Paliperidone

Paliperidone (trade name Invega), also known as 9-hydroxyrisperidone, is an atypical antipsychotic developed by Janssen Pharmaceutica. Invega is an extended release formulation of paliperidone that uses the OROS extended release system to allow for once-daily dosing. Paliperidone palmitate (trade name Invega Sustenna) is a long-acting injectable formulation of paliperidone palmitoyl ester indicated for once-monthly injection after an initial titration period. Chemically, paliperidone is one of many active metabolites of the older atypical antipsychotic risperidone (paliperidone is 9-hydroxyrisperidone, i.e. risperidone with an extra hydroxyl group). It is indicated for the acute and maintenance treatment of schizophrenia.

Pharmacology
While its specific mechanism of action is unknown, it is believed paliperidone and risperidone act via similar, if not identical, pathways; therapeutic effect may be due to a combination of D2 and 5-HT2A receptor antagonism. Paliperidone also has antagonist effect at α1 and α2 adrenergic receptors and at H1 histamine receptors. It does not bind to muscarinic acetylcholine receptors.

Paliperidone (as Invega) was approved by the FDA for the treatment of schizophrenia in 2006. It is marketed for the treatment of schizophrenia and for bipolar mania. Clinical trials of paliperidone for the treatment of schizoaffective disorder are also planned. It may also be used off-label for other conditions. Like risperidone, its possible use in people with autism and Asperger syndrome may be studied. Recently, the long-acting injectable form of paliperidone, marketed as INVEGA Sustenna, was approved by the FDA on July 31, 2009.

Side effects and adverse reactions
The most common side effects of paliperidone are restlessness and extrapyramidal disorder, including involuntary movements, tremors and muscle stiffness. Some users reported experiencing sexual dysfunction while administering this drug in combination with SSRIs such as Zoloft. Invega website's Important Safety Information page includes this warning: Elderly Patients with dementia-related psychosis treated with atypical antipsychotic drugs are at an increased risk of death compared to placebo. Invega (paliperidone) is not approved for the treatment of patients with dementia-related psychosis.

Neuroleptic malignant syndrome is a rare, but potentially lethal reaction to the medication. Heart rhythm changes—potentially serious—may make paliperidone risky for people with some heart conditions.

Other risks include:
 * Tardive dyskinesia, a serious, sometimes permanent side effect reported with INVEGA and other neuroleptics. The risk of tardive dyskinesia increases with total dose and thus becomes more likely the longer a person takes Invega.
 * High blood sugar and diabetes
 * Hyperprolactinemia, or elevated levels of the hormone prolactin, potentially leading to the absence of a menstrual period; breasts producing milk; the development of breasts by males; and erectile dysfunction.
 * Complications associated with pre-existing narrowing or blockage of the gastrointestinal tract (esophagus, stomach or small or large intestine)
 * Fainting or lightheadedness when standing up or sitting up too quickly.
 * Impairment of alertness and driving ability
 * Risk in people with a seizure disorder or a history or health conditions that make seizures more likely
 * Extrapyramidal effects -- persistent movement disorders or muscle disturbances, such as restlessness, tremors, and muscle stiffness.
 * Caution should be exercised before prescribing Invega to pregnant or nursing women.
 * Increased sensitivity to heat, difficulty cooling off, and increased likelihood of dehydration.