Hello, your description sounds like rhabdomyolysis. Depending on the cause and the extent of this condition, it can be very serious and cause damage to the kidneys and other organs. When the creatinine is very high and unless he s got acute renal failure, he should drink enough fluids to increase the volume of urine and protect his kidneys. Besides that, keeping an eye on the electrolytes might be useful. I can t say why he is feeling weak. Perhaps a low potassium? The rhabdomyolysis itself, unless very very severe is not supposed to make him feel weak. He should also avoid any kind of drugs, alcohol and muscle exertion. I hope I ve helped! You can contact me again, if you d like any clarifications or further information. Kind Regards!