STAPHCILLIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for STAPHCILLIN (STAPHCILLIN).
Semisynthetic penicillin; inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), inhibiting transpeptidation, and activating autolytic enzymes.
| Metabolism | Hepatic and renal; primarily excreted unchanged in urine via tubular secretion; minor metabolism to inactive metabolites. |
| Excretion | Primarily renal (70-90% as unchanged drug via glomerular filtration and tubular secretion); minor biliary excretion (<5%) and fecal elimination (<1%). |
| Half-life | 0.5-1 hour in adults with normal renal function; prolonged to 2-4 hours in renal impairment. Infants: 1-2 hours. |
| Protein binding | ~20-30%, primarily to serum albumin. |
| Volume of Distribution | 0.1-0.3 L/kg; indicates distribution primarily into extracellular fluid, with limited CNS penetration unless meninges inflamed. |
| Bioavailability | IM: 70-80%; oral: not available (acid-labile, must be parenteral). |
| Onset of Action | IM: 30-60 min; IV: immediate (peak after IV bolus). |
| Duration of Action | 4-6 hours; may be extended in renal dysfunction. Bactericidal effect persists as long as serum concentrations exceed MIC. |
| Molecular Weight | 404.5 |
1-2 g IV every 4-6 hours.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 10-50 mL/min: 1-2 g every 6-8 hours; CrCl <10 mL/min: 1-2 g every 8-12 hours. |
| Liver impairment | No dosage adjustment required for mild to moderate hepatic impairment; severe impairment (Child-Pugh class C) use with caution. |
| Pediatric use | Infants and children: 25-50 mg/kg IV every 6 hours. |
| Geriatric use | Start at lower end of dosing range; monitor renal function and adjust based on CrCl. |
| 1st trimester | Penicillinase-resistant penicillin; no known teratogenicity; generally considered safe if indicated. |
| 2nd trimester | Safe; used for susceptible infections during pregnancy. |
| 3rd trimester | Safe; may theoretically increase risk of neonatal jaundice or diarrhea, but clinical significance is low. |
Clinical note
Comprehensive clinical and safety monograph for STAPHCILLIN (STAPHCILLIN).
| Placental transfer | Crosses placenta; achieves fetal serum concentrations 10-50% of maternal levels. |
| Breastfeeding | Excreted into breast milk in small amounts; unlikely to cause adverse effects in nursing infants; compatible with breastfeeding. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to penicillinsHypersensitivity to any beta-lactam antibiotic
| Precautions | Serious hypersensitivity reactions including anaphylaxis, Clostridioides difficile-associated diarrhea, Superinfection with non-susceptible organisms, Use caution in renal impairment, Neurologic adverse effects with high doses |
| Food/Dietary | No significant food interactions, but grapefruit juice may affect drug absorption. Take on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption. Avoid alcohol. |
| Clinical Pearls |
Loading safety data…
| L1 (Safe) |
| Teratogenic Risk | Methicillin (STAPHCILLIN) is a penicillinase-resistant penicillin. No adequate and well-controlled studies in pregnant women. Animal studies have not demonstrated teratogenicity. However, potential risks include alteration of gut flora and rare hypersensitivity reactions. Use only if clearly needed. |
| Fetal Monitoring | Monitor maternal renal function due to potential nephrotoxicity. Observe for signs of hypersensitivity (rash, fever, eosinophilia). Monitor fetal growth and well-being if used for prolonged periods. |
| Fertility Effects | No known adverse effects on fertility. Methicillin does not impair reproductive function in animal studies. |
| STAPHCILLIN (methicillin) is a penicillinase-resistant penicillin used for susceptible staphylococcal infections. It is not active against MRSA. Administer IV or IM; avoid intra-arterial injection. Monitor renal function and CBC, as it can cause interstitial nephritis and bone marrow suppression. Use with caution in patients with penicillin allergy; cross-allergenicity with cephalosporins is low but possible. Peak serum levels occur 15-30 min after IV administration. |
| Patient Advice | Take this medication exactly as prescribed; do not miss doses. · Complete the full course even if you feel better. · Report any signs of allergic reaction (rash, itching, swelling, difficulty breathing) immediately. · May cause diarrhea; if severe or with blood/mucus, contact your doctor. · Avoid grapefruit juice during therapy. |