The short answer
Magnesium-containing antacids can reduce absorption of oral cefdinir. Current capsule directions advise at least 2 hours before or after the antacid. The direct evidence used a combined aluminum/magnesium product, so its measured effect should not be attributed to magnesium alone.
What this answer covers
Oral cefdinir capsules with magnesium-containing antacids. Combined Maalox TC is the directly studied exposure; unrelated routes and untested nutritional forms are not assumed equivalent.
- Supplement or preparation
- Magnesium
- Medication ingredient
- cefdinir
What did the clinical study show?
The original FDA review describes a four-way crossover study in 16 adults. Cefdinir 300 mg given with 30 mL of the combined antacid produced about 38% lower peak concentration and 44% lower overall exposure. Giving the products two hours apart caused much smaller changes. These were measurements of antibiotic reaching the blood, not a count of treatment failures.
How should I arrange the doses?
Follow the current cefdinir capsule instruction: leave at least 2 hours between the antibiotic and the relevant antacid, whether the antacid comes first or second. If the stomach medicine is taken repeatedly, ask for a schedule that preserves prescribed antibiotic doses. A different antibiotic may have different intervals, so the name on the prescription matters.
How closely does the evidence match my product?
The tested product was a magnesium/aluminum antacid. Magnesium glycinate, citrate and other nutritional formulations were not isolated in that experiment. Their exact salt and elemental amount should stay visible when a pharmacist reviews the schedule; they should not automatically receive the antacid’s measured percentage effect.
What if I already took them together?
Keep the exact antacid, amount and dose times available when asking the pharmacist for advice. The study does not supply a formula for taking extra cefdinir to compensate for reduced absorption. The practical aim is to correct the future schedule while preserving the prescribed treatment, rather than assuming a laboratory percentage determines your next antibiotic dose.
Evidence and practical considerations
Absorption & effectiveness
Magnesium-containing antacids can reduce absorption of oral cefdinir. Current capsule directions advise at least 2 hours before or after the antacid. The direct evidence used a combined aluminum/magnesium product, so its measured effect should not be attributed to magnesium alone.
- Exact scope
- magnesium-containing oral antacids, directly tested in a mixed aluminum/magnesium product with oral cefdinir capsules; infant suspension explicitly separated
- Medication form and route
- oral
- Timing or duration
- Single-dose crossover experiment; spacing precaution applies to each day of overlapping oral treatment.
What remains uncertain
- Sixteen adults, one combined antacid and a single antibiotic dose; no isolated mineral effect or quantified infection outcome.
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: magnesium-containing oral antacids, directly tested in a mixed aluminum/magnesium product.
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: 16 adult men and women aged 23-62 years in a four-way crossover study.
Concurrent antacid reduced cefdinir peak by 38% and total exposure by 44.4%; separated treatments showed smaller changes. Reviewer accepted the two-hour interval recommendation.
How this applies: Exact cefdinir capsule study with tested combined antacid. Does not directly test magnesium glycinate or nutritional aluminum exposure. Article-specific counterparty: magnesium-containing oral antacids, directly tested in a mixed aluminum/magnesium product.
Combined aluminum/magnesium antacid prevents isolating either component. Sponsor study reviewed by FDA, not an independent published trial; measured drug exposure rather than clinical cure. The review Tmax wording conflicts with label and is not used.
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: 24828dddf3c3a093
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.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.