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Half maximal inhibitory concentration (IC 50) is a measure of the potency of a substance in inhibiting a specific biological or biochemical function. IC 50 is a quantitative measure that indicates how much of a particular inhibitory substance (e.g. drug) is needed to inhibit, in vitro, a given biological process or biological component by 50%. [1]
The EC 50 of a quantal dose response curve represents the concentration of a compound where 50% of the population exhibit a response, [5] after a specified exposure duration. For clarification, a graded dose response curve shows the graded effect of the drug (y axis) over the dose of the drug (x axis) in one or an average of subjects.
For antagonists, half maximal inhibitory concentration (IC50) is used to measure the potency of antagonists. IC50 means the concentration of antagonist needed to give a 50% inhibition. [33] It can be directly compared with EC50, which is commonly used to measure the potency of an agonist.
5α-RIs that were under development for potential clinical use but were never marketed or are used in research include the following: 4-MA – inhibits types 1 and 2 (IC 50 Tooltip half-maximal inhibitory concentration = 8.5 nM), but also 3β-HSD Tooltip 3β-hydroxysteroid dehydrogenase inhibitor, investigated extensively but found to be hepatotoxic [1]
Wortmannin, a steroid metabolite of the fungi Penicillium funiculosum, Talaromyces wortmannii, is a non-specific, covalent inhibitor of phosphoinositide 3-kinases (PI3Ks). ). It has an in vitro inhibitory concentration (IC 50) of around 5 nM, making it a more potent inhibitor than LY294002, another commonly used PI3K inhib
[3] [5] As (S,S)-CE-158, its inhibitory potencies (IC 50 Tooltip half-maximal inhibitory concentration) at the monoamine transporters are 227 nM at the dopamine transporter (DAT), 11,970 nM at the norepinephrine transporter (NET) (53-fold lower), and inactive at the serotonin transporter (SERT).
It is most efficacious as a releaser of norepinephrine, with an EC 50 of 109 nM (DA), 41.4 nM (NE), and 5,246 nM . [2] It also functions as a weak monoamine oxidase inhibitor (MAOI) (IC 50 Tooltip half-maximal inhibitory concentration = 130 μM for MAO-A Tooltip monoamine oxidase A and 750 μM for MAO-B Tooltip monoamine oxidase B). [3]
Propylamphetamine is inactive as a dopamine releasing agent in vitro and instead acts as a low-potency dopamine reuptake inhibitor with an IC 50 Tooltip half-maximal inhibitory concentration of 1,013 nM. [3] The drug can be N-dealkylated to form amphetamine (10–20% excreted in urine after 24 hours).