especially high-fiber or high-fat meals, as they reduce absorption. Avoid acidic beverages (e.g., fruit juices, colas) which may degrade the drug. Take with a full glass of water. |
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| Teratogenic Risk | Penicillin VK (phenoxymethylpenicillin) is classified as FDA Pregnancy Category B. Animal studies have not demonstrated fetal risk, and no adequate human studies exist for first trimester. However, penicillin VK is considered safe throughout pregnancy when clinically indicated. No known teratogenicity. Risk of neonatal coagulopathy if maternal administration near term due to gut flora alteration, but not directly teratogenic. |
| Fetal Monitoring | No specific maternal-fetal monitoring required. Monitor for maternal allergic reactions. In prolonged therapy, monitor for signs of superinfection. For high-dose therapy, monitor renal function in patients with pre-existing renal impairment. |
| Fertility Effects | No known adverse effects on fertility. Penicillin VK does not impair fertility in animal studies. No human data suggest negative impact on reproductive function. |
| Clinical Pearls | PFIZERPEN VK (penicillin V potassium) is a narrow-spectrum penicillinase-sensitive penicillin. It is the drug of choice for group A streptococcal pharyngitis and for prophylaxis of rheumatic fever. It is acid-stable and can be given orally, but absorption is impaired by food. Dosing should be adjusted for renal impairment (CrCl <10 mL/min, dose every 12 hours). It has poor activity against H. influenzae and is not reliable for serious staphylococcal infections. Allergy cross-reactivity with cephalosporins is rare but possible. |
| Patient Advice | Take on an empty stomach (1 hour before or 2 hours after meals) for best absorption. · Complete the full course even if you feel better to prevent resistance. · If a dose is missed, take it as soon as possible; if near next dose, skip the missed dose. Do not double dose. · Common side effects include nausea, vomiting, diarrhea, and rash. Contact doctor if severe diarrhea or allergic symptoms occur. · Do not take with acidic beverages like fruit juices or sodas; take with water. · Inform clinician about any kidney disease or history of allergies. |