Calcium, iron, magnesium and aluminium bind some drugs in the gut and cut their absorption. The well-established cases are levothyroxine, fluoroquinolones, tetracyclines and oral bisphosphonates. For these, spacing matters: levothyroxine is usually separated from calcium or iron by about four hours, and quinolones or tetracyclines taken at least two hours before the mineral. Antacids count, and so do many multivitamins.
- Separate levothyroxine from calcium or iron by about four hours.
- Give fluoroquinolones or tetracyclines at least two hours before calcium, iron or antacids.
- Take oral bisphosphonates alone, fasting, as labelled.
- Ask about antacids and multivitamins when reviewing these drugs.
Why it matters
Unrecognised chelation explains many cases of apparent treatment failure.
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