I don't know. But, it is so easy to prepare the standard 50 mg tablets to what ever doseage you want, and it ought to save a lot of money.
The tablets dissolve very easily in water. I take a 50 mg tablet and put it in a small bottle with 50 ml of water. Let it set overnight to dissolve. 1 ml of the dissolved liquid will contain 1 ml of Naltrexone . If you want to start off with 2 mg LDN, then withdraw 2 ml (I use a syringe with the needle removed) and squirt it into orange juice or some something similiar. If you want 4.5 mg, then withdraw 4.5 ml. (Likewise, you can mix 50 mg Naltrexone into 25 ml of water, and 1 ml of solution will give 2 mg of LDN. Mix 2.5 ml of this solution to give 4.5 mg LDN.)
I just started 2 weeks ago. Too early to see how things are working, but I am starting a 2 mg and will gradually work up towards the magical 4.5 mg.