In Reply: Dr Carter points to differences in rates of medication absorption from his research comparing the effects of brand-name and generic verapamil on older patients and attributes these differences to clinical characteristics of this patient subgroup. Dr Zema suggests that variations in the chemical structure of different verapamil preparations may play a role. A third possibility is intraparticipant biological variability, because differences in verapamil pharmacokinetics have been noted in individual patients taking brand-name Isoptin SR (Abbott Laboratories, Abbott Park, Illinois).1 However, we disagree with the conclusion that generic cardiovascular medications cannot be substituted for brand-name drugs. First, there are inconsistencies with the findings. For example, in one study2 the generic formulation exhibiting an enhanced effect on one electrocardiographic measurement also demonstrated a slightly diminished effect on supine mean arterial pressure, as well as no significant effect on heart rate and standing mean arterial pressure. Second, none of the variations reported in the relevant studies showed meaningful effects on patient outcomes.
Kesselheim AS, Misono AS, Shrank WH. Equivalence of Generic and Brand-Name Drugs for Cardiovascular Disease—Reply. JAMA. 2009;301(16):1654-1656. doi:10.1001/jama.2009.523