Slick, while you're vet is at it (giving Max Vitamin B shots) have him add in some potassium. I believe Max's "weakness" can be directly attributed to a deficiency in potassium that is very common in CRF cats. When I first brought Tubby in and thought he was a goner, the vet immediately knew the reason he couldn't lift his butt was because his potassium deficiency was making his back legs weak. I had thought it was arthritis myself, but the vet immediately knew it had nothing to do with arthritis - and I'm soooo sorry it too this long for this to dawn on me!

Tubby got his potassium replenished with an additive that was included in the fluids we gave him. Between the fluids and the potassium, we noticed an immediate improvement in Tubby. Since Max doesn't do well with the fluids, ask the vet if he can include the potassium in Max's shots, or maybe there's a pill you can give him.

Here's some information from the web:
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POTASSIUM DEFICIENCY IN THE CAT



Hypokalemia is the medical term for a depletion of potassium in the body. Potassium is one of the essential electrolytes that keeps the body healthy and functioning properly. It is very important in kidney, muscle and heart function.

The most common cause of hypokalemia (low potassium) is chronic kidney disease. Poorly functioning kidneys leak potassium into the urine. Cats fed certain diets or given a supplement to acidify the urine may be more likely to suffer from potassium loss. Potassium deficiency is also common in older cats (twelve years of age or more) in general, with or without kidney disease. Older cats are less efficient at absorbing potassium from their food and they tend to lose more of it in their urine. Even without obvious signs of kidney disease, all older cats have some degree of decreased kidney function, which occurs naturally with time.

SIGNS. In the beginning stages of potassium deficiency, signs are very subtle, and often attributed to “old age” or other diseases. Cats may show weight loss, muscle weakness or stiffness, poor hair coat, poor appetite, and listlessness. These signs are usually not evident until the condition has become severe and possibly life threatening.

DIAGNOSIS. Diagnosis is confirmed by the determination of low levels of blood potassium through blood testing. Laboratory results must be interpreted in relation to clinical signs and history, since cats may have a normal blood potassium level and still have serious total body potassium depletion. This is because the body mobilizes stores of potassium from the muscle tissue to keep the amount of potassium in the blood constant. Low blood potassium levels don’t appear until all the muscle stores of potassium have been used up. It then takes a long time to restore potassium levels to a healthy amount in both blood and muscle tissues.

TREATMENT. Although severe potassium deficiencies may require hospitalization and intensive care, along with intravenous potassium administration, the treatment for chronic but not life-threatening hypokalemia is to add potassium to the diet. The most common brand of supplement, Tumil-Kä, is a source of potassium gluconate. It is available in a tablet, a paste similar to a hairball remedy, or a powder that can be mixed in canned food. Most cats will readily accept one of these forms of supplement.

RESPONSE TO TREATMENT. Visible response to supplementation can take 4-8 weeks. Your veterinarian will want to recheck your cat’s blood to monitor potassium levels on a regular basis. This will ensure the appropriate dosage is achieved and maintained. Lifelong therapy is usually required once hypokalemia has been diagnosed.
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Again, I'm sooooo sorry it took me this long to remember this, but I think it was your recent descriptions of how Max has a hard time lifting his back end that triggered my memories of Tubby.

{{{hugs}}} to you and good luck. I adored the pictures of Max with all his stuffy friends. He's such a cutie pie.

Oh, and I don't know if Max will tolerate them, but they do make diapers for doggies that may work for Max. If you remember, Peanut did quite well with them. I think it made her look totally pathetic, but she didn't seem to mind them and they took a huge load off my mind. Instead of spending time on finding pee spots and cleaning them, you can spend time snuggling with your little boy.