TABLE 9.

Drug interactions of the new fluoroquinolones

Interaction with	Fluoroquinolone
	Ciprofloxacin	Clinafloxacin	Gatifloxacin	Grepafloxacin	Levofloxacin	Moxifloxacin	Sparfloxacin	Trovafloxacin
Metal ion-containing drugs (eg antacids, iron, sucralfate)	Yes	Yes*	Yes	Yes*	Yes	Yes	Yes	Yes
Mechanism	Chelation resulting in reduced fluoroquinolone bioavailability
Recommendation	Avoid concomitant administration if possible. Otherwise, administer the fluoroquinolone 2 h before or 6 h after the metal ion containing drug.
Theophylline†	Yes (+)	Yes (++/ND)	ND	Yes (++)	No	No	No	No
Mechanism	Inhibition of theophylline metabolism, resulting in reduced theophylline clearance
Recommendation	For ciprofloxacin and clinafloxacin, monitor theophylline levels and adjust theophylline dosage where necessary. For grepafloxacin, reduce theophylline dosage by 50% and monitor theophylline levels. For levofloxacin, moxifloxacin, sparfloxacin and trovafloxacin, monitor for clinical signs of theophylline toxicity.
Warfarin	Yes/No‡	ND	ND	No	No§	No	No	No
Mechanism	Reduced metabolism of warfarin
Recommendation	For ciprofloxacin, monitor prothrombin time or another suitable coagulation parameter.
Phenytoin	Yes/No‡	ND	ND	ND	ND	ND	ND	ND
Mechanism	Reduced metabolism of phenytoin
Recommendation	For ciprofloxacin, monitor phenytoin levels.
Drugs prolonging the QTc interval	No	ND	ND	Yes	No	No	Yes	ND
Mechanism	Additive prolongation of the QTc interval
Recommendation	For grepafloxacin and sparfloxacin, avoid concomitant administration with other drugs know to cause prolongation of the QTc interval.

^*Theoretical interaction, not actually documented by studies.

^†For theophylline: + 10% to 50% increase in theophylline peak concentration reached in the plasma/serum (C_max) and area under the plasma concentration time curve (AUC), ++ greater than 50% increase in theophylline C_max and AUC; ++/ND greater than 50% increase in theophylline concentrations, but only one case report has been published on the interaction.

^‡Interaction has been reported rarely.

^§Interaction with levofloxacin studied using a single dose of warfarin. ND No data. Adapted from references 6,9,13,129,218,222,233–251