Antihistamines motion sickness

This compound has antihistaminic activity and is usehil in the therapy of motion sickness. It may also be effective in the control of post-operative nausea and vomiting. It is classified as FDA Category B for Pregnancy, ie, no demonstrated risks shown in animal studies however, no controlled trials in pregnant women. Large doses may cause drowsiness and dry mouth owing to decreased secretion of saUva. 

The prototype of the antihistamines based on benzhydrol, diphenhydramine (3), is familiar to many today under the trade name Benadryl . Light-induced bromination of diphenylmethane affords benzhydryl bromide (2). This is then allowed to react with dimethylaminoethanol to give the desired ether. Although no mechanistic studies have been reported, it is not unlikely that I he bromine undergoes SNi solvolysis in the reaction medium the carbonitjm ion then simply picks up the alcohol. It might be noted in passing that the theophyline salt of 4 is familiar to many Iravelers as a motion sickness remedy under the trade name Oram amine . 

Because the vestibular system is replete with muscarinic-type cholinergic and histaminic (Hx) receptors, anticholinergics and antihistamines are the most commonly used pharmacologic agents to prevent and treat motion sickness. 

Antihistamines are commonly used to prevent and treat nausea and vomiting due to motion sickness, vertigo, or migraine headache.1,17 Their efficacy is presumably due to the high concentration of histamine (Hx) and muscarinic cholinergic receptors within the vestibular system. Similarly to scopolamine, antihistamines such as diphenhydramine and... 

All other antihistaminics produced side reactions.44 One, dramamine, is often very effective for the prevention of motion sickness, but it is not effective for all individuals. A recently tested antihistaminic, vibazine,45 was found to have effects that lasted from 1 hour to over 8 hours in different individuals. Of the 545 patients tested, 31 showed effects after 8 hours or more. Of the whole group, 33 (6 per cent) showed moderate to severe side reactions. 

Motilium contains domperidone, v/hich is a dopamine antagonist and acts on the chemoreceptor trigger zone. It is ineffective in motion sickness. Stugeron contains cinnarizine Avomine and Phenergan contain promethazine and Kwells contains hyoscine hydrobromide. Cinnarizine and promethazine are antihistamines, which are indicated in motion sickness and hyoscine hydrobromide is an antimuscarinic agent that is also used in motion sickness. 

Promethazine is an antihistamine, which leads to sedation and is therefore used in motion sickness when a sedative effect is desired. 

Domperidone is a dopamine antagonist that acts on the chemoreceptor trigger zone. It can therefore be used as an anti-emetic in nausea and vomiting, for example, to counteract side-effects of cytotoxic therapy and to treat nausea associated with dopaminergic drugs used in Parkinson s disease. Unlike hyoscine butlybromide and antihistamines, domperidone is ineffective in motion sickness. 

Motion sickness. Effective prophylaxis can be achieved with the parasympatholytic scopolamine (p. 106) and H antihistamines (p. 114) of the diphenyl-methane type (e.g., diphenhydramine, meclizine). Antiemetic activity is not a property shared by all parasympatho-lytics or antihistamines. The efficacy of the drugs mentioned depends on the actual situation of the in vidual (gastric filling, ethanol consumption), environ-... 

Scopolamine is useful for prevention of motion sickness when the motion is very stressful and of short duration. A transdermal preparation (Transderm-Scop) with a 72-hour duration of action has been marketed for this purpose. Blockade of chohnergic sites in the vestibular nuclei and reticular formation may account for the effectiveness of this agent. When the motion is less stressful and lasts longer, the antihistamines (Hj-antagonists) are probably preferable to the antimus-... 

Many of these drugs have effects that are not mediated by Hi-receptors (Table 38.2). The antimuscarinic activity of several first-generation Hj-blockers may account for their effectiveness in combating motion sickness and their limited ability to suppress parkinsonian symptoms. The phenothiazines have some capacity to block a-adrenoceptors, whereas cyproheptadine Periactin) is an antagonist at serotonin receptors. Diphenhydramine Benadryl), pyrilamine (Ryna), and promethazine Phen-ergan) are effective local anesthetics. Many second-generation antihistamines also have been found to inhibit the non-histamine-mediated release of various... 

Another important use of Hj-antagonists is in the treatment of motion sickness. Diphenhydramine (Benadryl), dimenhydrinate (Dramamine), cyclizine (Marezine), and meclizine (Antivert) have anticholinergic activity and are the preferred antihistaminic agents for reducing the symptoms of motion sickness. 

Mr. Smith has severe motion sickness during air travel. He will be flying to Brazil next week, and you, his physician, would hke to prescribe an antihistamine to prevent motion sickness. Which of the following would be most effective ... 

B. Although scopolamine effectively combats motion sickness, it is an antimuscarinic agent, not an antihistamine. Dimenhydrinate is an antihistamine with signihcant antimuscarinic properties that are likely to contribute to its anti-motion sickness activity. Chlorpheniramine, fexofenadine, and tripelennamine are antihistamines without signihcant efficacy in the treatment of motion sickness. 

Mechanism of Action An antihistamine and anticholinergicthat competes for H,-receptor sites on effector cells of the G1 tract, blood vessels, and respiratory tract. The anticholinergic action diminishesvestibular stimulation and depresses labyrinthine function. Therapeutic Effect Prevents symptoms of motion sickness. Pharmacokinetics Well absorbed following PO administration. Metabolized in liver. Excreted in urine. Half-life Unknown. 

The antihistamines also decrease motion sickness, which is thought to be secondary to anticholinergic effects (Babe and Serafin, 1996). 

The unpleasant sedative CNS effect of most antihistamines, combined with their slight anticholinergic activity, is exploited for the prevention of motion sickness. Diphenhydramine (2.5), in the form of an 8-chlorotheophylline salt (dimenhydrinate, 4.148), is widely used for this purpose. The theophylline derivative was originally added to counteract the drowsiness produced by diphenhydramine, since it is a central excitant related to caffeine. 

The same molecules used to treat allergies and cold symptoms have many other uses. Antihistamines are particularly effective as antiemetics in suppressing nausea associated with gastrointestinal illnesses. They can also be used to treat the symptoms of motion sickness or even vestibular disturbances (vertigo). Because of their ability to induce sedation, antihistamines are widely used in over-the-counter sleep aids. 

CNS disorders Scopolamine and hyoscine are effectively used in the treatment of nausea, vomiting and motion sickness. Centrally acting anticholinergic/ antihistaminics e.g. trihexyphenidyl are used in parkinsonism. 

The prototype antihistamine of this group is diphenhydramine. It has antimuscarinic and pronounced central sedative properties and also an antitussive effect. The mechanism of the latter is unclear, but diphenhydramine is a common ingredient of propriety preparations for the treatment of coughs and colds. It is an effective anti-emetic, especially useful for prevention and treatment of motion sickness. Because of its anticholinergic properties it is occasionally used in the treatment of mild forms of Parkinson s disease. It is also of use in the treatment of drug-induced extrapyramidal effects. Piperazine derivatives... 

Cyclizine has antimuscarinic properties and is a potent anti-emetic, effective for the control of postoperative and drug-induced nausea and vomiting. It has been used to prevent motion sickness, although diphenhydramine and promethazine are more effective. It is available in oral and parenteral formulations. In contrast to many other first-generation antihistamines sedation is not marked. It is available in tablet form as the hydrochloride and in injectable form as the lactate. Because of its anticholinergic action, blurred vision and dry mouth are associated with clinical doses. When given by rapid intravenous injection tachycardia may be a problem. Meclozine is a related drug which, like cyclizine, is used primarily for motion sickness. 

Scopolamine (see Chapter 8) and certain first-generation Hi antagonists are the most effective agents available for the prevention of motion sickness. The antihistaminic drugs with the greatest effectiveness in this application are diphenhydramine and promethazine. 

It has been claimed that the antihistaminic agents effective in prophylaxis of motion sickness are also useful in Meniere s syndrome, but efficacy in the latter application is not established. 

Antihistaminics Moderate efficacy in motion sickness and chemotherapy-induced emesis ... 

Diphenhydramine (Benadryl) [OTC] [Antihistamine/ Antitussive/Antiemeticj Uses Tx prevent allergic Rxns, motion sickness, potentiate narcotics, sedation, cough suppression, Tx of extrapyramidal (dystonic) Rxns Action Antihistamine, antiemetic Dose Adults. 25-50 mg IV/EM Feds. > 2 y. 2—5 mg/kg IV/EM Caution [B, —] Contra Acute asthma Disp Tabs,... 

Some antihistamines are particularly effective in alleviating the onset of motion sickness. Some antihistamines have been found helpful in relieving persistent, unproductive coughs that frequently accompany bronchitis or coughs associated with allergy. They are used in connection with perennial... 

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