Drug Interaction Report

MONITOR: Coadministration of topical formulations containing lidocaine with class IB antiarrhythmic agents such as mexiletine or tocainide may have additive and potentially synergistic toxic effects. Mexiletine, tocainide and lidocaine are structural analogs, and all have antiarrhythmic effects. The clinical significance of the interaction has not been established; the degree of systemic absorption of topical lidocaine may be dependent on the duration of application and the applied surface area.

MANAGEMENT: Caution and clinical monitoring is recommended with the concomitant use of lidocaine-containing topical formulations and class IB antiarrhythmic drugs (e.g., mexiletine, tocainide). Advise patients to contact their physician if they experience adverse effects such as chest pain, palpitations, nausea, vomiting, lightheadedness, nervousness, dizziness or tremors.

ADJUST DOSING INTERVAL: Bulk-forming laxatives such as guar gum, psyllium, polycarbophil, or methylcellulose may affect the bioavailability of concomitantly administered substances due to their effect on the rate of gastrointestinal transit and gastric emptying.

MANAGEMENT: In general, oral medications should be administered at least 2 hours before or 2 hours after dosing of the bulk-forming laxative.