As zuclopenthixol decanoate (Clopixol), it is a long acting intramuscular injection. Its main use is as a long acting injection given every two or three weeks to people with schizophrenia who have a poor compliance with medication and suffer frequent relapses of illness. There is some evidence it may be more helpful in managing aggressive behaviour.
As zuclopenthixol acetate (Clopixol, Acuphase, Cisordinol- Acutard), it is a shorter acting intramuscular injection used in the acute sedation of psychotic inpatients. The effect peaks at 48–72 hours providing 2–3 days of sedation.
As zuclopenthixol dihydrochloride (Clopixol), it is a tablet used in the treatment of schizophrenia in those who are compliant with oral medication.
As a long acting injection, zuclopenthixol decanoate comes in a 200 mg and 500 mg ampoule. Doses can vary from 50 mg 4 weekly to the maximum licensed dose of 600 mg weekly. In general, the lowest effective dose to prevent relapse is preferred. The interval may be shorter as a patient starts on the medication before extending to 3 weekly intervals subsequently. The dose should be reviewed and reduced if side effects occur, though in the short term an anticholinergic medication benztropine may be helpful for tremor and stiffness, while diazepam may be helpful for akathisia. 100 mg of zuclopenthixol decanoate is roughly equivalent to 20 mg of flupentixol decanoate or 12.5 mg of fluphenazine decanoate.
In acutely psychotic and agitated inpatients, 50 – 200 mg of zuclopenthixol acetate may be given for a calming effect over the subsequent three days, with a maximum dose of 400 mg in total to be given. As it is a long-acting medication, care must be taken not to give an excessive dose.
In oral form zuclopenthixol is available in 10, 25 and 40 mg tablets, with a dose range of 20–60 mg daily.
Zuclopenthixol has high affinity for both dopamine D1 and D2 receptors, for α1-adrenoceptors and 5-HT2 receptors but no affinity for cholinergic muscarine receptors. It has weak histamine (H1) receptor affinity and no α2-adrenoceptor blocking activity.
Chronic administration of zuclopenthixol (30 mg/kg/day for two years) in rats resulted in small, but significant, increases in the incidence of thyroid parafollicular carcinomas and, in females, of mammary adenocarcinomas and of pancreatic islet cell adenomas and carcinomas. An increase in the incidence of mammary adenocarcinomas is a common finding for D2 antagonists which increase prolactin secretion when administered to rats. An increase in the incidence of pancreatic islet cell tumours has been observed for some other D2 antagonists. The physiological differences between rats and humans with regard to prolactin make the clinical significance of these findings unclear.
Other permanent side effects are similar to many other typical antipsychotics, namely extrapyramidal symptoms as a result of dopamine blockade in subcortical areas of the brain. This may result in symptoms similar to those seen in Parkinsons Disease and include a restlessness and inability to sit still known as akathisia, a slow tremor and stiffness of the limbs. Zuclopenthixol is thought to be more sedating than the related flupentixol, though possibly less likely to induce extrapyramidal symptoms than other typical depots. As with other dopamine antagonists, zuclopenthixol may sometimes elevate prolactin levels; this may occasionally result in amenorrhoea or galactorrhoea in severe cases. Neuroleptic malignant syndrome is a rare but potentially fatal side effect. Any unexpected deterioration in mental state with confusion and muscle stiffness should be seen by a physician.