Sunday, January 12, 2014

Duloxetine (Cymbalta) part 7

Pharmacology
Pharmacodynamics
The antidepressant properties of duloxetine are due to blocking the reuptake of serotonin and possibly also noradrenalin within the central nervous system.[47] Major depressive disorder is believed to be due in part to an increase in pro-inflammatory cytokines within the central nervous system. Antidepressants including ones with a similar mechanism of action as duloxetine, i.e. serotonin metabolism inhibition, cause a decrease in proinflammatory cytokine activity and an increase in anti-inflammatory cytokines; this mechanism may apply to duloxetine in its effect on depression but research on cytokines specific to duloxetine therapy is lacking.[48] The analgesic properties of duloxetine in the treatment of diabetic neuropathy and central pain syndromes such as fibromyalgia are believed to be due to sodium ion channel blockade.[49]
It is also considered a less potent inhibitor of dopamine reuptake. However, duloxetine has no significant affinity for dopaminergic, adrenergic, cholinergic, histaminergic, opioid, glutamate, and GABA receptors and can therefore be considered to be a selective reuptake inhibitor at the 5-HT and NA transporters. Duloxetine undergoes extensive metabolism, but the major circulating metabolites do not contribute significantly to the pharmacologic activity.
Pharmacokinetics
Duloxetine has an elimination half-life of about 12 hours (range 8 to 17 hours) and its pharmacokinetics are dose proportional over the therapeutic range. Steady-state is usually achieved after 3 days.
Elimination of duloxetine is mainly through hepatic metabolism involving two P450 isozymes, CYP2D6 and CYP1A2.
When orally administered it is well absorbed. There is an average 2-hour lag until absorption begins with maximum plasma concentrations occurring about 6 hours post dose. Food does not affect the Cmax of duloxetine, but delays the time to reach peak concentration from 6 to 10 hours. Duloxetine is highly bound (>90%) to proteins in human plasma, binding primarily to albumin and α1-acid glycoprotein.

Metabolism and Elimination — Only trace amounts (<1%) of unchanged duloxetine are present in the urine and most of the dose (approx. 70%) appears in the urine as metabolites of duloxetine with about 20% excreted in the feces.

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