Ribociclib may potentiate rosuvastatin effect in causing late onset rhabdomyolysis.

A woman in her 50s with metastatic hormone receptor positive breast cancer developed rhabdomyolysis and subsequent acute kidney injury while on a combination of ribociclib and rosuvastatin therapy. She had been taking both medications long term and had recently recommenced her ribociclib at her usual dose after a routine 1 week break. Cyclin-dependent kinase 4/6 inhibitors have been implicated in causing rhabdomyolysis by potentiating statin effect by way of inhibition of cytochrome P450 enzymatic action and decreasing hepatic membrane transporter function. This is the first case in which the combination of ribociclib and rosuvastatin has been shown to cause this adverse effect. It is also one of the first to demonstrate this effect occurring years after commencement of therapy. Continued vigilance for this side effect should be maintained long term.