Taking medicines at home is a common part of cancer treatment. It is important to take the medicine safely and as instructed.
Everything you take by mouth, including food, drink and medicine, needs to be broken down to be absorbed by the body. This process happens in the gut (digestive system).
A group of enzymes called cytochrome P (CYP) are an important part of this process. Most of these enzymes are made by the liver but can also be found in other parts of the body including the gut.
There are many CYP enzymes. We know that certain ones affect how cancer drugs are broken down and absorbed into the body. These include:
The amount of these enzymes in the body can affect how well the cancer drug is absorbed and this affects how well the drug works and the possible side effects.
If too little of the cancer drug is absorbed it might not work as well. And you might need a bigger dose which can possibly cause more side effects. If too much of the drug is absorbed you could have bad side effects from your cancer drug.
Foods and drugs, including herbal supplements, affect how much CYP enzymes there are in the body.
Foods that affect CYP enzymes
The best known foods that affect the CYP enzymes are grapefruit and Seville oranges. This includes their juice and other products that are mostly made from these for example marmalade.
Some of the foods that are known to affect CYP enzymes include:
- grapefruit and grapefruit juice
- Seville oranges
- star fruit
- vegetables such as cabbage and onion
Drugs that affect CYP enzymes
There are many different types of drugs that can affect the CYP enzymes. These include:
- targeted drugs
- some chemotherapy drugs
- certain antibiotics
- anti fungal drugs
- HIV treatment
- drugs to stop fits (an anti convulsant)
- drugs called calcium channel blockers
- anti depressants
Herbal supplements that affect CYP enzymes
There are many herbal supplements that affect the CYP enzymes. Some of the known ones include:
- St. John’s Wort
- black cohosh
- gingko biloba
- milk thistle
For your safety
You must tell your doctor or pharmacist if you start a new medication or are thinking of taking some herbal supplements. They will be able to tell you if they might affect the CYP enzymes.
They will also be able to advise you about any foods, medications or herbal supplements that might affect these enzymes.
You might have another medical condition for which you are taking medication that might affect the CYP enzymes. If this is the case your doctor might need to change the dose of your cancer drug.
Taking part in clinical trials
You might not be able to take part in clinical trials if you are taking a medication that affects the CYP enzymes. Talk to your doctor or a member of the trial team if you are thinking of joining of a clinical trial. If possible you might be able to join the trial if you can take another medication that doesn’t affect the CYP enzymes.