phenothiazine derivatives, any of a group of drugs that have a three-ring structure in which two benzene rings are linked by a nitrogen and a sulfur. They represent the largest and oldest group of antipsychotic compounds in clinical medicine. Chlorpromazine and prochlorperazine can be viewed as the prototypes of the many phenothiazines and their congeners that are used as adjuncts to general anesthesia and as antiemetics, antipsychotic agents (major tranquilizers), and antihistamines. This group of drugs largely revolutionized the practice of psychiatric medicine, a process that is now continuing with the introduction of the newer atypical antipsychotics such as risperidone and olanzapine. Unlike the barbiturates, which act exclusively on the central nervous system (CNS), the phenothiazines exert significant influence on many organ systems of the body at once. For example, they exert antiadrenergic, anticholinergic, and antihistaminic activity. The effects on the CNS differ according to individual drug and patient status. All phenothiazine tranquilizers are withheld from patients with severe CNS depression or epilepsy and are given with caution to those with liver disease.
