Ristech Plus

Uses

Risperidone tablet is used for the treatment of acute and chronic schizophrenic psychoses, and other psychotic conditions, in which positive symptoms (such as hallucinations, delusions, thought disturbances, hostility, suspiciousness), and/or negative symptoms (such as blunted affect, emotional and social withdrawal, poverty of speech) are prominent. Risperidone also alleviate affective symptoms (such as depression, guilt feelings, anxiety) associated with schizophrenia. Risperidone is also effective inmaintaining the clinical improvement during continuation therapy in patients who have shown an initial treatment response. Risperidone is in dicated for the treatment of mania in bipolar disorder.

Trihexyphenidyl Hydrochloride is used for an adjunct treatment of all forms of parkinsonism (postencephalitic, arteriosclerotic & idiopathic). Additionally, it is used for the control of extrapyramidal disorders caused by central nervous system drugs such as dibenzoxazepines, phenothiazines, thioxanthenes & butyrophenones.

Ristech Plus is also used to associated treatment for these conditions: Acute Mania, Irritability, Mixed manic depressive episode, Psychosis, Schizophrenia, Acute Manic episode, Agitated psychotic stateExtrapyramidal disorder, Extrapyramidal symptoms caused by butyrophenones, Extrapyramidal symptoms caused by dibenzoxazepines, Extrapyramidal symptoms caused by phenothiazines, Extrapyramidal symptoms caused by thioxanthenes, Idiopathic Parkinson's Disease, Parkinsonism post encephalitic, Arteriosclerotic Parkinsonism

How Ristech Plus works

Though its precise mechanism of action is not fully understood, current focus is on the ability of risperidone to inhibit the D2 dopaminergic receptors and 5-HT2A serotonergic receptors in the brain. Schizophrenia is thought to result from an excess of dopaminergic D2 and serotonergic 5-HT2A activity, resulting in overactivity of central mesolimbic pathways and mesocortical pathways, respectively.

D2 dopaminergic receptors are transiently inhibited by risperidone, reducing dopaminergic neurotransmission, therefore decreasing positive symptoms of schizophrenia, such as delusions and hallucinations. Risperidone binds transiently and with loose affinity to the dopaminergic D2 receptor, with an ideal receptor occupancy of 60-70% for optimal effect. Rapid dissociation of risperidone from the D2 receptors contributes to decreased risk of extrapyramidal symptoms (EPS), which occur with permanent and high occupancy blockade of D2 dopaminergic receptors. Low-affinity binding and rapid dissociation from the D2 receptor distinguish risperidone from the traditional antipsychotic drugs. A higher occupancy rate of D2 receptors is said to increase the risk of extrapyramidal symptoms and is therefore to be avoided.

Increased serotonergic mesocortical activity in schizophrenia results in negative symptoms, such as depression and decreased motivation. The high-affinity binding of risperidone to 5-HT2A receptors leads to a decrease in serotonergic activity. In addition, 5-HT2A receptor blockade results in decreased risk of extrapyramidal symptoms, likely by increasing dopamine release from the frontal cortex, and not the nigrostriatal tract. Dopamine level is therefore not completely inhibited. Through the above mechanisms, both serotonergic and D2 blockade by risperidone are thought to synergistically work to decrease the risk of extrapyramidal symptoms.

Risperidone has also been said to be an antagonist of alpha-1 (α1), alpha-2 (α2), and histamine (H1) receptors.[L1212] Blockade of these receptors is thought to improve symptoms of schizophrenia, however the exact mechanism of action on these receptors is not fully understood at this time.

Trihexyphenidyl is a non-selective muscarinic acetylcholine receptor antagonist but binds with higher affinity to the M1 subtype. In vivo studies have shown that trihexyphenidyl demonstrates higher affinity for central muscarinic receptors located in the cerebral cortex and lower affinity for those located peripherally. Other studies suggest that trihexyphenidyl may modify nicotinic acetylcholine receptor neurotransmission, leading indirectly to enhanced dopamine release in the striatum. Although the anticholinergic has proven to be useful in the treatment of symptoms associated with Parkinson’s disease or other movement disorders, its mechanism of action has yet to be fully elucidated.

Dosage

Ristech Plus dosage

Psychoses: 2 mg in 1-2 divided doses on 1st day then 4 mg in 1-2 divided doses on second day (Slower titration appropriate in some patients); usual dose range 4-6 mg daily; doses above 10 mg daily only if benefit considered to outweigh risk (max. 16 mg daily). Elderly (or in hepatic or renal impairment) initially 1 mg daily in two divided doses increased in steps of 1-2 mg twice daily. Child under 15 years not recommended.

Mania:Initially 2 mg once daily increased if necessary in step of 1 mg daily; usual dose range 1-6 mg daily; Elderly (or in hepatic or renal impairment) initially 1 mg daily in two divided doses increased in steps of 1-2 mg twice daily.

Schizophrenia: Risperidone should be generally administered at 1 mg BID initially, with increases in increments of 1 mg BID on the second and third day, as tolerated, to a target dose of 3 mg BID by the third day. Further dosage adjustments, if indicated, should generally occur at intervals of not less than 1 week. When dosage adjustments are necessary, small dose increments or decrements of 1-2 mg are recommended.

Dosage should be individualized. The initial dose should be low and then increased gradually, especially in patients over 60 years of age. Whether Trihexyphenidyl may best be given before or after meals should be determined by the way the patient reacts.

Idiopathic Parkinsonism: 1 mg of Trihexyphenidylmay be administered the first day. The dose may then be increased by 2 mg increments at intervals of three to five days.

Drug-Induced Parkinsonism: Commence therapy with a single 1 mg dose increase the total daily dosage to 5-15 mg range if the extrapyramidal manifestations are not controlled.

Concomitant Use with Levodopa: When Trihexyphenidyl is used concomitantly with levodopa, the usual dose is 3-6 mg daily.

Side Effects

Insomnia, agitation, anxiety, headache, less commonly drowsiness, impaired concentration, fatigue, blurred vision, constipation, nausea and vomiting, dyspepsia, abdominal pain, hyperprolactinaemia, urine incontinence, tachycardia, hypertension, edema, rash, rhinitis, cerebrovascular accident, neurtropenia and thrombocytopenia have been reported.

Minor side effects such as dryness of the mouth, blurring of vision, dizziness, mild nausea or nervousness. Patients with arteriosclerosis or with a history of idiosyncrasy to other drugs may exhibit reactions of mental confusion, agitation, disturbed behavior, or nausea and vomiting. Potential side effects are constipation, drowsiness, urinary hesitancy or retention, pupil dilation, increased intraocular tension, vomiting and headache.

Toxicity

Symptoms of overdose include lethargy, dystonia/spasm, tachycardia, bradycardia, and seizures. LD₅₀=57.7 mg/kg (rat, oral) and 34 mg/kg (rat, intravenous).

Symptoms of overdose include mydriasis, dryness of mucous membranes, red face, atonic states of bowels and bladder, and hyperthermia in high doses. Trihexyphenidyl causes agitation, confusion, and hallucinations due to its effects on the central nervous system. Untreated overdose may result in death, especially in children. Respiratory depression and cardiac arrest may be seen as premortal signs.

Patients experiencing an overdose of trihexyphenidyl may experience dry mouth, anhidrosis, mydriasis, nausea, vomiting, tachycardia, hyperpyrexia, reduced gastrointestinal motility, urinary hesitancy or retention, rash, hyperthermia, confusion, restlessness, agitation, poor coordination, paranoia, psychosis, delirium, hallucinations, coma, respiratory failure, circulatory failure, and death. Patients should be treated with symptomatic and supportive care which may include airway maintenance and the use of physostigmine.

Precaution

Special precaution should be taken in case of preexisting cardiovascular diseases, discontinue use if signs and symptoms of tardive dyskinesia occur, renal and hepatic impairment, elderly epilepsy, Parkinson's disease and in pregnancy.

Patients with cardiac, liver, or kidney disorders, or with hypertensioon, should closely be monitored. Since trihexyphenidyl has parasympatholytic activity, it should be used with caution in patients with glaucoma, obstructive disease of the gastrointestinal or genitourinary tracts, and in elderly males with possible prostatic hypertrophy. Trihexyphenidyl is not recommended for use in patients with tardive dyskinesia unless they have concomitant Parkinson’s disease. Abrupt withdrawal of treatment for parkinsonism may result in acute exacerbation of parkinsonism symptoms; therefore, abrupt withdrawal should be avoided.

Interaction

Risperidone May antagonize the effects of levodopa and dopamine agonists. Chronic administration with Carbamazepine reduces plasma clearance of Risperidone. Chronic administration with Clozapine may decrease the clearance of Risperidone. Risperidone may enhance the effects of certain antihypertensives.

Cannabinoids, barbiturates, opiates, and alcohol may have additive effects with trihexyphenidyl, and thus, an abuse potential exists. Concurrent use of alcohol or other CNS depressants with trihexyphenidyl may cause increased sedative effects. It may be contraindicated in patients taking monoamine oxidase inhibitors & tricycllic antidepressants.

Volume of Distribution

The volume of distribution of risperidone is approximately 1 to 2 L/kg.

Elimination Route

Well absorbed. The absolute oral bioavailability of risperidone is 70% (CV=25%). The relative oral bioavailability of risperidone from a tablet is 94% (CV=10%) when compared to a solution.

Trihexyphenidyl is absorbed from the gastrointestinal tract. Trihexyphenidyl reaches a C_max of 7.2 ng/mL, with a T_max of 1.3 hours, and an AUC of 201 ng*h/mL.

Half Life

3 hours in extensive metabolizers Up to 20 hours in poor metabolizers

The mean elimination half life of trihexyphenidyl is 3.2 ± 0.3 hours.

Clearance

Risperidone is cleared by the kidneys. Clearance is decreased in the elderly and those with a creatinine clearance (ClCr) between 15-59 mL/min, in whom clearance is decreased by approximately 60%.

Elimination Route

Risperidone is extensively metabolized in the liver. In healthy elderly subjects, renal clearance of both risperidone and 9-hydroxyrisperidone was decreased, and elimination half-lives are prolonged compared to young healthy subjects.

Data regarding the route of elimination of trihexyphenidyl are not readily available. However, it is likely eliminated predominantly in the urine.

Pregnancy & Breastfeeding use

Pregnancy: Although, in experimental animals, Risperidone did not show direct reproductive toxicity, some indirect, prolactin- and CNS-mediated effects were observed, No teratogenicity effect of Risperidone was noted in any study. The safety of Risperidone for use during human pregnancy has not been established.

Lactation: In animal studies, Risperidone and 9-hydroxyrisperidone are excreted in the milk. It has been demonstrated that Risperidone and 9-hydroxyrisperidone are also excreted in human breast milk. Therefore, women receiving Risperidone should not breast feed.

Pregnancy Category C. It is not known whether the drug is excreted in human milk and therefore trihexyphenidyl should only be used if the expected benefit to the mother outweighs the potential risk to the infant.

Contraindication

Risperidone is contraindicated in patients with a known hypersensitivity to the product.

Trihexyphenidyl is contraindicated in patients with hypersensitivity in patients to trihexyphenidyl HCl or to any of the tablet or elixir ingredients. Trihexyphenidyl is also contraindicated in patients with narrow angle glaucoma. Blindness after long-term use due to narrow angle glaucoma has been reported.

Acute Overdose

Drowsiness, sedation, tachycardia, hypotension, and extrapyramidal symptoms may occur. In case of severe extrapyramidal symptoms, anticholinergic medication should be administered. Close medical supervision and monitoring should continue until the patient recovers. There is no specific antidote to Risperidone.

Overdosage with trihexyphenidyl produces typical central symptoms of atropine intoxication ( the central anticholinergic syndrome). Signs & symptoms are: dilated and sluggish pupils, warm, dry skin, facial flushing, decreased secretions of mouth, pharynx, nose and bronchi, foul smelling breath, tachycardia etc. Neuropsychiatric signs such as delirium, disorientation, anxiety, hallucinations etc. The condition can progress to stupor, coma, paralysis, cardiac, respiratory arrest and death.

Storage Condition

Store in a cool and dry place, protected from light.

Innovators Monograph

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