Grey has diarrhea due to meds

So a few weeks ago my recently adopted grey tested positive for hookworms.

This week he has been on Panacur and he was also prescribed NexGard for his monthlies.

Three days on the Panacur and I was asked to give him the NexGard (they wanted to wait for his heartworm test to come back).

Since that day he has had nothing but diarrhea, almost every few hours.

Are there any remedies to this? I want him to feel better asap. Just not sure what to do.

EDIT: Thank you for all the kind advice. His stomach is doing a lot better now. Rice and Olewo was the trick. Now it’s just the process of getting this worms out!