CEPHALEXIN
(sef-a-lex'in)
Cefanex, Ceporex_A, Keflet, Keflex, Keftab, Novolexin_A
Classifications: antiinfective; antibiotic; first-generation cephalosporin
Prototype: Cefazolin
Pregnancy Category: B

Availability

250 mg, 500 mg capsules; 250 mg, 500 mg, 1 g tablets; 125 mg/5 mL, 250 mg/5 mL suspension

Actions

Semisynthetic derivative of cephalosporin C. Broad-spectrum, first-generation cephalosporin antibiotic with antiinfective activity similar to that of cefazolin but reportedly less potent. Preferentially binds to one or more of the penicillin-binding proteins (PBP) located on cell walls of susceptible organisms. This inhibits third and final stage of bacterial cell wall synthesis, thus killing the bacterium. Ineffective against many gram-negative or anaerobic organisms. Cross-allergenicity between cephalosporins and penicillins has been reported.

Therapeutic Effects

It is active against many gram-positive aerobic cocci and much less active against gram-negative bacteria. Effectively treats osteomyelitis, otitis media, streptococcal pharyngitis, prostate and respiratory infections, skin and urinary tract infections, eliminating or reducing infection.

Uses

To treat infections caused by susceptible pathogens in respiratory and urinary tracts, middle ear, skin, soft tissue, and bone.

Contraindications

Hypersensitivity to cephalosporins and related antibiotics; pregnancy (category B), lactation. Safe use in infants <1 mo not established.

Cautious Use

History of hypersensitivity to penicillin or other drug allergy; severely impaired renal function.

Route & Dosage

Mild to Moderate Infection
Adult: PO 250–500 mg q6h
Child: PO 25–100 mg/kg/d in 4 divided doses

Skin and Skin Structure Infections
Adult: PO 500 mg q12h

Otitis Media
Child: PO 75–100 mg/kg/d in 4 divided doses

Administration

Oral

Cephalexin oral suspension should be refrigerated; discard unused portions 14 d after preparation. Label should indicate expiration date. Keep tightly covered. Shake suspension well before pouring.

Adverse Effects (1%)

Body as a Whole: Angioedema, anaphylaxis, superinfections. GI: Diarrhea (generally mild), nausea, vomiting, anorexia, abdominal pain. CNS: Dizziness, headache, fatigue. Skin: Rash, urticaria.

Diagnostic Test Interference

False-positive urine glucose determinations using copper sulfate reagents, e.g., Clinitest, Benedict's reagent, but not with glucose oxidase (enzymatic) tests, e.g., Tes-Tape, Diastix, Clinistix. Positive direct Coombs' test may complicate transfusion cross-matching procedures and hematologic studies.

Interactions

Drug: Probenecid decreases renal elimination of cephalexin.

Pharmacokinetics

Absorption: rapidly absorbed from GI tract; stable in stomach acid. Peak: 1 h. Distribution: Widely distributed in body fluids with highest concentration in kidney; crosses placenta. Elimination: 80–100% eliminated unchanged in urine in 8 h; excreted in breast milk. Half-Life: 38–70 min.

Nursing Implications

Assessment & Drug Effects

Determine history of hypersensitivity reactions to cephalosporins and penicillin and history of other drug allergies before therapy is initiated.
Lab tests: Evaluate renal and hepatic function periodically in patients receiving prolonged therapy.
Monitor for manifestations of hypersensitivity (see Signs & Symptoms, Appendix F). Discontinue drug and report their appearance promptly.

Patient & Family Education

Take medication for the full course of therapy as directed by physician.
Keep physician informed if adverse reactions appear.
Be alert to S&S of superinfections (see Appendix F). These symptoms should be reported promptly and appropriate therapy instituted.
Do not breast feed while taking this drug.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug