Interaction fact sheet
Antibiotics and minerals: calcium, magnesium, iron, zinc
Take separately: some antibiotics become ineffective when taken with minerals.
Tetracycline and fluoroquinolone antibiotics bind to calcium, magnesium, iron and zinc in the gut. When taken together, much less of the antibiotic is absorbed, and the infection may not be adequately treated.
In brief
- Mechanism
- Minerals with multiple electrical charges form a complex with the antibiotic that the gut cannot absorb: this is chelation.
- Magnitude
- Interaction found in 22–76% of patients taking a fluoroquinolone, depending on the study, with a sharp reduction in absorption.
- Who is affected
- People taking doxycycline, minocycline, ciprofloxacin, levofloxacin, ofloxacin or moxifloxacin.
- What to do
- Take the antibiotic at least 2 hours before or 4–6 hours after the minerals, according to the package leaflet.
The antibiotics concerned
Two classes are mainly affected. Tetracyclines, such as doxycycline, often prescribed for acne or certain infections, and fluoroquinolones, such as ciprofloxacin or levofloxacin. Amoxicillin and most other common antibiotics are not affected by this mechanism.
An interaction that's far from trivial
A review of fluoroquinolones estimates that this interaction affects 22–76% of treated patients, depending on the study. Magnesium- and aluminum-containing antacids have the strongest effect, but iron, zinc and calcium supplements are also involved. A 2019 review notes that this can lead to treatment failure.
For tetracyclines, the interaction with iron has been described since the 1970s: even when taken a few hours apart, iron still reduces their absorption.
In practice
What you can do
- While taking a tetracycline or fluoroquinolone, pause your mineral supplements if possible.
- Otherwise, take the antibiotic at least 2 hours before or 4–6 hours after, according to the package leaflet.
- Remember multivitamins, stomach-coating medicines and antacids: they often contain these minerals.
When to seek advice
- An infection that is not improving after 48–72 hours of treatment.
- Prescribed iron or calcium that you cannot stop: ask your pharmacist how to schedule your doses.
Main sources
- 01Lomaestro BM, Bailie GR. Absorption interactions with fluoroquinolones. 1995 update. Drug Safety, 1995. PubMed
- 02Pitman SK et al. Revisiting oral fluoroquinolone and multivalent cation drug-drug interactions: are they still relevant? Antibiotics, 2019. PubMed
- 03Neuvonen PJ. Interactions with the absorption of tetracyclines. Drugs, 1976. PubMed
Frequently Asked Questions (FAQ)
Can you take magnesium with an antibiotic?
With a tetracycline or fluoroquinolone, not at the same time. The simplest option is to pause magnesium during treatment. This interaction does not occur with amoxicillin.
Does milk interfere with doxycycline?
Calcium in milk reduces tetracycline absorption, slightly less for doxycycline than for older tetracyclines. Avoid taking the tablet with milk.
How many hours between iron and ciprofloxacin?
Take ciprofloxacin at least 2 hours before or 6 hours after iron. Your pharmacist can help you plan the timing.