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 1 citation row for the Calcium + Fosfomycin pair, each linking to PubMed by PMID where available. Full sourcing methodology at https://nutristackapp.com/methodology/interactions.

Supplement × Prescription·timing-sensitive·Moderate evidence

Calcium + Fosfomycin

Q: Can I take Calcium and Fosfomycin together?

Yes, if you separate them in time. Calcium and Fosfomycin have a documented timing-sensitive interaction. Oral fosfomycin tromethamine is a single-dose therapy whose efficacy depends on achieving adequate urinary concentrations. Calcium is a divalent cation that can bind fosfomycin in the gut and reduce its oral absorption, lowering the urinary levels needed to clear an uncomplicated urinary tract infection.

Q: How does this affect a NutriStack Stack Score?

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

Timing Sensitive Moderate evidence

Oral fosfomycin tromethamine is a single-dose therapy whose efficacy depends on achieving adequate urinary concentrations. Calcium is a divalent cation that can bind fosfomycin in the gut and reduce its oral absorption, lowering the urinary levels needed to clear an uncomplicated urinary tract infection.

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 Fosfomycin

Pair type

Timing Sensitive

Evidence

Moderate

Source citations

Scope

Supplement × Prescription

Last verified

June 4, 2026

Timing SensitiveModerate evidence

What is happening. Oral fosfomycin tromethamine is a single-dose therapy whose efficacy depends on achieving adequate urinary concentrations. Calcium is a divalent cation that can bind fosfomycin in the gut and reduce its oral absorption, lowering the urinary levels needed to clear an uncomplicated urinary tract infection.

Mechanism. Divalent cation (calcium) chelation of fosfomycin in the gastrointestinal tract forms a poorly absorbed complex, decreasing oral bioavailability and the resulting urinary antibiotic concentration.

Recommendation. Take the single fosfomycin dose on its own and avoid calcium supplements (or calcium-rich antacids and large dairy doses) for several hours around it. Because fosfomycin is usually a one-time dose, simply skip the calcium supplement on the day of treatment or separate it from the antibiotic.

Stack Score

How it moves the number.

Effect on the composite score

If both Calcium and Fosfomycin 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

1Patel SS, Balfour JA, Bryson HM. Fosfomycin tromethamine. A review of its antibacterial activity, pharmacokinetic properties and therapeutic efficacy as a single-dose oral treatment for acute uncomplicated lower urinary tract infections. Drugs. 1997.Needs sourceNo link

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