The comparative pharmacodynamics of remifentanil and its metabolite, GR90291, in a rat electroencephalographic model. 1999

E H Cox, and M W Langemeijer, and J M Gubbens-Stibbe, and K T Muir, and M Danhof
Division of Pharmacology, Leiden/Amsterdam Center for Drug Research, Leiden University, The Netherlands.

BACKGROUND The purpose of this study was to investigate the in vivo pharmacodynamics and the pharmacodynamic interactions of remifentanil and its major metabolite, GR90291, in a rat electroencephalographic model. METHODS Remifentanil and GR90291 were administered according to a stepwise infusion scheme. The time course of the electroencephalographic effect (0.5-4.5 Hz) was determined in conjunction with concentrations of the parent drug and the metabolite in blood. RESULTS Administration of remifentanil resulted in concentrations of remifentanil and GR90291 in the ranges 0-120 ng/ml and 0-850 ng/ml, respectively. When the metabolite was administered, concentrations of the metabolite in the range 0-220 microg/ml and no measurable concentrations of remifentanil were observed. The mean +/- SE values of the pharmacokinetic parameters clearance and volume of distribution at steady state were 920+/-110 ml x min(-1) x kg(-1) and 1.00+/-0.93 l/kg for remifentanil and 15+/-2 ml x min(-1) x kg(-1) and 0.56+/-0.08 l/kg for GR90291. The relative free concentrations in the brain, as determined on the basis of the cerebrospinal fluid/total blood concentration ratio at steady state, were 25+/-5% and 0.30+/-0.11% for remifentanil and GR90291, respectively. Concentration-electroencephalographic effect relations were characterized on the basis of the sigmoidal Emax pharmacodynamic model. The mean +/- SE values for the maximal effect (Emax), the concentration at which 50% of the maximal effect is obtained (EC50), and Hill factor for remifentanil were 109+/-12 microV, 9.4+/-0.9 ng/ml, and 2.2+/-0.3, respectively (n = 8). For GR90291, the mean +/- SE values for EC50 and the Hill factor were 103,000+/-9,000 microg/ml and 2.5+/-0.4, respectively (n = 6). CONCLUSIONS Analysis of the data on the basis of a previously postulated, mechanism-based pharmacokinetic-pharmacodynamic model for synthetic opioids revealed that the low in vivo potency of GR90291 can be explained by a low affinity to the mu-opioid receptor in combination with a poor brain penetration.

UI MeSH Term Description Entries
D007262 Infusions, Intravenous The long-term (minutes to hours) administration of a fluid into the vein through venipuncture, either by letting the fluid flow by gravity or by pumping it. Drip Infusions,Intravenous Drip,Intravenous Infusions,Drip Infusion,Drip, Intravenous,Infusion, Drip,Infusion, Intravenous,Infusions, Drip,Intravenous Infusion
D008297 Male Males
D010880 Piperidines A family of hexahydropyridines.
D001921 Brain The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM. Encephalon
D004347 Drug Interactions The action of a drug that may affect the activity, metabolism, or toxicity of another drug. Drug Interaction,Interaction, Drug,Interactions, Drug
D000077208 Remifentanil A piperidine-propionate derivative and opioid analgesic structurally related to FENTANYL. It functions as a short-acting MU OPIOID RECEPTOR agonist, and is used as an analgesic during induction or maintenance of general anesthesia, following surgery, during childbirth, and in mechanically ventilated patients under intensive care. 3-(4-Methoxycarbonyl-4-((1-oxopropyl)phenylamino)-1-piperidine)propanoic Acid Methyl Ester,GI 87084B,GI-87084B,GI87084B,Remifentanil Hydrochloride,Remifentanil Monohydrochloride,Ultiva
D000701 Analgesics, Opioid Compounds with activity like OPIATE ALKALOIDS, acting at OPIOID RECEPTORS. Properties include induction of ANALGESIA or NARCOSIS. Opioid,Opioid Analgesic,Opioid Analgesics,Opioids,Full Opioid Agonists,Opioid Full Agonists,Opioid Mixed Agonist-Antagonists,Opioid Partial Agonists,Partial Opioid Agonists,Agonist-Antagonists, Opioid Mixed,Agonists, Full Opioid,Agonists, Opioid Full,Agonists, Opioid Partial,Agonists, Partial Opioid,Analgesic, Opioid,Full Agonists, Opioid,Mixed Agonist-Antagonists, Opioid,Opioid Agonists, Full,Opioid Agonists, Partial,Opioid Mixed Agonist Antagonists,Partial Agonists, Opioid
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D017208 Rats, Wistar A strain of albino rat developed at the Wistar Institute that has spread widely at other institutions. This has markedly diluted the original strain. Wistar Rat,Rat, Wistar,Wistar Rats
D051381 Rats The common name for the genus Rattus. Rattus,Rats, Laboratory,Rats, Norway,Rattus norvegicus,Laboratory Rat,Laboratory Rats,Norway Rat,Norway Rats,Rat,Rat, Laboratory,Rat, Norway,norvegicus, Rattus

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