TY - JOUR T1 - Quantification of Pharmacodynamic Interactions between Dexmedetomidine and Midazolam in the Rat JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 347 LP - 355 VL - 294 IS - 1 AU - Cornelis J. J. G. Bol AU - John P. W. Vogelaar AU - Jian-Ping Tang AU - Jaap W. Mandema Y1 - 2000/07/01 UR - http://jpet.aspetjournals.org/content/294/1/347.abstract N2 - The pharmacodynamic (PD) interaction between the benzodiazepine agonist midazolam and the α2-adrenergic agonist dexmedetomidine was characterized for defined measures of anesthetic action and cardiovascular and ventilatory side effects in 33 rats. For various combinations of constant plasma concentrations of midazolam (0.1–20 μg/ml) and dexmedetomidine (0.3–19 ng/ml) obtained by target-controlled infusion, the whisker reflex (WR), righting reflex (RR), startle reflex to noise (SR), tail clamp response (TC), and corneal reflex (CR) were assessed. EEG (power in 0.5–3.5-Hz frequency band), mean arterial pressure, and heart rate were recorded continuously. Blood gas values and arterial drug concentrations were determined regularly. The nature and extent of PD interaction was quantified by the model parameter synergy (SYN < 0, antagonism; SYN = 0, additivity; andSYN > 0, synergy). With increasing drug concentrations WR was lost first, followed by RR, SR, TC, and CR. These effects were accompanied by an increase of the EEG measure. The drug interaction was synergistic for all stimulus-response measures and the degree of synergy increased with deeper levels of central nervous system depression (SYN was 7.3, 145, 560, 374, and 1490 for WR, RR, SR, TC, and CR, respectively). The cardiovascular side effects of dexmedetomidine, evaluated at similar PD endpoints, were reduced in the presence of midazolam. Ventilatory side effects were minor for all drug combinations. The nature and extent of the PD interactions were not reflected in the EEG measure. The American Society for Pharmacology and Experimental Therapeutics ER -