Retrospective assessment of potential interaction between levofloxacin and warfarin.
OBJECTIVE
There is currently a controversy regarding interactions between levofloxacin and warfarin. The aim of this study was to determine the clinical relevance of this interaction in our setting.


METHODS
A university hospital in Barcelona, Spain.


METHODS
We carried out a retrospective evaluation of all patients hospitalized in our hospital during the period 2000-2005, selecting all those concomitantly treated with levofloxacin and warfarin for the study. The following data were compiled: demographic information, concomitant medication, comorbid conditions, and relevant analytical parameters, particularly the international normalized ratio (INR), including values taken before, during, and after concomitant administration of the two study drugs. Patients for whom INR values during concomitant administration were not available were excluded. Differences in INR before and during the potential interaction, and before and after the interaction were analyzed with the Wilcoxon t test using SPSS (V12.0). In addition, patients were stratified according to presence or not of toxic habits (smoking/alcohol consumption) to investigate the possible impact of these factors on the interaction under study.


RESULTS
Among the 30 patients identified, 9 were excluded because INR data during concomitant administration of warfarin and levofloxacin were not available. Statistical analysis demonstrated significant increase in INR (P = 0.001) following addition of levofloxacin to warfarin therapy.


CONCLUSIONS
The results of this study reaffirm the hypothesis that concomitant administration of levofloxacin and warfarin leads to INR increase; hence close monitoring of INR is advisable when patients are prescribed this combination of drugs.
Mercadal Orfila
Gabriel
G
Pharmacy Department, Hospital Universitari de Bellvitge, Barcelona, Spain. gabriel.mercadal@hgmo.es
Gracia García
Berta
B
Leiva Badosa
Elisabet
E
Perayre Badía
María
M
Reynaldo Martínez
Concepción
C
Jodar Masanés
Ramón
R
D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000009:adverse effects; D000925:Anticoagulants / Q000008:administration & dosage; D015415:Biomarkers / Q000032:analysis; D004347:Drug Interactions; D005260:Female; D006801:Humans; D007297:Inpatients; D019934:International Normalized Ratio / Q000706:statistics & numerical data*; D064704:Levofloxacin; D008297:Male; D008875:Middle Aged; D015242:Ofloxacin / Q000008:administration & dosage* / Q000009:adverse effects*; D012189:Retrospective Studies; D013997:Time Factors; D014859:Warfarin / Q000008:administration & dosage* / Q000009:adverse effects*
D000900:Anti-Bacterial Agents; D000925:Anticoagulants; D015415:Biomarkers; D014859:Warfarin; D064704:Levofloxacin; D015242:Ofloxacin