Xeloda Works by Converting Into a Cancer-Fighting Drug Inside Your Body

Xeloda (Capecitabine) is a pill that turns into the chemotherapy drug 5-fluorouracil (5-FU) after you swallow it. What makes it unique is that much of this conversion happens right inside tumor tissue, which helps target cancer cells while reducing some side effects compared to IV chemotherapy.

If you've been prescribed Xeloda and want to understand what it actually does in your body, this guide explains it in plain English — no medical degree required.

What Xeloda Does in Your Body

Xeloda is what pharmacologists call a prodrug. That means the pill itself isn't the active medication. Instead, your body converts it through a series of chemical steps into the drug that actually fights cancer.

Here's the process, simplified:

Step 1: You Swallow the Pill

Capecitabine is absorbed through your intestines and enters your bloodstream. At this point, it's not yet active.

Step 2: Your Liver Starts the Conversion

In the liver, an enzyme called carboxylesterase converts Capecitabine into an intermediate compound called 5'-DFCR.

Step 3: Another Enzyme Takes Over

A second enzyme, cytidine deaminase (found in the liver and tumor tissue), converts 5'-DFCR into another intermediate called 5'-DFUR.

Step 4: The Final Step — In the Tumor

The last conversion — from 5'-DFUR to 5-fluorouracil (5-FU) — is carried out by an enzyme called thymidine phosphorylase. Here's the key: this enzyme is found at much higher concentrations in tumor tissue than in normal tissue. That means more of the active drug is released right where it's needed — at the cancer cells.

Step 5: 5-FU Kills Cancer Cells

Once activated, 5-FU works by blocking an enzyme called thymidylate synthase, which cancer cells need to copy their DNA. Without DNA replication, the cells can't divide and grow. They die.

This is the same mechanism as IV 5-FU, which has been a cornerstone of cancer treatment for decades. Xeloda simply delivers it in a smarter, more targeted way.

How Long Does It Take to Work?

Xeloda doesn't produce overnight results. Cancer treatment takes time, and the drug works gradually over multiple cycles.

• Each cycle is 21 days — 14 days taking the medication, followed by 7 days off
• Response assessment typically happens after 2–3 cycles (6–9 weeks), usually with imaging scans
• Adjuvant treatment (after surgery) is typically 6–8 cycles over several months
• Metastatic treatment continues as long as the cancer responds and side effects are tolerable

Your oncologist will monitor your progress with blood tests and scans to see how well Xeloda is working.

How Long Does It Stay in Your System?

Capecitabine and its metabolites have a relatively short half-life — about 45 minutes to 1 hour for Capecitabine itself. The active metabolite 5-FU also has a short half-life. This means the drug clears your system relatively quickly, which is one reason for the twice-daily dosing schedule.

However, the effects on cancer cells (DNA damage and cell death) continue even after the drug is cleared. The 7-day rest period between cycles allows your normal cells — especially in the gut, skin, and blood — to recover from the treatment.

What Makes Xeloda Different From IV Chemotherapy?

Xeloda offers several advantages over traditional IV 5-FU:

Oral Convenience

You take Xeloda at home as a pill, twice a day with meals. There's no need for IV infusion pumps, port placements, or regular trips to the infusion center. For many patients, this means less disruption to daily life.

Tumor-Targeted Activation

Because the final activation step relies on thymidine phosphorylase — which is more concentrated in tumors — Xeloda delivers more 5-FU to cancer tissue relative to normal tissue. This doesn't eliminate side effects, but it's a meaningful pharmacological advantage.

Similar Effectiveness

Clinical trials have shown that Xeloda is at least as effective as IV 5-FU/leucovorin for adjuvant colon cancer treatment, with the added convenience of oral dosing.

Different Side Effect Profile

While Xeloda causes many of the same side effects as IV 5-FU (diarrhea, nausea, myelosuppression), it's more likely to cause hand-foot syndrome and less likely to cause certain IV-related complications. For a full breakdown, see our Xeloda side effects guide.

The DPD Factor

One important consideration: your body needs the enzyme DPD (dihydropyrimidine dehydrogenase) to safely break down 5-FU. People with DPD deficiency can experience dangerously high levels of 5-FU, leading to potentially fatal toxicity. This applies to both Xeloda and IV 5-FU. DPD testing is recommended before starting either treatment.

Final Thoughts

Xeloda is a cleverly designed chemotherapy that uses your body's own enzymes to activate a cancer-fighting drug right where it's needed most. Its oral format and tumor-targeted activation make it a preferred choice for many patients with breast and colorectal cancers.

Understanding how your medication works can help you feel more in control of your treatment. If you want to learn more about Xeloda's uses and dosing, check out our guide on what Xeloda is and what you need to know. If you're looking for drug interaction information, see our Xeloda drug interactions guide.

And if you need help finding Xeloda at a pharmacy near you, Medfinder can show you where it's in stock in seconds.