Clonidine prolongs fentanyl-induced ventilatory depression

Abstract

The aim of the present study was to investigate the effect of intravenously (i.v.) administered fentanyl and clonidine on ventilation in 12 healthy male volunteers (age 30.8±4.9 years) who either received fentanyl alone (1.5≥μg kg⁻¹) or fentanyl (1.5≥μg kg⁻¹) in combination with clonidine (3≥μg kg⁻¹). The effect on ventilation was measured with a CO₂ rebreathing system. The respiratory depression caused by fentanyl disappeared 120 min after injection. The corresponding slopes were 7430±2075 mL kPa⁻¹ prior to (t₀) and 6263±1864 mL kPa⁻¹ 120 min post-application (base-line vs. t₁₂₀; P=0.106). An impaired ventilatory response was observed during CO₂ rebreathing at t₁₂₀ after the injection of fentanyl and clonidine. Before drug administration, the slope of the response curves was 7700±2800 mL kPa⁻¹, which was reduced to 5480±2135 mL kPa⁻¹ (P<0.035) at t₁₂₀. These data suggest a prolongation of a fentanyl-induced ventilatory depression when used in combination with clonidine.