An additional property of many antipsychotic drugs is blockade of certain calcium channels on neurons, cardiac muscle, and smooth muscle. Thioridazine and pimozide are potent calcium channel blockers, which may explain their cardiac toxicity, including prolongation of the QT interval and, for thioridazine, increased risk of torsade de pointes ventricular tachycardia. It has been hypothesized that the calcium antagonist properties of thioridazine may also be responsible for retrograde ejaculation, which is another side effect of the drug. The antipsychotic drugs in common use are equally efficacious, with the exception of clozapine, which is more effective for the treatment of schizophrenia. The high-potency drugs tend to cause more extrapyramidal side effects.
Most antipsychotics have long half-lives.
Antipsychotic drugs are the mainstay of treatment of acute psychoses, whether the psychoses are the result of an acute exacerbation of schizophrenia, acute mania, or another major psychiatric disorder. Before an acutely psychotic patient is treated, it is important that acute medical illness or drug toxicity be ruled out as a cause of the syndrome by obtaining as thorough a history as possible, monitoring vital signs, performing a physical examination, and ordering relevant laboratory work. Benzodiazepines are relatively free of serious side effects if used carefully for a limited time. An adequate dosage of an antipsychotic drug should produce benefit within four to six weeks. Increased insight and better judgment are unreliable criteria for monitoring purposes, although these changes may occur.