Posted by Jonathan on May 5, 2001, at 0:19:39
In reply to Re: Cough develops after starting Remeron, posted by SalArmy4me on May 4, 2001, at 1:15:52
> ....Allegra is a good medication to counter that side-effect, and allegra itself should have minimal side-effects.
Allegra (fexofenadine) is an antagonist at H1 receptors for histamine; so is mirtazapine (Remeron/Zispin), although this may not contribute to its antidepressant action.
Mirtazapine's affinity for H1 receptors is actually more than 10x higher than for 5-HT2A and more than 100x higher than for norepinephrine alpha-2. The latter two receptor types are both significantly blocked by therapeutic doses, implying that the concentration in the brain of someone taking 30 mg/day or more is high enough to block almost all the central H1 receptors -- this anti-H1 effect accounts for most of mirtazapine's sedating and appetite-stimulating action in the first six weeks of treatment. It would, therefore, also block nearly all the peripheral histamine receptors of the same type.
Fexofenadine is non-sedating because it cannot easily cross from the blood to the brain: its concentration at central H1 receptors is too low to cause sedation after doses which would block the peripheral H1 receptors (thus bringing about its antitussive and anti-allergy actions) but only if they weren't already blocked by mirtazapine. You shouldn't need to combine Allegra or any other H1-antihistamine with Remeron; if you do it will do you no harm but simply have no further effect.
Note that this does NOT apply to the H2-antihistamines like ranitidine (Zantac) used as anti-ulcer drugs: these affect a different histamine receptor and therefore can usefully be taken with mirtazapine.
See Figure 6.4 in
http://www.medscape.com/PCI/depression/depression.ch06/pnt-depression.ch06.html
or compare Slides 36 and 44 of Dr Elliott Richelson's recent Grand Rounds:
http://psychiatry.uchicago.edu/grounds/010402/
Jonathan.
poster:Jonathan
thread:61559
URL: http://www.dr-bob.org/babble/20010424/msgs/61664.html