Do Fluoroquinolones Alter the Effects of Warfarin Therapy?

To the Editor. — We read the article by Jolson et al1with interest, and we are concerned over the lack of objective, balanced information presented. We are aware of at least two published clinical trials2,3that did not validate the potential warfarin-fluoroquinolone interaction. The information provided by Jolson et al, as well as the published literature that has generated interest and concern about this potential interaction, has been derived from individual case reports. One cannot evaluate the predictability of an interaction from case reports alone, without appropriate clinical trials to support the interaction. Jolson et al state that the five patients had steady-state baseline prothrombin time (PT) ratios between 1.5 and 2 times the control ratio. They failed to mention their criteria for determining steady state. Additionally, reporting PT ratios rather than international normalized ratios (INRs) makes it difficult for the reader to judge steady-state criteria or