Background: The administration p.r.n. (as needed) of sedative medications is a widespread practice in the management of acute dyscontrol of child psychiatric inpatients. Its efficacy, however, has never been tested in a controlled clinical trial.
Method: Twenty-one male inpatients, aged 5-13 years, participated in a double-blind, placebo-controlled study of the p.r.n. use of diphenhydramine, a sedative antihistaminic often used in child psychiatry wards. The patients' DSM-III-R diagnoses were conduct disorder, attention-deficit hyperactivity, and major depression. Each patient in acute dyscontrol blindly received either oral or intramuscular doses of diphenhydramine 25-50 mg (N = 9) or placebo (N = 12). The Conners Abbreviated 10-Item Teacher Rating Scale and the Clinical Global Impressions scale were completed before and 0.5, 1, and 2 hours after the dose.
Results: Repeated measures ANOVA showed significant time effects, but no difference due to drug. The intramuscular route tended to be more effective than the oral, regardless of whether active drug or placebo was given.
Conclusion: The data indicate that if p.r.n. administrations are effective, this is a placebo effect. Likewise, intramuscular administrations are more effective because of a route effect ("the needle") and not because of a specific pharmacologic activity.