ANTIPSYCHOTICS-ATYPICAL
As we have already dealt in the last post with the typical traditional neuroleptics (antipsychotics) here we will deal with some neuroleptics or antipsychotics which are not typical in action and are not only acting against dopamine but they are also acting against serotonin(5-HT) at its receptors. Moreover, they are rarely associated with extrapyramidal side effects. In general, they have a wider therapeutic index and are safer than typical neuroleptics.
The therapeutic index is the ratio between the toxic dose(the amount of the drug which can produce minimal toxicity, TD) to the effective dose(the amount of the same drug that can produce the required effect, ED).
Therapeuic Index (TI) = TD / ED
If the result is greater then the drug is safer. The atypical neuroleptic drugs are safer than typical neuroleptics as their toxic dose, TD (numerator) is higher than their effective dose, ED(denominator).
1.Clozapine:-
It is chemically a derivative of the compound benzodiazepine. It is a potent serotonin receptor blocker along with its normal dopamine blockade effects.
Therapeutical Uses:-
1. Clozapine is an effective way of treating schizophrenia associated with suicide mentality. It improves self-confidence. It is more effective than phenothiazines, the typical neuroleptics.
2. Also, it improves negative aspects of schizophrenia such as blunted emotions, withdrawal, reduced ability to establish relationships)
Toxicity and Acute Side Effects
1.Prolonged usage may leads to serious side effects such as decreased WBC,cardiac inflammations,agranulocytosis,bone marrow suppression,neutropenia,seizures,hypotension etc.etc.
2. Acute side effects are such as fewer extrapyramidal effects than typical neuroleptics along with constipation, bedwetting, tremor etc.etc.
2.Risperidone:-
Chemically it is a derivative of the compound Benzisoxazole.
Like clozapine this drug also has a greater blockade affinity for serotonin receptors along with its usual dopamine blocking effects.
Fortunately, these drugs have a lack of anticholinergic effects and hence they have minimal extrapyramidal side effects.
Therapeutics:-
Risperidone unlike clozapine is effective against both positive(obsessive) and negative (withdrawal) types of schizophrenia hence it is the first-line medicine.
Precaution:-
The drug is said to prolong the QT intervals in the ECG hence care should be taken with the cardiac patients with QT abnormalities.
3.Olanzapine:-
Mechanism of actions is very similar to clozapine and risperidone by blocking both 5-HT and dopamine receptors.
Uses
Schizophrenia
Side effects:-
1.Anticholinergic (refer o cholinergic antagonists)
2.Minimal extrapyramidal effects
3.Sedation
4.Orthostatic hypotension.
