Haloperidol mechanism of action

Atypicals clinically help patients by transiently occupying D2 receptors and then rapidly dissociating to allow normal dopamine neurotransmission. This keeps prolactin levels normal, spares cognition, and obviates EPS. One theory of atypicality is that the newer drugs block 5-HT2A receptors at the same time as they block dopamine receptors and that, somehow, this serotonin-dopamine balance confers atypicality. This, however, is not borne out by the results. While 5-HT2A receptors are readily blocked at low dosages of most atypical antipsychotic drugs (with the important exceptions of remoxipride and amisulpride, neither of which is available for use in Canada) the dosages at which this happens are below those needed to alleviate psychosis. In fact, the antipsychotic threshold occupancy of D2 for antipsychotic action remains at about 65% for both typical and atypical antipsychotic drugs, regardless of whether 5-HT2A receptors are blocked or not. At the same time, the antipsychotic threshold occupancy of D2 for eliciting EPS remains at about 80% for both typical and atypical antipsychotics, regardless of the occupancy of 5-HT2A receptors.

The intravenous route is not FDA approved and is generally not recommended except when no other alternatives are available. Intravenous administration appears to be associated with a higher risk of QT prolongation and torsade de pointes (TdP) than other forms of administration. The manufacturer recommends ECG monitoring for QT prolongation and arrhythmias if IV administration is required. A dose in the range of 1 to 5 mg IV has been suggested, with the dose being repeated at 30 to 60 minute intervals, if needed. A maximum IV dose has not been established. The lowest effective dose should be used in conjunction with conversion to oral therapy as soon as possible.

The precise mechanism whereby the therapeutic effects of haloperidol are produced is not known, but the drug appears to depress the CNS at the subcortical level of the brain, midbrain, and brain stem reticular formation. Haloperidol seems to inhibit the ascending reticular activating system of the brain stem (possibly through the caudate nucleus), thereby interrupting the impulse between the diencephalon and the cortex. The drug may antagonize the actions of glutamic acid within the extrapyramidal system, and inhibitions of catecholamine receptors may also contribute to haloperidol's mechanism of action. Haloperidol may also inhibit the reuptake of various neurotransmitters in the midbrain, and appears to have a strong central antidopaminergic and weak central anticholinergic activity. The drug produces catalepsy and inhibits spontaneous motor activity and conditioned avoidance behaviours in animals. The exact mechanism of antiemetic action of haloperidol has also not been fully determined, but the drug has been shown to directly affect the chemoreceptor trigger zone (CTZ) through the blocking of dopamine receptors in the CTZ.

An encephalopathic syndrome (characterized by weakness, lethargy , fever, tremulousness and confusion, extrapyramidal symptoms, leukocytosis , elevated serum enzymes, BUN , and fasting blood sugar) followed by irreversible brain damage has occurred in a few patients treated with lithium plus HALDOL. A causal relationship between these events and the concomitant administration of lithium and HALDOL has not been established; however, patients receiving such combined therapy should be monitored closely for early evidence of neurological toxicity and treatment discontinued promptly if such signs appear.

Haloperidol mechanism of action

haloperidol mechanism of action

An encephalopathic syndrome (characterized by weakness, lethargy , fever, tremulousness and confusion, extrapyramidal symptoms, leukocytosis , elevated serum enzymes, BUN , and fasting blood sugar) followed by irreversible brain damage has occurred in a few patients treated with lithium plus HALDOL. A causal relationship between these events and the concomitant administration of lithium and HALDOL has not been established; however, patients receiving such combined therapy should be monitored closely for early evidence of neurological toxicity and treatment discontinued promptly if such signs appear.

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