I used "Cetaphil" as a soap substitute, even when showering (it's Ph balanced) to pre-empt any dermatology problems and it appeared to work although I got very dry and 'thin' skin.
A chemist may be able to assist, but if you get no joy, hopefully your doc can prescribe something to help.
cetaphil was good, so is aveeno, eucerin, please tell him not to take hot shower, and to stay out of sun. i tried benadryl but it did not do much, so had to go to dermatologist and they gave me atarx which helped me soooooo much, they also gave me a creme which i have mixed with the cetaphil to put on rash. i used a plastic container with lid, and when i get out of shower just smear that all over where the rash is. I know how he must feel, that drove me insane until i got it under control. I am also not a doctor, i can only tell you what was suggested to me, and what has happened to me, our problems may not be the same, But on the itching and itching driving you crazy? YES i have gone thru it!!!! ( lol and it's not funny!!!)
also tell him to try not to scratch so much that scratching feels soooooo good , but its' not good, my rash started spreading, and i also do not take showers daily anymore if i can get away with it, the water is very harsh on skin. also drink plenty of water (try to at least)
Any of the nice thick moisturizers that won't come off easily will be very helpful. Personally for me and a bunch of folks on here was the Gold Bond Triple Therapy Anti Itch Medicated Lotion (Green Bottle, Red Top) worked the best. The secret is though don't just put it on once a day, use it several times a day. And when the itching stops after a few days...don't discontinue or the rash will come right back.
I found out that the hard way.
In addition he should be drinking half his body weight in ounces of water a day. The dehydration issue really is a big deal for people on treatment unfortunately. It will end though when tx is over.
I used pure olive oil soap to shower then Aveeno oatmeal lotion and that helped quite a bit.
I found information on this forum 9+ months ago that a filter for clorine elimination/reduction on your showerhead may help prevent the skin dryness that in turn may cause or irritate riba rash. I have used this filter on my shower and never got the rash. I have extremely sensitive skin and used Lubriderm twice a day and the clorine filter and went the entire winter/spring/summer treating for Hep C.
Hope this information helps.