Meclizine also is a dopamine antagonist at D1-like and D2-like receptors but does not cause catalepsy in mice, perhaps because of its anticholinergic activity. Chemistry
Meclizine is a first-generation antihistamine (nonselective H1 antagonist) of the piperazine class. It is structurally and pharmacologically similar to buclizine, cyclizine, and hydroxyzine, but has a shorter half-life of six hours compared to cyclizine and hydroxyzine with about 20 hours (though half-life should not be confused with duration). It is used as an antivertigo/antiemetic agent, specifically in the prevention and treatment of nausea, vomiting, and dizziness associated with motion sickness. Meclizine is sometimes combined with opioids, especially ones of the open-chain class like methadone, dextropropoxyphene, and dipipanone. Similarly, Diconal is a combination drug containing dipipanone and cyclizine. Synthesis
(4-Chlorphenyl)-phenylmethanol is halogenated with thionyl chloride before adding acetylpiperazine. The acetyl group is cleaved with diluted sulfuric acid. An N-alkylation of the piperazine ring with 3-methylbenzylchloride completes the synthesis. Alternatively, the last step can be replaced by a reductive N-alkylation with 3-methylbenzaldehyde. The reductive agent is hydrogen, and Raney nickel is used as a catalyst. Meclizine is obtained and used as a racemate, a 1:1 mixture of the two stereoisomers. Drug forms contain the racemic dihydrochloride. Names
Meclizine is an international nonproprietary name.It is sold under the brand names Bonine, Bonamine, Antivert, Postafen, Sea Legs, and Dramamine II (Less Drowsy Formulation). Emesafene is a combination of meclizine (1/3) and pyridoxine (2/3). In Canada, Antivert Tab (which is no longer available) was a combination of meclizine and nicotinic acid. Notes
References
External links
"Meclizine". Drug Information Portal.
Treatment
There is no cure for this disorder; however, symptoms can usually be managed by limiting exposure to daytime sun and some types of artificial lighting. Most types of artificial lighting emit light in the problematic wavelengths, with fluorescent lighting being the worst offender. Color temperature can be a good indicator of what light is most detrimental, as the higher the color temperature, the more violet light (380–450 nm) is emitted. Incandescent and LED lighting in the soft white range (2700–3000 K) produce the least problematic light. Additionally, selecting lower wattage bulbs can reduce the overall output of light. Since the photosensitivity results from light in the visible spectrum, most sunscreens are of little use (with the exception of non-nano zinc oxide which provides uniform protection between 290–400 nm and some protection up to 700 nm). Sun protective clothing can also be very helpful, although clothing with UPF values are only rated based on their UV protection (up to 400 nm) and not on their protection from the visible spectrum. Some sun protective clothing manufacturers use zinc oxide in their fabrics, such as Coolibars ZnO Suntect line, which will offer protection from visible light.Some patients gradually build a protective layer of melanin by regularly exposing themselves for short times to ultraviolet radiation.Window films which block UV and visible light up to 450 nm can provide relief from symptoms if applied to the patients automobile and home windows. An example of such would be Madico Amber 81 which can protect through the 500 nm range.