Diphenhydramine dosage

Some antihistamines such as diphenhydramine, dimenhy-drinate, and meclizine are available without a prescription, making self-treatment convenient for patients. Antihistamines are available in a variety of dosage forms, including oral capsules, tablets and liquids. Liquid formulations are convenient for children or adults who are unable to swallow solid dosage forms. 

Children 6 to 12 years of age - 4 mg/day, preferably at bedtime. DIPHENHYDRAMINE HYDROCHLORIDE Individualize dosage. 

Extrapyramidal symptoms Extrapyramidal symptoms, manifested primarily as acute dystonic reactions, occur in approximately 0.2% to 1% of patients treated with the usual adult dosages of 30 to 40 mg/day. These usually are seen during the first 24 to 48 hours of treatment, occur more frequently in children and young adults, and are even more frequent at the higher doses used in prophylaxis of vomiting caused by cancer chemotherapy. If symptoms occur, they usually subside following 50 mg diphenhydramine IM. Benztropine 1 to 2 mg IM may also be used to reverse these reactions. 

Recommended dosage and monitoring requirements Campath therapy should be initiated at a dose of 3 mg administered as a 2-hour intravenous infusion daily. When the Campath 3 mg daily dose is tolerated, the daily dose should be escalated to lOmg and continued. When the lOmg dose is tolerated, the maintenance dose of Campath 30mg may be initiated.The maintenance dose of Campath is 30mg/day administered three times per week on alternate days (i.e., Monday, Wednesday, and Friday) for up to 12 weeks. In most patients, escalation to 30 mg can be accomplished in 3 to 7 days. Premedication should be given prior to the hrst dose, at dose escalations, and as clinically indicated. The premedication used in clinical studies was diphenhydramine 50 mg and acetaminophen 650 mg administered 30 minutes prior to Campath infusion. Patients should receive anti-infective prophylaxis to minimize the risks of serious opportunistic infections. 

Recommended dosage and monitoring requirements In patients with AML in first untreated relapse, two 2-hour intravenous doses of 9 mg/m separated by a 14-day interval, are recommended. Patients should receive diphenhydramine and acetaminophen one hour before Mylotarg administration. 

Dimenhydrinate, which is promoted almost exclusively for the treatment of motion sickness, is a salt of diphenhydramine. The piperazines (cyclizine and meclizine) also have significant activity in preventing motion sickness and are less sedating than diphenhydramine in most patients. Dosage is the same as that recommended for allergic disorders (Table 16-2). Both scopolamine and the Hi antagonists are more effective in preventing motion sickness when combined with ephedrine or amphetamine. 

H. P. Yuan and D. C. Locke, HPLC method for the determination of diphenhydramine in liquid and solid drug dosage forms and its application to stability testing, Drug Dev. Ind. Pharm., 77 2319 (1991). 

A 22-year-old man who had had ADHD since the age of 8 years took methylphenidate, and had an adequate response for 14 years (52). However, his symptoms worsened and he switched from methylphenidate to mixed amfetamine salts 20 mg bd. A month later he continued to have difficulty in focusing on tasks, and the dosage was eventually increased to 45 mg tds over several weeks, with symptomatic improvement. However, 5 days later, he awoke feeling nauseated and agitated and had choreiform movements of his face, trunk, and limbs. He had also taken escitalopram 10 mg/day for anxiety and depression for 2 months before any changes in his ADHD medications. He was treated with intravenous diphenhydramine, lora-zepam, and diazepam without improvement in the chorea. Amfetamine was withdrawn and 3 days later his chorea abated. He restarted methylphenidate and the movement disorders did not recur. 

Peak concentrations of these drugs are achieved rapidly in the skin and persist after plasma levels have declined. This is consistent with inhibition of wheal and flare responses to the intra-dermal injection of histamine or allergen, which last for 36 hours or more after treatment, even when concentrations in plasma are very low. Such results emphasize the need for flexibihty in the interpretation of the recommended dosage schedules (Table 24-2) less frequent dosage may suffice. Doxepin, a tricyclic antidepressant (see Chapter 17), is one of the most potent antihistamines available it is -800 times more potent than diphenhydramine. This may account for the observation that topical doxepin can be effective in the treatment of chronic urticaria when other antihistamines have failed. 

Antihistamines are most effective for damping input from the vestibular system. The usual canine dosage of diphenhydramine is 2-4 mg/kg orally every 8 hours. 

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