Switch to a Longer half life = more chemical in your system? And not tapering?

I have a question about half life when switching and tapering.  I am currently tapering down an anti-depressive drug at the moment and switching to a longer half life one to help it. As I am intolerant to serotonin based meds and need to get off.

I’m now down to 37.5mg of Effexor XR (half life about 12 hours) and going to switch to Zoloft (half life about 26 hours). Now to get the dose right I’ve looked up the tables and 37.5mg is equal to 25mg of Zoloft (both are half the usual daily dose) right. Good. But the problem in my head is half life. It’s twice as long! So if I do the math:

Effexor 25mg a day (equivalent of Zoloft), it drops 2 half life’s so down to 6mg when I take the next days dose. Ok

Zoloft 25mg daily dosing, goes down only 1 half life to 12.5mg when I take the next days dose and so on.

So my question is am I actually getting an equal dose of serotonin as the half life is twice the amount so each day it increases by a higher amount compared to the Effexor. I don’t want to go up the serotonin ladder so to speak but rather down or at least equal for now and then down. Or am I completely missing something here and mistaken here??

It’s the same with the benzodiazepines rule: switch 3mg Xanax to 30mg diazepam then taper it but the Xanax will never be more than 5mg in your system if you do the math with its half life however the diazepam will be several 100mg in your system after successive doses. Aren’t you ODing yourself even higher than before?

Thanks

Hi BBZedd,

You're asking a good question, and hopefully I can answer it for you.

It's my understanding that when creating a drug conversion chart, benzo-to-benzo or SSRI-to-SSRI etc., the half-life is a BIG part of the equation.

You mention 3mg alprazolam being equal to 30mg of diazepam; actually the Ashton equivalent for 3mg of alprazolam is 60mg of diazepam, and more importantly, the conversion chart is saying that 60mg of diazepam will feel equivalent to 3mg alprazolam ONLY after the user has built up enough doses to be a their peak blood serum level. With diazepam this can take many days of regular dosing.

To put it another way, the first 60mg diazepam dose, from what I've read, feels like a drop in the bucket compared to 3mg alprazolam. Many buddies who've been prescribed a sudden cross from a short-to-long benzodiazepine have expressed that the new drug isn't working at all for them; their doctor usually forgot to mention that the new drug wouldn't reach full potency until after days if not weeks of regular dosing. In the mean time, their short-acting benzo is being rapidly eliminated from their blood.

This is why Dr. Ashton's crossover schedules to diazepam from short-acting benzos are step-wise and gradual; I understand that there is still usually an uncomfortable lapse in blood serum levels when done over 4-6 week-long steps, but it's more tolerable.

So the short of it is, I think the half-life is already a part of the crossover chart, but going from a short-to-long half-life will result in a dip in blood serum levels. If the conversion chart you're using, which are all quite speculative IMO, is reasonably accurate then you won't be "go up the serotonin ladder" when you cross; instead I'd expect a lapse in dose strength and possibly side-effects from this temporary withdrawal.

I hope this helps.