Sedation chlorphenamine

It is usual to give a sedating antihistamine, for example chlorphenamine 10 mg by intramuscular or slow intravenous injection, because of the relatively short half-life of epinephrine (adrenaline), and because of the active role of histamine in anaphylaxis. In addition, the inflammatory reaction can be moderated by the administration of a corticosteroid, such as hydrocortisone 200 mg by intramuscular or slow intravenous injection. Corticosteroids may take several hours to act, but can be of some help in so-called biphasic anaphylactic reactions. 

Q4 Antihistamines are effective in managing many of the troublesome symptoms of allergic rhinitis. Histamine is a neurotransmitter and a mediator of type 1 hypersensitivity reactions, such as urticaria and hay fever. There are several types of histamine receptors and these allergic conditions can be treated with Hi receptor antagonists, such as promethazine, chlorphenamine and fexofenadine. First-generation antihistamines, such as promethazine, cause sedation and possess side effects associated with actions on muscarinic receptors. Fexofenadine is a newer drug with a longer duration of action, which does not sedate the patient. 

The signal characteristic of the second-generation antihistamines is their freedom from sedation (2,16). The relative lack of sedative properties in the second-generation antihistamines has been ascribed to their relative hydrophi-licity. Little is known about intracerebral concentrations of antihistamines and their metabohtes, but positron emission tomography has shown that the first-generation antihistamine chlorphenamine occupied a larger fraction of brain histamine Hi receptors than terfenadine (SEDA-20,164). Differential affinity for, or different actions on, central and peripheral Hi receptors (SEDA-21,171) could also explain variations in sedative effect, but differences in receptor binding have only been shown for loratadine in vitro (45). 

In a comparison of diphenhydramine, chlorphenamine, cetirizine, loratadine, and placebo in 15 healthy elderly subjects, there were no significant differences between the first- and second-generation antihistamines (62). In another study, even the first-generation sedative drug chlorphenamine failed to cause significant sedation in a group of children (63). 

Sedating antihitamines available without prescription are chlorphenamine... 

Sedating antihistamines (chlorphenamine, promethazine) can be used for night-time relief of irritable dermatitis. 

A 35-year-old man developed generalized convulsions and a mixed acidosis attributed to abuse of SS Bron tablets, an over-the-counter antitussive medication sold in Japan that contains chlorphenamine. He was confused, with bilateral pinpoint pupils. The blood pressure was 143/94 mmHg, the heart rate 113/minute, and the respiratory rate 16/minute. There was a metabolic acidosis and the blood lactate concentration was 300 mg/1. He had generalized convulsions that were treated with diazepam 20 mg. Midazolam was continuously administered intravenously for sedation and 12 hours later he recovered consciousness and became alert with no further convulsions. The serum concentration of chlorphenamine on admission was 0.43 mg/1, i.e. more than 20 times greater than the mean peak concentration after a single dose (4—17 pg/1). 

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