Cephalexin

General

• Type: 1st generation cephalosporin
• Dosage forms
  • Tabs: 250mg, 500mg, 750mg
  • Liquid: 125mg/5mL; 250mg/5mL
• Common Trade Names: Keflex, Keftab, Biocef

Adult Dosing

General

• 250-500mg PO q6h
• Max: 4g/day

Indications by Disease

Disease	Dose	Context
Acute cystitis	250mg QID x 5d	Outpatient, Women Uncomplicated
Cellulitis	500mg PO q6hrs	Outpatient
Erysipelas	500mg (6.25mg/kg) PO q6hrs x 10 days	Alternative
Felon	500mg PO q6hrs daily x 7 days	Outpatient
Impetigo	500mg (6.25mg/kg) PO q6hrs x 10 days	Oral therapy
Mastitis	500mg PO q6hrs	First line alternative
Pyelonephritis	500mg QID PO x 10-14 days (OR consider 1000mg BID)	Outpatient
Streptococcal pharyngitis	20 mg per kg PO BID (maximum 500 mg per dose) x 10 days	Penicillin Allergy (mild)
Suppurative parotitis	500mg (12.5mg/kg) PO four times daily	Outpatient

Pediatric Dosing

General

• 25-50mg/kg/day PO divided q6-12h
• Max: 500mg/dose

Skin Infections

• 25-50mg/kg/day PO divided q12h
• Max: 500mg/dose

Indications by Disease

Disease	Dose	Context
Acute cystitis	25-50mg/kg/day PO divided q6-8h x 7-10 days (max 500mg/dose)	Pediatric
Acute otitis media	75-100mg/kg/day PO divided q12h x 10 days; Max: 4,000mg/24h	Otitis Media
Cellulitis	25-50mg/kg/day PO divided q6-8h (max 500mg/dose)	Pediatric Outpatient
Endocarditis	50mg/kg PO (max 2g)	Pediatric Dental Prophylaxis, mild PCN Allergy
Erysipelas	25-50mg/kg/day PO divided q6-8h x 10 days (max 500mg/dose)	Pediatric
Impetigo	25-50mg/kg/day PO divided q6-8h x 7-10 days (max 500mg/dose)	Pediatric Oral
Pharyngitis	40mg/kg/day PO divided q12h x 10 days; Max: 500mg/dose	Streptococcal Pharyngitis (>1 Year)
Pyelonephritis	25-50mg/kg/day PO divided q6-8h x 10-14 days (max 500mg/dose)	Pediatric Outpatient
Streptococcal pharyngitis	20mg/kg PO BID x 10 days (max 500mg/dose)	Pediatric PCN Allergy
Suppurative parotitis	50mg/kg/day PO divided QID (max 500mg/dose)	Pediatric Outpatient

Special Populations

• Pregnancy Rating: B
• Lactation risk categories: Enters breast milk/L3
• Renal
  • Adult
    • CrCl 50-90: give q6-8h
    • CrCl 10-50: give q8-12h
    • CrCl <10: give q12-24h
    • Hemodialysis: give dose after dialysis, no supplement
    • Peritoneal dialysis: no supplement
  • Pediatric
    • CrCl 30-50: give q8h
    • CrCl 10-29: give q12h
    • CrCl <10: give q24h
    • Hemodialysis: give dose after dialysis, no supplement
    • Peritoneal dialysis: no supplement
• Hepatic (Adult & Pediatric)
  • Not defined

Contraindications

• Allergy to class/drug
  • See also Cephalosporin Cross-reactivity
• Caution advised with contraceptives

Adverse Drug Reactions

Serious

• Anaphylaxis
• Angioedema
• Erythema Multiforme
• Stevens-Johnson Syndrome
• Toxic Epidermal Necrolysis
• Clostridium difficile
• Neutropenia
• Thrombocytopenia
• Hemolytic anemia
• Hemorrhage
• Hepatitis
• Cholestatic jaundice
• Seizures

Common

• Diarrhea
• Nausea/vomiting
• Rash
• Headache
• Dizziness
• Transaminitis
• Eosinophilia

Pharmacology

• Half-life: 1h (~20hr ESRD)
• Metabolism: Minimal
• Excretion: Primarily urine (>90% unchanged)
• Mechanism of Action:
  • Bactericidal, inhibits cell wall

Antibiotic Sensitivities

Group	Organism	Sensitivity
Gram Positive	Strep. Group A, B, C, G	S
	Strep. Pneumoniae	S
	Viridans strep	S
	Strep. anginosus gp	X1
	Enterococcus faecalis	R
	Enterococcus faecium	X1
	MSSA	S
	MRSA	R
	CA-MRSA	R
	Staph. Epidermidis	I
	C. jeikeium	R
	L. monocytogenes	R
Gram Negatives	N. gonorrhoeae	R
	N. meningitidis	R
	Moraxella catarrhalis	R
	H. influenzae	R
	E. coli	S
	Klebsiella sp	S
	E. coli/Klebsiella ESBL+	R
	E coli/Klebsiella KPC+	R
	Enterobacter sp, AmpC neg	R
	Enterobacter sp, AmpC pos	R
	Serratia sp	R
	Serratia marcescens	X1
	Salmonella sp	R
	Shigella sp	R
	Proteus mirabilis	S
	Proteus vulgaris	R
	Providencia sp.	R
	Morganella sp.	R
	Citrobacter freundii	R
	Citrobacter diversus	R
	Citrobacter sp.	R
	Aeromonas sp	X1
	Acinetobacter sp.	R
	Pseudomonas aeruginosa	R
	Burkholderia cepacia	R
	Stenotrophomonas maltophilia	R
	Yersinia enterocolitica	X1
	Francisella tularensis	X1
	Brucella sp.	X1
	Legionella sp.	R
	Pasteurella multocida	R
	Haemophilus ducreyi	X1
	Vibrio vulnificus	X1
Misc	Chlamydophila sp	X1
	Mycoplasm pneumoniae	X1
	Rickettsia sp	X1
	Mycobacterium avium	X1
Anaerobes	Actinomyces	X1
	Bacteroides fragilis	R
	Prevotella melaninogenica	X1
	Clostridium difficile	X1
	Clostridium (not difficile)	X1
	Fusobacterium necrophorum	X1
	Peptostreptococcus sp.	S

Key

• S susceptible/sensitive (usually)
• I intermediate (variably susceptible/resistant)
• R resistant (or not effective clinically)
• S+ synergistic with cell wall antibiotics
• U sensitive for UTI only (non systemic infection)
• X1 no data
• X2 active in vitro, but not used clinically
• X3 active in vitro, but not clinically effective for Group A strep pharyngitis or infections due to E. faecalis
• X4 active in vitro, but not clinically effective for strep pneumonia

See Also

• Antibiotics (Main)
• Cephalosporin Cross-reactivity

References

• Sanford 2010
• Epocrates
• Lexicomp