SeriousTiming Sensitive
Iron
Iron can reduce oral Cefdinir absorption when taken together.
Recommendation: Take cefdinir at least 2 hours before or after iron supplements; iron-fortified infant formula is handled separately by pediatric labeling.
Cefdinir
Prescription ·Strong evidence ·Reviewed May 2026
Cefdinir is a third-generation oral cephalosporin antibiotic used to treat mild to moderate bacterial infections including acute bacterial sinusitis, acute otitis media, pharyngitis/tonsillitis, community-acquired pneumonia, acute exacerbations of chronic bronchitis, and uncomplicated skin infections. It provides broad activity against many gram-positive and gram-negative organisms by interfering with bacterial cell wall synthesis. A clinically important feature is that iron-containing products and many antacids markedly reduce its absorption.
What it's good for
The bottom line
Evidence rating strong. Most-documented uses: acute bacterial sinusitis (maxillary sinusitis), acute otitis media (middle ear infection), acute exacerbation of chronic bronchitis. 3 sources indexed (2004–2019), with 5 interaction records on file.
The science
How it works, mechanistically.
Core mechanism
Cefdinir is a beta-lactam antibiotic that exerts its bactericidal effect by binding to penicillin-binding proteins (PBPs) located in the bacterial cell wall. By inhibiting these enzymes, it blocks the final transpeptidation step of peptidoglycan cross-linking, weakening the cell wall and leading to osmotic lysis and bacterial death. As a third-generation cephalosporin it is relatively stable against many bacterial beta-lactamases, giving it expanded gram-negative coverage compared with earlier-generation agents while retaining useful activity against common gram-positive pathogens such as streptococci and methicillin-susceptible staphylococci.1,2
Class
Cephalosporin antibiotic
Dosing
Dosing & protocol.
Common range
Adults and adolescents: 300 mg orally every 12 hours, or 600 mg once daily, for 5 to 10 days depending on the infection. Pediatric (6 months to 12 years): 7 mg/kg every 12 hours or 14 mg/kg once daily (max 600 mg/day). Dose reduction is required in significant renal impairment (creatinine clearance below 30 mL/min).
Recommended form
Oral capsule (300 mg) or oral powder for suspension; may be taken with or without food.
Cefdinir may be taken with or without food. However, iron supplements, iron-fortified foods or formula, and aluminum- or magnesium-containing antacids substantially reduce absorption by forming insoluble complexes; separate cefdinir from these products by at least 2 hours. Co-administration with iron can also turn the stool reddish.2
Depletions
What it depletes.
Nutrients this medication can lower over time, and what to replace.
Vitamin K
MildLike other broad-spectrum cephalosporins, cefdinir suppresses gut bacteria that synthesize menaquinone (vitamin K2). Reduced bacterial vitamin K production can lower vitamin K status, an effect most relevant during prolonged courses or in patients with poor dietary intake. (Cefdinir lacks the N-methylthiotetrazole side chain associated with the strongest cephalosporin-induced hypoprothrombinemia, so the risk is lower than with agents such as cefoperazone or cefamandole.)
Replace Vitamin K2 (menaquinone)Monitor Prothrombin time / INR (especially in patients on warfarin or with poor intake)Onset Days to weeks of therapy, mainly with prolonged courses or in patients with low dietary vitamin K intake or other risk factors
Iron
ModerateCefdinir is not depleted by iron, but the two form a clinically important interaction: cefdinir chelates ferrous iron in the gut to produce a non-absorbable insoluble complex. Concurrent iron supplements or iron-fortified foods markedly reduce cefdinir absorption (and the complex can cause reddish stools), while the binding can also reduce the amount of supplemental iron available for absorption. Separating doses preserves both. This is included as a clinically significant nutrient-drug interaction rather than a true depletion of body iron stores.
Monitor Not routinely monitored; separate dosing rather than supplementOnset Acute, occurs with any co-administered dose; manage by separating cefdinir and iron by at least 2 hours
Safety
Full safety detail.
Side effects
- Diarrhea
- Nausea
- Abdominal pain
- Vaginal candidiasis (yeast infection)
- Headache
- Rash
- Reddish stool when taken with iron-containing products
- Clostridioides difficile-associated diarrhea (uncommon but serious)
Contraindications
- Known hypersensitivity to cefdinir or other cephalosporins1,2
- History of severe (anaphylactic) reaction to penicillins or other beta-lactams (use caution due to cross-reactivity)
- Caution in patients with significant renal impairment (dose adjustment required)2
- Caution in patients with a history of colitis or gastrointestinal disease
Interactions
Interaction records.
SeriousTiming Sensitive
Magnesium Glycinate
Magnesium Glycinate can reduce oral Cefdinir absorption when taken together.
Recommendation: Separate cefdinir from magnesium-containing antacids or high-dose mineral products by at least 2 hours.
ModerateTiming Sensitive
Probiotics
Cefdinir can suppress or kill bacterial probiotic organisms if taken at the same time, although selected probiotics may lower antibiotic-associated diarrhea risk.
Recommendation: Separate probiotic doses from the antibiotic by at least 2 hours when feasible; avoid probiotic use in severely immunocompromised patients or patients with central lines unless clinician-directed.
ModerateTiming Sensitive
Calcium
High-dose calcium supplements and calcium-containing antacids can bind cefdinir in the gut and modestly reduce its absorption through divalent-cation chelation, similar in principle to the well-documented iron interaction. While the effect is generally smaller than with iron, large concurrent calcium doses may lower antibiotic exposure.
Recommendation: Separate calcium supplements or calcium-based antacids from cefdinir by at least 2 hours. Take cefdinir on a consistent schedule and avoid combining each dose with large calcium loads.
ModerateTiming Sensitive
Zinc
Zinc supplements supply divalent zinc cations that can chelate cefdinir in the gastrointestinal tract by the same mechanism that drives the iron and magnesium interactions, potentially reducing antibiotic absorption when taken together.
Recommendation: Separate zinc supplements from cefdinir by at least 2 hours to avoid diminished antibiotic absorption.
Sources
Sources, by evidence tier.
Numbered references. Citations throughout the page link here.
Reviews & position papers
1- 1Cefdinir: a review of its use in the management of mild-to-moderate bacterial infectionsNeeds reviewNo linkPerry CM, Scott LJ · Drugs · 2004
Cefdinir achieved high clinical cure rates in sinusitis, otitis media, pharyngitis, bronchitis, and skin infections with a tolerability profile typical of cephalosporins.
Reference material
2- 2Omnicef (cefdinir) capsules and oral suspension - US prescribing informationNeeds reviewNo linkAbbVie / Abbott Laboratories · FDA Prescribing Information · 2019
Approved for acute sinusitis, otitis media, pharyngitis/tonsillitis, community-acquired pneumonia, acute exacerbation of chronic bronchitis, and uncomplicated skin infections; renal dose adjustment needed below CrCl 30 mL/min.
- 3Effect of iron and antacids on cefdinir oral bioavailabilityNeeds reviewNo linkManufacturer pharmacokinetic data · FDA Prescribing Information (Drug Interactions) · 2019
Iron supplements reduced cefdinir absorption by about 80% and aluminum/magnesium antacids by about 40%; dosing separation of 2 hours is recommended.
Keep exploring
Deep dives & adjacent profiles.
This page is educational. Do not start, stop, or change a supplement or medication based on it without checking with a qualified healthcare professional.
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