Tuesday, November 08, 2005

Side effects: antidepressants for chronic pain

The web page linked above has an excellent table of the pharmacalogical effects of various drugs used for chronic pain. I came across it many moons ago but foolishly did not save a link, and only now have found it again. I will save a copy here to make sure I don't lose it again.

Antidepressant Effects
Drug Antimuscarinic
Activity1
Antihistaminic
Activity2
α-1 blocker3 NE reuptake
inhibition4
5-HT reuptake
inhibition5
T1/2 (hours)*
Amitriptyline 3 3 3 2 4 32–40
Doxepin 2 4 3 1 2 8–25
Imipramine 2 1 1 2 4 6–20
Desipramine 1 0 1 4 3 12–54
Nortriptyline 1 1 2 2 3 15–90
Trazodone 0 0.5 2 0 3 3–9
Fluoxetine 0.5 0 0 1 4 168–210
Bupropion 0 0 0 0 0 0
  1. Blocks the muscarinic-type acetylcholine receptors, an effect commonly called anticholinergic. Causes side effects like increased heart rate, dry mouth, digestive slowing, and so forth.
  2. Blocks H1 and H2 histamine receptors. Causes side effects like drowsiness, reduced stomach acid, and so forth. Probably helps allergies, not that you'd take these drugs for that.
  3. Blocks α-1 (alpha-1) receptors. Causes a variety of effects, most notably relaxation of smooth muscle. This causes small blood vessels to dilate, lowering blood pressure, possibly enough to cause dizziness or even fainting.
  4. Blocks the norepinephrine reuptake transporter, thus exposing brain cells to more of the neurotransmitter norepinephrine. May be responsible for antidepressant effects.
  5. Blocks the 5-HT reuptake transporter. (5-HT stand for 5-hydroxytryptamine, also known as serotonin.) This exposes brain cells to more of the neurotransmitter serotonin.
*Half-life, the time it takes for half of a dose to leave the body.

So what does all that mean? For starters, that I ought to try switching from amitriptyline to nortriptyline. It ought to give much less of the obnoxious side effects, but retain much of the anti-migraine value.


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