Neuroscience Week 3: Benzos and Barbs Flashcards
Describe the differences between barbiturates and benzodiazepines in pharmacokinetic and pharmacodymanic factors
Describe the neuronal mechanism of actions of the anxiolytic (sedative) drugs.
Understand the main side effects, drug interactions, toxicities, issues of tolerance of the sedative drugs.
How do spasmolytic drugs act and where do they act?
Understand the key side effects with the skeletal muscle relaxants (spasmolytic agents)
Katzung Basic & Clinical Pharmacology Chpt 22 and 27
Ideal Sedative characteristics
Anxiolytic - calming
little effect on motor or mental function
little CNS depression
often will produce hypnosis with a high enough dose
Ideal Hypnotic Characteristics
- produce drowsiness encourage sleep (onset and maintenance)
- more pronounced CNS depression
Clinical Uses of Sedative-hypnotics
- For the relief of anxiety
- For insomnia
- For sedation and amnesia before and during medical and surgical procedures
- As a component of balanced anesthesia (intravenous administration)
- For treatment of epilepsy and seizure states
- For control of ethanol or other sedative-hypnotic withdrawal states
- For muscle relaxation in specific neuromuscular disorders
- Treatment of serotonin syndrome (benzodiazepines along with blocking serotonin synthesis with cyproheptadine )
Treatment of serotonin syndrome
(benzodiazepines along with blocking serotonin synthesis with cyproheptadine )
Barbiturate Examples
4 listed
- Phenobarbital
- Pentobarbital
- Secobarbital
- Thiopental
Benzodiazepines Examples
- Alprazolam
- Chlordiazepoxide
- Diazepam
- Midazolam
- Lorazepam
- Oxazepam
- Flumazenil (antagonist)
Nonbenzodiazepines hypnotics Examples
3 listed
- Zolpidem
- Zaleplone
- Eszopiclone
5-HT-1A agonist anxiolytic examples
Buspirone
Benzodiazepines and Barbiturates examples
- Benzodiazepines bind to receptors
- Barbiturates bind inside the Cl- channel so it is difficult to reverse this
Barbiturates MOA features
- ↑duration of channel opening
- nonspecific membrane actions
- no specific antagonist
- overdose risk
Benzodiazepine MOA features
↑ frequency of channel opening
acts predominately at the GABAA receptor
antagonist = flumazenil (RO15- 1788)
Antagonist of Benzodiazepines
Flumazenil
Factors that affect Barbiturate duration of action
- •Lipid solubility The higher the ↑ lipid solubility the ↑redistribution rate and the ↑ cyto P450 metabolism
- protein binding
- extent of ionization (pka)
Barbiturates Pharmicokinetic tolerance
Increasing capacity to metabolize barbiturates overtime due to the induction of cytochrome P450 enzymes
Barbiturate Pharmacodynamic tolerance
Increasing amounts of barbiturate at the target site will be required to maintain a given level of drug action on the target site.
Barbiturate Toxicity
- Maintain airways, supportive measures hydration, forced diuresis and alkalization, often not enough and hemodialysis is needed
- only the unionized form is reabsorbed therefore ionize the blood and urine by ↑ pH (Sodium bicarbonate)
- Inducing emesis only if drug was very recently taken and there are no signs. Activated charcoal modestly effective if given soon after the drug is taken. CNS stimulants like Bemegride can be given. There is No direct reversal agent Respiratory arrest occurs at 4X lower dose and cardiac arrest
Advantage of Benzodiazepines
- higher therapeutic index
- lower incidence of tolerance
- lower abuse liability
- fewer drug interactions and side effects
Factors responsible for benzodiazepine onset and duration of action
- ↑ Lipid solubility- decreases onset time and increases protein binding and redistribution
- Generation of active metabolites (critical for the duration of action) ↑ duration of action
- metabolized through microsomal enzymes but not inductive.
- Renal excretion
Important consideration for Benzodiazepines: Lorazepam example
5 different active metabolites
Factors affecting Biodisposition of Benzodiazepines
- Elderly patients and those with liver dysfunction will have longer elimination half-lives of most benzodiazepines and all barbiturates. Need to reduce the dose. Will see more sedation and more amnesia in the elderly.
- Metabolism involving glucuronide conjugation is less affected by old age or liver disease than oxidative metabolism
- Lorazepam, Oxazepam and Temazepam are conjugated extrahepatically (glucoronidated). Can be used in the presence of liver dysfunction
Benzodiazepines that can be used in elderly and those with liver disfunction
Lorazepam, Oxazepam and Temazepam are conjugated extrahepatically. Can be used in the presence of liver dysfunction
Are benzodiazepines really a wonder drug?
- Pharmacodynamic tolerance occurs particularly with long acting benzos
- Abuse does occur, albeit infrequently, typically with the short acting benzos
- Cross-tolerance and overdose can occur with other sedative-hypnotics
- Withdrawal syndrome can occur and removal is best done gradually.
- Flumazenil is a benzodiazepine antagonist and is used to reverse CNS effects of bdzs and some of the newer ‘non-bdzs’ (zolpidem, zalephon, eszopiclone)
‘non-bdzs’
(zolpidem, zalephon, eszopiclone)
Serotonin Syndrome and treatment with Benzodiazepines
- Excess synaptic serotonin can lead to a potentially fatal syndrome. Clinical presentation is hypertension hyperreflexia, tremor, clonus, hyperthermia, hyperactive bowel sounds, diarrhea, mydriasis, agitation coma. Onset occurs within hours. Brought on by SSRIs, second-generation antidepressants MAOIs, sumatriptan MDMA, tramadol, fentanyl.
- Treatment is benzodiazepines and supportive measures
Benzodiazepines and barbiturates sleep architecture
problematic for chronic users ↓ REM sleep and ↑ REM latency
Zolpidem
Ambien®, Zaleplon Sonata®, Eszopiclone Lunesta ® :short-acting, fewer amnesic effects, does not negatively affect sleep architecture, increases Slow wave sleep, metabolized by CYP 3A4, additive with ethanol. Acts at the Benzodiazepine site to increase GABA-A activity.
Buspirone
BuSpar® partial agonist at 5-HT1A for generalized anxiety, no additive effect with sedative hypnotics. Reduces and delays onset of REM sleep. Tolerance development is minimal, little or no rebound anxiety or withdrawal. Metabolized by CYP3A4 Can cause tachycardia + paresthesias
Meprobamate
Equanil®, Miltown® | Trancot™ unknown, anxiolytic