What is in a Bicillin (Penicillin G Benzathine) Injection?
A Bicillin injection contains penicillin G benzathine in an aqueous suspension with sodium citrate buffer and several excipients including sodium citrate, povidone, carboxymethylcellulose sodium, lecithin, methylparaben, and propylparaben. 1
Active Ingredient
- Penicillin G benzathine: This is formed by the reaction of dibenzylethylene diamine with two molecules of penicillin G 1
- Chemical designation: (2S, 5R, 6R)-3-Dimethyl-7-oxo-6-(2-phenylacetamido)-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid compound with N,N'-dibenzylethylenediamine (2:1), tetrahydrate 1
Inactive Ingredients/Excipients
The formulation contains (as w/v):
- Approximately 0.65% sodium citrate (buffer)
- 0.59% povidone
- 0.54% carboxymethylcellulose sodium
- 0.53% lecithin
- 0.12% methylparaben (preservative)
- 0.013% propylparaben (preservative) 1
Sodium Content
- Contains approximately 0.11 mEq of sodium per 600,000 units of penicillin G (approximately 2.59 mg of sodium per 600,000 units) 1
Physical Properties
- Appears as a viscous and opaque suspension
- Available in 1 mL, 2 mL, and 4 mL sizes containing the equivalent of:
- 600,000 units (actual volume of 1.17 mL contains 620,100 units)
- 1,200,000 units (actual volume of 2.34 mL contains 1,240,200 units)
- 2,400,000 units (actual volume of 4.67 mL contains 2,475,100 units) 1
Pharmacological Properties
- Extremely low solubility, resulting in slow release from intramuscular injection sites
- Hydrolyzed to penicillin G after injection
- Produces lower but much more prolonged blood levels compared to other parenteral penicillins
- After 1,200,000 units administration, detectable blood concentrations may persist for up to 4 weeks 1
- Approximately 60% of penicillin G binds to serum protein 1
Clinical Applications
Bicillin (penicillin G benzathine) is commonly used for:
- Treatment of syphilis at various stages 2
- Secondary prevention of rheumatic fever 3
- Treatment of group A streptococcal pharyngitis 2
- Management of certain skin and soft tissue infections 2
Important Considerations
- Not for intravenous administration (deep intramuscular injection only)
- Penicillin allergy testing may be required for patients with suspected allergies 3
- Desensitization protocols exist for patients who require penicillin despite confirmed allergies 2
Bicillin's unique formulation allows for prolonged release of penicillin G, making it particularly useful for conditions requiring sustained antibiotic levels without frequent dosing.