Use of clozapine in people with intellectual disabilities and psychoses

Review question

What is the evidence that clozapine can be helpful for adults with intellectual disabilities who have psychoses?

Background

People with intellectual disability have a low score on intelligence tests. They have problems in areas like self-care, social relationships, work, education and dealing with the challenges of daily life. To make a diagnosis of intellectual disability, we use tests in which we compare the performance of an individual person on certain tasks with other people of his or her age. People with intellectual disabilities are unable to process information as efficiently as people without intellectual disability. Depending on the severity of their condition, they need varying degrees of support to cope with the demands and expectations of life. Those who have a mild intellectual disability are able to manage their affairs with some additional support. Those who have a severe intellectual disability, most of the time are unable to live independently and require support on a daily basis.

Psychosis is a disorder of the mind in which people hear voices when there is no external source of the voices and they harbour unfounded beliefs called delusions. Psychosis affects their behaviour, relationships, performance at work, and other spheres of daily life. Psychosis is three times more common in people with an intellectual disability than those without an intellectual disability. Psychosis is treated with a group of drugs called antipsychotics. These drugs can have different desired and undesired (i.e. side effects) effects in different people. When at least two antipsychotics are not effective in treating the symptoms of psychosis, it is labelled as treatment-resistant psychosis. Clozapine is recommended for treatment-resistant psychosis.

People who have an intellectual disability and who also suffer from psychosis are at a higher risk of developing treatment-resistant psychosis. We systematically reviewed all available evidence which examined the effects of clozapine in people with intellectual disabilities and psychoses.

Study characteristics

The evidence is current to 15 December 2014. Although there were reports on studies involving only one person or groups of small numbers of people, we did not find any trial that compared groups of people with intellectual disabilities and psychoses who were prescribed clozapine, with other groups of people prescribed other drugs or who took no drugs at all.

Key results

Current research provides no evidence to support the use of clozapine in adults with intellectual disabilities and psychoses. Clinicians working with these individuals often rely on evidence from the general population (i.e. those without an intellectual disability) to prescribe clozapine. There is an urgent need for further research in this area.

Authors' conclusions: 

There are currently no RCTs that assess the efficacy and side effects of clozapine in people with intellectual disabilities and psychoses. Given the use of clozapine in this vulnerable population, there is an urgent need for a RCT of clozapine in people with a dual diagnosis of intellectual disability and psychosis to fill the evidence gap.

Read the full abstract...
Background: 

Psychosis is three times more common in people with an intellectual disability than in those without an intellectual disability. A low intelligence quotient (IQ) is a defining characteristic for intellectual disability and a risk factor for poor outcome in psychosis. Clozapine is recommended for treatment-resistant psychosis. The effect of psychotropic medication can be different in people with intellectual disability; for example, they may be more prone to side effects. People with an intellectual disability and psychosis form a special subgroup and we wanted to examine if there is randomised controlled trial (RCT) data in this population to support the use of clozapine.

Objectives: 

To determine the effects of clozapine for treating adults with a dual diagnosis of intellectual disability and psychosis.

Search strategy: 

We searched CENTRAL, Ovid MEDLINE, Embase and eight other databases up to December 2014. We also searched two trials registers, the Cochrane Schizophrenia Group's Register of Trials, and contacted the manufacturers of clozapine.

Selection criteria: 

RCTs that assessed the effects of clozapine, at any dose, for treating adults (aged 18 years and over) with a dual diagnosis of intellectual disability and psychotic disorder, compared with placebo or another antipsychotic medication.

Data collection and analysis: 

Three review authors independently screened all titles, abstracts and any relevant full-text reports against the inclusion criteria.

Main results: 

Of the 1224 titles and abstracts screened, we shortlisted 38 full-text articles, which we subsequently excluded as they did not meet the inclusion criteria. These studies were not RCTs. Consequently, no studies are included in this Cochrane review.

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