Dosing and uses of Keflex (cephalexin)
Adult dosage forms and strengths
capsule
- 250mg
- 500mg
- 750mg
oral suspension
- 125mg/5mL
- 250mg/5mL
tablet
- 250mg
- 500mg
Genitourinary Tract Infections
250 mg PO q6hr; dosage range, 1-4 g/day in divided doses
Bone Infections
250 mg PO q6hr; dosage range, 1-4 g/day in divided doses
Uncomplicated Cystitis
250 mg PO q6hr or 500 mg PO q12hr; dosage range, 1-4 g/day in divided doses
Otitis Media
250 mg PO q6hr; dosage range, 1-4 g/day in divided doses
Skin/Skin Structure Infections
250 mg PO q6hr or 500 mg PO q12hr; dosage range, 1-4 g/day in divided doses
Respiratory Tract Infections
250 mg PO q6hr; dosage range, 1-4 g/day in divided doses
Streptococcal Pharyngitis
250 mg PO q6hr or 500 mg PO q12hr; dosage range, 1-4 g/day in divided doses
Cellulitis and Mastitis
500 mg PO q6hr; dosage range, 1-4 g/day in divided doses
Renal Impairment
CrCl <10 mL/min: 250-500 mg PO q12-24hr
CrCl 10-50 mL/min: 500 mg PO q8-12hr
Hepatic Impairment
Not studied
Dosing Considerations
Susceptible organisms
- Gram-positive cocci, gram negative bacilli, gram-positive bacilli, gram-negative cocci, anaerobes
Pediatric dosage forms and strengths
capsule
- 250mg
- 500mg
oral suspension
- 125mg/5mL
- 250mg/5mL
tablet
- 125mg
- 250mg
Uncomplicated Cystitis
<15 years: 25-50 mg/kg/day PO divided q6-8hr for 10 days; not to exceed 4 g/day
>15 years: 250 mg PO q6hr; dosage range, 1-4 g/day in divided doses
Genitourinary Tract Infections
25-50 mg/kg/day PO divided q6-8hr for 10 days; not to exceed 4 g/day
Beta-Hemolytic Streptococcal Infections
25-50 mg/kg/day PO divided q6-8hr for 10 days; not to exceed 4 g/day
Bone Infections
25-50 mg/kg/day PO divided q6-8hr for 10 days; not to exceed 4 g/day
Otitis Media
75-100 mg/kg/day PO divided q6hr for 10 days; not to exceed 4 g/day
Skin/Skin Structure Infections
25-50 mg/kg/day PO divided q6-8hr for 10 days; not to exceed 4 g/day
Respiratory Tract Infections
25-50 mg/kg/day PO divided q6-8hr for 10 days; not to exceed 4 g/day
Streptococcal Pharyngitis
25-50 mg/kg PO q12hr for 10 days; not to exceed 500 mg q12hr
Cellulitis and Mastitis
Adolescents: 500 mg PO q6hr; dosage range, 1-4 g/day in divided doses
Keflex (cephalexin) adverse (side) effects
Frequency not defined
Abdominal pain
Agitation
Anemia
Angioedema
Confusion
Diarrhea
Dizziness
Dyspepsia
Elevated transaminases
Eosinophilia hemolytic
Epidermal necrolysis
Erythema multiform
Fatigue
Gastritis
Genital pruritus
Hallucinations
Headache
Hemolytic anemia
Hypersensitivity
Nephritis
Neutropenia
Pseudomembranous colitis
Thrombocytopenia
Transient hepatitis
Toxic epidermal necrolysis
Urticaria
Vaginal discharge
Vomiting
Warnings
Contraindications
Documented hypersensitivity
Cautions
Endocarditis prophylaxis is appropriate only for high-risk patients, per American Heart Association guidelines
Adjust dose in severe renal insufficiency (high doses may cause CNS toxicity)
Superinfections and promotion of nonsusceptible organisms may occur with prolonged use or repeated therapy
Prolonged treatment, hepatic or renal disease, or nutritional deficiency may be associated with increased international normalized ratio (INR)
Prolonged use is associated with fungal or bacterial superinfection
Use with caution in patients with history of hypersensitivity to penicillin
Pregnancy and lactation
Pregnancy category: B
Lactation: Drug excreted in breast milk; use with caution
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Keflex (cephalexin)
Mechanism of action
Binds to one or more of the penicillin binding proteins, which in turn inhibits synthesis of bacterial cell walL
Absorption
Bioavailability: 90%; absorption delayed in young children
Peak serum time: 1 hr
Peak plasma concentration: 10-18 mcg/mL (500-mg dose)
Distribution
Distributed widely into most tissues and fluids; penetrates CSF poorly
Protein bound: 6-15%
Metabolism
Minimally metabolized in liver
Elimination
Half-life: 0.5-1.2 hr
Excretion: Urine (80-100% as unchanged drug)
