The effect of antihistamines on the laryngeal chemoreflex.

The laryngeal chemoreflex (LCR) consists of apnea, laryngospasm, and cardiovascular changes in neonates after laryngeal irritation and has been implicated in sudden infant death syndrome and apnea of infancy. Antihistamines attenuate a similar vagally mediated pulmonary chemoreflex. The intravenous antihistamine effect on the LCR was studied in neonatal piglets. Laryngeal muscle activity, respiration, blood pressure, and pulse were measured during water stimulation of the LCR. After baseline LCR recordings, intravenous diphenhydramine (2.5 mg/kg) or cimetidine (20 mg/kg) was bolused (control group received saline). LCR measurements were repeated over 7 hours. Diphenhydramine significantly shorted apneas (P < .05) 3 to 7 hours after drug bolus, which is believed to be secondary to central atropinic effects. Cimetidine demonstrated no attenuation of the LCR.