I have no experience with it.
That does not help him much.
Diamox (acetazolamide) works best as a preventative starting 1-2 days before you need it and/or before any additional significant change in altitude (especially sleeping altitude) - even then it is not a very powerful drug despite a variety of medical studies. I have used it from here to the Himalaya. Sometimes not. It does not help everyone, some not at all. Proper dose is half of a 250 mg twice daily.
Yes, test doses before going up are advisable to be sure of any side effects AND actual drug allergy. They DO happen. Ask my wife.
