Antihistamines mydriasis caused

Anticholinergics, central nervous system stimulants and depressants, antihistamines, and phenothiazines can all cause mydriasis (Box 35-1). 

The acute poisoning that occurs with most antihistaminics does not cause severe CNS depression as would be expected based on their sedative properties, but is manifested by mydriasis, fever, flushing, CNS excitement, hallucinations, ataxia, athetosis, and convulsions. Some of these effects, which resemble those of atropine poisoning, may be due to their anticholinergic properties. Diazepam is an effective antidote to poisoning and should be used to reverse the CNS excitement and convulsions. 

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