Hydroxyzine Pamoate - Not To Exceed 400mg per day?

[JamHarmReduction]

A prescription for hydroxyzine pamoate was written with the instructions NTE 400mg/day (Not to exceed).

I am curious as to why, on a pharmacological basis, that hydroxyzine pamoate should be limited to 400mg per day.

I have searched the internet, and have seen various sites that list dosages of hydroxyzine to be limited to 400mg, or 600mg, as well as limiting other anti-histamines be limited to a certain amount per day, but none that explain why. So far it seems like just an arbitrary number that someone put out there, and it has been continued. I have not seen any information that it is something like acetaminophen (Tylenol) that should not exceed 2000mg per day, due to risk of liver damage, and death.

 

[MagickalKat777]

I don't really think this belongs in NPD.

High doses of anticholinergic agents cause, among other things, hallucinations, delirium, irregular heartbeat, tachycardia, respiratory depression, seizures, coma, and death.

That would likely be the reasoning of such a limitation on dosage.

 

[Help?!?!]

^Hydroxyzine has very low mACH affinity so I don't think it would cause anticholinergic effects at any dose really though i'm not entirely sure.

 

[Kittycat5]

It probably came from clinical studies that showed no increase in efficacy but had a ton of side effects.

 

[MagickalKat777]

^Hydroxyzine has very low mACH affinity so I don't think it would cause anticholinergic effects at any dose really though i'm not entirely sure.

Dosage warnings seem to be applied to all first generation antihistamines across the board, regardless of muscarinic acetylcholine affinity.

Hallucinations have been reported with it though, regardless of it having almost no mACh affinity so there is something there. I would think that you'd be far more likely to get knocked out before you would hallucinate, however.

Generally things that make you hallucinate in a high dose have those labels. Doesn't DXM have a max daily dosage cap as well? I know that Marezine (cyclizine) does although that's a powerful mACh antagonist.

 

[sekio]

I'd imagine at 400mg+ effects like drowsiness, dry mouth, constipation and the like start being a problem.