Easy-to-read medicine information about clozapine – what it is, how to take it safely and possible side effects.
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What is clozapine?
Clozapine is used to treat schizophrenia. It does not cure this condition, but is used to help ease the symptoms and help you on your recovery path. It can help improve symptoms such the experience of hearing voices (hallucinations), ideas that distress you and don't seem to be based in reality (delusions), and difficulty in thinking clearly (thought disorder).
Clozapine is used when people have tried at least 2 other antipsychotic medicines and found they did not work well enough or for people who have difficultly managing side effects with other antipsychotics.
Clozapine belongs to a group of medicines called antipsychotics. Read more about antipsychotic medication. In New Zealand, clozapine is available as tablets or a liquid.
The dose of clozapine is different for different people, depending on your response. Your doctor will start you on a low dose and increase it slowly as your body gets used to it.
- Generally people start with 12.5 mg once or twice on day 1, increased to 25 mg once or twice on day 2. Over the following 2 to 3 weeks your dose would be increased gradually by 25 mg to 50 mg a day, until you are taking the dose which will give you the most benefit. This is usually 300-450 mg a day but can be up to a maximum of 900 mg per day.
- Dose increases may vary depending upon your response to treatment and your medical history.
- Always take your clozapine exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much clozapine to take, how often to take it and any special instructions.
How to take clozapine
- Clozapine is usually taken twice a day. However, if your total dose is 200 mg or less, you may be able to take the whole amount in one dose, usually in the evening. Try to take your clozapine dose at the same times each day.
- You can take clozapine with or without food.
- Swallow clozapine tablets with a full glass of water or other liquid. Liquid clozapine may be taken alone or in water. Shake the bottle for 10 seconds before use.
- If you forget to take your dose, take it as soon as you remember, if it is within 4 to 6 hours of when it was due. But if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
- If you forget to take clozapine for more than 48 hours, you must contact your doctor or the clinic you normally attend. Your dose may need to be adjusted.
- Keep taking clozapine every day. It usually takes a few weeks to start working and it can take a few months before you feel the full benefits.
- Do not stop taking clozapine suddenly as your symptoms may return if you stop taking it too early; speak to your doctor or nurse before stopping.
Precautions – before starting clozapine
- Do you have any heart problems such as an irregular heartbeat or low blood pressure?
- Do you have Parkinson’s Disease or epilepsy?
- Are you over 60 years old?
- Do you have diabetes or problems with high cholesterol?
- Do you smoke, or have you recently stopped smoking?
- Do you have problems with constipation?
- Do you have problems with your liver or kidneys?
- Are you pregnant or breastfeeding?
- Are you taking any other medicines, including medicines you can buy without a prescription, such as herbal and complementary medicines?
If any of these apply, it’s important that you tell your doctor or pharmacist before you start clozapine. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care, that your pharmacist will tell you about.
Precautions – while taking clozapine
- Alcohol: avoid alcohol while you are taking clozapine, especially when you first start treatment. Drinking alcohol while taking clozapine can cause drowsiness and affect concentration, putting you at risk of falls and other accidents. It can also cause agitation, aggression and forgetfulness. If you do drink alcohol, drink only small amounts and see how you feel. Do not stop taking your medication.
- Smoking: smoking affects the way your body breaks down (metabolises) clozapine. If you start smoking, or stop smoking while you are taking clozapine, tell your healthcare provider. Your dose of clozapine may need to be adjusted. If you wish to stop smoking while you are taking clozapine, your doctor can plan a smoking cessation programme with you and monitor your clozapine levels.
- Caffeine: keep your caffeine intake stable. Sources of caffeine include coffee, cola or high-energy drinks. Sudden increases or decreases in your caffeine intake can alter (increase or decrease) the levels of clozapine in your blood. This can be harmful.
Clozapine can affect your white blood cells called neutrophils. These cells help to fight infections and keep your immune system healthy.
- When clozapine causes a drop in the number of these cells, it leads to a condition called neutropenia. A more severe reduction in your white blood cells is called agranulocytosis. A drop in neutrophils puts you at greater risk of picking up infections.
- It is important to check your white blood cell count with regular blood tests because you may not notice any symptoms until you have an infection.
- Checking the number of your white blood cells helps to find any changes before they cause problems. You will not be allowed to collect your clozapine prescription unless you have an up-to-date blood result.
- You will need to have a blood test within 10 days before starting clozapine treatment, then every week for the first 18 weeks of treatment. Then you will need to have blood tests every 4 weeks throughout treatment.
Clozapine may cause changes in your blood glucose level, cholesterol level and heart function. To check these things, your doctor will monitor your physical health. You will have your weight checked regularly. You may also need to have your liver, cholesterol and glucose levels checked. You will also have your blood pressure measured and may need an ECG test to check your heart rate.
Possible side effects
Like all medicines, clozapine can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.
Constipation is a very common side effect of clozapine (up to 6 in every 10 people taking clozapine may experience constipation). This can be very uncomfortable and if not treated, it can lead to serious problems.
- You can prevent constipation by increasing the fluid and fibre intake in your diet, and exercising regularly. You may also need to take laxatives. Read more about preventing constipation.
- If you have problems with constipation before starting clozapine, tell your doctor. You will be started on a laxative when you start taking clozapine.
- If you develop constipation while taking clozapine, it is important to contact your healthcare provider straight away for immediate treatment. These symptoms include:
- not having a bowel movement for 2 days or more
- severe tummy pain
- bloating or gas in your tummy
- feeling sick (nausea) or being sick (vomiting)
- reduced appetite.
- Diarrhoea (runny poos) can also be a symptom of constipation.
- You are at increased risk of constipation during the first 4 months of starting clozapine, if you have an increase in your clozapine dose, if you are taking other medicines that are likely to cause constipation, if your diet changes, and if you are stopping smoking.
- Clozapine can affect your white blood cells which fight infection. This can put you at greater risk of picking up infections.
- At the first sign of infection (such as fever, cold or flu symptoms, muscle aches, headache, or sore throat) you need to contact your doctor or mental health worker for an urgent blood test to check your white blood cells.
Other side effects
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Clozapine interacts with a number of medicines and herbal supplements so check with your doctor or pharmacist before you take any other medicines.
The following links has more information on clozapine. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.
- Clozapine: safe prescribing BPAC, Sept 2017
- Safer prescribing of high-risk medicines: Clozapine. BPAC, July 2014
- Clozapine. Malignant constipation can kill Goodfellow Gems