Omnicef - Drug Monograph

Introduction

Omnicef (cefdinir) is a third-generation oral cephalosporin antibiotic approved by the FDA in 1997. It is a broad-spectrum antimicrobial agent effective against both gram-positive and gram-negative bacteria. Omnicef is commonly prescribed for various community-acquired infections due to its favorable safety profile and convenient once- or twice-daily dosing regimen.

Mechanism of Action

Cefdinir exerts its bactericidal effect by inhibiting bacterial cell wall synthesis through binding to essential penicillin-binding proteins (PBPs). This disruption of peptidoglycan cross-linking in the bacterial cell wall leads to osmotic instability and eventual cell lysis. As a beta-lactam antibiotic, cefdinir demonstrates time-dependent killing activity against susceptible organisms.

Indications

FDA-approved indications include:

• Acute bacterial exacerbations of chronic bronchitis
• Acute community-acquired pneumonia
• Acute maxillary sinusitis
• Pharyngitis/tonsillitis
• Uncomplicated skin and skin structure infections
• Acute bacterial otitis media

Off-label uses may include certain urinary tract infections and other susceptible infections when appropriate.

Dosage and Administration

• 300 mg every 12 hours OR 600 mg once daily
• Duration: 5-10 days depending on infection

• 7 mg/kg every 12 hours OR 14 mg/kg once daily
• Maximum dose: 600 mg daily
• Available as 125 mg/5 mL and 250 mg/5 mL oral suspension

• Renal impairment: Adjust dose for CrCl <30 mL/min
• Hepatic impairment: No dosage adjustment required
• Elderly: Consider renal function adjustments

• May be taken with or without food
• Oral suspension should be shaken well before use
• Complete full course of therapy despite symptom improvement

Pharmacokinetics

Contraindications

• Known hypersensitivity to cefdinir or other cephalosporins
• History of severe allergic reactions to penicillins (cross-reactivity risk)
• Patients with carnitine deficiency or metabolic disorders

Warnings and Precautions

• Clostridium difficile-associated diarrhea: May range from mild to life-threatening colitis
• Hypersensitivity reactions: Cross-sensitivity with penicillin-class antibiotics (~10%)
• Superinfections: May result in bacterial or fungal overgrowth
• Direct Coombs test seroconversion: May occur without hemolytic anemia
• Renal impairment: Requires dosage adjustment
• Phenylketonuria: Oral suspension contains phenylalanine
• Iron-containing products: May reduce absorption (separate administration by 2 hours)

Drug Interactions

• Antacids containing aluminum or magnesium: Reduce cefdinir absorption (separate by 2 hours)
• Iron supplements and iron-fortified foods: May cause reddish stools and reduce absorption
• Probenecid: May increase cefdinir concentrations
• Oral contraceptives: Potential decreased efficacy (recommend backup contraception)

Adverse Effects

• Diarrhea (8%)
• Nausea (3%)
• Vaginal moniliasis (3%)
• Headache (2%)
• Abdominal pain (1%)

• Pseudomembranous colitis
• Severe hypersensitivity reactions (anaphylaxis, Stevens-Johnson syndrome)
• Hematologic effects (neutropenia, thrombocytopenia)
• Hepatic enzyme elevations
• Renal dysfunction
• Seizures (rare)

Monitoring Parameters

• Clinical response to therapy
• Signs of superinfection or C. difficile infection
• Renal function in at-risk patients
• Complete blood count with prolonged therapy
• Allergy symptoms
• Compliance with therapy

Patient Education

• Complete entire course even if feeling better
• Report severe diarrhea, bloody stools, or abdominal pain
• Inform healthcare provider of any allergy history
• Separate iron supplements and antacids by 2 hours
• Oral suspension may be stored refrigerated for 10 days
• Pinkish or reddish discoloration of stools may occur (harmless)
• Report rash, itching, or difficulty breathing immediately
• Use backup contraception if taking oral contraceptives

References

1. FDA Prescribing Information: Omnicef (cefdinir) [Revised 2012] 2. Pichichero ME. Use of selected cephalosporins in penicillin-allergic patients. Drug Saf. 2007;30(9):791-797 3. Harrison CJ, Woods C, Stout G, Martin E, Selim MA. Pharmacodynamics of cefdinir against Streptococcus pneumoniae. Antimicrob Agents Chemother. 2005;49(6):2487-2491 4. Guay DR. Cefdinir: an advanced-generation, broad-spectrum oral cephalosporin. Clin Ther. 2002;24(4):473-489 5. Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. CLSI supplement M100. 2023 6. Gilbert DN, Chambers HF, Eliopoulos GM, Saag MS, Pavia AT. The Sanford Guide to Antimicrobial Therapy. 53rd ed; 2023 7. Lexicomp Online. Cefdinir monograph. Wolters Kluwer Clinical Drug Information [accessed 2023]