Comparative Pharmacology
Head-to-head clinical analysis: PFIZERPEN G versus PFIZERPEN A.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PFIZERPEN G versus PFIZERPEN A.
PFIZERPEN G vs PFIZERPEN-A
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.
Penicillin G inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidase activity and activating autolytic enzymes.
Serious infections caused by susceptible gram-positive aerobic and anaerobic bacteria (e.g., Streptococcus, Enterococcus, Clostridium)MeningitisSyphilisActinomycosisAnthraxRat-bite feverListeriosisNeurosyphilisEndocarditis (as part of combination therapy)
Serious infections caused by susceptible gram-positive aerobes and anaerobes (e.g., streptococcal, meningococcal, clostridial)Syphilis (Treponema pallidum)ActinomycosisProphylaxis of rheumatic fever and bacterial endocarditisOff-label: Group B streptococcal infection in neonates, Lyme disease
2-4 million units (1.2-2.4 g) IV every 4-6 hours; maximum 24 million units per day.
1-2 million units intramuscularly or intravenously every 4 hours; or continuous intravenous infusion of 20-30 million units per day.
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).
Terminal elimination half-life: 0.6-0.8 hours in adults with normal renal function; prolonged to 7-10 hours in end-stage renal disease (ESRD). In neonates, half-life ranges 2-4 hours.
Primarily renally eliminated; undergoes tubular secretion with minimal hepatic metabolism.
Primarily renal tubular secretion (90% unchanged). Minimal hepatic metabolism.
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 (60-70% unchanged via glomerular filtration and tubular secretion); hepatic metabolism minor (<10%); biliary/fecal elimination <10%.
Approximately 60-80% bound to serum albumin.
Approximately 60-65% bound primarily to serum albumin, with minor binding to alpha-1-acid glycoprotein.
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).
0.2-0.3 L/kg; low Vd reflects limited tissue distribution (primarily extracellular fluid). Higher in neonates (0.4-0.5 L/kg).
Intramuscular: 60-100% (variable) due to slow absorption. Oral: 15-30% (unreliable, therefore not used).
Oral bioavailability: negligible (<10%) due to acid lability; IM bioavailability: ~80-100% with rapid absorption.
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.
For GFR 10-50 mL/min: administer every 6-8 hours. For GFR <10 mL/min: administer every 12 hours or reduce dose by 50%.
No adjustment required; primarily renally excreted.
No specific adjustment required; caution in severe hepatic impairment due to potential risk of encephalopathy.
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.
Neonates <7 days: 50,000 units/kg intramuscularly or intravenously every 12 hours. Neonates 7-28 days: 50,000 units/kg every 8 hours. Infants and children: 100,000-250,000 units/kg/day divided every 4-6 hours.
Dose based on renal function; consider lower initial doses due to age-related decline in GFR.
Use with caution; adjust dosing interval based on renal function; monitor for electrolyte disturbances.
No FDA black box warning.
None listed by FDA for this formulation; however, rapid IV administration may cause severe or fatal anaphylaxis. No specific boxed warning.
["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"]
Hypersensitivity reactions (anaphylaxis) can occur; skin testing recommended in patients with penicillin allergy history. Neurologic adverse effects (e.g., seizures) with high doses or renal impairment. Electrolyte disturbances with large IV doses (potassium or sodium salt). Prolonged use may lead to superinfection due to Clostridium difficile.
["History of immediate-type hypersensitivity (e.g., anaphylaxis, urticaria) to any penicillin","Use of procaine penicillin G in patients with known procaine sensitivity"]
Known hypersensitivity to penicillins. Use with caution in patients with history of severe immediate allergy to cephalosporins or carbapenems (possible cross-sensitivity).
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 significant food interactions; may be taken with or without food. Avoid alcohol to reduce risk of disulfiram-like reaction (rare).
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.
Penzicillin G (PFIZERPEN-A) is generally considered low risk in pregnancy. Animal studies have not shown teratogenicity. In humans, no increased risk of major congenital malformations has been observed. Use in the first trimester: no evidence of teratogenic effects. Second and third trimesters: no specific fetal risks, but may cause altered fetal gut flora. High doses near term may increase risk of kernicterus in jaundiced neonates.
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. The milk-to-plasma ratio is approximately 0.2. Doses up to 1.2 million units daily are considered compatible with breastfeeding. Theoretical risk of alteration of infant gut flora and sensitization. Monitor infant for rash and gastrointestinal disturbances.
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.
Pregnancy increases volume of distribution and renal clearance of penicillin G, leading to lower serum concentrations. Dose adjustments may be necessary, especially in the third trimester. Increased dosing frequency or higher doses may be required for serious infections. Monitor clinical response and consider therapeutic drug monitoring when available.
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.
Administration with penicillin skin testing recommended prior to therapy; monitor for immediate hypersensitivity reactions; adjust dose in renal impairment (CrCl <10 mL/min) to q12h; preferred for neurosyphilis due to high CNS penetration; use with probenecid to increase serum levels; check for cross-reactivity in patients with cephalosporin allergy; reconstitute with sterile water for injection; avoid IM injection in neonates due to risk of sterile abscess; maintain adequate hydration to prevent crystalluria with high doses.
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.
Complete the full course of therapy even if you feel better.Report any skin rash, hives, difficulty breathing, or swelling immediately.Take with food if gastrointestinal upset occurs.Avoid alcohol while on treatment.Inform your doctor if you have kidney disease or are pregnant.Store oral suspension in refrigerator; discard after 14 days.Do not skip doses; take at evenly spaced intervals.