What kind of interaction is it?

Timing-sensitive: the two substances can be taken on the same day but should be separated by a minimum time window.

Is this interaction backed by published research?

Yes. NutriStack lists 2 citation rows for the Calcium + Cefdinir pair, each linking to PubMed by PMID where available. Full sourcing methodology at https://nutristackapp.com/methodology/interactions.

Supplement × Prescription·timing-sensitive·Emerging evidence

Calcium + Cefdinir

Q: Can I take Calcium and Cefdinir together?

Yes, if you separate them in time. Calcium and Cefdinir have a documented timing-sensitive interaction. 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.

Q: How does this affect a NutriStack Stack Score?

-5 to your Stack Score per scored timing-sensitive row.

Timing Sensitive Emerging evidence

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.

Supplement × Prescription

Open the interaction checker → Read the methodology

From the database

What the row says.

Every entry follows the same shape: what is happening, the mechanism, and the recommendation.

Substances

Calcium and Cefdinir

Pair type

Timing Sensitive

Evidence

Emerging

Source citations

Scope

Supplement × Prescription

Last verified

June 4, 2026

Timing SensitiveEmerging evidence

What is happening. 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.

Mechanism. Divalent calcium cations can complex with the cephalosporin in the gastrointestinal tract, reducing the fraction of drug available for absorption.

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.

Timing

Timing & separation.

Space the doses apart by at least this window to avoid the conflict.

Minimum separation

120

Stack Score

How it moves the number.

Effect on the composite score

If both Calcium and Cefdinir are in the same stack, this pair applies −5 to your Stack Score (per scored timing-sensitive row).

The full algorithm, the clamping rules, and four worked stacks are at /methodology/stack-score.

Sources

Sources, by evidence tier.

Every claim on this page is cited. PMIDs link straight to PubMed.

Reference material

1Cefdinir prescribing information. Pharmacokinetics and drug interactions with antacids and metal cations.Needs sourceNo link
2Lomaestro BM, Bailie GR. Absorption interactions with fluoroquinolones and other antibiotics: divalent and trivalent cation chelation. Drug Safety. 1995.Needs sourceNo link

Check your full routine

One pair was the worked example.

Drop your supplements and prescriptions into NutriStack and it runs every pair at once: every interaction, synergy, timing rule, and contraindication, each linked to its primary source.

Open the interaction checker → Browse the research index