GEOCILLIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GEOCILLIN (GEOCILLIN).
Geocillin (carbenicillin indanyl sodium) is a penicillin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), leading to cell lysis and death. It exhibits bactericidal activity against susceptible gram-negative and gram-positive bacteria.
| Metabolism | Carbenicillin indanyl sodium is hydrolyzed in the liver and plasma to release carbenicillin, the active moiety. Carbenicillin is primarily excreted unchanged by the kidneys via glomerular filtration and tubular secretion. |
| Excretion | Primarily renal (70-80% unchanged via tubular secretion and glomerular filtration); minor biliary/fecal (<5%). |
| Half-life | 1.2 hours (normal renal function); prolonged to 7-10 hours in severe renal impairment (CrCl <10 mL/min). |
| Protein binding | 80-90% bound to serum albumin. |
| Volume of Distribution | 0.3-0.5 L/kg (moderate distribution, mainly extracellular fluid; low CNS penetration unless meninges inflamed). |
| Bioavailability | Oral: 25-40% (acid-labile, food reduces absorption); IM: 100% (well absorbed). |
| Onset of Action | Oral: 30-60 minutes; IM: 15-30 minutes; IV: immediate. |
| Duration of Action | Oral/IM: 4-6 hours; IV: 2-4 hours. Clinical effect persists for 24-48 hours after last dose due to post-antibiotic effect (gram-positive organisms). |
250-500 mg orally every 6 hours.
| Dosage form | TABLET |
| Renal impairment | GFR 10-50 mL/min: 250-500 mg every 12-24 hours; GFR <10 mL/min: 250-500 mg every 24-48 hours. |
| Liver impairment | No adjustment required for mild to moderate impairment; severe impairment: use with caution, monitor for toxicity. |
| Pediatric use | Children 2-12 years: 25-50 mg/kg/day orally divided every 6 hours; maximum 2 g/day. |
| Geriatric use | Use same dosing as adults; monitor renal function and adjust accordingly. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for GEOCILLIN (GEOCILLIN).
| Breastfeeding | Carbenicillin is excreted into breast milk in low concentrations. The M/P ratio is not established. It is considered compatible with breastfeeding by the American Academy of Pediatrics. Theoretical risk of diarrhea, candidiasis, or allergic reaction in the infant. Use with caution in nursing mothers. |
| Teratogenic Risk | Geocillin (carbenicillin indanyl sodium) is a penicillin-class antibiotic. It crosses the placenta. No adequate, well-controlled studies in pregnant women. Animal studies have not shown fetal harm. Generally considered low risk; however, use only if clearly needed. First trimester: theoretical risk of altered gut flora. Second and third trimesters: no known teratogenicity. Potential for neonatal diarrhea or allergic sensitization with prolonged use near term. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to carbenicillin, any penicillin, or other beta-lactam antibiotics"]
| Precautions | ["Serious and occasionally fatal hypersensitivity reactions (anaphylaxis) may occur","Clostridium difficile-associated diarrhea (CDAD) has been reported","Use with caution in patients with renal impairment; dose adjustment may be necessary","Potential for electrolyte disturbances due to high sodium content (each tablet contains 23 mg of sodium)","Prolonged use may result in overgrowth of nonsusceptible organisms"] |
| Food/Dietary | Take with food or meals to increase absorption. Avoid acidic beverages (e.g., fruit juice, soda) as they may degrade the drug. No specific food restrictions. |
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| Fetal Monitoring | No specific fetal monitoring required. Monitor maternal renal function during prolonged therapy due to sodium content. Observe for signs of hypersensitivity or diarrhea in the mother. In late pregnancy, monitor for neonatal effects if used near delivery. |
| Fertility Effects | No known adverse effects on fertility in animal studies. No human data available. Reversible effects on spermatogenesis in some penicillin derivatives have been reported but not specifically for carbenicillin. |
| Clinical Pearls | Geocillin (carbenicillin indanyl sodium) is an oral carboxypenicillin with activity against Pseudomonas aeruginosa and certain Proteus species. It is acid-stable but absorption is incomplete; administer with food to enhance bioavailability. Monitor renal function as accumulation can occur in renal impairment, increasing neurotoxicity risk. Not effective against penicillinase-producing organisms. |
| Patient Advice | Take Geocillin exactly as prescribed; complete the full course even if you feel better. · Take with food to improve absorption and reduce stomach upset. · Notify your doctor if you experience diarrhea, rash, or unusual bleeding. · This medication may cause false-positive urine glucose tests; inform your healthcare provider. · Do not take with other medications without consulting your doctor, especially probenecid or methotrexate. |