Mechanism of Action
The major action of all antipsychotics in the nervous system is to
block receptors for the neurotransmitter dopamine; however, the therapeutic
mechanism of action is only par-tially understood. Dopamine receptors are
classified into subcategories (D1, D2, D3, D4, and D5), and D2, D3, and D4 have
been associated with mental illness. The typical antipsychotic drugs are potent
antagonists (blockers) of D2, D3, and D4. This makes them effective in treating
target symptoms but also produces many extrapyramidal side effects (discussion
to follow) because of the blocking of the D2 receptors. Newer, atypical
antipsychotic drugs, such as clozapine (Clozaril), are relatively weak blockers
of D2, which may account for the lower incidence of extrapyrami-dal side
effects. In addition, atypical antipsychotics inhibit the reuptake of
serotonin, as do some of the antidepressants, increasing their effectiveness in
treating the depressive aspects of schizophrenia. Paliperidone (Invega) is the
new-est atypical antipsychotic, gaining approval for distribution in the United
States in January 2007. It is chemically similar to risperidone (Risperdal);
however, it is an extended-release preparation. This means the client can take
one daily dose in most cases, which may be a factor in increased compliance.
A new generation of antipsychotics, called dopamine system
stabilizers, is being developed. These drugs are thought to stabilize dopamine
output; that is, they preserve or enhance dopaminergic transmission when it is
too low and reduce it when it is too high. This results in control of symptoms
without some of the side effects of other antipsy-chotic medications.
Aripiprazole (Abilify), the first drug of this type, was approved for use in
November 2002. In clini-cal trials, the most common side effects were headache,
anxiety, and nausea.
Four antipsychotics are available in depot injection, a time-release form of medication for maintenance
therapy. Two con-ventional antipsychotics use sesame oil as the vehicle for
these injections, so the medication is absorbed slowly over time; thus, less
frequent administration is needed to maintain the desired therapeutic effects.
Prolixin (decanoate fluphenazine) has a duration of 7 to 28 days, and Haldol
(decanoate haloperi-dol) has a duration of 4 weeks. After the client’s
condition is stabilized with oral doses of these medications, administration by
depot injection is required every 2 to 4 weeks to maintain the therapeutic effect.
Risperidone (Risperdal Consta) Paliperi-done (Invega Sustenna), atypical
antipsychotics, encapsulates active medication into polymer-based microspheres
that degrade slowly in the body, gradually releasing the drug at a controlled
rate. Risperdal Consta, 25 mg, is given every 2 weeks. Paliperidone (Invega
Sustenna) 117mg is given every 4 weeks.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2024 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.