Partial agonists definition

As with Section 6.8.5 (inverse agonists), the pA2 is derived by equating the response produced by the full agonist in the absence of the partial agonist (Equation 6.77 with [B] = 0) to the response in the presence of a concentration of the partial agonist that produces a dose ratio of 2 (by definition, the pA2). For calculation of KB from 10-pA2 ... 

Both DCI and IEG are now classified as partial agonists. Partial agonist, by definition, is a comparative description. When substance B is unable to produce as large a maximum response as... 

Buprenorphine 4-6 20-30 Partial agonist. Can act as antagonist in concomitant treatment with other opioid. Also available as plaster without definite advantages as concerns the method of administration. Probably lower risk of dependence... 

Intrinsic activity Intrinsic activity is the maximal stimulatory response induced by a compound in relation to that of a criven reference compound. This term has evolved with common use. It was introduced by Ariens as a proportionality factor between tissue response and receptor occupancy. The numerical value of intrinsic activity (alpha) could ran from unity (for full agonists, i.e., agonist inducing the tissue maximal response) to zero (for antacyonists). The fractional values within this ran denoting partial agonists. Arien-8 original definition equates the molecular nature of alpha to maximal response only when response is a linear function of receptor occupancy. This function has... 

Daveu C, Bureau R, Baglin I, Prunier H, Lancelot LC, Rault S. Definition of a pharmacophore for partial agonists of serotonin 5-HT3 receptors. J Chem Inf Comput Sci 1999 39 362-369. 

Hoyer, D. and Boddeke, H.W.G.M. (1993) Partial agonists, full agonists, antagonists dilemmas of definition. Trends Pharmacol. Sci. 14 270-273. 

F. Efficacy Efficacy, often called maximal efficacy, is the maximal effect (E,.,.,) an agonist can produce if the dose is taken to very high levels. Efficacy is determined mainly by the nature of the receptor and its associated effector system. It can be measured with a graded dose-respon.se curve (Figure 2-1) but not with a quantal dose-response curve. By definition, partial agonists have lower maximal efficacy than full agonists (see below). 

The majority of these compounds are agonists or partial agonists. Pure antagonists, devoid of any agonistic activity at presynaptic receptors (somatodendritic autoreceptors) or postsynaptic receptors were identified only very recently (for details of the definition of agonists, partial agonists and antagonists, see [6]). 

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