The FDA has required the manufacturer of Plavix, an antiplatelet drug used in addition to aspirin to prevent cardiovascular events in high-risk patients,1 to add a boxed warning to the package insert about the risk of a poor response to the drug in patients with genetic polymorphisms of the cytochrome P450 enzyme CYP2C19. Clopidogrel is a prodrug and CYP2C19 is mainly responsible for its bioactivation. The Medical Letter reported last year that several studies have found higher rates of cardiovascular events, including stent thrombosis, in patients with these polymorphisms taking clopidogrel.2

At least one genetic polymorphism leading to poor metabolism of clopidogrel has been reported to occur in 15% of Caucasians, 17% of African Americans and 30% of Asians.3 Since many patients take clopidogrel to protect against life-threatening events, and some continue to do so for extended periods of time, it might be worthwhile to test for these polymorphisms. Such tests, requiring small amounts of blood or saliva, are commercially available from clinical laboratories. More directly, patients who are taking clopidogrel could have platelet aggregation assays to determine whether the drug is being activated.

However, the best course of action for patients who prove to be poor metabolizers of clopidogrel is not clear. They could be treated with higher doses of clopidogrel, but the doses that would be safe and effective in such patients have not been established. Alternatively, they could be treated with prasugrel (Effient), a similar antiplatelet drug that does not require CYP2C19 for activation, instead of clopidogrel, but prasugrel has a greater effect on platelets and may cause more bleeding.4

1. Antiplatelet and anticoagulant drugs. Treat Guidel Med Lett 2008; 6:29.
2. PPI interactions with clopidogrel revisited. Med Lett Drugs Ther 2009; 51:13.
3. Z Desta et al. Clinical significance of the cytochrome P450 2C19 genetic polymorphism. Clin Pharmacokinet 2002; 41:913.
4. Prasugrel (Effient) vs. clopidogrel (Plavix). Med Lett Drugs Ther 2009; 51:69.

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Everolimus (Afinitor – Novartis) and pazopanib (Votrient – GlaxoSmithKline), two oral multikinase inhibitors, have been approved by the FDA for treatment of advanced renal cell carcinoma. Sunitinib (Sutent) and sorafenib (Nexavar), two other oral multikinase inhibitors, and temsirolimus (Torisel), an IV multikinase inhibitor, were approved earlier for the same indication.

A Medical Letter reader recently received a diagnosis of athlete’s foot and a prescription for Naftin gel, for which his pharmacy charged $145, and his insurance company required a $70 copay because this formulation was not included in its formulary. Do patients need to pay prices like these to treat tinea pedis?

The FDA has approved velaglucerase alfa (Vpriv – Shire), a new formulation of glucocerebrosidase prepared from human fibroblasts, for treatment of the nonneurologic form of Gaucher’s disease (Type 1). Patients with Gaucher’s disease have a congenital deficiency of glucocerebrosidase that leads to accumulation of glucosylceramide, the end-product of sphingolipid catabolism, in the lysozymes of reticuloendothelial cells in the liver, spleen and bone marrow.Velaglucerase is the second form of the enzyme now available in the US; imiglucerase (Cerezyme – Genzyme), which is produced by recombinant DNA technology from Chinese hamster ovary cells, was marketed earlier but has recently been in short supply.1 These agents are usually given as an IV infusion every 2 weeks. Both velaglucerase and imiglucerase have been shown to increase serum hemoglobin concentrations and platelet counts and decrease the size of the spleen. Velaglucerase contains the exact amino acid sequence of the human enzyme, while imiglucerase has one amino acid difference, but their activities are similar.2 The main difference between them may be in their cost. Cerezyme costs about $200,000 per year, while Vpriv is expected to cost about 15% less.2

1. Differentiation will be key challenge for Shire’s Gaucher disease drug Vpriv. The Pink Sheet. March 8, 2010; 72: 27.
2. B Brumshtein et al. Characterization of gene-activated human acid-beta-glucosidase: crystal structure, glycan composition, and internalization into macrophages. Glycobiology 2010; 20:24.

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