💊 Cephalexin (Cephalexin)

🏷️ Brand names & manufacturers

Cephalexin🏭 AvKAREDailyMed

Cephalexin🏭 Teva Pharmaceuticals USA, Inc.DailyMed

Cephalexin🏭 Lupin Pharmaceuticals, Inc.DailyMed

✅ What it is used for

• Respiratory tract infections caused by susceptible bacteria (Streptococcus pneumoniae and Streptococcus pyogenes)
• Otitis media
• Skin and skin structure infections
• Bone infections
• Genitourinary tract infections, including acute prostatitis
• Not for non-bacterial infections; this helps reduce the development of drug-resistant bacteria

🧪 Active ingredient

The active ingredient is cephalexin (monohydrate), a bactericidal antibiotic that works by inhibiting bacterial cell-wall synthesis.

🌿 Benefits

• Treats susceptible bacterial infections of the respiratory tract, ear, skin, bone, and genitourinary tract
• Can be taken with or without food
• Available as capsules and oral suspension

📝 How to use

• The dose and duration are set by your doctor or pharmacist based on the type and severity of infection, kidney function, age, and weight; do not change it without advice.
• It can be taken with or without food.
• Treatment usually lasts 7 to 14 days depending on the infection type and severity; for beta-hemolytic streptococcal infections at least 10 days is recommended.
• For the oral suspension: it is prepared at the time of dispensing by adding water to the powder and shaking well, and it should be kept in the refrigerator after mixing.
• Complete the course prescribed by your doctor even if symptoms improve.

💊 Dosage forms

• Capsules 250 mg and 500 mg
• Powder for oral suspension 125 mg/5 mL and 250 mg/5 mL (cherry mixed fruit flavor)

🔄 Drug interactions

• Metformin: increases metformin blood levels; monitor the patient and adjust the metformin dose, watching for low blood sugar.
• Probenecid: inhibits the kidney excretion of cephalexin; co-administration is not recommended.
• May interfere with urine glucose tests (false-positive result).

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👨‍⚕️ For healthcare professionals

Mechanism of action

Cephalexin is a bactericidal cephalosporin that inhibits bacterial cell-wall synthesis. It is acid stable, about 10–15% protein bound, and excreted by glomerular filtration and tubular secretion, with over 90% excreted unchanged in urine within 8 hours. Average peak serum levels at 1 hour are about 9, 18, and 32 mcg/mL after 250 mg, 500 mg, and 1 g doses, respectively.

Labeled dosing

Adults and patients ≥15 years: usual dose 250 mg every 6 hours, or 500 mg every 12 hours, for 7–14 days; for more severe infections up to 4 g daily in 2–4 equally divided doses. Pediatric (>1 year): 25–50 mg/kg/day in equally divided doses for 7–14 days; 50–100 mg/kg/day in severe infections; 75–100 mg/kg/day for otitis media; at least 10 days for beta-hemolytic streptococcal infections. Dose adjustment is required in severe renal impairment and ESRD (CrCl <30 mL/min). Final dosing is determined by the physician or pharmacist.

• Resistance: methicillin-resistant staphylococci and most enterococci are resistant; no activity against Pseudomonas spp. or Acinetobacter calcoaceticus, and not active against most isolates of Enterobacter spp., Morganella morganii, and Proteus vulgaris.
• Inquire about beta-lactam hypersensitivity history before prescribing; cross-hypersensitivity may occur in up to 10% of patients with penicillin allergy.
• Consider C. difficile-associated diarrhea in any patient with diarrhea after antibiotic use, even up to two months after therapy.
• Direct Coombs' test seroconversion may occur; evaluate for hemolytic anemia if anemia develops.
• Monitor renally impaired patients longer for toxicity and drug interactions due to delayed clearance; seizure potential.
• Metformin: after a single 500 mg dose, plasma metformin Cmax and AUC rose by an average of 34% and 24% and renal clearance fell by 14%; monitor for hypoglycemia and adjust the metformin dose.
• Avoid co-administration with probenecid.
• False-positive urine glucose with Benedict's or Fehling's solution.
• Laboratory changes reported with the class: prolonged prothrombin time, increased BUN, creatinine, alkaline phosphatase, bilirubin, and LDH.

🎓 Key points for students

• Cephalosporin antibacterial with bactericidal activity (inhibits cell-wall synthesis).
• Active against: methicillin-susceptible S. aureus, penicillin-susceptible S. pneumoniae, S. pyogenes, E. coli, H. influenzae, Klebsiella pneumoniae, Proteus mirabilis, Moraxella catarrhalis.
• Inactive against Pseudomonas, methicillin-resistant staphylococci, and most enterococci.
• Excreted almost entirely unchanged by the kidney; dose reduction needed in renal impairment.
• Contraindication: hypersensitivity to cephalexin or other cephalosporins.
• Key warnings: hypersensitivity and cross-reactivity with penicillins, C. difficile-associated diarrhea, positive Coombs' test, seizures.
• Interactions: metformin (raised levels), probenecid (slows cephalexin excretion), false-positive urine glucose.