Posted by bodhisattva_guy on February 10, 2011, at 1:04:23
In reply to Switch from Effexor IR to Cymbalta, posted by molley55 on February 6, 2011, at 12:10:41
Duloxetine (cymbalta)
http://books.google.com/books?id=Rf8aGXexUKMC&pg=PA79
Duloxetine is an antidepressant that inhibits both serotonin and norepinephrine reuptake. Although similar to venlafaxine(effexor), duloxetines's greater potency at noradrenergic reuptake is thought to contribute to its greater efficacy in pain treatment than venlafaxine. It is approved by the FDA for use in major depression, generalized anxiety disorder, diabetic neuropathic pain, and fibromyalgia. The recommended therapeutic doses range from 40-60 mg daily, but lower doses (20-30 mg daily) should be used for the first week of treatment to avoid adverse effects. Although clinical studies do not support doses higher than 60 mg daily, our experience suggests that higher doses are usually necessary for pain syndromes related to fibromyalgia and other autoimmune diseases. Common adverse effects are nausea, decreased appetite, constipation, headache, dry mouth, insomnia, and somnolence. Men, but not women, treated with duloxetine experience more difficulty achieving orgasm compared to placebo. Increases in both systolic and diastolic blood pressure of approximately 2 mm Hg and an increase in heart rate of 3-4 beats per minute. Some patients experience palpitations but clinically significant changes in electrocardiograms were not different in duloxetine and placebo groups in premarketing studies. The drug is among a class of agents that increase urethral resistance, which may lead to urinary hesitation. Duloxetine has an elimination half-life ranging from 8-17 hours, with hepatic metabolism by P450 isozymes CYPIA2 and CYP2D6. Numerous metabolites are produced, but it is believed that the primary therapeutic effect is from the parent compound.
Venlafaxine's half life is 4-5 hours, but it's metabolite which is just as active has a half-life of 9-15 (11) hours. It is absorbed somewhat slowly, with T[max] of 4-4 hours (it takes that long for body to fully absorb the dose you've taken). It is down-regulated beta-adgrenergic receptors which is associated with more rapid onset of AD effects. It is also considered effective antianxiety agent.Have you considered desvenlafaxine ? Only few differences among these two meds - main one being that 50 mg is good enough for initiation and maintenance. (I suppose it's due to it's much longer half life and t[max]. At lower doses venlafaxine acts on serotonin and higher doses (225 mg and more) causes stronger effect on NE receptors.
It is recommended to switch to longer half-life agent after stopping effexor IR. Similar effect might be achieved by bupropion with 20 h half life after chronic dosing. It is twice as active on NE than DO, and limited or no effects on SE.
Since it is consider to have no effects on SE - you don't have to worry about serotonin syndrome.
But I would be worried about possible psychotic type of effects.
poster:bodhisattva_guy
thread:978754
URL: http://www.dr-bob.org/babble/20110130/msgs/979037.html