CYCLAPEN-W
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CYCLAPEN-W (CYCLAPEN-W).
Cyclacillin is a beta-lactam antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), leading to cell lysis and death. It has a similar spectrum to ampicillin but with increased acid stability and oral absorption.
| Metabolism | Cyclacillin is partially metabolized in the liver to penicilloic acid and other metabolites. Approximately 20-40% of the dose is excreted unchanged in urine via glomerular filtration and tubular secretion. |
| Excretion | Primarily renal (90-100% unchanged via glomerular filtration and tubular secretion); minor biliary/fecal elimination (<10%). |
| Half-life | 0.5-1 hour in adults with normal renal function; prolonged to 2-6 hours in renal impairment. |
| Protein binding | Approximately 80% bound; primarily to serum albumin. |
| Volume of Distribution | 0.3-0.4 L/kg; indicates distribution primarily into extracellular fluid. |
| Bioavailability | Oral: 60-70% (decreased by food); IM: nearly 100%. |
| Onset of Action | Oral: 30-60 minutes; IM: 15-30 minutes; IV: immediate (within minutes). |
| Duration of Action | 4-6 hours for oral/IM; clinical effect lasts 6-8 hours due to post-antibiotic effect. |
| Molecular Weight | 563.6 Da (sulfamethoxazole: 253.3 Da; penicillin V: 350.3 Da; combined as salt) |
250-500 mg orally every 6 hours for mild to moderate infections; 500 mg orally every 6 hours for severe infections.
| Dosage form | TABLET |
| Renal impairment | CrCl 10-50 mL/min: 250-500 mg every 8-12 hours; CrCl <10 mL/min: 250-500 mg every 12-18 hours. |
| Liver impairment | No adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B). Use with caution in severe impairment (Child-Pugh C) due to risk of encephalopathy. |
| Pediatric use | Children >1 month: 25-50 mg/kg/day orally divided every 6 hours. Maximum 2 g/day. |
| Geriatric use | No specific dose adjustment, but monitor renal function. Use lowest effective dose due to age-related renal decline. |
| 1st trimester | Avoid unless clearly needed. Fetal risk not excluded. Use only if benefit outweighs risk. |
| 2nd trimester | Caution. No known teratogenicity but limited human data. |
| 3rd trimester | Avoid in late pregnancy due to risk of kernicterus in neonates from sulfonamide component (sulfamethoxazole) by displacing bilirubin. |
Clinical note
Comprehensive clinical and safety monograph for CYCLAPEN-W (CYCLAPEN-W).
| Placental transfer | Both components cross placenta. Penicillin V: low to moderate transfer. Sulfamethoxazole: significant transfer, achieving fetal serum concentrations 50-100% of maternal levels. |
| Breastfeeding | Sulfamethoxazole and penicillin V are excreted in breast milk in low amounts. Sulfamethoxazole may cause kernicterus in jaundiced or premature infants. Caution in nursing mothers of such infants. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Hypersensitivity to penicillins, sulfonamides, or any componentHistory of severe allergic reaction (e.g., anaphylaxis) to beta-lactamsSulfonamide allergyPorphyriaConcomitant use with dofetilide (sulfamethoxazole inhibits its metabolism)
| Precautions | Serious and occasionally fatal hypersensitivity reactions (anaphylaxis) have been reported., Prolonged use may result in overgrowth of nonsusceptible organisms, including Clostridium difficile-associated diarrhea., Use with caution in patients with renal impairment; dose adjustment may be necessary., Use in patients with mononucleosis may increase risk of maculopapular rash. |
| Food/Dietary | No significant food interactions. May be taken with or without food. Avoid alcohol to minimize potential adverse effects. |
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| Lactation Rating | L3 (Moderately Safe) - use with caution |
| Teratogenic Risk | Penicillin V (Cyclapen-W) is generally considered low risk for teratogenicity across all trimesters. Animal studies have not shown fetal harm, and human data do not indicate an increased risk of major malformations. However, use only if clearly needed, especially during the first trimester. |
| Fetal Monitoring | No specific fetal monitoring required. Standard clinical monitoring for maternal allergic reactions, gastrointestinal side effects, and signs of superinfection. In neonates, monitor for diarrhea, rash, or candidiasis. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies have not demonstrated impaired fertility. |
| Clinical Pearls | Cyclapen-W (cyclacillin) is an aminopenicillin with similar spectrum to ampicillin but with better oral absorption and less gastrointestinal upset. It is not effective against beta-lactamase-producing organisms. Ensure patient has no history of penicillin allergy before prescribing. Dose adjustment may be needed in renal impairment. |
| Patient Advice | Take this medication exactly as prescribed, even if you feel better. · Complete the full course of therapy to prevent resistance. · Notify your doctor if you develop rash, diarrhea, or difficulty breathing. · Store at room temperature away from moisture and heat. |