Painful, grooved, brown crust on tongue?

My 96 year old father is in the hospital, having had surgery for prostate and bladder problems. He is on antibiotic drip and has not eaten for over a week, because he has a problem with his mouth and tongue. The diagnosis is thrush, but no change after about 4 days on Nizoral. His tongue has a brown -- or possibly slightly orange-ish brown, but basically brown crust. He says it feels like a cut in his mouth. My sister says it looks like tire tracks or grooves in his mouth. He can't stand anything in his mouth. He wants to die, and this may be what does him in. But we are trying to look at the possibility of another diagnosis or a secondary diagnosis. Can you offer any further diagnosis, and if it is thrush, can you comment on the failure of the Nizoral to make a difference? Perhaps due to the ongoing antibiotics and his debilitated system, but just reaching out for more insight. Thank you very much.