Published: 2 June 2022


Drug-drug interaction: Levothyroxine and ciprofloxacin

Published 2 June 2022
Prescriber Update 43(2): 20
June 2022

Key messages

  • Case reports in the literature describe situations where concomitant use of levothyroxine and ciprofloxacin led to changes in thyroid function tests.
  • If concomitant use is indicated, an interval of six hours between the administration of these medicines is recommended.

The Centre for Adverse Reactions Monitoring (CARM) received a report (CARM ID: 139087) where a patient taking levothyroxine had symptoms of hypothyroidism after taking a course of ciprofloxacin. The reported symptoms were a low heart rate, extreme fatigue and feeling cold. The symptoms improved upon stopping ciprofloxacin and temporarily increasing the levothyroxine dose. The reporter suspected an interaction between these medicines.


Ciprofloxacin is a fluoroquinolone antibiotic indicated in adults for infections caused by ciprofloxacin-sensitive pathogens.1

Levothyroxine is indicated for the treatment of hypothyroidism.2

The interaction

There is limited evidence in the literature explaining this interaction.

A case report describes two patients on stable levothyroxine therapy who began concomitant ciprofloxacin. 3 Both patients subsequently experienced decreased free thyroxine and increased thyroid-stimulating hormone (TSH), which resolved upon stopping ciprofloxacin or separating administration by six hours.

A randomised cross-over study suggests that co-administration of ciprofloxacin reduces the intestinal absorption of levothyroxine.4

If concomitant use is indicated

Systemic ciprofloxacin may decrease the serum concentration of levothyroxine. Therefore, if patients taking levothyroxine require concomitant ciprofloxacin:

  • instruct them to separate administration by six hours
  • inform them about this potential interaction and the signs and symptoms to look out for (eg, fatigue, lethargy or feeling cold)
  • monitor them for any changes in thyroid function.

Data sheet update

The ciprofloxacin and levothyroxine data sheets are being updated to include information about this possible interaction.


  1. Viatris Ltd. 2022. Ciplox New Zealand data sheet 28 January 2022. URL: (accessed 5 April 2022).
  2. Pharmacy Retailing (NZ) Limited trading as Healthcare Logistics. 2019. Eltroxin New Zealand data sheet 23 May 2019. URL: (accessed 5 April 2022).
  3. Cooper JG, Harboe K, Frost SK, et al. 2005. Ciprofloxacin interacts with thyroid replacement therapy. BMJ 330(7498): 1002. DOI: 10.1136/bmj.330.7498.1002 (accessed 12 April 2022).
  4. Goldberg AS, Tirona RG, Asher LJ, et al. 2013. Ciprofloxacin and rifampin have opposite effects on levothyroxine absorption. Thyroid 23(11): 1374-8. DOI: 10.1089/thy.2013.0014 (accessed 12 April 2022).
Hide menus
Show menus
0 1 2 4 5 6 7 9 [ /