• Finally, interactions can occur at the level of drug action, such as the combination of verapamil, a calcium channel blocker, and a beta-blocker. Both slow the heart rate by different mechanisms, and the combination is relatively contraindicated because heart block can result. Because of this interaction many textbooks and computer pro-grams warn against concomitant use of any beta-blocker and any calcium channel blocker. This creates a great deal of confusion and distrust of drug interaction warnings, because most health care providers know that drugs in these two classes are often employed successfully and safely in patients with hypertension.
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