guanfacine pharmokinetics

[doctordog]

I'm a bit confused about Guanfacine IR. The half-life is listed as around 17 hours, yet it's regularly dosed b.i.d. -- q.i.d. Is it similar to dexamphetamine where the half-life is rather long, yet the therapeutic action is less so?

To expand on that, I took a dose in the morning and fell asleep for about 6 hours due to the sedation. When I woke up, I was more energetic, anxious and felt unusually sensitive to the cold, with cold hands/feet. My biochemistry is zilch, but I googled and it appears that cold intolerance is linked to *low blood pressure* .. yet, vasoconstriction on stimulants etc. can also cause cold peripheries.

So would it be more likely that the cold intolerance was a rebound effect, or a side-effect of the drug?

 

[sekio]

If it's your first dose in a while, I'd call it rebound effects.

Just because the drug persists in the body, doesn't mean it will continue to produce effects. The drug could distribute to fatty tissues or somewhere that it's still in the body but can't produce an effect.

If it's dosed 2-4x a day then I would say that it has a short duration of effects compared to its half life.