Cefdinir

Introduction Overview

Generic Name

cefdinir

Brand Name

Omnicef

Dosage Form

Oral capsule, oral suspension (liquid)

Drug Class

Third generation cephalosporins

Pharmacokinetics

Absorption:
Cefdinir is administered orally and exhibits rapid absorption from the gastrointestinal tract. After oral administration, peak plasma concentrations are typically reached within 2 to 4 hours. The presence of food can slightly delay the time to peak concentration but does not significantly affect the overall extent of absorption, allowing cefdinir to be taken with or without food. Oral bioavailability is approximately 20-25%, limited due to partial dissolution and incomplete absorption in the gut. The acidic environment and gastrointestinal transit time influence the dissolution of cefdinir capsules and suspension.

Distribution:
Following absorption, cefdinir distributes widely into various body tissues and fluids. It demonstrates moderate plasma protein binding, approximately 60-70%, primarily to albumin. The volume of distribution ranges from 0.35 to 0.42 L/kg, indicating distribution into extracellular fluids. Cefdinir penetrates well into respiratory tract tissues, middle ear effusions, and bronchial mucosa, making it effective for treating respiratory infections. However, penetration into cerebrospinal fluid is poor and generally insufficient for treating central nervous system infections. Distribution into breast milk has been documented, warranting caution in lactating patients.

Metabolism:
Cefdinir undergoes minimal metabolic transformation in the body. It remains primarily in its unchanged active form following absorption and systemic distribution. This low metabolic requirement reduces variability due to hepatic enzyme interactions, enhancing predictability in patients with normal liver function. Its minimal metabolism also reduces formation of potentially toxic metabolites and decreases the risk of hepatic drug-drug interactions.

Elimination:
The elimination half-life of cefdinir ranges between 1.7 to 2.5 hours in subjects with normal renal function. The drug is predominantly excreted unchanged via the kidneys through glomerular filtration and active tubular secretion. Approximately 60-70% of an administered dose is recovered in the urine within 24 hours. Renal impairment significantly decreases cefdinir clearance, prolonging half-life and necessitating dosage adjustment to prevent accumulation. Hemodialysis can partially remove cefdinir, though supplemental dosing post-dialysis may be indicated. Fecal excretion constitutes a minor elimination pathway. Clinical monitoring in patients with renal dysfunction is essential to avoid toxicity.

Dosage Forms

Available Dosage Forms:
Omnicef is available as:
- Oral capsule: 300 mg
- Oral suspension (liquid): 125 mg/5 mL and 250 mg/5 mL formulations conforming to FDA-approved preparations.

Dosages for Adults and Adolescents:
The typical adult dose for most bacterial infections is 300 mg every 12 hours or 600 mg once daily, administered orally. For pharyngitis and tonsillitis caused by Streptococcus pyogenes, the dosage is commonly 300 mg twice daily for 10 days. Treatment duration and dosing frequency may vary based on infection severity, microbial susceptibility, and clinical response.

Specific Patient Populations:
- Pediatric Patients: Dosage is weight-based. For children 6 months and older, 14 mg/kg/day divided into one or two doses is recommended; maximum dosages generally should not exceed adult doses.
- Renal Impairment: In patients with creatinine clearance less than 30 mL/min, dosage adjustment is critical. It is advised to extend dosing intervals to every 24 or 48 hours depending on renal function severity.
- Geriatric Population: Generally, no special adjustment is needed unless renal function is compromised.

Cefdinir oral suspension contains sucrose; caution should be exercised in diabetic patients. In addition, the suspension should be shaken well before administration and stored at room temperature, discarding any unused portion after 10 days to ensure stability and efficacy.

Mechanism Of Action

Cefdinir is a third-generation cephalosporin antibiotic that exerts its antibacterial effect by targeting bacterial cell wall synthesis. It binds to penicillin-binding proteins (PBPs), which are critical enzymes involved in the last stages of peptidoglycan cross-linking in bacterial cell walls. By competitively inhibiting these PBPs, cefdinir disrupts the synthesis of the peptidoglycan layer, essential for bacterial cell wall structural integrity and rigidity.

This disruption leads to weakening of the bacterial cell wall, causing osmotic instability and eventual cell lysis due to the inability to withstand internal turgor pressure. Cefdinir's action is bactericidal, leading to the rapid death of susceptible bacteria. It is effective against a broad spectrum of Gram-positive and Gram-negative organisms, including strains resistant to earlier generation cephalosporins due to its chemical structure that confers resistance to many beta-lactamases.

Cefdinir shows enhanced activity against beta-lactamase-producing bacteria compared to first- and second-generation cephalosporins. However, it is not effective against bacteria producing extended-spectrum beta-lactamases (ESBLs). The drug's cellular entry is facilitated through porin channels in the outer membrane of Gram-negative bacteria, allowing it to reach target PBPs.

Clinical studies have demonstrated cefdinir's efficacy in respiratory tract infections, skin and soft tissue infections, and otitis media, corroborating the mechanistic basis of its bactericidal activity. Its mechanism is similar to other beta-lactam antibiotics but offers improved pharmacodynamic and pharmacokinetic properties leading to broader clinical applications.

Pharmacological Actions

Bactericidal activity through inhibition of bacterial cell wall synthesis.
Broad-spectrum antibiotic effective against various Gram-positive and Gram-negative pathogens.
Resistant to degradation by many beta-lactamases produced by bacteria.
Effective penetration into respiratory tract tissues and middle ear fluid.
Minimal metabolism, excreted primarily unchanged by kidneys.
Demonstrates time-dependent killing characteristic typical of beta-lactams.
Inhibits penicillin-binding proteins leading to defective peptidoglycan cross-linking.
Exhibits efficacy against common respiratory pathogens such as Streptococcus pneumoniae and Haemophilus influenzae.
Stable oral absorption with flexibility of administration with or without food.
Limited effect on normal intestinal flora but may cause alterations leading to potential diarrhea.
Low protein binding enhances tissue distribution.
Maintains activity in mildly acidic environments such as infected tissues.
Synergistic potential with other antibiotics against certain resistant strains has been reported.

Therapeutic Or Clinical Uses

Treatment of community-acquired pneumonia
Acute bacterial exacerbations of chronic bronchitis
Acute otitis media in pediatric patients
Pharyngitis and tonsillitis caused by Streptococcus pyogenes
Uncomplicated skin and skin structure infections
Sinusitis caused by susceptible bacteria
Alternative therapy for infections caused by beta-lactamase-producing strains
Used in outpatient settings due to oral formulation
Treatment of urinary tract infections caused by susceptible organisms
Prophylaxis for certain bacterial infections in selected clinical scenarios
Management of mild to moderate infections when first-line therapy is contraindicated or ineffective

Side Or Adverse Effects

Nausea and vomiting
Diarrhea, including antibiotic-associated diarrhea
Vaginal itching or discharge indicative of yeast overgrowth
Headache
Rash and other hypersensitivity skin reactions including urticaria
Potential for Clostridium difficile-associated diarrhea and colitis
Rare allergic reactions ranging from mild hypersensitivity to anaphylaxis
Alterations in blood counts such as eosinophilia or neutropenia (rare)
Transient elevation of liver enzymes
Renal impairment in predisposed individuals with overdose or prolonged use
Possible red discoloration of stool when concomitant iron supplement is used
Diaper rash in infants receiving oral suspension
Fever and chills as part of hypersensitivity or infection progression
Seizures in cases of overdose or in patients with pre-existing CNS disorders
Rare severe cutaneous adverse reactions such as Stevens-Johnson syndrome

Precautions

Assess for allergy to cephalosporins or penicillins prior to administration
Use caution in patients with renal impairment; dosage adjustment is necessary
Monitor for signs of superinfection, including Clostridium difficile colitis
Avoid concomitant use with antacids or mineral supplements containing aluminum, magnesium, or iron within 2 hours of dosing
Inform patients to complete full course of therapy even if symptoms improve
Use caution in diabetic patients due to sucrose content in oral suspension
Monitor for allergic reactions, especially in individuals with history of drug hypersensitivity
Consider potential impact on microbiological testing results during or shortly after therapy
Use cautiously during pregnancy; benefits must outweigh risks
Cefdinir may interfere with certain laboratory blood or urine glucose tests leading to false results
Store oral suspensions properly and discard after 10 days to avoid degradation
Avoid use in viral infections as cefdinir is ineffective against viruses
Monitor patients on concomitant nephrotoxic drugs closely
In pediatric patients, ensure appropriate weight-based dosing
Educate patients about the risk of diarrhea and when to report severe symptoms

Warnings

Contraindicated in individuals with known allergy to cefdinir or other cephalosporins
Risk of severe hypersensitivity reactions including anaphylaxis exists
Potential for development of antibiotic-resistant bacteria if treatment course is not completed
May cause Clostridium difficile-associated diarrhea, which can occur during or after treatment
Use with caution in patients with history of gastrointestinal disease, particularly colitis
Not effective against viral infections and misuse can lead to adverse outcomes
Potential for hemolytic anemia in rare cases associated with cephalosporin use
Use in pregnancy and breastfeeding should only occur if clearly needed, weighing benefits versus risks
Overdose can lead to CNS disturbances including seizures
Do not administer with antacids or iron-containing supplements within two hours to avoid reduced absorption
Monitor renal function in patients with impaired kidney function
Suspension may lose potency if not stored properly or used beyond recommended time
Watch for signs of bleeding or easy bruising due to possible platelet dysfunction
Risk of false-positive Coombs test associated with cefdinir
Avoid use in patients with mononucleosis due to increased risk of rash

Contraindication

Known hypersensitivity to cefdinir
Allergy to other cephalosporins or beta-lactam antibiotics
History of severe allergic reactions to penicillin that contraindicate cephalosporin use
Patients with prior anaphylaxis to cefdinir or related compounds
Known intolerance or allergy to components of the oral suspension formulation
Severe renal failure without appropriate dose adjustment
Use in neonates not established and generally contraindicated
Patients with a history of antibiotic-associated colitis
Rarely, patients with glucose-6-phosphate dehydrogenase deficiency may have adverse reactions
Patients showing signs of viral infections where antibiotic treatment is unnecessary

Drug Interactions

Probenecid decreases renal excretion of cefdinir, leading to increased and prolonged serum concentrations
Oral iron supplements reduce cefdinir absorption and bioavailability if taken concurrently within two hours
Antacids containing aluminum or magnesium decrease cefdinir absorption if administered concomitantly
Multivitamins with minerals that contain iron may similarly affect cefdinir absorption
Concomitant use with nephrotoxic agents (e.g., aminoglycosides) requires monitoring for renal impairment
May interfere with certain laboratory glucose tests, causing false positive or false negative results
Concurrent use with live bacterial vaccines (e.g., typhoid) may reduce vaccine efficacy
Warfarin and other anticoagulants do not have a well-established interaction but monitoring is prudent due to potential disruption of gut flora
No significant interactions with cytochrome P450 enzymes due to minimal metabolism by liver enzymes
Concomitant use with other antibiotics may lead to antagonistic or synergistic effects depending on combination
Absorption can be affected by gastric pH modifying agents
Combination with oral contraceptives has not demonstrated reduced efficacy but caution is advised
Potential interactions with antidiabetic agents may require glucose monitoring
Herbal supplements are not documented to have significant interactions but prudence recommended
Interference with urine glucose testing reagents can lead to misinterpretation of diabetic control

Preparations Of The Drug

Omnicef 300 mg oral capsules
Omnicef oral suspension 125 mg/5 mL powder for reconstitution
Omnicef oral suspension 250 mg/5 mL powder for reconstitution
Generic cefdinir capsules and suspensions available as equivalents
Suspension includes sucrose as an excipient, requiring caution in diabetic patients
Dosing syringes or calibrated measuring devices provided with suspensions for accurate administration
Packaging includes detailed prescribing information and medication guides
Storage recommendations include room temperature in a dry place, away from excessive heat and moisture
Discard oral suspension 10 days after reconstitution to minimize degradation and microbial contamination
Capsule formulations may include gelatin and other non-active excipients, which should be considered in patients with allergies