Classification
Valproates belong to drugs with a polyvalent (combined) action. Due to their complex mechanism of action, which includes several equivalent components, it is extremely difficult to classify this drug into a single narrow pharmacological group (e.g., exclusively as a GABAergic agent or strictly as a sodium channel blocker). It is impossible to isolate a single predominant effect. The main representatives of this combined group are valproic acid and topiramate. In clinical practice, the drug is used both as the acid itself and in the form of its sodium salt — sodium valproate.
Mechanism of Action (Triple Effect)
The pharmacodynamics of the drug are based on three independent mechanisms that together provide a pronounced anticonvulsant effect:
- Sodium channel blockade. The drug directly affects neuronal membranes in the epileptogenic focus, significantly reducing their excitability and preventing the generation of pathological discharges.
- Calcium channel blockade. Valproic acid specifically blocks T-type calcium channels.
- Effect on the GABA system. The drug significantly increases the concentration of gamma-aminobutyric acid (the primary inhibitory neurotransmitter) in brain structures. This is achieved through two parallel processes:
- Inhibition of catabolism: blockade of the enzyme GABA transaminase prevents the degradation of existing GABA.
- Stimulation of synthesis: increasing the activity of glutamate decarboxylase accelerates the formation of new GABA molecules.
Indications and Pharmacokinetics
The drug features a broad spectrum of activity and demonstrates high clinical efficacy in virtually all known forms of epilepsy. The main indications include partial seizures, myoclonic epilepsy, and generalized seizures (both absence and tonic-clonic).
When administered orally, valproates are well absorbed in the gastrointestinal tract. The time to reach peak plasma concentration depends on the specific dosage form, but averages about 2 hours. The drug undergoes extensive metabolism: it is excreted primarily by the kidney as oxidation products or as conjugates with glucuronic acid (glucuronides).
Safety Profile
Despite its high efficacy, therapy with valproic acid requires monitoring due to potential adverse effects affecting various body systems:
- Central nervous system: patients may experience somnolence, tremor, ataxia, involuntary rhythmic eye movements (nystagmus), and double vision (diplopia).
- Gastrointestinal tract: dyspeptic symptoms frequently develop, including nausea, vomiting, diarrhea, and epigastric pain.
- Hematopoietic system: anemia, decreased platelet count (thrombocytopenia), and overall impaired blood clotting may occur.
- Allergic reactions: in most cases, these are limited to various skin manifestations.
The drug has strict contraindications. It must not be prescribed to patients with severe hepatic impairment or major pancreatic pathology.