Side effects of CDK inhibitors
The most common side effects in palbociclib (Ibrance) and ribociclib (Kisqali) were low white blood cell counts, a side effect known as neutropenia. White blood cells play a central role in the immune system, and neutropenia is known to lead to a higher risk of infection. Bardia did not find this result surprising, as white blood cells are directly affected by CDK inhibitors’ cell division function. The good news is that taking a CDK inhibitor has no permanent effects on the body. White blood cell count will rise and any impact on the individual will be normalized upon going off the drug or reducing dosage.
Neutropenia is not as prevalent an issue in abemaciclib as it is in the other two CDK inhibitors. Instead, more common side effects such as diarrhea and fatigue are more common. With all CDK inhibitors, some mild side effects can include nausea and some alopecia, but they rarely impact a person’s day-to-day lifestyle and can be eliminated simply by lowering the dosage or planning on taking breaks.
Bardia and his team turned their attention to drug interactions and discovered that certain drugs interacted with the new CDK inhibitors. Drugs that interfered with the production of CYP3A—an enzyme responsible for breaking down CDK 4 and CDK 6 enzymes in the liver—were found to lead to high levels of the CDK inhibitors in the liver. As such, Bardia and his team wrote in their review to be aware of interactions with the antibiotic clarithromycin, and even grape juice.