{"id":88,"date":"2012-03-26T10:38:00","date_gmt":"2012-03-26T17:38:00","guid":{"rendered":"https:\/\/phcprimarycare.org\/?p=88"},"modified":"2014-02-19T13:49:05","modified_gmt":"2014-02-19T21:49:05","slug":"lexapro-celexa-and-the-difference-between-red-and-green-jelly-beans","status":"publish","type":"post","link":"https:\/\/phcprimarycare.org\/?p=88","title":{"rendered":"Lexapro, Celexa, and the difference between red and green jelly beans"},"content":{"rendered":"

If you request Lexapro (escitalopram) for your patient, the PHC formulary requires a trial and failure or a contraindication to two formulary agents, one of which must be citalopram . Why?\u00a0 Is it just to make things difficult, or is there an actual sensible reason?\u00a0 The answer has to do with ISOMERS.\u00a0 Bear with me for a few minutes while I explain what I mean.\u00a0 Isomers are molecules that have the same atomic structure but are mirror images of each other.\u00a0 Imagine a 50:50 mixture of red and green jelly beans.\u00a0 The green jelly beans taste like mint, while the red jelly beans have no taste at all. The red jelly beans won\u2019t hurt you, but they don\u2019t do anything to satisfy your need for jelly beans.\u00a0 Citalopram can be thought of as a red-green jelly bean mixture.\u00a0 Lexapro consists of exclusively green jelly beans.\u00a0 Citalopram is a racemic mixture of the levo isomer \u2013 the green jelly beans \u2013 and an inactive mirror-image dextro isomer \u2013 the red jelly beans.\u00a0 Half of citalopram is Lexapro (the \u201cL\u201d in Lexapro stands for left). \u00a0Chemical mixtures containing both isomers are referred to as RACEMIC mixtures.\u00a0 About half of all drugs in current use have this handedness property and nearly 90% of recently approved drugs are racemic mixtures.<\/p>\n

Many if not most drugs originate as racemic mixtures.\u00a0 Usually, one of the isomers is active (the EUTOMER) with the other isomer (the DISTOMER) being much less so or inactive.\u00a0 The distomer usually contributes little to the activity of the drug but can sometimes contribute to toxicity, side effects, or changes in metabolism.\u00a0 As drugs are usually developed and undergo trials in their racemic forms, those drugs with toxic or interfering distomers are weeded out.<\/p>\n

The list of drugs where activity resides in a single isomer is long and includes beta blockers, ACE inhibitors, calcium channel antagonists, and beta agonist bronchodilators.\u00a0 Other drugs with single active isomers include ethosuximide, propafenone, ofloxacin, moxalactam, warfarin, terfenadine, loratadine, atorvastatin, amphetamine, omeprazole, pantoprazole, and lansoprazole.\u00a0\u00a0 In none of these cases is the distomer harmful.\u00a0 A few drugs have equally active isomers: cyclophosphamide, flecainide, and fluoxetine.\u00a0 Some drugs metabolically move between isomers.<\/p>\n

Isomers may undergo differences in metabolism based upon protein binding, genetics or selectivity of the metabolic pathways.\u00a0 This is the case with many antiarrhythmic medications and occasionally beta blockers.<\/p>\n

Advances in the ability to produce only the eutomer (active isomer) of a current racemic drug has introduced three factors:<\/p>\n