Originally Posted by
Dying_Swan
I know you said quetiapine has a short half life of 6-7 hours. I'm just wondering how it can help depression if half of it is out of my system by the time I wake up? Is it supposed to do its job when I'm asleep? Sorry if it's a silly question,
The only silly questions are those that are never asked.
Quetiapine seems to work by enhancing the ability of antidepressants to grow new brain cells (neurogenesis) in the hippocampal regions of the brain. Its active metabolite norquetiapine is also a fairly potent noradrenaline, aka norepinephrine, reuptake inhibitor which may add to its effectiveness at higher doses.
As for the short half-life, norquetiapine has a similar half-life, but I don't know whether this actually lengthens the time the med remains effective as the NRI antidepressant impact is distinct from the parent drugs neurogenesis affect. I think they probably run in parallel rather than serially. Either way, with daily dosing plasma levels of both quetiapine and norquetiapine reach a *steady-state in about 2 days at which point their plasma levels will remain pretty much constant across 24 hours. But for a good therapeutic outcome immediate-release quetiapine should be taken 2-3 times a day. The XR formulation only needs to be taken once daily, preferably in the evening.
* as a rule of thumb it takes about 5 half-lives for a med's plasma levels to stabilize to a steady-state with regular dosing