Can You Take Abemaciclib With Lopinavir and Ritonavir?

No. The U.S. FDA labels abemaciclib and lopinavir/ritonavir as contraindicated—meaning these medications should not be used together. This is the most serious level of drug-interaction warning. The combination poses a documented risk to the effectiveness of HIV treatment and raises concern about resistance to protease inhibitors, the class of antiretroviral drugs to which lopinavir/ritonavir belongs. If you are currently taking both medications, do not stop either one on your own; contact your prescribing physician and pharmacist immediately to discuss your treatment options.

What the Source Says

The FDA drug label for lopinavir and ritonavir (brand name KALETRA) explicitly warns that abemaciclib and other anticancer agents may interact with this HIV medication combination. The source record classifies this interaction as contraindicated severity—the highest level of clinical concern.

According to the FDA label, the documented concern is bidirectional:

• Anticancer agents (including abemaciclib) may increase in blood concentration, potentially raising the risk of cancer-drug side effects.
• Lopinavir/ritonavir may decrease in blood concentration, potentially reducing its ability to suppress HIV and increasing the risk of virologic failure and resistance to protease inhibitors.

The FDA label notes that this risk is particularly acute with one structurally similar anticancer agent (apalutamide), which carries an explicit contraindication due to the potential for loss of virologic response and resistance to KALETRA or to the entire class of protease inhibitors. Although the source record does not specify a distinct mechanism for abemaciclib, the pattern suggests a shared pharmacological concern across multiple anticancer agents in this interaction class.

Source provenance: This information comes directly from the FDA-approved drug label for lopinavir and ritonavir, which is the regulatory source-of-record for U.S. prescribers and pharmacists.

How to Understand This

To make sense of this interaction, it helps to understand what each drug does and how they may interfere with each other.

Abemaciclib is a cancer medication (specifically, a cyclin-dependent kinase 4 and 6 inhibitor, or CDK4/6 inhibitor) used to treat certain types of breast cancer. It works by blocking proteins that allow cancer cells to divide.

Lopinavir and ritonavir are antiretroviral medications used to treat HIV. Ritonavir is a potent inhibitor of a liver enzyme called CYP3A4, which breaks down many drugs in the body. When combined with lopinavir, ritonavir acts as a "booster," slowing the breakdown of lopinavir so that blood levels of the HIV medication remain high enough to suppress viral replication.

Why the conflict matters: Both abemaciclib and lopinavir/ritonavir depend on the same liver enzymes (CYP3A4 and others) for their breakdown and removal from the body. When these drugs are taken together, they compete for the same metabolic pathways. This competition can result in:

• Higher-than-expected levels of abemaciclib in the bloodstream, increasing the risk of cancer-drug toxicity.
• Lower-than-expected levels of lopinavir in the bloodstream, reducing the drug's antiviral potency and raising the risk that HIV will develop resistance to protease inhibitors.

Important clarification on mechanism: The source FDA drug label does not specify a detailed mechanism for the abemaciclib–lopinavir/ritonavir interaction. The above explanation draws on well-established general pharmacology of how these drug classes interact via shared liver metabolism, but the source record itself does not detail the exact pathway. What the source does specify is the clinical outcome concern: potential for decreased lopinavir/ritonavir effectiveness and increased anticancer-agent concentration.

Who Should Pay Particular Attention

This contraindication applies broadly to anyone taking abemaciclib who also requires HIV treatment with lopinavir/ritonavir. However, a few populations warrant particular consideration:

• Patients with HIV who have also been diagnosed with certain breast cancers: These individuals face a genuine clinical dilemma, as both conditions require treatment. The contraindication means that alternative cancer medications or alternative HIV regimens must be explored.
• Patients already on stable lopinavir/ritonavir therapy: If abemaciclib is being considered for cancer treatment, the switch to abemaciclib while continuing lopinavir/ritonavir would directly trigger this contraindication.
• Patients receiving abemaciclib who may need to start or switch to lopinavir/ritonavir: Changes to HIV therapy (e.g., due to resistance or intolerance to a current regimen) must account for the current cancer medication.

In all cases, the prescriber and pharmacist must be aware of all medications in use so they can work together to find a safe alternative.

Hypothetical Examples

Scenario 1 (documented risk): A person living with HIV has been stable on lopinavir/ritonavir for several years. A new breast-cancer diagnosis prompts an oncologist to recommend abemaciclib. Based on the FDA contraindication, adding abemaciclib while continuing lopinavir/ritonavir would risk both increased abemaciclib toxicity and reduced HIV-drug efficacy. The prescriber and HIV specialist would need to discuss whether an alternative cancer drug or an alternative HIV regimen is more feasible, given the patient's overall health, treatment history, and tolerability.

Scenario 2 (documented risk): A person is beginning treatment for cancer with abemaciclib and is later diagnosed with HIV or experiences virologic failure on their current HIV regimen, making a switch to lopinavir/ritonavir necessary. The contraindication means that proposing lopinavir/ritonavir while continuing abemaciclib would not be an appropriate solution. Instead, the healthcare team would explore alternative antiretroviral combinations that do not carry this same interaction risk with abemaciclib.

What to Discuss With a Pharmacist or Physician

If you are taking or considering taking both abemaciclib and lopinavir/ritonavir, these conversations are essential:

• "Are there alternative cancer medications I could take instead of abemaciclib that do not interact with my HIV regimen?" Other anticancer agents may be available, and your oncologist may be able to select one with a more favorable interaction profile.
• "Are there alternative HIV medications I could take instead of lopinavir/ritonavir?" Modern HIV treatment offers numerous protease-inhibitor and non-protease-inhibitor options, and your HIV specialist may identify a regimen that is safe to use alongside abemaciclib.
• "What should I do if I am already taking both of these drugs?" Do not stop either medication on your own. Your prescriber and pharmacist need to work together urgently to revise your treatment plan. Stopping HIV medication abruptly can lead to viral rebound and resistance; stopping cancer medication abruptly may allow cancer progression.
• "How will my treatment team monitor me while we transition to a new regimen?" Depending on the change, you may need blood tests to check HIV viral load, drug levels, cancer-marker levels, or liver and kidney function.
• "Are there any other medications or supplements I'm taking that might also interact with abemaciclib or lopinavir/ritonavir?" These two drugs interact with many other medications, and your full medication list should be reviewed by your pharmacist.

These questions are not a substitute for individualized medical advice. Your prescriber and pharmacist are best positioned to understand your specific situation, treatment goals, and available alternatives.

Key Takeaways

• Abemaciclib and lopinavir/ritonavir are labeled as contraindicated by the FDA—they should not be used together.
• The contraindication stems from documented concerns that these drugs interfere with each other's blood levels: abemaciclib may accumulate to toxic levels, and lopinavir/ritonavir may drop to ineffective levels, risking HIV treatment failure and drug resistance.
• If you are currently taking both medications, contact your prescriber and pharmacist immediately; do not stop either drug on your own.
• Safe alternatives exist. Your healthcare team can explore either a different cancer medication or a different HIV regimen that does not carry this contraindication.
• The FDA drug label is the official source of this contraindication and is binding for U.S. prescribers and pharmacists.

Sources

• DailyMed (National Library of Medicine) — A searchable database of FDA-approved drug labels, including the full prescribing information for lopinavir and ritonavir (KALETRA). You can access the current label by searching for "lopinavir ritonavir."
• Open FDA — A public-facing API and database of FDA drug information, adverse-event reports, and enforcement actions.
• RxNorm (National Library of Medicine) — A standardized vocabulary of medications maintained by the NIH, useful for verifying drug names and identifiers.
• PubMed (National Center for Biotechnology Information) — A searchable archive of peer-reviewed biomedical literature for background reading on anticancer agents, antiretroviral drugs, and drug–drug interaction mechanisms.

Abemaciclib and lopinavir/ritonavir are a contraindicated pair according to FDA drug labeling. This is a serious warning that applies to all patients, regardless of age or other health conditions. If you take either of these medications or are considering them, use the medication-checking tool at checkdruginteractions.com to review your full medication list for interactions, and confirm all medication decisions with your pharmacist or physician. Do not change, start, or stop any medication without professional guidance.