Pain Service - Ketamine

This leaflet provides information on a medicine called Ketamine which is used to treat pain that is difficult to control. If you have any questions after reading this, please ask your doctor.

What is Ketamine?

Ketamine is a liquid drug which has been used as an anaesthetic agent for many years. More recently it has been used at low doses in the management of severe pain especially neuropathic (nerve) pain.

How does Ketamine work?

Ketamine works mainly by blocking the action of a chemical in the nervous system that is important in creating persistent pain. This reduces the amplification of the messages sent to the brain that tell you that you are in a lot of pain.

What is the benefit of taking Ketamine?

It is helpful in some patients to reduce the severity of pain when other types of painkillers have not worked.

When is Ketamine prescribed?

Ketamine is usually prescribed when other painkillers have not worked. It may be prescribed by itself, or in combination with other painkillers. It is always started by a doctor who specialises in treating chronic pain.

What dose of Ketamine is usually prescribed?

Your doctor will usually start off by prescribing a low dose of Ketamine and then slowly increasing it. This is because like any medicine Ketamine has a number of side-effects. Starting off with a low dose and slowly increasing it allows your body to get used to these effects.

It also allows your doctor to see how well your symptoms are responding to Ketamine. The usual starting dose is 10 mg four times a day. This may be increased further as necessary under the supervision of your doctor. How much Ketamine you will need depends upon how well it is working for you and if you are having any side-effects.

How should you take the prescribed Ketamine?

You should only take the prescribed dose. Measure the exact amount in a plastic reusable syringe. The medicine should then be swallowed.

What should I do if I miss a dose?

If you miss a dose try to take it as soon as you remember. However if it is almost time for your next usual dose, wait until then to take your medicine and skip the missed dose. Never double up the dose to make up for a missed dose. If you are sick within one hour of taking a dose of Ketamine repeat the dose as soon as you feel better. If you miss more than one dose through being unwell, contact your doctor.

How well or quickly does Ketamine work?

For some people Ketamine can work very quickly (within a few hours). For other people it may take a few weeks of taking reasonable doses of Ketamine before their pain improves. Some patients do not find Ketamine to be helpful. It is not possible to tell who will respond to Ketamine.

Can I take other medicines if I take Ketamine?

In general, Ketamine should not affect your other medicines. Other painkillers such as weak opioids (e.g. codeine), non steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, or paracetamol can be taken at the same time as Ketamine.

If you are already taking a strong opioid such as morphine, and you are started on Ketamine your doctor will usually reduce the dose of your morphine. This is because you may not need the same amount of strong opioid while taking Ketamine.

Before you take or buy any new medicines always tell your doctor or pharmacist that you are taking Ketamine.

What is the length of treatment?

The length of treatment will depend on why you were started on Ketamine and how well it works.

You will be reviewed periodically to assess whether your Ketamine can be reduced or discontinued. It may be necessary for your doctor to change the dose during your treatment.

You can continue to take ketamine for as long as it helps your pain if you are not having any side effects.

Is Ketamine addictive?

It is very rare for someone who is taking Ketamine for pain relief to become addicted. However, it is sometimes taken illegally in high doses and drug abusers can become addicted to it.

If you need to stop taking Ketamine it should be stopped slowly. This is because stopping it suddenly can result in severe rebound pain. This is when pain comes back quickly and can be severe.

What are the possible risks/side-effects?

Tiredness or sleepiness may occur for a short period of time after taking the prescribed dose. You may also experience a sensation that everything feels ”unreal” or “far away” and this will last for only a short time.
 
As with all medicines Ketamine has a number of side-effects. The most common side-effects include:

• Drowsiness
• Vivid dreams
• Hallucinations (feeling, seeing or hearing something that is not actually there)
• Dysphoria (feeling unwell or unhappy)

These symptoms can also be signs that your dose of Ketamine is too high.

Less commonly reported side-effects include an increase in blood pressure, and a fast heart rate.

We do not know what the long term problems are with using this medicine. Some studies suggest that there may be problems with memory loss or thought processing, but it is not known if this is a problem at the dose being used the clinic.

More recently there have been reports of Ketamine causing problems with kidney function, ulcers in the bladder and urinary tract (the tube that passes urine out of your body), and lower abdominal pain on long term use. Most of these patients had been using ketamine for recreational purposes. However, there were some who were taking it for pain reasons.

If you have any of the following problems:

• Pain on passing water
• Blood in the urine
• Needing to pass urine more often then please contact your GP or your pain nurse or pain doctor

Who cannot take Ketamine?

Normally you should not take Ketamine if you have:

• Raised pressure within the skull
• Raised pressure inside the eye (glaucoma)
• Recent history of epilepsy
• Recent history of psychosis
• Severe high blood pressure

Do I need to have any tests when taking Ketamine?

While you are taking Ketamine you will need to have your blood pressure taken regularly. In addition you will also be monitored for problems with your urinary tract. Your doctor or nurse will ask you if you have any problem such as stinging when you pass water, if you are passing water more often than normal and if you have any blood in the urine.

Can I drink alcohol if I am taking Ketamine?

You should avoid drinking alcohol if you are taking Ketamine. This is because alcohol may increase some of the side-effects of Ketamine.

Can I drive if I am taking Ketamine?

Taking Ketamine does not automatically mean that you cannot drive. People who take the same amount of Ketamine every day for pain are usually fit to drive. When you first start taking Ketamine or when your dose is increased you may feel drowsy. You should use common sense and not drive if you feel drowsy.

Note: Your doctor may have told you that you are fit to drive, but remember it is your responsibility to decide whether you are fit to drive on each occasion.

Where should I keep my Ketamine?

Ketamine should be stored out of the reach of children, in a cool place away from sunlight.

Where can I get my Ketamine?

You will need to get a supply of this medicine from the hospital pharmacy. Please ring the pharmacy few days in advance before you run out of supply. You will need an in-hospital prescription from a pain consultant.

Pharmacy Contact Numbers:

Fairfield General Hospital - 0161 778 355
Rochdale Infirmary - 01706 517308
Royal Oldham Hospital - 0161 622 0962

References:

1. Blonk M. et al. Use of oral ketamine in chronic pain management: A review. European Journal of pain. 2009.
2. Norfolk and Norwich University Hospitals NHS Foundation Trust: Ketamine Patient Information Leaflet.
3. The Newcastle upon Tyne Hospitals NHS Foundation Trust: Ketamine for Pain Patient Information Leaflet
4. Wigan and Leigh NHS Trust patient information leaflet and informed consent leaflet - Oral ketamine treatment
5. Cotttrell et al . Urinary tract disease associated with chronic ketamine use. BMJ 336: 973 2008.