Z-Drugs (Non-Benzodiazepine Hypnotics)

General mechanism of action and pharmacodynamics

Although Z-drugs are not benzodiazepines in terms of chemical structure, they exert their effects through the same receptor system. The molecules of these drugs bind to specific benzodiazepine sites and act as allosteric modulators.

As a result of their action, the sensitivity of GABA-A receptors to the main inhibitory neurotransmitter of the central nervous system, gamma-aminobutyric acid (GABA), is increased. This leads to an increase in the frequency of chloride channel opening. Chloride ions ($Cl^-$) rush massively into the neuron, triggering hyperpolarization of the cell membrane. Potent inhibitory processes develop in the CNS.

Depending on the dosage, the drugs produce two main effects:

• Hypnotic (main therapeutic effect);
• Sedative (manifests at low doses).

Zaleplon and Zopiclone: Drug Profile

Each representative of the group has a unique chemical nature and specific impact on sleep.

Zaleplon (Zaleplon) is a pyrazolopyrimidine derivative. It interacts with benzodiazepine sites on GABA-A receptors. The main feature of the drug is its pronounced effect on sleep latency, meaning it significantly accelerates the onset of sleep. The drug provides a full eight-hour sleep, while its half-life is only 2 hours. Zaleplon is optimal for correcting transient insomnia in a short course (usually 7 to 10 days).

Zopiclone (Zopiclone) belongs to cyclopyrrolone derivatives. It is a medium-duration hypnotic agent. The effect appears within 20–30 minutes after administration and lasts about 6–8 hours. The drug stimulates both $\omega_1$- and $\omega_2$-benzodiazepine receptors, without affecting the total duration of rapid eye movement (REM) sleep. Its S-isomer, eszopiclone, is also used in clinical practice.

Among the specific adverse reactions of zopiclone, patients often note a characteristic bitter or metallic taste in the mouth. Nausea, irritability, depressed mood, and allergic manifestations are possible. In the post-somnic period (after awakening), dizziness and coordination disorders may occur. The "rebound" phenomenon after withdrawal is mild. The drug is strictly contraindicated in children under 15 years of age, pregnant and breastfeeding women, and patients with decompensated respiratory failure.

Features of Zolpidem

Zolpidem (Zolpidem) is an imidazopyridine derivative. Like zopiclone, it is a medium-duration drug with a half-life ranging from 2 to 3 hours.

The key distinctive feature of zolpidem is high selectivity. It is a selective agonist exclusively for $\omega_1$-benzodiazepine receptors. Due to this, it practically does not distort sleep architecture. However, because of its high selectivity, zolpidem does not possess the effects inherent to classical benzodiazepines:

• does not act as a myorelaxant (does not relax muscles);
• does not produce an anxiolytic (anti-anxiety) effect;
• does not exhibit anticonvulsant activity.

During zolpidem administration, side effects such as daytime drowsiness, headaches, and ataxia may develop. Specific psychiatric disturbances such as hallucinations and nightmares are possible. The rebound phenomenon upon withdrawal is minimal.

Safety and Therapy Monitoring

Despite high efficacy, long-term use of Z-drugs is associated with serious risks. In particular, regular intake of zolpidem or zopiclone can lead to tolerance and the development of pronounced drug dependence. To avoid these complications, the duration of continuous treatment is strictly limited and should not exceed 4 weeks.

In situations of acute overdose with zaleplon, zopiclone, or zolpidem, a specific antidote is used in medical practice: flumazenil. This drug acts as a competitive antagonist of benzodiazepine receptors, rapidly blocking them and neutralizing the toxic effects of the hypnotics.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Structure and function of the GABA-A receptor complex
• Differences between omega-1 and omega-2 benzodiazepine receptor subtypes
• Physiological sleep structure: non-REM and REM sleep phases
• Mechanisms of drug dependence formation on hypnotics
• Pharmacodynamics and specific clinical uses of flumazenil

Other topics in the section "Agents Used in Psychiatry and Neurology"

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