Enhanced Hypoprothrombinemia with Warfarin Due to Azithromycin

OBJECTIVE: To report a case of probable azithromycin—warfarin drug interaction with enhanced hypoprothrombinemic effect of warfarin. CASE SUMMARY: An 83-year-old African American man stabilized on warfarin therapy (10 mg on Wednesdays, 7.5 mg on other days) developed a prolonged prothrombin time one...

Full description

Saved in:
Bibliographic Details
Published in:The Annals of pharmacotherapy 2004-06, Vol.38 (6), p.982-985
Main Authors: Rao, Krishnamoorthy B, Pallaki, Muralidhar, Tolbert, Sandra R, Hornick, Thomas R
Format: Article
Language:English
Subjects:
Aged
Aged, 80 and over
Anti-Bacterial Agents - adverse effects
Anticoagulants - adverse effects
Azithromycin - adverse effects
Drug Interactions
Humans
Hypoprothrombinemias - chemically induced
Male
Warfarin - adverse effects
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:OBJECTIVE: To report a case of probable azithromycin—warfarin drug interaction with enhanced hypoprothrombinemic effect of warfarin. CASE SUMMARY: An 83-year-old African American man stabilized on warfarin therapy (10 mg on Wednesdays, 7.5 mg on other days) developed a prolonged prothrombin time one day after starting azithromycin 500 mg. The elevated prothrombin time normalized 3 days after azithromycin was discontinued. After the initial increase in the international normalized ratio, the absence of any significant confounding factors affecting the anticoagulant effect of warfarin in our patient and the numerous reports of such interactions indicate that an interaction between azithromycin and warfarin may have been responsible for the elevated prothrombin time seen in this patient. An objective causality assessment revealed that the adverse event was probably related to the combination of these drugs. DISCUSSION: Azithromycin, unlike erythromycin and clarithromycin, is not known to inhibit the cytochrome P450 enzyme system and is presumed to be the macrolide of choice in patients already on warfarin. However, previously reported cases of azithromycin—warfarin interactions support the possibility that azithromycin does interact with warfarin, although the exact mechanism is not understood. CONCLUSIONS: Azithromycin may interact with warfarin and enhance its hypoprothrombinemic effects. This effect may be delayed for 4–8 days after a course of azithromycin has been completed. Periodic monitoring of the prothrombin time is recommended when using azithromycin in patients taking warfarin.
ISSN:1060-0280
1542-6270
DOI:10.1345/aph.1D489