Risperidone is an atypical antipsychotic agent for two reasons. First, it is chemically unrelated to the older antipsychotic drugs. Second, unlike older antipsychotic drugs that primarily inhibit the actions of dopamine, a chemical in the brain, risperidone may also have some action against another brain chemical, serotonin. The proper level of both dopamine and serotonin are influential in maintaining mental well-being.
An advantage of using risperidone over one of the older antipsychotic drugs is a lower incidence of parkinsonian-like side effects. These side effects may be sufficiently troublesome to cause patients to discontinue treatment for their schizophrenia. For this reason, patients who have had negative experiences with older antipsychotics may benefit from risperidone. Also, some patients who showed little improvement with older antipsychotic drugs respond better to risperidone.
Risperidone is available in 0.25-mg, 0.5-mg, 1-mg, 2-mg, 3-mg, and 4-mg tablets and a solution containing 1 mg of drug in each milliliter of solution.
Recommended dosage
For treating psychotic disorders in adults, the usual starting dose of risperidone is 1 mg twice daily. Dosage is increased gradually until a target dose of 3 mg twice daily is reached. Some patients do just as well with a single daily dose (6 mg once a day, for example). There is little clinical evidence to indicate that increasing the daily dose beyond 8 mg offers additional benefit. However, higher doses may contribute to additional side effects. If the dose needs to be adjusted, the changes should made no more often than once per week.
In older patients (over age 60), starting dosage should not exceed 1 mg daily. Most patients should not take more than 3 mg daily. People with low blood pressure and those who have kidney disease should take a similarly reduced dose.
Precautions
Patients with a history of cardiovascular disease or low blood pressure should take risperidone only after discussing the risks and benefits with their physician, and then with close physician monitoring.
Risperidone has occasionally been associated with seizures. People with a past history of seizures should discuss with their doctor whether risperidone is the right antipsychotic for them to use.
People taking risperidone should avoid operating a motor vehicle or other dangerous machinery until they see how risperidone affects them. Some people have trouble regulating their body temperature while taking risperidone. Patients receiving this drug should be aware of this and avoid extremes in outdoor temperatures.
Side effects
The most common and bothersome side effect associated with risperidone is decreased blood pressure while standing up (known as orthostatic hypotension). This can cause dizziness or fainting. A decrease in blood pressure usually occurs early in therapy, while the proper dose is being established. It is more common in older patients than in younger ones. Usually, this side effect disappears entirely with time. If it continues, the physician may decrease the dose. Meanwhile, people taking risperidone should be aware of this side effect and get up slowly if they have been sitting for an extended time.
The most common nervous system side effects of risperidone include insomnia, agitation, anxiety, and headache. Early in therapy, patients may experience an inability to think clearly or perform certain tasks that require mental alertness. High doses of risperidone can cause unwanted sleepiness in about 40% of patients.
Antipsychotic drugs, including risperidone, can cause side effects that are similar to the symptoms of Parkinson's disease. The patient does not have Parkinson's disease, but may have shaking in muscles at rest, difficulty with voluntary movements, and poor muscle tone. These symptoms normally disappear if the drug is stopped.
The most common gastrointestinal side effects include nausea, vomiting, constipation, and difficulty digesting food.
Up to 10% of patients taking risperidone experience rhinitis (runny nose).
Interactions
There is very little information about how risperidone interacts with other drugs. However, because some patients receiving risperidone experience lowered blood pressure while standing, it is expected that other drugs that lower blood pressure may increase the incidence and severity of this side effect when taken with risperidone.
BOOKS
American Society of Health-System Pharmacists. AHFS Drug Information 2002. Bethesda: American Society of Health-System Pharmacists, 2002.
O'Brien, Charles P. "Drug Addiction and Drug Abuse." In Goodman & Gillman's The Pharmacological Basis of Therapeutics, edited by Joel G. Hardman, Ph.D. and Lee E. Limbird, Ph.D. Tenth Edition. New York: McGraw-Hill, 2001.
