Moderate
Probable
Description
Ciprofloxacin can reduce levothyroxine absorption through complex formation and potential effects on gut motility and transport, risking under-replacement in hypothyroid patients on long courses.
Mechanism
In vitro and case data suggest ciprofloxacin may form metal ion-mediated complexes with levothyroxine in the GI tract, impairing absorption. Ciprofloxacin may also alter CYP enzymes relevant to T4 deiodination.
Clinical Significance
Case reports document elevated TSH and symptom recurrence in hypothyroid patients during ciprofloxacin courses; the effect is more pronounced with simultaneous administration.
Management
Administer levothyroxine at least 4 hours apart from ciprofloxacin; monitor TSH if a prolonged ciprofloxacin course (>7 days) is required; dose adjustment may be needed.