| Meclizine Hydrochloride Pellets |
| Structure |
 |
|
| Introduction |
| Meclizine (proposed INN is meclozine) is an antihistamine considered to be an antiemetic. It is sold under the brand names of Bonine, Bonamine, Antivert, Postafen, and Dramamine (Less Drowsy Formulation), and is most commonly used to inhibit nausea and vomiting. Emesafene is a combination of meclizine (1/3) and pyridoxine (2/3). An alternative to dimenhydrinate (Dramamine, Gravol, Gravamin, and Vertirosan), meclizine is considered to be equally effective, but with reduced side effects. Note that in Canada, Antivert (no longer available) was a combination of meclizine and nicotinic acid.
Meclizine is the first-generation antihistamine of the piperazine class. It differs from the protoype of this class, cyclizine, primarily in having an average half-life of 6 hours vs. 20 hours for cyclizine (though half-life should not be confused with frequency of duration). Meclizine is less anticholinergic than many other antihistamines and other agents used for their anti-emetic and anti-pruritic effects. Along with the aforementioned efficacy against nausea and itching, meclizine also shares the anxiolytic, analgesic-sparing (potentiating), sedative, and other effects of its chemical relatives cyclizine and hydroxyzine to varying extents. Related to this is the reported ability of meclizine to potentiate the anti-spasmodic, anti-diarrhoeal, and other effects of diphenoxylate, loperamide, and difenoxin. Meclizine is sometimes combined with opioids, especially ones of the open-chain class like methadone, dextropropoxyphene and dipipanone (originally combined with meclizine's parent drug cyclizine, the brand name of this combination is Diconal). The trend of mixing piperazine antihistamines has caught on in the United States, with some methadone users potentiating their doses with meclizine or hydroxyzine (cyclizine has only just recently been introduced to the U.S. OTC market in 2009, sold under the brand name Marezine at higher prices than generic equivalents of meclizine and hydroxyzine). |
| Pharmacology: |
| Facing the loss of patent protection and competition from generic drug manufacturers, AstraZeneca developed and heavily marketed esomeprazole (Nexium) as a replacement in 2001, Esomeprazole is the S-enantiomer in the pure form. According to AstraZeneca, omeprazole undergoes a chiral shift in vivo which converts the inactive R-enantiomer to the active S-enantiomer doubling the concentration of the active form. This chiral shift is accomplished by the CYP2C19 isozyme of cytochrome P450, which is not found equally in all human populations. Those who do not metabolize the drug effectively are called "poor metabolizers." The approximate proportion of the poor metabolizer phenotype in different populations is as follows: • Caucasians 10% • Asian 20% • South Pacific Islands 70% In theory, by using pure esomeprazole the effect on the proton pump will be equal in all patients, eliminating the "poor metabolizer effect". |
| Uses: |
| Motion sickness Meclizine is effective in inhibiting the symptoms of motion sickness, such as nausea, vomiting, and dizziness. Vertigo Meclizine may be effective in relieving vertigo experienced as a result of inner ear infections or other conditions. |
| Risks of use: |
| Drowsiness Drowsiness may result as a side effect of taking meclizine. While the effects are less than those of dimenhydrinate, users are advised not to operate heavy machinery while under the influence. The consumption of alcohol while under the influence of meclizine may result in additional drowsiness. Anticholinergics Because of its possible anticholinergic action, meclizine should be used carefully with patients who suffer from asthma, glaucoma, or an enlarged prostate gland. |