The short answer
Iron supplements can substantially lower oral cefdinir absorption. The current label recommends at least 2 hours between cefdinir and iron, in either direction. This is a practical minimum from product guidance, not proof that every iron preparation has no residual effect; an older study found reduced later exposure even when iron followed cefdinir by three hours.
What this answer covers
Oral cefdinir capsules and oral iron supplements. Infant formula with cefdinir suspension is considered separately; its findings do not clear therapeutic iron doses.
- Supplement or preparation
- Iron
- Medication ingredient
- cefdinir
How much can iron change absorption?
The label reports about 80% less absorption with ferrous sulfate providing 60 mg elemental iron and about 31% less with an iron-containing multivitamin providing 10 mg. The FDA review describes the underlying small crossover studies. These results show why the dose and preparation matter; they are not universal percentages for every iron salt or a prediction of an individual infection outcome.
Does a two-hour gap eliminate every effect?
Current labeling advises at least 2 hours before or after iron. The FDA interval study found smaller, statistically nonsignificant residual changes with that schedule. A separate older study still found reduced later cefdinir exposure when two iron tablets were given three hours afterward. Its abstract incompletely describes the iron preparation, so ask the pharmacist about your exact product rather than assuming any gap guarantees zero interaction.
What about iron-fortified infant formula?
Formula is an important exception to a blanket iron warning. A small infant study with cefdinir suspension found no significant change in overall exposure, although the peak was modestly lower; the FDA considered the effect clinically minimal. This does not establish the same result for iron drops, supplements or highly fortified cereals. Feeding advice should reflect the actual product and child.
Why can stool look red?
Cefdinir or its breakdown products can form a colored, poorly absorbed complex with iron in the intestine. The label describes reddish stool during co-use. Do not assume every red or bloody-looking stool is this harmless color change: seek clinical advice for watery or bloody diarrhea, pain or fever, especially during or after antibiotic treatment.
Evidence and practical considerations
Absorption & effectiveness
Iron supplements can substantially lower oral cefdinir absorption. The current label recommends at least 2 hours between cefdinir and iron, in either direction. This is a practical minimum from product guidance, not proof that every iron preparation has no residual effect; an older study found reduced later exposure even when iron followed cefdinir by three hours.
- Exact scope
- oral iron supplements including ferrous sulfate and iron-containing multivitamins; formula exposure remains separate with oral cefdinir capsules; infant suspension explicitly separated
- Medication form and route
- oral
- Timing or duration
- Single-dose human studies and current label guidance during oral co-use. Different iron preparations and intervals showed different residual effects.
What remains uncertain
- Small studies and heterogeneous iron exposures, with incomplete preparation detail in the older abstract. Two-hour spacing reduces risk but does not establish zero interaction for all products.
Factors that may matter: exact formulation and dose; order and interval of doses; single versus repeated administration; patient population and product ingredients.
Read the supporting source summaries
Source 1: regulatory product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Patients receiving oral cefdinir; capsule antacid studies distinguished from infant suspension data.
Mixed antacid lowers peak and overall exposure about 40%. Ferrous sulfate and iron multivitamins reduce absorption by 80% and 31%. Advises at least two hours before or after relevant antacids or iron. Iron-fortified infant formula has no significant effect; red stool can reflect an unabsorbed iron complex.
How this applies: Exact cefdinir parent RxCUI 25037 in oral capsule form. Suspension/infant results are explicitly separated; other cephalosporins are not substituted. Article-specific counterparty: oral iron supplements including ferrous sulfate and iron-containing multivitamins; formula exposure remains separate.
Does not provide exact effects for every magnesium or iron salt. Label summary and FDA review derive from overlapping trials, not independent evidence. No quantified infection failure.
Source 2: original regulatory clinical-study review
accessdata.fda.gov · Source check Sep 10, 2026
Population: 15 men aged 19-48 in iron/multivitamin crossover study; 11 men and women aged 25-52 in interval study.
Cefdinir exposure measures decreased about 79-83% with ferrous sulfate and 30-38% with multivitamin. Two-hour separation left smaller, statistically nonsignificant changes of roughly 14-30%; reviewer accepted at least two hours spacing.
How this applies: Direct oral cefdinir and specific iron products; interval evidence retained without presenting it as perfect protection for every formulation. Article-specific counterparty: oral iron supplements including ferrous sulfate and iron-containing multivitamins; formula exposure remains separate.
Small single-dose sponsor studies; lack of statistical significance is not exact bioequivalence or a guarantee for every preparation. Shares trial basis with current label.
Source 3: original regulatory clinical-study review
accessdata.fda.gov · Source check Sep 10, 2026
Population: 15 healthy infants aged 6-12 months in a two-way crossover study.
Overall exposure was not significantly changed; peak was about 20% lower with fortified formula, with borderline statistical significance. Reviewer considered effect clinically minimal.
How this applies: Direct low-level formula-iron context, explicitly route/formulation/population bounded; does not clear therapeutic iron supplementation. Article-specific counterparty: oral iron supplements including ferrous sulfate and iron-containing multivitamins; formula exposure remains separate.
Specific infant formula and suspension, not supplemental iron tablets or highly fortified cereal. The approximate iron amount in the historical scan differs from current label summary; no numeric formula-iron amount is used.
Source 4: original human pharmacokinetic study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: Healthy male volunteers in randomized three-way crossover; exact sample size not in inspected abstract.
Concurrent iron lowered AUC0-12 from 10.3 to 0.78 microgram-hour/mL. Iron three hours after cefdinir still lowered the later AUC3-12 from 8.03 to 4.60, although early exposure was unchanged.
How this applies: Exact cefdinir human study. Retains residual interaction at three hours as a limit on interpreting universal timing claims. Article-specific counterparty: oral iron supplements including ferrous sulfate and iron-containing multivitamins; formula exposure remains separate.
Abstract-only access does not establish exact iron formulation; no claim based solely on secondary summaries. Different antibiotic dose and incompletely characterized iron preparation; no clinical cure outcome.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Exact-drug labels, original clinical research and formulation limits checked; complete private article and current-claim adjudications prepared. | |
| Research summary published |
Article revision: abebf8c5252c327e
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
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Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.