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To the Editor: Dr Kesselheim and colleagues¹ evaluated the clinical equivalence of generic and brand-name drugs used in cardiovascular disease. I agree in general with their statement that " . . . the best evidence for clinical equivalence emerged from high-quality prospective RCTs in patients with cardiovascular disease involving β-blockers, calcium channel blockers, and statins." However, I would not lump the 3 chemical classes of calcium channel antagonists together.

Phenylalkylamines, such as the verapamil derivatives, are marketed as a racemic mixture of enantiomers. The 2 enantiomers have been shown to have different pharmacodynamic activities. S-verapamil has demonstrated 20 times the potency on a weight basis compared with R-verapamil with regard to negative dromotropic effects on the cardiac conduction system.² Most of the vasodilatory effects of this agent have been attributable to the R-enantiomer.²

With respect to pharmacokinetics, racemic verapamil undergoes enantiomer preferred metabolism by both cytochromes 3A4 and 1A2.³ Moreover, administration of racemic intravenous, . . . [Full Text of this Article]

Michael James Zema, MD
mjzema@optonline.net
State University of New York
Stony Brook

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RELATED ARTICLE

Clinical Equivalence of Generic and Brand-Name Drugs Used in Cardiovascular Disease: A Systematic Review and Meta-analysis
Aaron S. Kesselheim, Alexander S. Misono, Joy L. Lee, Margaret R. Stedman, M. Alan Brookhart, Niteesh K. Choudhry, and William H. Shrank
JAMA. 2008;300(21):2514-2526.
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Equivalence of Generic and Brand-Name Drugs for Cardiovascular Disease
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JAMA. 2009;301(16):1654.
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Equivalence of Generic and Brand-Name Drugs for Cardiovascular Disease
James A. Reiffel
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Equivalence of Generic and Brand-Name Drugs for Cardiovascular Disease—Reply
Aaron S. Kesselheim, Alexander S. Misono, and William H. Shrank
JAMA. 2009;301(16):1655-1656.
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