Since drowsiness may occur As with all IM preparations, hydroxyzine HCl IM should be injected well within the body of a relatively large muscle. In advertent subcutaneous injection may result in significant tissue damage. In infants and small children the periphery of the upper outer quadrant of the gluteal region should be used only when necessary, such as in burn patients, in order to minimize the possibility of damage to the sciatic nerve. The deltoid area should be used only if well developed such as in certain adults and older children and then only with caution to avoid radial nerve injury. IM injections should not be made into the lower and mid- third of the upper arm.
Aspiration is necessary to help avoid inadvertent injection into a blood vessel.
Drowsiness is usually transitory and may disappear in a few days of continued therapy or upon reduction of the dose. Involuntary motor activity including rare instances of tremor and convulsions have been reported, usually with doses considerably higher than those recommended. Clinically significant respiratory depression has not been reported at recommended doses. The absence of adverse effects has been further demonstrated in experimental studies in which excessively high doses were administered. The most common manifestation of hydroxyzine HCl overdosage is hypersedation.