Calcium Channel Blockers: Toxicity

TOXICITY

The common side effects seen in chronic therapy (Table 19.3) are mostly related to vasodilation—headaches, dizziness, facial flushing, hypotension, and so forth. High doses of verapamil in elderly patients are known to cause constipation. Serious side effects, especially fol-lowing the intravenous use of verapamil, include marked negative inotropic effects and depression of preexisting sick sinus syndrome, A-V nodal disease, and enhancement of the action of other cardiodepressant drugs. Their use is generally contraindicated in obstruc-tive conditions (e.g., aortic stenosis). No consistent or significant changes in lipid and glucose levels have been reported with chronic therapy. Non–sustained release formulations of nifedipine are contraindicated in hyper-tension because of sympathetic rebound that may ag-gravate existing left ventricular dysfunction.