CEPHALEXIN

CEPHALEXIN
(sef-a-lex'in)
Ceporex A, Keflex, Novolexin A
Classifications: beta-lactam antibiotic; first-generation cephalosporin;
Therapeutic: antibiotic
; 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

Action

Semisynthetic beta-lactam cephalosporin. 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.

Therapeutic Effect

Broad-spectrum, first-generation cephalosporin antibiotic active against many gram-positive aerobic cocci and much less active against gram-negative bacteria or anaerobic organisms.

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; viral infections. Safe use in infants <1 mo not established.

Cautious Use

History of hypersensitivity to penicillin or other drug allergy; severely impaired renal function; GI disease, colitis; hepatic disease; coagulopathy; pregnancy (category B), lactation.

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., TesTape, 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 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% 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.

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

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