BICILLIN L-A
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BICILLIN L-A (BICILLIN L-A).
Penicillin G benzathine is a slow-release formulation that provides prolonged tissue concentrations. It inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidation, and activating autolytic enzymes, leading to cell lysis.
| Metabolism | Primarily renal excretion (90% unchanged via tubular secretion). Minimal hepatic metabolism. |
| Excretion | Renal: 60-90% unchanged; biliary/fecal: minor (<10%) |
| Half-life | Terminal half-life: 30-60 hours (prolonged due to slow absorption from IM depot; clinically allows single-dose regimen for syphilis) |
| Protein binding | 60-70% bound to serum albumin |
| Volume of Distribution | 0.3-0.4 L/kg (confined to extracellular fluid; low CNS penetration) |
| Bioavailability | IM (aqueous suspension): ~100% (complete absorption from depot) |
| Onset of Action | IM: 24-48 hours (slow release from depot) |
| Duration of Action | IM: 3-4 weeks (sustained bactericidal levels) |
1.2 million units intramuscularly as a single dose for treatment of streptococcal pharyngitis; for syphilis, 2.4 million units intramuscularly weekly for 1-3 weeks depending on stage.
| Dosage form | INJECTABLE |
| Renal impairment | No dosage adjustment required for mild to moderate renal impairment; for severe impairment (GFR <10 mL/min), administer dose every 2 weeks. |
| Liver impairment | No dosage adjustment recommended for hepatic impairment; Child-Pugh classification does not significantly alter pharmacokinetics. |
| Pediatric use | For children weighing <27 kg: 600,000 units intramuscularly single dose; for children ≥27 kg: 1.2 million units intramuscularly single dose. |
| Geriatric use | No specific dosage adjustment; monitor renal function and consider potential for reduced clearance in elderly with impaired renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for BICILLIN L-A (BICILLIN L-A).
| Breastfeeding | Penicillin G is excreted in breast milk in low concentrations; M/P ratio not established. Considered compatible with breastfeeding; monitor infant for potential disruption of gastrointestinal flora, rash, or diarrhea. |
| Teratogenic Risk | FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; inadequate human studies. Penicillin G crosses placenta but poses low risk of congenital malformations. Use only if clearly needed during pregnancy. |
| Fetal Monitoring |
■ FDA Black Box Warning
NOT FOR INTRAVENOUS USE. Inadvertent IV administration has been associated with cardiopulmonary arrest and death. Use only deep IM injection.
| Serious Effects |
["Known hypersensitivity to penicillins or cephalosporins","Intravenous administration (absolute contraindication)"]
| Precautions | ["Risk of anaphylaxis (immediate hypersensitivity reactions, including urticaria, angioedema, laryngospasm, bronchospasm, hypotension) in penicillin-allergic patients.","Severe and potentially fatal nonallergic reactions (e.g., Hoigne syndrome: confusion, hallucinations, seizures, dyspnea, tachycardia) after IM injection.","Jarisch-Herxheimer reaction (fever, chills, myalgia, headache) commonly occurs in syphilis treatment.","Use with caution in patients with renal impairment (risk of neurotoxicity with high doses).","May cause Clostridioides difficile-associated diarrhea (pseudomembranous colitis).","Avoid injection into or near nerves or blood vessels (risk of nerve damage, thrombosis, or inadvertent IV administration)."] |
| Food/Dietary | No significant food interactions. Avoid alcohol during treatment as it may increase the risk of adverse effects and reduce therapeutic efficacy. |
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| Monitor maternal renal function, CBC with differential, and signs of allergic reactions. In pregnancy, assess fetal growth and development via ultrasound if long-term therapy; no special fetal monitoring required for single-dose use. |
| Fertility Effects | No known adverse effects on fertility or reproductive performance based on available data. |
| Clinical Pearls | BICILLIN L-A (penicillin G benzathine) is a long-acting intramuscular formulation providing sustained low serum levels. Administer deep IM in the upper outer quadrant of the gluteus maximus; do not inject IV or intra-arterially (risk of embolic/toxic reactions). Use for syphilis (including neurosyphilis in combination) and group A streptococcal infections. Monitor for anaphylaxis, especially in penicillin-allergic patients. Rotate injection sites with repeated doses. |
| Patient Advice | This injection provides long-lasting antibiotic coverage and must be administered by a healthcare professional. · Complete the full course as prescribed even if you feel better. · Report any signs of allergic reaction (rash, itching, swelling, difficulty breathing) immediately. · The injection may cause pain, swelling, or induration at the site; apply cold compresses as needed. · Avoid alcohol during treatment to minimize side effects and ensure effectiveness. · Inform your doctor if you are pregnant, breastfeeding, or have kidney disease. |