BICILLIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BICILLIN (BICILLIN).
Benzathine penicillin G inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidase activity and autolysin inhibition, leading to cell lysis.
| Metabolism | Primarily excreted unchanged in urine; minor hepatic metabolism. |
| Excretion | Primarily renal (60–70% unchanged via glomerular filtration and tubular secretion); minor biliary/fecal elimination (<10%) |
| Half-life | Terminal elimination half-life: 0.5–1 hour (prolonged in renal impairment); clinical context: requires probenecid for extended action |
| Protein binding | ~55–60% bound, primarily to serum albumin |
| Volume of Distribution | 0.3–0.4 L/kg; indicates distribution primarily into extracellular fluid |
| Bioavailability | Intramuscular: ~60–70% for aqueous suspensions; oral: negligible (<10%) due to acid lability |
| Onset of Action | Intramuscular: 1–2 hours for therapeutic serum levels; intravenous: immediate |
| Duration of Action | Intramuscular benzathine penicillin G: up to 4 weeks; aqueous forms: 4–6 hours |
| Brand Substitutes | Penclox Capsule, Verclox Capsule, Veaclox 250mg/250mg Capsule, Penmix Plus Capsule, Bactimox Plus Capsule |
Benzathine penicillin G 1.2 million units intramuscularly once for early syphilis; 2.4 million units intramuscularly weekly for 3 weeks for late latent syphilis.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for renal impairment; benzathine penicillin G is primarily hepatically cleared. |
| Liver impairment | No dose adjustment required for hepatic impairment; safety and efficacy not established in severe hepatic disease. |
| Pediatric use | Early congenital syphilis: 50,000 units/kg intramuscularly as a single dose (not to exceed 2.4 million units). Late congenital syphilis: 50,000 units/kg intramuscularly weekly for 3 weeks (not to exceed 2.4 million units per dose). |
| Geriatric use | Same dosing as younger adults; monitor for renal function and potential increased risk of adverse effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for BICILLIN (BICILLIN).
| Breastfeeding | Penicillin G is excreted into breast milk in low concentrations. The milk-to-plasma ratio is approximately 0.1-0.2. It is generally considered compatible with breastfeeding; the American Academy of Pediatrics rates it as compatible. Potential effects on the infant include alteration of gut flora and rare allergic reactions. No special precautions are required, but monitor infant for diarrhea or rash. |
| Teratogenic Risk | Penicillin G benzathine (Bicillin) is classified as FDA Pregnancy Category B. Animal reproduction studies have not demonstrated fetal risk, and there are no adequate well-controlled studies in pregnant women. However, penicillin is generally considered safe in all trimesters. There is no evidence of teratogenicity. In first trimester, theoretical risk from allergic reactions is negligible. Second and third trimesters: no known fetal adverse effects. Use only if clearly needed. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
["Hypersensitivity to penicillins or any component of the formulation","History of severe allergic reaction (e.g., anaphylaxis) to other beta-lactams"]
| Precautions | ["Severe hypersensitivity reactions including anaphylaxis","Risk of Clostridium difficile-associated diarrhea","Use caution in renal impairment (dose adjustment may be needed)","Potential for neurotoxicity with high doses or in renal failure"] |
| Food/Dietary | None significant. No dietary restrictions required. |
| Clinical Pearls |
Loading safety data…
| Fetal Monitoring | Monitor maternal vital signs during injection (risk of anaphylaxis). Assess fetal heart rate if indicated (e.g., for syphilis treatment in pregnancy to avoid Jarisch-Herxheimer reaction). No routine fetal monitoring required. Maternal monitoring includes renal function and signs of superinfection. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies have not shown impaired fertility. Use for infections may indirectly improve reproductive health by treating underlying conditions (e.g., syphilis). |
| Bicillin (penicillin G benzathine) is a long-acting injectable penicillin used primarily for syphilis and group A streptococcal infections. Administer deep intramuscular only; inadvertent intravenous administration can cause cardiac arrest and death. Rotate injection sites. For neurosyphilis, use aqueous penicillin G instead as Bicillin does not achieve adequate CSF levels. Confirm absence of penicillin allergy before use. |
| Patient Advice | This injection provides prolonged antibiotic coverage over several weeks. · You must receive this injection exactly as scheduled to ensure effective treatment. · Report any signs of allergic reaction immediately: hives, difficulty breathing, swelling. · Do not massage the injection site after administration. · Complete the full course even if symptoms improve. |