The short answer
Calcium does not consistently reduce overall levofloxacin absorption in healthy adults, but the preparation and patient matter. A small cystic-fibrosis study found lower antibiotic peaks even with a 2-hour gap. Ask your pharmacist for a tailored schedule instead of treating calcium exactly like iron or aluminum antacids.
What this answer covers
Oral levofloxacin with calcium carbonate; cystic-fibrosis findings are a distinct subgroup. Calcium-fortified juice is discussed as an indirect food comparison, not as a pure calcium supplement.
- Supplement or preparation
- Calcium
- Medication ingredient
- levofloxacin
What happens in healthy volunteers?
An early study found no change in overall levofloxacin bioavailability with calcium carbonate 1 g, while iron, aluminum and magnesium in separate arms did reduce it. The current UK tablet label also describes calcium salts as having only a minimal effect. This is why a general warning for every fluoroquinolone and every mineral is too broad.
Why does cystic fibrosis change the answer?
A later crossover study compared five adults with cystic fibrosis and five matched healthy volunteers. Levofloxacin 750 mg daily was studied with calcium carbonate three times daily, separated by two hours. Healthy volunteers had no significant interaction, but the cystic-fibrosis group had a 19% lower peak and a later peak. The two-hour gap did not prevent that subgroup effect.
What about calcium-fortified orange juice?
In 16 healthy volunteers, both ordinary and calcium-fortified orange juice lowered or delayed the peak without changing overall levofloxacin exposure. Because ordinary juice also had an effect, the authors considered juice components rather than calcium chelation alone. That study cannot establish how a calcium-only capsule behaves, or prove that the same timing rule fits all fortified drinks.
What is a sensible schedule for my situation?
Have your pharmacist consider the exact calcium product, your levofloxacin formulation, and any condition affecting digestion or absorption. For cystic fibrosis, the study authors favored maximizing separation rather than assuming two hours was enough; they did not establish one new precise interval. Do not interpret the healthy-volunteer results as proof that every calcium regimen is harmless or the subgroup result as a reason to abandon needed calcium treatment.
Evidence and practical considerations
Absorption & effectiveness
Calcium does not consistently reduce overall levofloxacin absorption in healthy adults, but the preparation and patient matter. A small cystic-fibrosis study found lower antibiotic peaks even with a 2-hour gap. Ask your pharmacist for a tailored schedule instead of treating calcium exactly like iron or aluminum antacids.
- Exact scope
- oral calcium carbonate, with a separate cystic-fibrosis subgroup and indirect juice evidence with oral levofloxacin hemihydrate tablets with strengths expressed as levofloxacin
- Medication form and route
- oral
- Timing or duration
- Single-dose studies in healthy volunteers and five-day steady-state treatment in the cystic-fibrosis study.
What remains uncertain
- Small and clinically different study populations. Overall exposure, peak concentration and infection outcomes are different endpoints. No universal safe calcium spacing interval established.
Factors that may matter: cystic fibrosis; intestinal transit and absorption; calcium form and dose; calcium in food versus supplements; other minerals in combined products.
Read the supporting source summaries
Source 1: regulatory product label
medicines.org.uk · Source check Sep 10, 2026
Population: Adults using this oral levofloxacin hemihydrate tablet.
Recommends at least 2 hours before or after iron, zinc and magnesium/aluminum antacids. Describes calcium salts as having a minimal effect on oral absorption.
How this applies: Explicit active-moiety strength supports the parent ingredient with oral hemihydrate restrictions. The calcium statement provides important contrast to a blanket class warning. Article-specific counterparty: oral calcium carbonate, with a separate cystic-fibrosis subgroup and indirect juice evidence.
Product guidance; it does not prove absence of a calcium interaction in every clinical subgroup or quantify a zinc-only effect. Shares the same broad evidence base as other labels and is not an independent trial.
Source 2: human pharmacokinetic study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: Healthy male volunteers in three randomized crossover studies; subgroup sizes were not given in the inspected abstract.
Relative antibiotic bioavailability was 56% with aluminum hydroxide, 78% with magnesium oxide, and 81% with ferrous sulfate. Calcium carbonate did not influence bioavailability under the tested regimen.
How this applies: DR-3355 is defined in the original abstract by the same pure (-)-(S) enantiomer hemihydrate chemical structure specified in current levofloxacin labeling, not racemic ofloxacin. Direct for the named salts with that oral preparation. Article-specific counterparty: oral calcium carbonate, with a separate cystic-fibrosis subgroup and indirect juice evidence.
Small early pharmacokinetic studies used a 100 mg dose rather than current usual tablet strengths. No infection outcomes. Results differ by mineral and cannot be treated as one class effect. Full clinical paper was not assessed; inspected source is the original author abstract.
Source 3: human pharmacokinetic study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: Five adults with cystic fibrosis and five matched healthy volunteers in an open-label randomized crossover study.
In cystic fibrosis, peak concentration decreased 19% and time to peak increased 37%; peak bioequivalence was not met. No significant interaction was found in the matched healthy volunteers.
How this applies: Direct, patient-specific evidence for calcium carbonate and oral levofloxacin. It qualifies a universal two-hour rule and should not be generalized to all calcium users. Article-specific counterparty: oral calcium carbonate, with a separate cystic-fibrosis subgroup and indirect juice evidence.
Only five people per group. A peak concentration change is not a measured treatment-failure rate; full paper was unavailable to verify all timing and total-exposure details. Full clinical paper was not assessed; inspected source is the original author abstract.
Source 4: human pharmacokinetic study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: Sixteen healthy volunteers in a single-dose crossover comparison.
Both juices lowered peak concentration by 14-18% and delayed the peak, without changing overall antibiotic exposure. Authors considered a juice-component transport effect rather than simple calcium chelation.
How this applies: Indirect food context for the calcium article. The findings prevent attributing every juice effect to calcium alone. Article-specific counterparty: oral calcium carbonate, with a separate cystic-fibrosis subgroup and indirect juice evidence.
Fortified and unfortified juice are mixed exposures; cannot isolate calcium or establish an effect for calcium tablets. Clinical outcomes were not tested. Full clinical paper was not assessed; inspected source is the original author abstract.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Original product guidance and clinical studies checked; complete private article drafted with exact preparation limits and claim dispositions. | |
| Research summary published |
Article revision: 5fbec2335f85d023
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?
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Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.