Diphenhydramine definitely suppresses fentanyl-induced cough during general anesthesia induction: a double-blind, randomized, and placebo-controlled study

 Fentanyl-induced cough (FIC) is a known complication and many studies have been conducted to prevent it. The aim of this study was to evaluate the effectiveness of Diphenhydramine as an antihistamine in suppressing of FIC during induction of anesthesia.

In a prospective double-blind randomized controlled trial, a total of 100 patients, ASA Class I and II, scheduled for elective laparoscopy surgery were randomly assigned into two equally sized groups (n = 50). Diphenhydramine diluted with distil water as 10mg/ml. Then, patients in Group D, received diphenhydramine 30 mg (3ml) through peripheral IV line within 1 min and Group C received same volume normal saline 0.9% as placebo. Two min later, fentanyl 2 µg/kg was administered through the peripheral IV line within 5 sec in all patients. The occurrence and intensity of cough within 2 min after the fentanyl injection were observed and recorded by a resident who was blinded to the study groups. The frequency of PONV, analgesic requirement in recovery room and as a secondary outcome were recorded.

The incidences of FIC were 47% in control group and there is no any cough in the diphenhydramine group (P = 0.02). The frequency of PONV was also reduced in diphenhydramine group (16% vs 40%) and less number of patients in diphenhydramine group were needed to analgesia in recovery room (60% vs 82%)

Our study determines that diphenhydramine (30 mg, IV) bolus injection 2 min before fentanyl injection can prevent FIC and PONV and also reduce analgesic requirement in recovery room.