Theoretical potential for a calcium antagonist to affect activity of SA and AV nodes should be noted, and care should be taken in pre-existing abnormalities. Use with caution in congenital or documented acquired QT prolongation, in patients treated concomitantly with medications known to prolong QT interval such as class I and III antiarrhythmics, tricyclic antidepressants, certain antipsychotics, antibiotics, antihistaminic agents. Use with caution in poor cardiac reserve, and in hepatic impairment (antihypertensive effect may be increased). Patients with rare hereditary problems of galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption should not take this drug.