Antipsychotic and Neuroleptic Drugs
Antipsychotic and Neuroleptic Drugs Information
The term antipsychotic is applied to a group of drugs used to treat psychosis. Common conditions with which antipsychotics might be used include schizophrenia, mania and delusional disorder, although antipsychotics might be used to counter psychosis associated with a wide range of other diagnoses.
These drugs are also referred to as neuroleptics or neuroleptic drugs.
There are currently two main types of antipsychotics in use, the typical antipsychotics and the atypical antipsychotics. A newer antipsychotic drug group has been discovered called the partial dopamine agonists, although research and clinical trials are still being conducted so medications from this group are not widely available.
Typical antipsychotics are sometimes referred to as major tranquilizers because some of them can tranquilise and sedate when taken in large doses. This term is increasingly disused because many antipsychotics do not have strong sedating properties and the terminology implies a connection with benzodiazepines whereas none exists.
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Common Antipsychotic Drugs
Commonly used antipsychotic medications are listed below by drug group. Trade names appear in brackets.
Typical antipsychotics
- The Phenothiazines: chlorpromazine (Thorazine, Largactil), fluphenazine (Perimitil, Prolixin), perphenazine (Trilafon), prochlorperazine (Compazine), thioridazine (Melleril), trifluoperazine (Stelazine)
- droperidol (Inapsine)
- haloperidol (Haldol)
- pimozide (Orap)
- promazine (Sparine)
Atypical antipsychotics
- clozapine (Clozaril)
- olanzapine (Zyprexa)
- risperidone (Risperdal)
- quetiapine (Seroquel)
- ziprasidone (Geodon)
Partial dopamine agonists
- aripiprazole
The typical antipsychotic drugs are now out of patent meaning any pharmaceutical company is legally allowed to produce cheap generic versions of these medications. Whilst this makes them a great deal cheaper than the atypical drugs which are still in patent, atypical drugs are preferred as a first line treatment due to the fact that they generally have less side effects and seem to have additional benefits for the 'negative symptoms' of schizophrenia, a typical condition for which they might be prescribed.
Drug Action and Effectiveness
All antipsychotic drugs tend to block the D2 neuroreceptors in the dopamine pathways in the brain, so the normal effect of dopamine release in the relevant synapses is reduced.
It is the blockade of D2 receptors in the mesolimbic pathway of the brain which is thought to produce the intended antipsychotic effect.
Typical antipsychotics are not particularly selective and also block the same receptors in the mesocortical pathway, tuberoinfundibular pathway and the nigrostriatal pathway. Blocking D2 receptors in these other pathways is thought to produce some of the unwanted side effects that the typical antipsychotics can produce (see below).
Atypical antipsychotic drugs have a similar blocking effect on D2 receptors but seem to be a little more selective, targetting the intended pathway to a larger degreee than the others. They also block or partially block serotonin receptors (particularly 5HT2A,C and 5HT1A receptors).
This combination of effects on both dopamine and serotonin receptors might be why atypical antipsychotic drugs tend to have less side effects than typicals and have a seemingly additional effect on the 'negative symptoms' of schizophrenia.
Anti-psychotics can be classified on a spectrum of low potency to high potency, where potency refers to the ability of the drug to bind to dopamine receptors, and not to the effectiveness of the drug. High potency antipsychotics such as haloperidol typically have doses of a few milligrams and cause less sleepiness and calming effects than low potency antipsychotics such as chlorpromazine, which have dosages of several hundred milligrams.
There is generally a lag of a few days to a few weeks between the time the drug is started and the time that the medication begins to reduce psychosis. Why this is so remains unclear.
Some people who become psychotic do not seem to respond to antipsychotic medication, despite studies showing that the drug is blocking the same amount of receptors as in other people who do respond to the treatment. Again, it is still not clear why this might be.
Antipsychotic and Neuroleptic Drugs Side Effects
History and Design
The original antipsychotic drugs were happened upon largely by chance and were tested empirically for their effectiveness.
The first antipsychotic was chlorpromazine, which was developed as a surgical anesthetic. It was first used on psychiatric patients in the belief that it would have a calming effect. However, the drug soon appeared to reduce psychosis beyond this calming effect, and it is now believed that the reduction of psychosis produced by the drug is unrelated to the calming effect of the medication.
The newer atypical antipsychotics are supposedly rationally designed drugs in which a theoretical understanding of both the condition to be treated and the effect of certain molecules on the body is used to develop potential new drug candidates.
