Quetiapine: 7 things you should know
Medically reviewed by C. Fookes, BPharm Last updated on Sep 1, 2019.
1. How it works
- Experts aren't exactly sure how quetiapine works but research suggests it binds to receptors in the brain stimulated by chemicals (neurotransmitters) such as dopamine, histamine, and serotonin. Antipsychotic effects are thought to be related to a drug's ability to reduce transmission of dopamine in the reward center of the brain (known as the mesolimbic pathway).
- Quetiapine belongs to a group of medicines known as atypical antipsychotics. Atypical means that quetiapine is less likely than older antipsychotics to cause side effects, and may be more effective in the treatment of symptoms such as lack of motivation and social withdrawal.
- Quetiapine calms and sedates and is used to help reduce the incidence of psychotic thoughts in people with schizophrenia.
- Quetiapine also helps to calm acute manic episodes in people with bipolar I disorder. It may be used as sole therapy or in addition to lithium or divalproex. When used as maintenance therapy for manic episodes in bipolar 1 disorder, it is best used in addition to lithium or divalproex.
- Quetiapine may be used as sole therapy for the treatment of depressive episodes in people with bipolar I or bipolar II disorder.
- Quetiapine may also be used off-label for other conditions such as generalized anxiety disorder.
- Trials have established that quetiapine is effective in adolescents aged 13 to 17 with schizophrenia; however, quetiapine should only be used after careful consideration of the risks versus benefits involved with treatment.
- Quetiapine is also approved for the treatment of manic episodes in children aged 10 to 17 with bipolar I disorder.
- One of the most commonly used antipsychotics in the United States.
- Generic quetiapine is available.
If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:
- Weakness, lack of energy, headache, dry mouth, constipation, weight gain, changes in cholesterol and triglyceride levels.
- Drowsiness or dizziness that may affect your ability to drive or operate machinery or perform hazardous tasks. Alcohol may enhance these effects.
- Other common side effects include chills, cold sweats, confusion, and agitation.
- Some people, such as seniors, the frail, and those with a predisposition to low blood pressure may be more sensitive to the effects of quetiapine. A slower rate of dose titration and lower target dosages may be needed.
- A drop in blood pressure on standing, particularly during the initial dose-titration period. To counteract this effect, the dosage of quetiapine may need to be reduced then titrated back up slowly. May not be suitable for people with known cardiovascular disease (history of a heart attack, angina, heart failure, or arrhythmia), stroke or people at risk of dehydration. May increase blood pressure in adolescents.
- May not be suitable for people with diabetes or may precipitate diabetes especially in those with pre-existing risk factors (such as obesity and lack of physical activity).
- People with liver disease or taking other medications that may interact with quetiapine may need a dosage adjustment. Only one-sixth of the quetiapine dose is needed when taken with drugs that are CYP3A4 inhibitors (for example, ketoconazole, ritonavir, or nefazodone). A dosage increase of up to fivefold is recommended when quetiapine is taken with CYP3A4 inducers (such as phenytoin, carbamazepine, rifampin, or St John's wort).
- The use of antipsychotics in elderly patients with dementia has been associated with an increased risk of death, mostly due to cardiovascular or infectious causes. Quetiapine is not FDA-approved for use in elderly patients with dementia.
- May not be suitable for some people including those with cataracts, heart disease, high cholesterol, thyroid dysfunction, abnormal blood counts, high prolactin levels, or liver disease.
- Antipsychotics such as quetiapine have been associated with a serious syndrome called Neuroleptic Malignant Syndrome; symptoms include high body temperature, muscle rigidity, and mental disturbances. Seek urgent medical advice if these symptoms develop.
- As with other antipsychotics and antidepressants, quetiapine may increase the risk of suicidal thoughts or behavior, particularly in adolescents.
- May cause a discontinuation syndrome if abruptly stopped; symptoms include nausea, insomnia, headache, diarrhea, vomiting, irritability, and dizziness. Gradual withdrawal is advised.
Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.
- Immediate-release tablets can be administered either with or without food. Administer extended-release tablets without food or following a light meal (less than 300 calories). Swallow extended-release tablets whole, do not crush or chew.
- Most people are started on a lower dosage which is gradually increased to reduce the risk of side effects such as drowsiness and low blood pressure.
- Get up slowly when going from a lying down or sitting position to standing.
- Can be given once daily, or divided into three doses per day depending on response and tolerability.
- Talk to your doctor if you experience any changes in your mood or you develop anxiety, panic attacks, insomnia, get easily agitated, or have thoughts of suicide.
- Seek urgent medical advice if you develop a high temperature, muscle rigidity or confusion.
- Do not drive or operate machinery or perform hazardous tasks if quetiapine makes you sleepy or impairs your mental functioning.
- Your doctor may need to monitor your blood sugar levels before quetiapine initiation and periodically thereafter as occasionally quetiapine can precipitate diabetes in some people. Talk to your doctor if you feel excessively thirsty or are urinating more than normal.
- Your doctor may also need to monitor your lipid levels on quetiapine initiation and periodically thereafter as quetiapine may increase LDL-cholesterol and triglyceride levels.
- Quetiapine may make you gain weight. Ensure you eat healthy foods and keep up your physical activity levels as recommended by your doctor.
- Antipsychotic agents, such as quetiapine, have been associated with a disruption in the ability to regulate body temperature. If you are taking quetiapine, avoid strenuous exercise, exposure to extreme heat, or dehydration.
- Be careful when going from a sitting or lying down position to a standing position as quetiapine may make you feel dizzy or light-headed, which may increase your risk of falling.
- Do not take any other medication, including over-the-counter medication, without asking a doctor or pharmacist first if it is alright to take with quetiapine.
- Do not stop taking this medicine suddenly. If you feel you are not gaining any benefit from this drug, or the side effects are intolerable, talk with your doctor about slowly discontinuing it.
6. Response and Effectiveness
- Peak levels are reached 1.5 hours following a dose of immediate-release tablets or 6 hours following a dose of extended-release tablets.
- Beneficial effects on mood may be seen within two weeks. After 40 weeks, approximately 24% of patients taking quetiapine experienced a recurrence of a mood event compared with over 50% of those taking a placebo tablet (a pretend pill).
Medicines that interact with quetiapine may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with quetiapine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.
Quetiapine is metabolized through CYP3A4 hepatic enzymes. Dosage decreases (up to one-sixth of the quetiapine dose) are usually necessary when given with CYP3A4 inhibitors. Dosage increases (up to fivefold) are usually necessary when given with CYP3A4 inducers.
Common medications that may interact with quetiapine include:
- CYP3A4 inducers, such as carbamazepine, oxcarbazepine, phenytoin, rifampin, St John's Wort
- CYP3A4 inhibitors, such as clarithromycin, cyclosporine, fluconazole, ketoconazole, nefazodone, ritonavir, tamoxifen, verapamil
- dexamethasone, methylprednisone, and prednisone
- HIV medications, such as indinavir, nelfinavir, and ritonavir
- medications used to treat Parkinson's Disease, such as cabergoline and levodopa
- other antidepressants or antipsychotics
Avoid drinking alcohol or taking illegal or recreational drugs while taking quetiapine.
Note that this list is not all-inclusive and includes only common medications that may interact with quetiapine. You should refer to the prescribing information for quetiapine for a complete list of interactions.
- Quetiapine [Package Insert]. Revised 12/2018. AlignScience Pharma, Inc. https://www.drugs.com/pro/quetiapine-fumarate-tablets.html
- Guzman, F. Mechanism of Action of Quetiapine. Psychopharmacology Institute. http://psychopharmacologyinstitute.com/antipsychotics/quetiapine/mechanism-of-action/
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use quetiapine only for the indication prescribed.
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