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Sedative Hypnotic Drugs | SurgicoMed | Find Medical Solutions Top

Sedative Hypnotic Drugs

Posted by: | on August 17, 2013

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What Are Sedative Hypnotic Drugs?

Definition:-

Sedative Hypnotic Drugs are chemically heterogeneous class of drugs which produce dose dependent CNS depressant effects.”

These drugs are divided into sub-groups as;

  1. Benzodiazepines
    • Short Acting                         →    Triazolam
    • Intermediate Acting         →    Alprazolam
    • Long Acting                          →    Flurazepam
  2. Barbiturates
    • Ultra Short Acting          →    Thiopental
    • Short Acting                      →    Secobarbital
    • Long Acting                       →    Phenobarbital
  3. Miscellaneous Drugs
    • Buspirone
    • Zaleplon
    • Zlopidem
    • Ramelteon
    • Eszopiclone
    • Chloral Hydrate

What Is Pharmacokinetics Of Sedative Hypnotic Drugs?

(What the body does with the drugs!)
Absorption, Distribution, Metabolism, Excretion

Absorption

Most of these drugs are well absorbed from GIT due to lipid solubility so administered entrally.

Distribution

Because of lipid solubility, these drugs have good distribution to the brain.
♦ Lipid solubility indicates the ability to cross lipids barriers so such drugs are well distributed to brain with lipid barrier (Blood Brain Barrier)

Thiopental  →   ↑ (highest) lipid solubility  →   enters CNS rapidly  →   used as induction agent in anesthesia

Eszopiclone, zaleplon & zolpidem with higher lipid solubility also have rapid onset of action on CNS.
The CNS effects of these lipid soluble drugs are terminated by redistribution to other highly perfused organs or tissue like skeletal muscles.

Metabolism

Hepatic enzymes are responsible for metabolism of sedative hypnotics drugs in most cases except;

These two drugs undergo extra-hepatic conjugation & don’t form active metabolites.

The duration of action of these drugs ranges from few hrs (zolpidem,triazolam,eszopiclone & chloral hydrate) to >30 hrs (diazepam, phenobarbital & chlordiazepoxide)

Excretion

These drugs are excreted via urinary track after converting into their metabolites or partly unchanged (phenobarbital is excreted partly unchanged in the urine).

Mechanism of Action Of Sedative Hypnotics

Sedative Hypnotic Drugs act in a different ways depending upon its sub-groups;

What Is The Mechanism of Action Of Benzodiazepines?

Style:- facilitates neural membrane inhibition.
Location:-  Benzodiazepines receptors (BZ receptors) are present in brain regions like;
thalamus, limbic system & cerebral cortex.
Structure:-  BZ receptors form the part of GABAA receptor chloride ion channel macromolecular complex (a pentameric structure assembled from five subunits each with 4 transmembrane domains). An isoform of GABAA receptor comprises 2 α1, 2β2 & 1 γ2 subunits. In this isoform, the binding region for benzodiazepines are b/w α & γ subunits.
Elaboration:- Binding of benzodiazepines causes increase Chloride ion conductance which facilitates the inhibitory action of GABA. These drugs also increases the frequency of chloride ion channel opening.
Antagonists:-

What Is The Mechanism of Action Of Barbiturates?

Style:- depress the neural membrane activity in mid-brain reticular formation.
Location:-  Barbiturates receptors are present in brain regions like;
thalamus, limbic system & cerebral cortex.
Structure:-  Barbiturates receptors also form the part of GABAA receptor chloride ion channel macromolecular complex  but at the different sites from those with which benzodiazepines interact.
Elaboration:- Binding of barbiturates causes increase in GABA mediated chloride ion channel opening which facilitates the inhibitory action of GABA. These drugs may also block glutamic acid (excitatory transmitter) & sodium channels (at higher concentration).
Antagonists:- These aren’t antagonized by flumazenil.

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