Magnesium

"Can magnesium be low even though serum magnesium is in the normal range?"

Yes. Magnesium (along with calcium) is a critical electrolyte our plasma (circulatory system/ tissues) needs in the correct ratio with other electrolytes (Na, K, Ca) and in balance or we die. They are maintained in very tight ranges. Our bones are storage for calcium, for example, and our muscles are storage for magnesium. When you are low on magnesium, the first place you feel it is in your muscles (cramping), but your blood level would remain normal.

Sprycel (and the other TKI's) can and often does affect magnesium levels - mostly by interfering with the natural balance. Supplementing with Magnesium (not oxide version) usually takes care of this. I take 400 mg magnesium taurate per day (citrate version is good too).

Sprycel can also affect potassium levels. Low potassium can manifest similarly to low magnesium (cramping). But potassium is plentiful in food (veggies & citrus). Supplementing with potassium is usually not needed. And over supplementing can lead to cardiac issues. In contrast, over supplementing with magnesium just leads to bowel issues which are corrected by cutting back. Excess magnesium (& potassium) are eliminated by the kidney.

https://www.health.harvard.edu/staying-healthy/should-i-take-a-potassium...

If you drink coffee - odds are you are getting plenty of potassium. Avocado's are rich in potassium.