CEPHALEXIN
Clinical safety rating: safe
Probenecid may decrease cephalosporin excretion May cause diarrhea including Clostridium difficile-associated diarrhea.
Cephalexin is a first-generation cephalosporin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), thereby inhibiting transpeptidation and disrupting cell wall cross-linking, leading to cell lysis and death.
| Metabolism | Cephalexin is not extensively metabolized; it is primarily excreted unchanged in the urine via renal tubular secretion and glomerular filtration. Minor hepatic metabolism may occur but is not clinically significant. |
| Excretion | Renal: 80-90% unchanged by glomerular filtration and tubular secretion; biliary: <5%; fecal: <1% |
| Half-life | 0.5-1.2 hours in normal renal function; prolonged to 5-30 hours in severe renal impairment (CrCl <10 mL/min) |
| Protein binding | 6-10% bound to serum albumin |
| Volume of Distribution | 0.2-0.3 L/kg, indicating distribution primarily into extracellular fluid |
| Bioavailability | Oral: 90-100% (well absorbed) |
| Onset of Action | Oral: 1 hour (peak serum concentration at 1 hour) |
| Duration of Action | 6-8 hours; dosing interval adjusted based on renal function |
| Molecular Weight | 347.39 |
| Action Class | Cephalosporins: 1st generation |
| Brand Substitutes | Cefron 250mg Tablet, Cephin 250mg Tablet, Bectacef 250mg Tablet, H Cef 250mg Tablet, Arolexim 250mg Tablet |
Oral: 250-1000 mg every 6 hours; maximum 4 g/day.
| Dosage form | TABLET |
| Renal impairment | CrCl 30-50 mL/min: 500 mg every 6-8 hours; CrCl 15-29 mL/min: 500 mg every 12 hours; CrCl <15 mL/min: 500 mg every 24 hours; hemodialysis: 500 mg after dialysis. |
| Liver impairment | No adjustment required for any Child-Pugh class. |
| Pediatric use | Oral: 12.5-25 mg/kg every 6 hours; maximum 100 mg/kg/day for mild-moderate infections; for severe infections, up to 100 mg/kg/day in divided doses. |
| Geriatric use | Monitor renal function and adjust dose based on creatinine clearance; no specific age-based adjustments beyond renal considerations. |
| 1st trimester | Cephalexin crosses the placenta. Animal studies have not shown fetal harm, but there are no adequate well-controlled studies in pregnant women. It should be used during the first trimester only if clearly needed. |
| 2nd trimester | Cephalexin is generally considered safe during the second trimester. No known teratogenic effects; however, use only if clearly indicated. |
| 3rd trimester | Cephalexin is generally considered safe during the third trimester. It can be used for infections when clinically indicated. |
Clinical note
Probenecid may decrease cephalosporin excretion May cause diarrhea including Clostridium difficile-associated diarrhea.
| FDA category | Human |
| Placental transfer | Cephalexin crosses the placenta. Peak cord blood levels achieved after maternal dosing are approximately 1.5-5% of maternal serum levels. |
■ FDA Black Box Warning
No FDA boxed warning exists.
| Serious Effects |
Hypersensitivity to cephalexin or any cephalosporin antibioticHistory of immediate anaphylactic reaction to penicillins (cross-sensitivity may occur)
| Precautions | Hypersensitivity reactions including anaphylaxis can occur, especially in patients with penicillin allergy (cross-allergenicity). Prolonged use may result in superinfection with Clostridioides difficile-associated diarrhea (CDAD). Renal impairment patients require dose adjustment; monitor renal function in prolonged therapy. Seizures may occur with high doses in renal impairment. Use in patients with gastrointestinal disease (especially colitis) requires caution. False-positive urinary glucose tests may occur with Clinitest, but not with glucose oxidase methods. |
| Food/Dietary | No significant food interactions. Absorption may be slightly reduced by food, but not clinically significant. Avoid alcohol due to possible disulfiram-like reaction (rare with cephalexin; caution advised). |
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| Breastfeeding | Cephalexin is excreted into breast milk in small amounts (approximately 0.5-4.5% of maternal dose). It is unlikely to cause adverse effects in breastfed infants. However, monitor for potential gastrointestinal disturbances (e.g., diarrhea, candidiasis) in the infant. |
| Lactation Rating | L1 (Compatible) - The American Academy of Pediatrics considers cephalexin compatible with breastfeeding. |
| Teratogenic Risk | Pregnancy Category B. Animal studies show no fetal risk; no adequate human studies. No evidence of teratogenicity in first trimester; risk cannot be ruled out. Avoid only if clearly needed. |
| Fetal Monitoring | No specific monitoring required; standard prenatal care. Observe for hypersensitivity reactions. |
| Fertility Effects | No evidence of impaired fertility in animal studies. No human data on male or female fertility. |
| Clinical Pearls | Cephalexin is a first-generation cephalosporin with good activity against Gram-positive cocci (e.g., Streptococcus pyogenes, Staphylococcus aureus [MSSA]) and some Gram-negative organisms (e.g., Escherichia coli, Klebsiella pneumoniae). It is not effective against MRSA. Administer on empty stomach for optimal absorption; however, it can be taken with food to reduce GI upset. Dose adjustment required in severe renal impairment (CrCl < 30 mL/min). Avoid in patients with immediate-type hypersensitivity to penicillins due to cross-reactivity risk (approx. 5-10%). |
| Patient Advice | Take cephalexin exactly as prescribed, even if you feel better. Complete the full course to prevent resistance. · You may take this medication with or without food. If stomach upset occurs, take with a meal. · Call your doctor immediately if you develop watery/bloody diarrhea, rash, difficulty breathing, or swelling of lips/tongue. · Avoid alcohol while taking this medication and for 48 hours after finishing; alcohol may increase side effects (e.g., nausea, vomiting, flushing). · Store at room temperature, away from moisture and heat. Keep oral suspension refrigerated and discard after 14 days. |