Non drowsy antihistamines with opiates

[Tortoise]

Howdy
Swim would like to know if it is safe to use non-drowsy antihistamines with opiates (codeine in particular). He wants to get rid of itching and finds that regular antihistamines make him way too sleepy (he is very sensitive to them). He recalls reading somewhere that it is not safe though....

Any thoughts?

[tayo]

As far as I know, it is safe. Some anti-histamines can inhibit liver enzyme CYP3A4 (like drowsy hydroxyzine) EDIT: read it can also inhibit cyp2d6, that is not the one responsible for conversion to morphine.

What you've heard may be regarding antihistamines with ephedrine in them which are usually for allergies (if that's what you meant by "non-drowsy antihistamines") and this could present danger in the form of arrythmias, or respiratory depression from the combination of a bronchodilator with something that already slows the heart.
Hope that helps.