Effect of levofloxacin coadministration on the international normalized ratios during warfarin therapy.
OBJECTIVE
To evaluate the effect of levofloxacin coadministration on the international normalized ratio (INR) in patients receiving warfarin therapy.


METHODS
Prospective analysis.


METHODS
Outpatient clinic at a Veterans Affairs medical center.


METHODS
Eighteen adult patients receiving warfarin.


METHODS
On the basis of clinical diagnosis and judgment, levofloxacin was prescribed to the 18 patients for treatment of various types of infection. The INR was measured before and at 2-8-day intervals after the coadministration of levofloxacin therapy, and once after completing therapy. Warfarin dosages were adjusted when necessary.


RESULTS
Warfarin dosages were changed in seven patients as a result of the first nontherapeutic INR values obtained after start of levofloxacin therapy. Owing to a concern regarding noncompliance and the adverse effect of bleeding, warfarin dosage was adjusted in one patient even though his first INR value was in the high end of the therapeutic range (2.98, therapeutic range 2-3). One patient withdrew from the study after the first INR measurement after levofloxacin coadministration. Because of a concern about the possible bleeding complication, warfarin dosage was also adjusted in this patient after obtaining his first INR value. Therefore, only the INR values obtained before and the first INR values obtained after levofloxacin administration were compared to evaluate the effect of levofloxacin on INR determination of warfarin therapy. The INR values obtained before levofloxacin administration did not differ significantly from the first INR values obtained after levofloxacin coadministration (mean +/- SD 2.61 +/- 0.44 vs 2.74 +/- 0.83, 95% confidence interval -0.449-0.196, p=0.419).


CONCLUSIONS
The INR values measured before and after concomitant levofloxacin therapy were not significantly different. However, the ability to detect a significant difference may be affected by the small number of patients studied. Further studies with a larger sample are required to better determine the effect of levofloxacin coadministration on INR monitoring during warfarin therapy
Yamreudeewong
Weeranuj
W
School of Pharmacy, University of Wyoming, Laramie, USA.
Lower
Dennis L
DL
Kilpatrick
David M
DM
Enlow
Ann M
AM
Burrows
Margo M
MM
Greenwood
Mark C
MC
D000368:Aged; D000369:Aged, 80 and over; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D005260:Female; D006787:Hospitals, Veterans; D006801:Humans; D019934:International Normalized Ratio; D064704:Levofloxacin; D008297:Male; D008875:Middle Aged; D015242:Ofloxacin / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D014859:Warfarin / Q000008:administration & dosage / Q000627:therapeutic use*
D014859:Warfarin; D064704:Levofloxacin; D015242:Ofloxacin