Article: Risperidone

Risperidone
Systematic (IUPAC) name
4-[2-[4-(6-fluorobenzo[d]isoxazol-3-yl)- 1-piperidyl]ethyl]-3-methyl- 2,6-diazabicyclo[4.4.0]deca-1,3-dien-5-one
Identifiers
CAS number	106266-06-2
ATC code	N05AX08
PubChem	5073
DrugBank	APRD00187
Chemical data
Formula	C23H27N4FO2
Mol. weight	410.485
Pharmacokinetic data
Bioavailability	?
Metabolism	?
Half life	?
Excretion	?
Therapeutic considerations
Pregnancy cat.	C
Legal status	Rx Only
Routes	Oral tablet, quick dissolve tablets, oral drink and extended-release intramuscular injection

Risperidone (Belivon^®, Rispen^®, Risperdal^® in the United States) is an atypical antipsychotic medication. It is most often used to treat delusional psychosis (including schizophrenia), but risperidone (like other atypical antipsychotics) is also used to treat some forms of bipolar disorder, psychotic depression and Tourette syndrome.

Generally lower doses are used for autistic spectrum disorders than are used for schizophrenia and other forms of psychosis; risperidone has received a not approved letter from the Food and Drug Administration (FDA) for use in Autism.^[1]

Risperidone is now the most commonly prescribed antipsychotic medication in the United States.

Side effects

Risperdal Logo

Common side effects include nausea, anxiety, dizziness, insomnia, low blood pressure, muscle stiffness, muscle pain, sedation, tremors, increased salivation and weight gain (it is not uncommon for patients taking risperidone over long periods to gain upwards of 50 pounds or even more). It has also been known to cause sexual dysfunction.

Occasionally breast tenderness and eventually lactation in both genders may occur. Many antipsychotics are known to increase prolactin because they inhibit dopamine. However, Risperidone is known to increase prolactin to a greater extent than most other antipsychotics, such as quetiapine. It is thought that once Risperidone raises prolactin, it may cause tumors in the pituitary gland. This may reoccur even if the patient has switched to a different antipsychotic.^[2]

Like all antipsychotics, Risperidone can potentially cause tardive dyskinesia (TD), extrapyramidal symptoms (EPS), and neuroleptic malignant syndrome (NMS), although the risk is generally less than for the older typical antipsychotics.

For some personal reports of the effects of using risperidone for autism or Asperger's syndrome - occasionally beneficial especially at very low doses such as 0.5mg per day, but sometimes severely distressing even at low doses.

Pharmacology

Risperidone's receptor profile

Risperidone is a very strong dopamine blocker (antagonist); i.e., it inhibits functioning of postsynaptic dopamine receptors.

Risperidone also acts as a 5-HT_2A antagonist, and can be used to quickly and effectively block the effects of 5-HT_2A agonist drugs such as LSD.

It reaches peak plasma levels quickly regardless of whether it is administered as a liquid or pills. The strong dopamine-blocking reaction is known to make some people feel nauseated if they do things that normally trigger the dopamine response, such as eat a pleasing meal or experience orgasm. Risperidone is metabolised fairly quickly so this potential for nausea subsides usually in two to three hours.

Current forms

Risperidone is available in the form of ordinary tablets, fast-dissolving tablets, an oral solution, and in the form of a long-lasting injection, known as Risperdal Consta, given once every two weeks by the patient's care provider. This form may be especially useful in patients who are unwilling or unable to comply with a regular daily medication regimen.

Risperdal is manufactured by Johnson & Johnson (NYSE: JNJ), which also makes Risperdal Consta in conjunction with Alkermes, Inc.

Safety risks

In 2004, the Committee for the Safety of Medicines (CSM) in the UK issued a warning that risperidone and another atypical antipsychotic, olanzapine, should not be given to elderly patients with dementia, because of an increased risk of cerebrovascular adverse events including stroke.

A study in the June 2006 edition of the journal Pharmacotherapy has highlighted a possible link between risperdone and pituitary tumors. The study examined the FDA's Adverse Event Reporting System database and found 77 pituitary tumors associated with antipsychotics. Of these, risperidone was associated with 54 (70%). One co-author cautioned that "Our findings do not prove a causal relationship between antipsychotic medications and pituitary tumors" and "atypical antipsychotics are lifesaving medications for a lot of people. By no means are we advocating that people stop using them, especially risperidone".^[2][3]

Notes and references

1. ^ Janssen, L.P. (2005-05-20). Johnson & Johnson Pharmaceutical Research & Development, L.L.C. Receives Not Approvable Letter on RISPERDAL® in the Treatment of Autism. Press release. Retrieved on 2006-06-02.
2. ^ ^a b Szarfman A, Tonning J, Levine J, Doraiswamy P (2006). "Atypical antipsychotics and pituitary tumors: a pharmacovigilance study.". Pharmacotherapy 26 (6): 748-58. PMID 16716128.
3. ^ Tracey Koepke. "Antipsychotic Drug May Be Linked to Pituitary Tumors", DukeMedNews, Duke University Medical Center, 2006-05-30. Retrieved on 2006-06-02.