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ANESTHETIC PHARMACOLOGY

Selective Phosphodiesterase 5 Inhibition Does Not Reduce Propofol Sedation Requirements but Affects Speed of Recovery and Plasma Cyclic Guanosine 3',5'-Monophosphate Concentrations in Healthy Volunteers

Academic Unit of Anaesthesia and Intensive Care, Institute of Medical Sciences, University of Aberdeen, Aberdeen, Scotland, United Kingdom

Address correspondence and reprint requests to Thomas Engelhardt, MD, PhD, FRCA, Academic Unit of Anaesthesia and Intensive Care, Institute of Medical Sciences, University of Aberdeen, Aberdeen, AB25 2ZD, Scotland, UK. Address e-mail to t.engelhardt{at}abdn.ac.uk.

Cyclic guanosine 3',5'-monophosphate (cyclic GMP) has been implicated in modulating the effects of anesthesia. We hypothesized that limiting the breakdown of cyclic GMP through selective phosphodiesterase inhibition would influence propofol sedation requirements and plasma cyclic GMP concentrations. Ten volunteers received 100 mg of sildenafil or placebo orally in this placebo-controlled, double-blind, randomized crossover pilot study. Propofol sedation was achieved using a target-controlled infusion system until loss of verbal contact (LVC). Plasma cyclic GMP concentrations were determined at baseline, LVC, and 30 min after LVC. There was no difference in the amount of propofol used, predicted plasma concentration, or duration of sedation in volunteers after sildenafil compared with placebo treatment. Return of spontaneous verbal contact was faster after sildenafil (4 [3–8] min versus 6 [3–5] min, median [range], P = 0.019). Cyclic GMP concentrations were reduced during propofol sedation in the placebo group compared with baseline (P < 0.004). The plasma cyclic GMP concentrations were larger (P = 0.004) at LVC in the sildenafil group compared with placebo. We have shown that selective phosphodiesterase 5 inhibition decreases recovery time from propofol sedation without affecting propofol requirements. The decrease of plasma cyclic GMP concentrations during propofol sedation in the placebo group indicates a potential role of cyclic GMP in propofol anesthesia in humans.

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