Head injury: clonidine decreases plasma catecholamines.

Seven patients who had suffered head injury 3 to 5 days before the study was undertaken received clonidine (2.5 micrograms/kg iv over 10 min). This resulted in a reduction of plasma norepinephrine (p less than .05) and in normalization of plasma epinephrine (p less than .05). Neither common carotid blood flow nor diastolic blood flow as index of global cerebral perfusion as measured by pulsed Doppler changed. The reduction of sympathetic overactivity, probably due to the specific action of clonidine on alpha 2-adrenoceptors within the rostral ventrolateral medulla, may be of interest in the management of head injury because of the maintenance of cephalic hemodynamics.