Antihistamines tachycardia caused

Significant side effects have been estimated to occur in about 5% of patients on TCAs, most of these effects being attributed to their antimuscarinic properties, for example, blurred vision, dry mouth, tachycardia and disturbed gastrointestinal and urinary tract function. Orthostatic hypotension due to the block of alphai adrenoceptors and sedation resulting from antihistaminic activity frequently occur at therapeutic doses, particularly in the elderly. Excessive sweating is also a fairly common phenomenon, but its precise mechanism is uncertain. In the elderly patient, the precipitation of prostatic hypertrophy and glaucoma by the TCAs is also a frequent cause of concern. 

In overdose, the antihistamines cause convulsions, hallucinations, excitement, ataxia, incoordination, and athetosis. On exam patients may exhibit fixed, dilated pupils with a flushed face, sinus tachycardia, urinary retention, dry mouth, and fever. At high doses the patient can become comatose, which is often followed by cardiorespiratory collapse and death within 2 to 18 hours (Babe and Serafin, 1996). Treatment of overdose is mainly supportive, with efforts to manage the anti-colinergic effects. 

Antimuscarinic syndromes consist of tachycardia, dilated pupils, dry, flushed skin, urinary retention, decreased bowel sounds, mild elevation of body temperature, confusion, cardiac arrhythmias and seizures. They are commonly caused by antipsych-otics, tricyclic antidepressants, antihistamines, anti-spasmodics and many plants (see p. 160). 

Severe anaphylaxis has been reported in five patients who had already received several cycles (5-12) containing oxaliplatin 100 mg/m every 2 weeks (241). The predominant symptoms included reduced systolic blood pressure, flushing, sweating, headache, tachycardia, and respiratory distress. If retreatment with the causative platinum compound is required in such cases, premedication with a glucocorticoid and antihistamine may prevent recurrence. However, symptoms can occur despite premedication, making drug withdrawal necessary. 

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