risperidone

Risperidone is an atypical antipsychotic drug that is used for treating schizophrenia, bipolar mania, and autism. Other atypical antipsychotic drugs include olanzapine (Zyprexa), quetiapine (Seroquel), ziprasidone (Geodon), aripiprazole (Abilify) and paliperidone (Invega). Atypical antipsychotics differ from typical antipsychotics because they cause a lesser degree of movement (extrapyramidal) side effects and constipation. Risperdal Consta is an injectable, long-acting form of risperidone.

The exact mechanism of action of risperidone is not known, but, like other anti-psychotics, it is believed that risperidone affects the way the brain works by interfering with communication among the brain's nerves. Nerves communicate with each other by making and releasing chemicals called neurotransmitters. The neurotransmitters travel to other nearby nerves where they attach to receptors on the nerves. The attachment of the neurotransmitters either stimulates or inhibits the function of the nearby nerves.

Risperidone blocks several of the receptors on nerves including dopamine type 2, serotonin type 2, and alpha 2 adrenergic receptors. It is believed that many psychotic illnesses are caused by abnormal communication among nerves in the brain and that by altering communication through neurotransmitters, risperidone can alter the psychotic state. Risperidone was approved by the FDA in December 1993.

The most commonly-noted side effects associated with risperidone are:

• insomnia,
• headache,
• dizziness,
• hyperactivity,
• drowsiness,
• abdominal pain,
• fatigue,
• fever, and
• nausea.

Another important side effect which may also occur include extrapyramidal effects (sudden, often jerky, involuntary motions of the head, neck, arms, body, or eyes) also occur. Risperidone may cause a condition called orthostatic hypotension during the early phase of treatment (the first week or two). Patients who develop orthostatic hypotension have a drop in their blood pressure when they rise from a lying position and may become dizzy or even lose consciousness.

Studies involving risperidone suggest an increased risk of hyperglycemia-related adverse reactions as seen in people with diabetes. Although there is no clear link between risperidone and diabetes, patients should be tested during treatment for elevated blood sugars. Additionally, persons with risk factors for diabetes, including obesity or a family history of diabetes, should have their fasting levels of blood sugar tested before starting treatment and periodically throughout treatment to detect the onset of diabetes. Any patient developing symptoms that suggest diabetes during treatment should be tested for diabetes.

Risperidone can be administered once or twice daily. Initial oral dosing for treating schizophrenia is generally 2 mg/day. Dose increases can occur in increments of 1-2 mg/day, as tolerated, to a recommended dose of 4-8 mg/day. In children older than 13 years of age, risperidone should be initiated at 0.5 mg once daily, and can be increased in increments of 0.5 or 1 mg/day, as tolerated, to a recommended dose of 2.5 mg/day. Risperidone can be given with or without meals.

The recommended dose of Risperdal Consta is 12.5 to 25 mg injected into the deltoid or gluteal muscle every two weeks. Dosage should not be adjusted more frequently than every 4 weeks. Patients who have never received risperidone are started on oral risperidone in order to evaluate tolerability. Patients then may be transitioned to Risperdal Consta if oral risperidone is tolerated.

Bipolar mania is treated with oral doses of 2-3 mg/day initially. Dose may be increased by 1 mg/day at every 24 hours up to a dose of 6 mg/day. The dose of Risperdal Consta for bipolar mania is 12.5 to 25 mg injected into the deltoid or gluteal muscle every two weeks. Dosage should not be adjusted more frequently than every 4 weeks.

Risperidone may interfere with elimination by the kidneys of clozapine (Clozaril), a different type of antipsychotic medication, causing increased levels of clozapine in the blood. This could increase the risk of side effects from clozapine.

Serotonin reuptake inhibitors such as paroxetine (Paxil), Sertraline (Zoloft), and fluoxetine (Prozac) when taken with risperidone causes the metabolism (breakdown) of risperidone by the liver to be inhibited, which in turn causes elevated blood levels of risperidone and may increase the risk of adverse reactions from risperidone.

Antifungal drugs such as fluconazole (Diflucan), itraconazole (Sporanox), and ketoconazole (Nizoral) when taken with risperidone also cause the metabolism (breakdown) of risperidone by the liver to be inhibited, which in turn causes elevated blood levels and may increase the risk of adverse reactions from risperidone.

There are no adequate studies of risperidone in pregnant women. Some unwanted effects have been reported in animal studies. Risperidone can be used in pregnancy if the physician feels that the benefits outweigh the potential but unknown risks.

Risperidone is excreted in human breast milk. Women receiving risperidone should not breastfeed.

What preparations of risperidone are available?

• Tablets: 0.25, 0.5, 1, 2, 3, and 4 mg.
• Oral solution: 1 mg/mL.
• Orally disintegrating tablets: 0.25, 0.5, 1, 2, 3, and 4 mg.
• Powder for injection: 12.5, 25, 37.5, and 50 mg.

How should I keep risperidone stored?

Tablets should be kept at room temperature, 15 C to 25 C (59 F to 77 F).