Biological Therapies: Drug therapy Flashcards
What are antipsychotics?
Drugs effective in treating the most disturbing forms of psychotic illness such as schizophrenia and manic depression. It helps the patient get over the disorder functions as well as increasing their feelings of subjective well-being. This is usually recommended for the initial treatment for schizophrenia, after which a combination of medication and psychological treatment.
What do antipsychotic drugs do?
Dopamine antagonists work by blocking dopamine receptors in the synapses in the brain, reducing the action of dopamine. Initially, dopamine levels build up after taking chlorpromazine, but them production is reduced. This normalises neurotransmission in key areas of the brain, which in turn reduces symptoms like hallucinations.
What are typical antipsychotics used for?
They work by acting as antagonists in the dopamine system and aim to reduce the action of dopamine - they are strongly associated with the dopamine hypothesis.
What are atypical antipsychotic drugs used for?
Atypical antipsychotics such as clozapine have been around since the 1970’s. The aim of these drugs was to improve the effectiveness of drugs in suppressing psychoses such as schizophrenia and also minimise the side effects. They typically target a range of neurotransmitters including dopamine and serotonin.
What do typical antipsychotic drugs do?
These have been around since the 1950’s. Used to reduce the effects of dopamine antagonists in that they bind to but not stimulate dopamine receptors, thus blocking their action. By reducing stimulation of the dopamine system in the mesolimbic pathway, antipsychotic drugs eliminate hallucinations and delusions experienced by people with the disorder. These symptoms usually diminish within a few days of medication, although other symptoms may take several weeks before a significant improvement is noted. The effectiveness of dopamine antagonists led to the development of the dopamine hypothesis.
What is an example of a typical antipsychotic? And what other effect does it have?
Chlorpromazine also has an effect on histamine receptors which appears to lead to a sedation effect. Therefore it is also used to calm anxious patients when they are first admitted to hospital.
What leads to side effects from typical antipsychotics?
In order to block between 60 and 75% of D2 receptors, a similar number of these receptors in other areas of the brain must be also blocked. It is found that blocking dopamine receptors in the remaining pathways may be harmful for the person. This problem has been addressed by development of the atypical antipsychotic drugs.
What do typical antipsychotics do?
They carry a lower risk of extrapyramidal side effects, have a beneficial effect on negative symptoms and cognitive impairment, and are suitable for treatment-resistant patients. They also act on the dopamine system by blocking D2 receptors then rapidly dissociate to allow normal dopamine transmission. It is characteristic that is thought to be responsible for the lower levels of extrapyramidal side effects found with these drugs compared to conventional antipsychotics. Because atypical antipsychotics have very little effect on dopamine systems that control movement, they tend not to cause the movement problems found with typical antipsychotics.
What does clozapine do?
Clozapine binds to dopamine receptors as chlorpromazine does but also acts on serotonin and glutamine receptors. This drug was more effective than typical antipsychotics -clozapine reduces depression and anxiety in patients as well as improving cognitive functioning. It also improves mood, which is important as up to 50% of people suffering from schizophrenia attempt suicide.
What distinguished atypical from typical?
Rapid dissociation and typical only block D2 (dopamine) receptors, however atypical have a stronger affinity for serotonin receptors.
Strength: evidence shows that antipsychotics are moderately effective.
Thronley et al reviewed data from 13 trials and found that chlorpromazine was associated with better functioning and reduced symptom severity compared with a placebo. There is also support for the benefits of atypical antipsychotics. Meltzer et al concluded that clozapine is more effective than typical antipsychotics, and that it is 30-50% more effecting in treatment-resistant cases. Therefore the evidence suggests that antipsychotics are reasonably effective.
Limitation: antipsychotic drugs have side effects.
Typical antipsychotics are associated with dizziness, agitation, sleepiness, weight gain, etc. Long term use can lead to lip-smacking and grimacing due to dopamine super sensitivity. The most serious side effect is neuroleptic melignant syndrome (NMS) caused by blocking dopamine action in the hypothalamus (can be fatal due to disrupted regulation of several body symptoms). Atypical antipsychotics were developed to reduce side effects but some still exist and this is a serious limitation of antipsychotic drug therapies.
Limitation: the theoretical objection to the use of antipsychotic drugs.
The use of these drugs is strongly tied up with the dopamine hypothesis and the idea that there are higher than usual levels of dopamine in the subcortex in the brain. But there is evidence that this may not be correct and that dopamine levels in other parts of the brain are too low rather than too high. If so, antipsychotics shouldn’t work. This has undermined the faith of some people that any positive effects are actually due to the pharmacological effects of antipsychotics.
Limitation: there are doubts about the true effectiveness of antipsychotics.
It has been suggested that data from some successful trials have been published multiple times, exaggerating the positive effects. Also, most studies only review short-term effects. As antipsychotics have powerful calming effects, it is easy to demonstrate that they have a positive effect on patients despite the facts they may not be effective in reducing psychosis. This suggests that the effectiveness of antipsychotics may be overestimated by much of the empirical research.
Limitation: antipsychotic drugs may simply be a ‘chemical cosh’.
Antipsychotics may have been used in hospital situations to calm patients and make them easier for staff to work with, rather than to benefit the patients themselves. Short-term use of antipsychotics to calm patients is recommended by the National Institute for Health and Care Excellence (NICE). However this practice is seen by some as a human rights’ abuse. This raises ethical issues in the use of antipsychotic drugs with schizophrenia patients.
