Antipsychotics - Pharmacology

Psychosis is a disorder that is characterized by a number of symptoms. These include difficulty processing information and reaching a conclusion; experiencing delusions or hallucinations; being incoherent or in a catatonic state; or demonstrating aggressive violent behavior.

Psychosis is divided into major categories, once of which is schizophrenia. Schizophrenia is a chronic psychotic disorder where patients exhibit either positive or negative symptoms. Positive symptoms are exaggeration of normal function such as agitation, incoherent speech, hallucination, delusion, and paranoia. Negative symptoms are characterized by a decrease or loss of motivation or function such as social withdrawal, poor self care, and a decrease in the content of speech. Negative symptoms are more chronic and persistent than positive symptoms.

Psychosis is caused by an imbalance in the neurotransmitter dopamine in the brain. Anti psychotic medication, also known as dopamine antagonists, block the D2 dopamine receptors in the brain thereby reducing the psychotic symptoms.

A number of antipsychotic medications block the chemoreceptor trigger zone and vomiting (emetic) center of the brain. In doing so, it produces an antiemetic effect. Although blocking dopamine improves the patient’s thought processes and behavior, it can cause side effects.

These include symptoms of Parkinsonism (see Parkinsonism previously discussed in this chapter). Patients who undergo long-term treatment for psychosis using antipsychotic medications also might be prescribed drugs to treat the symptoms of Parkinsonism.

Antipsychotic medications are divided into two categories. These are sometimes called traditional and atypical. The typical category of antipsychotic medication is further subdivided into phenothiazines and nonphenothiazines.

Phenothiazines block norepinephrine causing sedative and hypotensive effects early in treatment.

Nonphenothiazines include butyrophenone haloperidol (Haldol) whose pharmacologics are similar to phenothiazines as it alters the effects of dopamine by blocking the dopamine receptor sites.

Atypical antipsychotic drugs are used to treat schizophrenia and other psychotic disorders for patients who do not respond to the typical antipsychotic medication.

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