Classification and historical background
Psychotropic drugs are medicinal substances that exert a targeted effect on human mental activity. Chlorpromazine (along with reserpine) became the key drug that marked the beginning of psychopharmacology's development in the mid-20th century.
In the modern classification of psychotropic drugs (which includes 6 main groups: antipsychotics, antidepressants, anxiolytics, sedatives, psychostimulants, and nootropics), chlorpromazine is classified as a typical antipsychotic.
According to their chemical structure, typical antipsychotics are divided into three groups:
- Phenothiazine derivatives (to which chlorpromazine belongs as an aliphatic derivative, unlike piperazine and piperidine derivatives).
- Butyrophenone derivatives (haloperidol, droperidol).
- Thioxanthene derivatives (chlorprothixene).
Pharmacokinetics: metabolism features
The biotransformation of the drug occurs in the liver via microsomal oxidation. The process involves endoplasmic reticulum enzymes, predominantly cytochrome P450.
A specific metabolic pathway of chlorpromazine is S-oxidation (cimetidine, for example, is metabolized via the same pathway). This distinguishes it from drugs that undergo aromatic or aliphatic hydroxylation, N-oxidation, or deamination.
Mechanism of action and receptor profile
The pharmacodynamics of chlorpromazine are determined by its broad receptor profile. The drug affects both the central and peripheral nervous systems.
- Antipsychotic effect: achieved by blocking postsynaptic dopamine D2 receptors in the mesolimbic system of the brain. This leads to the elimination of positive symptoms of psychosis (delusions and hallucinations). It is worth noting that chlorpromazine is inferior to haloperidol in the strength of its antipsychotic effect.
- Sedative effect: associated with the drug's inhibitory effect on the ascending reticular activating system of the brainstem.
- Effect on the autonomic nervous system: the drug exhibits pronounced M-anticholinergic activity (unlike haloperidol, in which this effect is weaker) and also blocks peripheral $\alpha$-adrenergic receptors.
Pharmacological effects and synergism
In addition to its primary antipsychotic, pronounced sedative, and anxiolytic (anti-anxiety) effects, chlorpromazine is characterized by synergism — the enhancement of effect when medicinal substances are used together.
Chlorpromazine engages in potentiation-type interactions. In this variant of synergism, one substance significantly enhances the action of another, and the final effect exceeds the simple arithmetic sum of the individual components' effects ($1 + 1 > 2$).
Clinical significance: Chlorpromazine potentiates the action of CNS depressants (general anesthetics, hypnotics). This makes it possible to artificially lower the dosages of toxic anesthetic drugs, reducing their concentration without losing efficacy.
Side effects
The drug's side effects stem directly from its non-selective receptor profile and are divided into peripheral and neuroendocrine.
Peripheral action: Drugs with a primary central effect often produce peripheral adverse reactions. The blockade of peripheral $\alpha$-adrenergic receptors by chlorpromazine leads to direct vasodilation and, consequently, a decrease in blood pressure.
Neuroendocrine effects (hyperprolactinemia): Chlorpromazine increases prolactin secretion by the anterior pituitary gland. The mechanism involves the blockade of D2 receptors, which removes the physiological inhibitory effect of dopamine (prolactin-inhibiting factor) on the secretion of this hormone.
Clinical consequences of elevated prolactin:
- Enhanced lactation (galactorrhea).
- Gynecomastia.
- Decreased gonadotropin production, leading to menstrual irregularities and impotence.
Formulations and prescription rules
According to the prescription reference, Aminazinum is available in enteral and parenteral forms:
- For oral administration: Coated tablets of 0.025, 0.05, and 0.1 g. Prescribed orally after meals. The maximum single dose (MSD) is 0.3 g, the maximum daily dose (MDD) is 1.5 g.
- For injections: 2.5% ampoule solution in volumes of 1, 2, 5, and 10 ml. For intravenous (IV) administration, the dosage is 0.025–0.05 g; for intramuscular (IM) administration, it is 0.1 g.
Briefly: answers to topical questions
What are the absolute contraindications to prescribing chlorpromazine?
An absolute contraindication to prescribing neuroleptics is the treatment of anticholinergic psychosis. In cases of narcotic intoxication and psychoses, neuroleptics with pronounced anticholinergic activity, including chlorpromazine, are contraindicated due to the risk of potentiating the psychosis.
What extrapyramidal disorders does chlorpromazine cause and what is the mechanism of their development?
Chlorpromazine can cause extrapyramidal disorders: drug-induced parkinsonism, acute dystonias, akathisia, and tardive dyskinesia. Among typical neuroleptics, the risk of extrapyramidal disorders is lower with drugs that have a pronounced anticholinergic effect, including chlorpromazine. The mechanism of tardive dyskinesia is associated with a compensatory increase in the sensitivity of the central nervous system to dopamine and the formation of additional receptors. To prevent acute dystonias, a slow dose escalation and frequent divided administration are recommended.
"AMINAZINE": A — Antipsychotic, M — M-anticholinergic, I — Inhibits reticular formation (sedation), N — Neuroendocrine disorders (prolactin).
Class and exam questions
What is the difference between summation and potentiation using chlorpromazine as an example?
Summation is when the effect equals the sum of the drugs' actions ($1+1=2$). Chlorpromazine, however, causes potentiation ($1+1>2$): it vastly enhances the effect of general anesthetics, making it possible to lower their dosage.
What is the mechanism of galactorrhea development when taking typical neuroleptics?
Chlorpromazine blocks D2 receptors in the pituitary gland. This removes the inhibitory effect of dopamine on prolactin secretion, causing hyperprolactinemia and, consequently, galactorrhea.
What else to study on this topic
- Comparative characteristics of aliphatic, piperazine, and piperidine phenothiazine derivatives.
- Differences in the receptor profiles of chlorpromazine and haloperidol.
- Dopaminergic pathways of the brain: mesolimbic, nigrostriatal, and tuberoinfundibular.
- Phases of drug biotransformation: the role of cytochrome P450 in microsomal oxidation.
- Types of synergism in pharmacology: additive effect and potentiation.
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