Pharmacological profile
The butyrophenone derivative group is distinguished by its pronounced antipsychotic activity. In terms of this specific effect, they surpass classical phenothiazine derivatives by 50–100 times.
In addition to the main neuroleptic effect, these substances possess important concomitant properties:
- Sedative effect — promote calming of the nervous system.
- Antiemetic effect — suppress the vomiting reflex.
An important distinction of butyrophenone derivatives from the phenothiazine series is their receptor profile. This group completely lacks anticholinergic properties. Furthermore, they exert only a weak blockade of peripheral $\alpha$-adrenergic receptors. As a result, the drugs have virtually no effect on vascular tone and do not lower blood pressure.
Drug interactions
Butyrophenone derivatives actively interact with other substances affecting the central nervous system. After good absorption from the gastrointestinal tract, they can significantly alter the effects of concomitant therapy.
Potentiation (enhancement of effect): Drugs of this group significantly enhance the action of other CNS depressants. These include:
- General anesthetics;
- Hypnotics;
- Narcotic analgesics;
- Alcohol.
Antagonism: In relation to psychostimulants, butyrophenone derivatives act as antagonists, suppressing their stimulating effect on the psyche.
Main drugs of the group
In clinical practice, two main representatives are most frequently used, differing in duration of action and indications.
Haloperidol
This is a potent antipsychotic with a pronounced sedative component. Indications for use:
- Management of psychomotor agitation states.
- Treatment of patients whose condition is resistant (refractory) to therapy with other neuroleptics.
- Conditions for which chlorpromazine is indicated (similar scope of application).
Haloperidol frequently causes motor side effects, and therefore is strictly contraindicated in any CNS diseases that are already accompanied by extrapyramidal symptoms.
Droperidol
Characterized by a very strong, but short-acting antipsychotic effect. Indications for use:
- Emergency management of acute attacks of psychomotor agitation (used as a 0.25% solution).
- Performance of neuroleptanalgesia — a specific type of anesthesia in which droperidol is combined with a potent narcotic analgesic fentanyl (there is a ready-made combination drug "Thalamonal").
Adverse reactions
The main and most dangerous side effect of the entire group of butyrophenone derivatives is the high incidence of extrapyramidal disorders. This is a complex of severe movement disorders that requires careful monitoring of the patient's condition during therapy and limits the use of the drugs in individuals with pre-existing lesions of the corresponding brain structures.
Briefly: answers to topical questions
What is the mechanism of the antipsychotic action of butyrophenone derivatives?
The mechanism of antipsychotic action consists in the blockade of postsynaptic dopamine (D₂) receptors in the central nervous system. Additionally, most neuroleptics block presynaptic dopamine (D₃), serotonin (5-HT), norepinephrine (α₁), histamine (H₁), and acetylcholine (M) receptors. However, the receptor profile of butyrophenone derivatives has differences: they are characterized by the complete absence of anticholinergic properties and only weak blockade of peripheral α-adrenergic receptors, due to which they practically do not lower blood pressure.
What are the contraindications for the use of haloperidol?
The main contraindication to the use of haloperidol is central nervous system diseases accompanied by extrapyramidal symptoms. Haloperidol frequently causes extrapyramidal disorders. Neuroleptics are contraindicated for the treatment of anticholinergic psychosis.
What specific extrapyramidal disorders do butyrophenone derivatives cause?
Butyrophenone derivatives cause early (reversible) and late (irreversible) extrapyramidal disorders. These include the following movement disorders:
- Drug-induced parkinsonism — manifests as tremor, muscle rigidity, and hypokinesia (motor retardation).
- Acute spasms (dystonia) — spastic contractions localized in the muscles of the face, neck, and back.
- Akathisia — marked motor restlessness and inability to sit still.
- Tardive dyskinesia — persistent involuntary excessive movements of the facial muscles (chewing, lip-smacking, blinking) and neck.
Class and exam questions
Why do butyrophenone derivatives cause almost no hypotension?
Unlike phenothiazines, they are completely devoid of anticholinergic properties and only insignificantly block peripheral alpha-adrenergic receptors, thus not causing a drop in blood pressure.
What drugs is it dangerous to combine this group with?
With alcohol, general anesthetics, hypnotics, and narcotic analgesics, since butyrophenones sharply potentiate their depressing effect on the CNS.
What is neuroleptanalgesia and what drug is used for it?
This is a method of combined analgesia and sedation. It utilizes the short-acting antipsychotic droperidol in combination with the narcotic analgesic fentanyl.
What is the main contraindication for prescribing haloperidol?
Haloperidol is contraindicated in central nervous system diseases accompanied by extrapyramidal symptoms, as it frequently precipitates pronounced movement disorders itself.
What else to study on this topic
- Mechanism of extrapyramidal disorders development during neuroleptic therapy
- Comparison of chlorpromazine and haloperidol: safety profile
- Principles and stages of neuroleptanalgesia
- Management tactics for patients resistant to standard neuroleptics
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