Comparative Pharmacology
Head-to-head clinical analysis: PFIZERPEN G versus PFIZERPEN AS.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PFIZERPEN G versus PFIZERPEN AS.
PFIZERPEN G vs PFIZERPEN-AS
Head-to-head clinical comparison of therapeutic indices and safety profiles.
Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidase activity and autolysin inhibition.
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.
Serious infections caused by susceptible gram-positive aerobic and anaerobic bacteria (e.g., Streptococcus, Enterococcus, Clostridium)MeningitisSyphilisActinomycosisAnthraxRat-bite feverListeriosisNeurosyphilisEndocarditis (as part of combination therapy)
Moderate to severe infections caused by penicillin-sensitive microorganisms (e.g., streptococcal, pneumococcal, gonococcal infections)Syphilis (primary, secondary, and latent)Anthrax (post-exposure prophylaxis)Rat-bite feverOff-label: Neurosyphilis (with probenecid)Off-label: Endocarditis prophylaxis
2-4 million units (1.2-2.4 g) IV every 4-6 hours; maximum 24 million units per day.
250-500 mg orally every 6-8 hours for moderate infections; 500 mg to 2 g intravenously every 4-6 hours for severe infections.
None Documented
None Documented
Terminal elimination half-life is 30-60 minutes in patients with normal renal function; prolonged to 2-10 hours in renal impairment (CrCl <10 mL/min).
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.
Primarily renally eliminated; undergoes tubular secretion with minimal hepatic metabolism.
Hepatic metabolism (minor); primarily renal elimination via glomerular filtration and tubular secretion (unchanged drug).
Primarily renal excretion via glomerular filtration and tubular secretion; 60-90% of dose excreted unchanged in urine within 6 hours. Biliary excretion accounts for less than 10%.
Primarily renal (60-80% as unchanged drug via tubular secretion and glomerular filtration); minor biliary/fecal elimination (10-20%)
Approximately 60-80% bound to serum albumin.
50-65% primarily to serum albumin
0.2-0.3 L/kg; limited distribution primarily to extracellular fluid; low penetration into CSF unless meninges inflamed (CSF concentrations 5-10% of serum).
0.3-0.4 L/kg; low Vd indicating limited extravascular distribution. Increased in neonates, pregnancy, and inflammatory states.
Intramuscular: 60-100% (variable) due to slow absorption. Oral: 15-30% (unreliable, therefore not used).
IM: 70-100%; Oral: 30-60% (variable due to gastric acid degradation). IV: 100%
GFR 10-50 mL/min: 2-4 million units IV every 6-8 hours; GFR <10 mL/min: 2-4 million units IV every 8-12 hours.
CrCl 10-50 mL/min: administer every 8-12 hours; CrCl <10 mL/min: administer every 12-18 hours; hemodialysis: supplement dose after dialysis.
No adjustment required; primarily renally excreted.
No dosage adjustment required for mild to moderate hepatic impairment; caution in severe impairment due to potential accumulation.
Neonates <7 days: 50,000-100,000 units/kg IV every 12 hours; infants and children: 100,000-250,000 units/kg/day IV divided every 4-6 hours.
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.
Dose based on renal function; consider lower initial doses due to age-related decline in GFR.
Use lowest effective dose; monitor renal function and adjust based on CrCl; increased risk of neurotoxicity (seizures) with high doses.
No 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.
["Severe hypersensitivity reactions (anaphylaxis, angioedema)","Clostridioides difficile-associated diarrhea (CDAD)","Neurotoxicity with high doses or renal impairment (seizures, myoclonus)","Electrolyte disturbances (sodium or potassium overload with high doses)","Renal impairment requires dose adjustment","Use in neonates requires caution due to immature renal function"]
["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"]
["History of immediate-type hypersensitivity (e.g., anaphylaxis, urticaria) to any penicillin","Use of procaine penicillin G in patients with known procaine sensitivity"]
["Hypersensitivity to penicillins or procaine","Previous immediate-type hypersensitivity reaction (e.g., anaphylaxis) to cephalosporins or other beta-lactams"]
Data Pending Review
Data Pending Review
No significant food interactions. However, oral absorption of oral penicillin V is decreased with food; administer on an empty stomach (1 hour before or 2 hours after meals). For injectable penicillin G, food does not affect administration.
No clinically significant food interactions. However, patients on prolonged therapy should maintain adequate hydration. No dietary restrictions required.
Penicillin G (PFIZERPEN G) is classified as FDA Pregnancy Category B. Animal reproduction studies have not demonstrated a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women. Generally considered low risk; use only if clearly needed. No known teratogenic effects in first trimester; second and third trimester use is considered safe.
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.
Penicillin G is excreted into human breast milk in small amounts (M/P ratio approximately 0.1-0.2). Concentrations are low and unlikely to cause adverse effects in the nursing infant. Considered compatible with breastfeeding by the American Academy of Pediatrics. Monitor infant for potential gastrointestinal disturbances or allergic reactions.
Penicillin G is excreted into breast milk in low concentrations (M/P ratio approximately 0.2). It is considered compatible with breastfeeding by the American Academy of Pediatrics. Potential risks include alteration of infant gut flora and allergic sensitization. Use with caution in infants with known penicillin allergy.
Pregnancy-induced increases in plasma volume and renal clearance may lead to lower serum concentrations of penicillin G. For serious infections (e.g., group B streptococcus prophylaxis), standard dosing is usually adequate, but higher doses or more frequent administration may be considered for severe infections, especially in late pregnancy. Monitor clinical response and adjust dose as needed. No fixed dose adjustment protocol; clinical judgment required.
Pharmacokinetic changes in pregnancy (increased volume of distribution, enhanced renal clearance) may require dose adjustments. Standard dosing may be insufficient for serious infections; consider higher doses or more frequent administration. Therapeutic drug monitoring (e.g., serum drug levels) is recommended for severe infections to ensure adequate exposure. No specific guidelines; adjust based on clinical response and infection severity.
Category C
Category C
PFIZERPEN G (penicillin G) is a narrow-spectrum penicillin primarily active against gram-positive cocci (e.g., Streptococcus pyogenes, Streptococcus pneumoniae) and some gram-negative cocci (e.g., Neisseria meningitidis). It is the drug of choice for syphilis (Treponema pallidum). For treatment of group A streptococcal pharyngitis, a single dose of benzathine penicillin G 1.2 million units IM is standard. Always inquire about penicillin allergy history before administration; anaphylaxis risk is ~0.04%. Use aqueous crystalline penicillin G for severe infections like meningitis (high CNS penetration with inflamed meninges). Monitor renal function in critically ill patients to adjust dosing. Pain at injection site is common with IM administration; consider using procaine penicillin G to reduce discomfort if appropriate.
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.
Complete the full course of medication even if you feel better.Report any signs of allergic reaction (rash, itching, difficulty breathing, swelling) immediately.This medication is given by injection; you may experience pain or redness at the injection site.Inform your doctor if you have kidney disease or a history of allergies, especially to penicillins or cephalosporins.Shake the vial well before use and use within the specified time after reconstitution.
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).