The effects of oral clonidine on hyperactive children with comorbid mental retardation were examined in 10 children (mean age 7.6 years) treated at the Department of Psychiatry, King George’s Medical College, Lucknow, India. In a 12-week, double-blind, randomized, placebo-controlled trial, using 3 fixed doses (4, 6, and 8 mcg/kg/day), Parent Questionnaire and Clinician Rating Scales showed a dose-related effect on hyperactivity, inattention, and impulsivity, and improvements in conduct abnormalities, frustration tolerance, cooperation, and interest in tasks. Whereas hyperactivity and impulsivity were improved with increasing doses from 4- to 8-mcg, improved attention occurred only at the 4- and 6-mcg doses. Drowsiness occurred in 5 children, and 1 child developed dry mouth and anorexia Systolic blood pressure was lowered 3% with 4-mcg dose, 6.9% with 6-mcg, and 8.9% with 8-mcg doses. Clonidine was considered safe and effective in hyperkinetic children with mental retardation. [1]

COMMENT. In this rather limited cohort of patients, the efficacy and safety of clonidine in the management of hyperactive, mentally retarded children has been demonstrated by controlled trial. Clonidine is a second line treatment for ADHD and is indicated primarily in patients with comorbid tics, oppositional defiance disorder, and sleep problems.

Hypoglycemic effect of clonidine. Four cases of hypoglycemia associated with clonidine stimulation of growth hormone secretion are reported from the Hospital for Sick Children, Toronto, Ontario [2]. Only one patient had growth hormone deficiency. Drowsiness after 0.15 mg/m2 dose AM may prolong fasting and mask early signs and symptoms, leading to severe hypoglycemia. One patient aged 3 years had a generalized tonic-clonic seizure with a serum glucose of 2.3 mmol/L EEG and head CT scan were normal.

Hypoglycemia is not a reported adverse reaction to clonidine in ADHD children, but blood sugar levels should be monitored in patients with suggestive symptoms. The PDR lists a transient elevation of blood glucose, not hypoglycemia, as a rare adverse reaction of clonidine.