Dangerous Drug Interaction: Warfarin-Macrolides

Impact: Potential for increased effects of warfarin¹

Mechanism of Interaction: Erythromycin inhibits the metabolism and subsequent clearance of warfarin from the body. The activity of warfarin may also be prolonged due to alterations in the intestinal flora and its production of vitamin K for clotting factor production.

Alternatives to Patient Management: The interaction between warfarin and macrolide antibiotics is highly probable and often delayed. Concomitant use of a macrolide with warfarin should be avoided; switch to an alternative antibiotic. Microbial pathogen identification prior to antibiotic initiation will decrease the prevalence of unnecessary drug interaction risk. Consider culture sensitivity screening as research indicates cautious use of any antibiotic with warfarin.

Monitoring/Precautions: If use of a macrolide is imperative, then monitor INR every other day and adjust warfarin dosing as necessary.² Signs and symptoms of an active bleed should be monitored daily with particular attention to the appearance and patterns of bruises. Signs of an active bleed include: coughing up blood in the form of coffee grinds (hemoptysis), gingival bleeding, nose bleeds, cola- or tea-colored urine (hematuria), and black, tarry stools (hemoccult positive?).

References: Follow this link for a complete list of references.

The above information serves only as a guide for use by qualified medical practitioners in understanding, handling and avoiding frequent and potentially dangerous drug interactions that occur in long-term care. This presentation is not intended to instruct a practitioner how to treat any medical condition, nor is it intended to replace a practitioner's best clinical judgment. AMDA expressly disclaims responsibility and liability for any adverse effects, damages or other consequences resulting from the use of any of the information contained in this presentation.