cephalexin hydrochloride
Keftab

cephalexin monohydrate
Biocef, Keflex, Novo-Lexin ◆

Available forms
Available by prescription only
cephalexin hydrochloride
Tablets: 500 mg
cephalexin monohydrate
Capsules: 250 mg, 500 mg
Suspension: 125 mg/5 ml, 250 mg/5 ml
Tablets (film-coated): 250 mg, 500 mg, 1 g

Indications and dosages
 Respiratory tract, GU tract, skin, soft-tissue, bone, and joint infections caused by susceptible organisms. Adults: 250 mg to 1 g P.O. q 6 hours.
Children: 25 to 50 mg/kg P.O. daily divided into four doses. For patients older than age 1 with streptococcal pharyngitis or skin and skin-structure infections, dose may be administered q 12 hours.
 Otitis media. Adults: 250 mg to 1 g P.O. q 6 hours.
Children: 75 to 100 mg/kg P.O. daily divided into four doses.
≡ Dosage adjustment. To prevent toxic accumulation in patients with creatinine clearance of less than 40 ml/minute, give reduced dosage as shown.

Creatinine clearance (ml/min) Adult dosage 11-40 500 mg q 8-12 hr 5-10 250 mg q 12 hr < 5 250 mg q 12-24 hr

Pharmacodynamics
Antibacterial action: Cephalexin is primarily bactericidal; it also may be bacteriostatic. Activity depends on the organism, tissue penetration, dosage, and rate of organism multiplication. It acts by adhering to bacterial penicillin-binding proteins, thereby inhibiting cell wall synthesis.
  Drug is active against many gram-positive organisms, including penicillinase-producing Staphylococcusaureus and S. epidermidis, Streptococcus pneumoniae, group B streptococci, and group A beta-hemolytic streptococci; susceptible gram-negative organisms include Klebsiella pneumoniae, Escherichia coli, Proteusmirabilis, and Shigella.

Pharmacokinetics
Absorption: Absorbed rapidly and completely from the GI tract after oral administration. The base monohydrate is probably converted to the hydrochloride in the stomach before absorption. Food delays but doesn’t prevent complete absorption.
Distribution: Distributed widely into most body tissues and fluids, including the gallbladder, liver, kidneys, bone, sputum, bile, and pleural and synovial fluids; CSF penetration is poor. Cephalexin crosses the placental barrier and is 6% to 15% protein-bound.
Metabolism: Not metabolized.
Excretion: Excreted primarily unchanged in urine by glomerular filtration and renal tubular secretion; small amounts of drug may appear in breast milk. Elimination half-life is about 1/2 to 1 hour in patients with normal renal function; 71/2 to 14 hours in patients with severe renal impairment. Hemodialysis or peritoneal dialysis removes cephalexin.

Contraindications and precautions
Contraindicated in patients hypersensitive to cephalosporins. Use cautiously in breast-feeding women and in patients with impaired renal function or penicillin allergy.

Interactions
Drug-drug. Loop diuretics, nephrotoxic drugs (aminoglycosides, colistin, polymyxin B, vancomycin): May increase risk of nephrotoxicity. Monitor patient closely.
Probenecid: Competitively inhibits renal tubular secretion of cephalosporins, resulting in higher prolonged serum levels of these drugs. May be used for this effect.

Adverse reactions
CNS: dizziness, headache, fatigue, agitation, confusion, hallucinations.
GI: pseudomembranous colitis,nausea, vomiting, diarrhea, gastritis, glossitis, dyspepsia, abdominal pain, anal pruritus, tenesmus, oral candidiasis.
GU: genital pruritus and candidiasis, vaginitis, interstitial nephritis.
Hematologic: neutropenia, eosinophilia, thrombocytopenia.
Musculoskeletal: arthritis, arthralgia, joint pain.
Skin: maculopapular and erythematous rash, urticaria.
Other: hypersensitivity reactions (serum sickness, anaphylaxis).

Effects on lab test results
• May increase ALT, AST, alkaline phosphatase, bilirubin, and LDH levels.
• May increase eosinophil count. May decrease hemoglobin, hematocrit, and neutrophil and platelet counts.

Overdose and treatment
Symptoms of overdose may include nausea, vomiting, epigastric distress, diarrhea, and hematuria.
 Treatment is supportive. Forced diuresis, peritoneal dialysis, hemodialysis, or charcoal hemoperfusion have not been established as beneficial.

Special considerations
• To prepare the oral suspension, add the required amount of water to the powder in two portions. Shake well after each addition. After mixing, store in refrigerator. Suspension is stable for 14 days without significant loss of potency. Store mixture in tightly closed container. Shake well before using.
• Because cephalexin is dialyzable, patients undergoing treatment with hemodialysis or peritoneal dialysis may require dosage adjustment.
• Drug causes false-positive results in urine glucose tests using cupric sulfate (Benedict’s reagent or Clinitest); use glucose oxidase test (Chemstrip uG, Diastix, or glucose enzymatic test strip) instead. Cephalexin also causes false elevations in serum or urine creatinine levels in tests using Jaffe reaction. Positive Coombs’ test results occur in about 3% of patients.
• With large doses or prolonged therapy, monitor patient for superinfection, especially if high-risk.
• If patient has renal impairment, monitor renal function test results before and during therapy.
Breast-feeding patients
• Drug appears in breast milk; use cautiously in breast-feeding women.
Pediatric patients
• Serum half-life is prolonged in neonates and infants younger than age 1. Safety and effectiveness in children haven’t been established.
Geriatric patients
• Reduce dosage in elderly patients who have diminished renal function.

Patient education
• Inform patient of potential adverse reactions.
• Instruct patient to take drug with food to avoid GI upset.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use