This Post is adapted from the Canadian Pharmacists Association (CPhA) Drug Monograph: Penicillin G/Penicillin V
Product Summary Table
Pharmacology
- Penicillins G and V, known as the natural penicillins, are bactericidal against susceptible organisms.
- Penicillins interfere with the synthesis of cell wall mucopeptides, resulting in the formation of defective cell walls that will lyse and eventually result in death of the organism.
- The spectra of activity of penicillins G and V are similar:
- Penicillin G is more active against gram-negative organisms (e.g., Neisseria) and some anaerobes than is penicillin V.
- Penicillin G can be given parenterally, enabling the attainment of high serum concentrations, and is used for the treatment of serious infections involving penicillin-susceptible bacteria.
- Penicillin V is more resistant to hydrolysis by acidic gastric secretions and is absorbed orally to a much greater extent than penicillin. Currently, only penicillin V is available orally, for the treatment of penicillin-susceptible infections of mild to moderate severity, in which the oral route of administration is desirable.
Indications
- Drug of choice for the following infections: actinomycosis, streptococcal pharyngitis, erysipelas, erysipeloid, leptospirosis, trench mouth, syphilis, bejel, pinta, yaws, clostridial and streptococcal necrotizing infections, P. multocida infections, leptospirosis, rat-bite fever and the prophylaxis of rheumatic fever.
- Penicillin G: treatment of infections due to susceptible organisms of moderate to severe infections.
- Penicillin V : treatment of mild to moderately severe infections.
- Penicillin G benzathine: moderately severe infections that respond to low levels of penicillin.
- Penicillin G and penicillin V: treatment of: actinomycosis caused by Actinomyces species; anthrax caused by B. anthracis; bronchitis, acute otitis media, pharyngitis, sinusitis, skin and soft tissue infections caused by susceptible organisms; erysipelas caused by susceptible strains of group A streptococci; erysipeloid (including endocarditis and septicemia) caused by E. rhusiopathiae; acute, necrotizing, ulcerative gingivitis (Vincent’s angina or “trench mouth”) caused by anaerobes and spirochetes; P. multocida infections; rat-bite fever caused by S. moniliformis or S. minor; scarlet fever caused by group A streptococci; Lyme disease caused by B. burgdorferi.
- Penicillin V: prophylaxis of rheumatic fever caused by group A streptococci.
- Penicillin V: reduce the incidence of S. pneumoniaesepticemia in children >5 years with sickle cell anemia.
- Parenteral penicillin G: treatment of bone and joint infections, bacterial endocarditis, intra-abdominal infections, meningitis, pericarditis, pneumonia and septicemia caused by susceptible organisms; listeriosis caused by L. monocytogenes; tetanus; yaws caused by T. pallidum pertenue; tertiary and neurosyphilis; gas gangrene caused by Clostridium species; leptospirosis caused by Leptospira species; diphtheria caused by C. diphtheriae, as an adjunct to antitoxin.
- Penicillin G benzathine: treatment of bejel caused by T. pallidum endemicum, pinta caused by T. carateum and yaws caused by T. pertenue. Penicillin G benzathine is also used for the treatment of pharyngitis and early or late benign syphilis (not neurosyphilis) and in the prophylaxis of diphtheria and recurrent rheumatic fever.
Warnings
- Serious and occasionally fatal hypersensitivity reactions have been reported in patients receiving penicillin therapy. Although anaphylaxis is more frequent following parenteral therapy, it has occurred in patients receiving oral penicillin.
- Cross-sensitivity between penicillins and cephalosporins is estimated to be very low, expected to be highest with first-generation cephalosporins.
Drug Interactions
- Bacteriostatic Antibiotics (e.g., chloramphenicol, erythromycin, tetracycline): Risk of decreasing the effectiveness of penicillin.
- Methotrexate: Increased serum levels of methotrexate through competitive inhibition of renal tubular secretion. If possible, consider alternate antibiotic therapy. If penicillin is necessary monitor for toxicity of methotrexate and modify dose or discontinue methotrexate as appropriate.
- Probenecid: Decreases renal tubular secretion of penicillin leading to higher and more prolonged serum concentrations, higher CSF concentrations and an increased risk of toxicity. Alternatively, it has been used therapeutically in select cases to increase penicillin serum levels.
Pregnancy and Lactation
- Usual doses appear to be safe in pregnant women.
- Penicillin does not appear in breast milk in sufficient quantities to treat infections in the infant but does appear in trace quantities which could lead to allergic sensitization or disruption of the gastrointestinal flora.
Dosage
- Oral therapy is generally used for the treatment of mild to moderately severe infections.
- Dosage must be individualized according to the causative organism, severity of the infection and host factors such as age and renal function.
- Penicillin V 500 000 units is equivalent to 300 mg.
- Penicillin G 500 000 units is equivalent to 312 mg.
- Usual therapeutic dosages are as follows:
- Oral: Penicillin V:
- Adults and Children >12 Years: 1-4 g daily in 3 to 4 divided doses.
- Children <12 Years: 25-100 mg/kg/day in 3 to 4 divided doses, maximum 3 g/day.
- Treatment of Group A beta-hemolytic streptococcal infections may be dosed every 12 hours for adults and children.
- Rheumatic Fever Prophylaxis:
- Prevention of recurrent Group A beta-hemolytic streptococcal infections in patients who have had rheumatic fever and/or chorea: penicillin V 250-300 mg orally twice daily.
- Oral: Penicillin V:
Source:
Canadian Pharmacists Association: Compendium of Pharmaceuticals and Specialties, online version (e-CPS), accessed on May 10, 2013
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