[Concomitant use of warfarin, analgesics and anti-inflammatory agents].

BACKGROUND

Concomitant use of warfarin and analgesics enhances the risk of bleeding. The frequency of such co-medication has not yet been investigated. The main aim of the present study was to determine the prevalence of concomitant use of warfarin and prescription analgesic drugs in Norway.

MATERIAL AND METHODS

All patients were included who were registered in the Norwegian Prescription Database as having received warfarin (Marevan) at Norwegian pharmacies from 2004 to 2006. Data were retrieved on prescription of warfarin and common analgesic drugs (paracetamol, weak opioids and NSAIDs). "Concomitant medication" was defined as the concurrent use of warfarin and analgesic drugs as prescribed by one or more different physicians at the same or different date, but within the time period for warfarin use.

RESULTS

The number of warfarin users was approximately 80,000 in 2006 (60 % men), 93 % were older than 50 years and the majority were on long-term treatment. 25 % of warfarin patients used weak opioids in each of the following years: 2004, 2005 and 2006, while 16 - 23 % were on NSAIDs and 29 - 31 % on paracetamol.

INTERPRETATION

A higher number of Norwegians is treated with warfarin than previously presumed. Concomitant use of common analgesics was likely for at least one fourth of the warfarin users. As the investigated analgesics may interact with and increase the effect of warfarin (through different mechanisms), the frequent co-prescribing of these drugs may be associated with an increased risk of bleeding.