The effects of fasting in Muslim patients taking warfarin

Anticoagulation with warfarin is influenced by dietary changes but the effect of fasting on warfarin therapy is unknown.

To study changes in international normalized ratio (INR) and the percentage of time within therapeutic range (%TTR) before, during and after the Muslim fasting month (Ramadan) in stable warfarinised Muslim patients.

In this prospective study, weekly INR readings were taken at home visits from participating patients during three study periods: before, during and after Ramadan. Readings were blinded to patients and their primary physicians except for when pre-set study endpoints were reached.

Among 32 participating patients, mean INR increased by 0.23 (P = 0.006) during Ramadan from the pre-Ramadan month and decreased by 0.28 (P < 0.001) after Ramadan. There was no significant difference (P = 1.000) in mean INR between the non-Ramadan months. %TTR declined from 80.99% before Ramadan to 69.56% during Ramadan (P = 0.453). The first out-of-range INR was seen around 12.1 days (95% CI, 9.0-15.1) after the start of fasting and returned to range at about 10.8 days (95% CI, 7.9-13.7) after Ramadan. Time above range increased from 10.80% pre-Ramadan to 29.87% during Ramadan (P = 0.027), while time below range increased from 0.57% during Ramadan to 15.49% post-Ramadan (P = 0.006). No bleeding or thrombotic events were recorded.

Fasting significantly increases the mean INR of medically stable patients taking warfarin and the likelihood of having an INR above therapeutic targets. For patients maintained at the higher end of INR target ranges or at increased risk of bleeding, closer monitoring or dosage adjustment may be necessary during fasting.