THOUSANDS OF Irish patients taking the anti-clotting drug warfarin may be at risk of complications if they receive an alternative brand of the drug, the State’s drug safety watchdog has said.
The warning to doctors to monitor closely clotting times in patients moving from their usual brand of warfarin to a different product is based on reports to the Irish Medicines Board.
These cite “clinically significant changes in INR [a measure of clotting used by doctors to calculate the correct dose] potentially associated with switches in warfarin brands”.
There are two brands of warfarin licensed and marketed in the Republic – Warfant and Warfarin Teva. The manufacturers of Warfarin Teva recently wrote to doctors highlighting the need for blood tests to be monitored when switching brands of warfarin.
An oral anticoagulant, warfarin is prescribed to prevent conditions such as deep vein thrombosis and pulmonary embolism, a potentially fatal disease in which blood clots travel to the lungs. It is also used to treat these clotting diseases.
An increasing number of people are prescribed warfarin when they develop the common heart rhythm disturbance atrial fibrillation. This irregular heartbeat promotes the accumulation of clots which may travel to the brain causing strokes and transient ischaemic attacks (mini-strokes). People who have had an artificial heart valve inserted are also given the anticoagulant drug.
In a reversal of the normal advice to doctors to prescribe generic drugs where possible for cost-benefit reasons, this week’s drug safety newsletter advises prescribers that “warfarin products should be prescribed and dispensed by brand name. It is important that patient records (including dispensing records) reflect the product dispensed with details of the brand name. The brand name should also be recorded in the patient’s warfarin book”.
Because the drug has a narrow “therapeutic window”, levels of warfarin in the blood must be kept within a narrow range.