Hycamtin Drug Interactions: What to Avoid and What to Tell Your Doctor

Drug interactions can make Hycamtin (topotecan) less effective or more dangerous. Because topotecan is a potent chemotherapy agent with a narrow therapeutic window, even seemingly minor interactions can have serious consequences. Before starting Hycamtin, tell your oncologist and pharmacist about every medication, supplement, and herbal product you take. This guide covers the most important interactions to know.

How Drug Interactions Work With Topotecan

Most of topotecan's significant drug interactions involve

P-glycoprotein (P-gp, also called MDR1) — a transporter protein found in many tissues that helps move topotecan out of cells and into the bloodstream for excretion. Drugs that inhibit P-gp cause topotecan levels in the body to rise above normal, increasing the risk of serious toxicity. This effect is especially pronounced with the oral capsule formulation (where the drug is absorbed through the gut, where P-gp is heavily expressed).

Topotecan is also substantially excreted by the kidneys. Drugs or conditions that reduce kidney function can raise topotecan levels by slowing its elimination.

Major Interactions: Avoid These With Oral Hycamtin

The Hycamtin prescribing information specifically recommends avoiding P-gp inhibitors when taking oral topotecan. These include:

Cyclosporine (Neoral, Sandimmune, Gengraf) — Immunosuppressant; is a P-gp inhibitor that significantly raises topotecan blood levels. Listed as a major interaction requiring avoidance or alternative therapy.

Ketoconazole — Antifungal medication; potent P-gp and CYP3A4 inhibitor that can substantially increase topotecan exposure.

Nilotinib (Tasigna) — Targeted cancer drug (BCR-ABL inhibitor); P-gp inhibitor. Avoid or use alternative. This is a "serious — use alternative" interaction.

Abiraterone (Zytiga) — Prostate cancer drug; P-gp inhibitor. Avoid or use alternative.

Felodipine (Plendil) — Calcium channel blocker for blood pressure; P-gp inhibitor. Labeled as a "serious — avoid" interaction for oral topotecan.

Moderate Interactions: Use With Caution or Monitor Closely

G-CSF (filgrastim, pegfilgrastim, sargramostim) — Colony-stimulating factors are often used to help rebuild white blood cell counts. However, starting G-CSF before Day 6 of each Hycamtin cycle (or less than 24 hours after the last topotecan dose) actually prolongs the duration of neutropenia. G-CSF should not begin until Day 6 at the earliest.

Cisplatin — When used together (as in the cervical cancer regimen), myelosuppression is more severe than with topotecan alone. Close blood count monitoring is essential.

Olaparib (Lynparza) — PARP inhibitor; pharmacodynamic synergism with topotecan. Both suppress bone marrow; combination increases myelosuppression risk. Monitor closely.

Abemaciclib (Verzenio) — CDK4/6 inhibitor; P-gp inhibitor that may increase topotecan levels. Use with caution and monitor.

Ferric maltol (Accrufer) — Iron supplement; may alter absorption of oral topotecan. Separate administration times and monitor.

Ofatumumab SC (Kesimpta) — Immunosuppressive therapy; additive immune suppression with topotecan increases infection risk.

Minor or Pharmacodynamic Synergism Interactions

Vitamin A and Vitamin E — Antioxidant supplements. Animal and laboratory data suggest antioxidants like vitamins A and E may enhance the efficacy and reduce toxicity of topotecan, though the clinical significance in humans is unclear. Discuss with your oncologist before taking high-dose antioxidants.

What About Food Interactions?

The FDA label for oral Hycamtin states that it can be taken with or without food. There is no specific restriction on grapefruit juice, unlike some other cancer drugs. However, if you are taking any other medications that interact with grapefruit (which inhibits CYP3A4), discuss this with your oncologist.

What to Tell Your Doctor Before Starting Hycamtin

Before starting Hycamtin, give your oncologist and pharmacist a complete medication list that includes:

All prescription drugs (especially immunosuppressants, antifungals, targeted cancer therapies, blood pressure drugs)

All over-the-counter medications (including pain relievers, antacids, iron supplements)

All vitamins and dietary supplements (especially antioxidants and herbal products)

Your kidney function status (low kidney function increases topotecan exposure and toxicity risk)

For a full guide to Hycamtin side effects and safety warnings, see Hycamtin Side Effects: What to Expect and When to Call Your Doctor.

To learn more about what Hycamtin is and how it's used, read What Is Hycamtin? Uses, Dosage, and What You Need to Know.