Antipsychotic drugs, specific agents

Tertiary-amine muscarinic receptor antagonists gain access to the central nervous system and are therefore the anticholinergic drugs used to treat parkinsonism and the extrapyramidal side effects of antipsychotic drugs. Specific agents used primarily for these conditions include benztropine mesylate (Cogentin) and trihexyphenidyl hydrochloride (Artane, others). 

Consequently, antipsychotic drugs all share a basic mechanism of action that involves dopamine receptor blockade. It is apparent, however, that they are not all equal in their ability to affect specific sub-types of dopamine receptors, and that their effectiveness and side effects are related to their affinity and preference for certain receptors. As indicated earlier, other neurotransmitters may also be involved in the pathogenesis of psychosis, and differences in specific antipsychotic medications may be related to their ability to directly or indirectly affect these other transmitters as well as block dopamine influence. Future studies will continue to clarify how current antipsychotics exert their beneficial effects and how new agents can be developed to be more selective in their effects on dopamine and other neurotransmitter pathways. 

The steady-state concentrations of antipsychotic drugs after multiple dosing have been measured to establish a relationship between plasma concentrations and clinical efficacy or to monitor adverse effects (360-363). The majority of drugs in the class seem to exhibit linear pharmacokinetics, despite the wide interindividual variations in pharmacokinetic properties observed for specific agents. Linear pharmacokinetics allows the dosage to be readily adjusted if the steady-state plasma concentration is in the sub-therapeutic or toxic range. 

Avoidance of active concomitant medication is the next important requirement. Such medication constitutes a major artifact because it can markedly weaken the drug—placebo difference. Thus, compared treatments may appear equally efficacious due to the concomitant medication and not any inherent efficacy of the experimental agent. Some studies have used multiple agents, in different doses, with some known to be specifically effective for the disorder under investigation. For example, in some studies, comparing carbamazepine or valproate with placebo or lithium, patients have also received adjunctive antipsychotics, making firm conclusions difficult (see the section Alternative Treatment Strategies in Chapter 10). 

Pioneers in the field recognized and wrote about the lobotomy-like effects of the neuroleptic drugs when they first came into use, but in recent years drug advocates have promoted the false impression that these medications have a specific antipsychotic or antischizophrenic effect. In reality, the overriding clinical effect of these highly toxic chemical agents is to render patients and inmates more emotionally flat and indifferent, more apathetic and docile, and less autonomous and self-directed. 

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