Chemotherapy drugs

Chemotherapy drugs are grouped into different classes, or types, depending on how they work. Some drugs work in more than one way and can belong to more than one drug class. Common drug classes include the following.

Alkylating agents stop cells from dividing by changing the cell's DNA so it can't be copied. Because cancer cells grow and divide quickly, they end up dying because they don't have time to repair the damaged DNA. Examples of alkylating agents include cyclophosphamide, cisplatin and carboplatin.

Anti-metabolites trick the cells into using the drug to make copies of its DNA, instead of using the DNA in the cell. The DNA that is created using the drug can't divide and create another cell, so the original cell dies. Examples of anti-metabolite drugs include fluorouracil (also called 5-fluorouracil or 5-FU) and gemcitabine.

Anthracyclines stop cells from dividing by interfering with enzymes used to make DNA. Examples of anthracyclines are doxorubicin and epirubicin.

Anti-tumour antibiotics bind to DNA so it can't work properly. This causes the cell to die. These drugs are different from antibiotics used to treat infection. Examples of anti-tumour antibiotics are bleomycin, idarubicin and doxorubicin.

Antimitotic drugs block the process of cell division (called mitosis) so cells can't divide and multiply. Paclitaxel and vinblastine are examples of this type of drug.

Topoisomerase inhibitors stop an enzyme called topoisomerase, which relaxes the strands of DNA so it can unwind to make 2 copies of the DNA. Topoisomerase also repairs mistakes in the DNA strands. Topoisomerase inhibitors stop the unwinding and repair of the DNA structure. When the DNA cannot be duplicated, the cell cannot grow and divide. There are 2 types of topoisomerase inhibitors. Topoisomerase 1 inhibitors break only one half of the DNA structure. The drugs irinotecan and topotecan are topoisomerase 1 inhibitors. Topoisomerase 2 inhibitors break both halves of the DNA. Examples of this type of drug are etoposide and epirubicin.

Liposomal drugs are chemotherapy drugs wrapped in a type of fat (or lipid) and water. The fat and water act together like a tiny bubble to get through the cell membrane and release the chemotherapy in the cell. The advantage of liposomal drugs is that you can be given higher doses of chemotherapy over a shorter time because the lipids help reduce side effects that chemotherapy can cause. Also, more of the chemotherapy drug can get into the cancer cells and stay in them longer. This makes liposomal drugs more effective than some other drug classes. Examples of liposomal chemotherapy drugs are pegylated liposomal doxorubicin and irinotecan liposome.

Some chemotherapy drugs don't fit into any of the classes above. Examples of these include:

• hydroxyurea
• asparaginase
• vorinostat

Chemotherapy drugs used to treat cancer are prescribed by the medical oncologist on your healthcare team. When deciding which chemotherapy drugs to offer, they will consider:

• the type of cancer, including any specific tumour markers or mutations it may have
• the stage of the cancer
• the types of cancer treatments you've had
• your overall health, including any medical problems you have
• your lifestyle and what you prefer or want
• the potential side effects of the chemotherapy drug

A chemotherapy drug can be given on its own or different chemotherapy drugs can be given together in a combination (called combination chemotherapy). Combining chemotherapy drugs can make chemotherapy work better than using a single drug because the different drugs attack cancer cells at different points in the cell cycle. It may also prevent cancer cells from developing drug resistance, allowing your treatment to work better.

Cancer cells can stop responding to a chemotherapy drug that had been working. This is called drug resistance or refractory cancer. Sometimes cancer cells can become resistant to several different drugs. This is called multi-drug resistance.

While most cancer cells respond to chemotherapy right away, some may be resistant to treatment right from the beginning. Those cells then keep dividing and make more drug-resistant cancer cells.

Researchers are studying how cancer cells become drug resistant. Cancer cells may be able to develop resistance because of:

• changes in the genes of the cell (mutations)
• characteristics of the area around the cancer cells, including other normal cells, blood vessels and tissue structures (called the tumour microenvironment)
• molecular changes in the cells

If the cancer is no longer responding to a certain chemotherapy drug or drug combination, your healthcare team may try different chemotherapy drugs. They may try using a different chemotherapy drug that makes the cancer cells more sensitive to the original chemotherapy drug, and then using the original drug again. Researchers are looking at using medicines that are used to treat other diseases to help the chemotherapy drugs work better.

When cancer cells have developed drug resistance to chemotherapy, your healthcare team may try combining chemotherapy drugs with targeted therapy or immunotherapy. If chemotherapy drugs no longer work, your healthcare team may offer treatment with just targeted therapy or immunotherapy.

Chemotherapy may not kill all cancer cells the first time the drug is given. Some cancer cells may survive and continue to grow. This is why chemotherapy treatments are usually given in cycles, so that they can destroy as many cancer cells as possible.

A regimen or protocol is the chemotherapy treatment plan itself. It includes the type of chemotherapy drugs to be used, the dosage (how much) of each drug, the order that the drugs are given and the frequency (how often).

A schedule is the plan for when to give each chemotherapy cycle. Some schedules may include chemoradiation (chemotherapy given during the same time period as radiation therapy). If you are having chemoradiation, some days you will have a chemotherapy treatment and then go for a radiation therapy treatment. Some days you will only have radiation therapy. If you are taking oral chemotherapy, you usually take your pills on the days you have radiation therapy.

A chemotherapy cycle is the total amount of time that includes chemotherapy treatment and the rest days that follow, up to the next time you are given chemotherapy. The rest period allows normal cells (such as blood cells) that have been damaged by chemotherapy to recover. After the rest period, a new cycle begins.

For example, a cycle may include having chemotherapy treatment each day for 3 days followed by a rest period of 25 days in a row. Another chemotherapy cycle may have chemotherapy on days 1, 8 and 15, followed by rest days from day 16 to day 28.

Most chemotherapy is given for 4 to 8 cycles. Your healthcare team will plan the number of cycles based on the goals of your treatment.

How chemotherapy gets into the body is called the route of administration.

Intravenous (or IV) chemotherapy is delivered through a needle into a vein or using a central venous catheter. This is the most common way of giving chemotherapy.

Oral chemotherapy is given by mouth. It's pills (tablets or capsules) that you swallow. You can usually take oral chemotherapy at home.

The following are less common ways of giving chemotherapy.

Topical chemotherapy is given as a cream or ointment that contains the chemotherapy drug and is applied on the skin. This type of chemotherapy is often used to treat non-melanoma skin cancer.

Intrathecal chemotherapy delivers the chemotherapy drugs into the cerebrospinal fluid (CSF) through a lumbar puncture. This is used for some cancers that start in the brain or spinal cord (central nervous system, or CNS) or with cancers that have a high chance of spreading to the brain.

Intraventricular chemotherapy gives the chemotherapy drugs into the CSF in the ventricles (fluid-filled cavities) of the brain. It is delivered using a device called an Ommaya reservoir. Intraventricular chemotherapy is sometimes used to treat brain tumours.

Intracavitary chemotherapy is given into a body cavity, such as the abdomen or the chest. It is given through a port-a-cath that has been put into skin near the rib cage. Sometimes the drugs used in intracavitary chemotherapy are warmed before they are put into the body cavity. This type of treatment may be used for ovarian cancer.

Intravesical chemotherapy gives high doses of liquid chemotherapy directly into the bladder to treat bladder cancer.

Intralesional chemotherapy injects the drug directly into a cancer tumour with a needle. This can only be used if the tumour is at or near the surface of the skin and can be reached with a needle. It is sometimes used to treat non-melanoma skin cancer.

Intra-arterial chemotherapy uses a needle to deliver the chemotherapy directly into an artery near the tumour rather than into a vein. This type of chemotherapy delivery may be used for head and neck cancers, retinoblastoma (a type of childhood eye cancer) and liver cancer or cancer that has spread to the liver from other parts of the body (liver metastases). It isn't used very often.

Intravenous (or IV) chemotherapy is given directly into your vein. It is the most common way that people are given chemotherapy. IV treatment can last anywhere from 15 minutes to several hours.

IV chemotherapy may be delivered through a needle into your vein on the back of your hand or on the inside of your lower arm (forearm). The needle is attached to a short flexible tube called a cannula. A nurse will put the needle into your vein, then slide the cannula over the needle and pull the needle out. They then insert the cannula into your vein and use a piece of medical tape or dressing to secure the cannula against your skin.

Once the cannula is secured, chemotherapy is typically given as an IV infusion. With an IV infusion, the cannula is connected to a bag containing the liquid chemotherapy drugs. During your chemotherapy treatment, the drugs will drip from the bag into the cannula. From there, the drugs enter your vein and flow into your bloodstream, and the blood carries the drugs throughout the body to the tumour and any cancer cells that have spread away from the tumour. A chemotherapy pump is often attached to the cannula to control the flow of the drugs into your vein, making sure it is delivered at a steady pace. Pumps are also called infusion pumps or infusors.

Some chemotherapy drugs are given using an IV push. This means the chemotherapy drugs are injected directly from a needle, rather than given by drip from a bag for a longer period of time. The needle is put into the cannula and the drug is injected at a steady pace, allowing it to quickly enter the bloodstream. If you are receiving drugs through an IV push, you may still have an IV infusion of other drugs at the same time.

Cannulas need to be taken out after each chemotherapy session, so you will need to have a needle each time you have chemotherapy. To avoid this, IV chemotherapy is often delivered through a device called a central venous catheter. This is inserted into a vein before you start chemotherapy and can remain in place until all of your chemotherapy treatment sessions are over. Having a central venous catheter means you won't need a new needle injected into your vein each time you have chemotherapy.

IV chemotherapy is given into a vein in your body. It is delivered through a central venous catheter (also called a CVC, central venous line or central line).

A central venous catheter is a thin plastic tube (catheter) that is placed under your skin and inserted into a large vein near your collarbone or heart. A small length of tube comes out of the hole in your chest, with a cap at the end. A chemotherapy pump may also be attached to the central venous catheter to control the speed and dose of the drugs going in.

You will be given a local anesthetic (the area will be numbed or frozen) or a general anesthetic (you will be asleep) when you have the central venous catheter inserted into your vein. Since the catheter is placed inside your body, you won't have to have a new needle put in every time you have chemotherapy. They can stay in place in your body for several months, and can be used to deliver chemotherapy drugs if you have treatment over a long period of time. Central venous catheters are made of a special plastic that reduces the risk that your body will have a reaction (such as itching, swelling or redness) to the tube.

A central venous catheter can also be used to give other fluids or medicines such as antibiotics or antinausea drugs if you need them. Your healthcare team can also use them to take blood for testing while you are in the hospital.

There are different types of central venous catheters. The following are some of the more common types used to give chemotherapy.

A tunnelled central venous catheter goes underneath the skin of your chest, enters a large vein near the collarbone and threads inside the vein to sit above the right chamber (atrium) of your heart. The other end of the catheter stays outside your body.

A peripherally inserted central catheter (PICC line) is put into a vein in your arm, near your elbow. It is threaded through your vein to rest above the right atrium of your heart. The other end of the PICC line stays outside your body.

A port-a-cath is a small bag of firm plastic (port) that is attached to a catheter. The port is placed just under your skin in your upper chest near your shoulder and the catheter goes into a large vein near your collarbone. You don't have a tube coming out of your body like other central venous catheters. Each time you have chemotherapy, a nurse pushes a needle through your skin into the port to give you chemotherapy. The drugs then go into the port and flow through the catheter into your vein.

Find out more about central venous catheters.

Side effects of IV treatment can include:

• infection at the needle entry site
• inflammation of the vein (phlebitis)
• bleeding
• blood clots

While rare, it's possible for the cannula or central venous catheter to move or become blocked. This may prevent the drug from being delivered into your vein and cause pain or discomfort. Tell your healthcare team if you feel discomfort during your IV chemotherapy treatment.