Classification and Historical Background
Psychotropic drugs are medications that exert a targeted effect on human mental activity. Chlorpromazine (along with reserpine) became a cornerstone drug that marked the dawn of psychopharmacology in the mid-20th century.
In modern classifications of psychotropic medications (comprising 6 main groups: antipsychotics, antidepressants, anxiolytics, sedatives, psychostimulants, and nootropics), chlorpromazine is classified as a typical antipsychotic.
Based on chemical structure, typical antipsychotics are divided into three groups:
- Phenothiazine derivatives (chlorpromazine belongs here as an aliphatic derivative, distinct from piperazine and piperidine derivatives).
- Butyrophenone derivatives (haloperidol, droperidol).
- Thioxanthene derivatives (chlorprothixene).
Pharmacokinetics: Metabolism
Biotransformation of the drug occurs in the liver via microsomal oxidation. The process involves endoplasmic reticulum enzymes, predominantly cytochrome P450.
A specific metabolic pathway for chlorpromazine is S-oxidation (cimetidine, for example, is metabolized via this 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 driven by its broad receptor profile. The drug affects both the central and peripheral nervous systems.
- Antipsychotic effect: Mediated through the blockade of postsynaptic dopamine D2 receptors in the mesolimbic system of the brain, leading to the resolution of positive symptoms of psychosis (delusions and hallucinations). Notably, chlorpromazine is less potent in its antipsychotic effect compared to haloperidol.
- Sedative effect: Associated with the drug's inhibitory effect on the ascending reticular activating system of the brainstem.
- Autonomic nervous system effects: The drug exhibits pronounced muscarinic receptor antagonism (unlike haloperidol, which has a weaker anticholinergic effect) and also blocks peripheral $\alpha$-adrenergic receptors.
Pharmacological Effects and Synergism
In addition to its primary antipsychotic, pronounced sedative, and anxiolytic (anti-anxiety) actions, chlorpromazine displays synergism—the enhancement of therapeutic effects when drugs are co-administered.
Chlorpromazine interacts via potentiation. In this type of synergism, one substance significantly amplifies the effect of another, and the combined outcome exceeds the simple arithmetic sum of the individual components ($1 + 1 > 2$).
Clinical significance: Chlorpromazine potentiates CNS depressants (general anesthetics, hypnotics). This allows for a reduction in the required doses of toxic anesthetic agents without losing efficacy.
Adverse Effects
Side effects stem directly from its non-selective receptor profile and are divided into peripheral and neuroendocrine reactions.
Peripheral effects: Drugs with primary central actions frequently cause peripheral adverse reactions. The blockade of peripheral $\alpha$-adrenergic receptors by chlorpromazine leads to direct vasodilation and, consequently, hypotension.
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 tone of dopamine (prolactin-inhibiting factor) on prolactin release.
Clinical consequences of elevated prolactin:
- Increased lactation (galactorrhea).
- Gynecomastia.
- Suppression of gonadotropins, leading to menstrual irregularities and impotence.
Formulations and Administration
Aminazinum is available in enteral and parenteral formulations:
- Oral administration: Dragees of 0.025, 0.05, and 0.1 g. Taken orally after meals. Maximum single dose (MSD) is 0.3 g, maximum daily dose (MDD) is 1.5 g.
- Injections: 2.5% solution in ampoules of 1, 2, 5, and 10 ml. For intravenous (IV) administration, the dose is 0.025–0.05 g; for intramuscular (IM) administration, it is 0.1 g.