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Questions and Answers
What is most likely to occur when a habitual user ingests a 100-mg dose of secobarbital at a social gathering?
What is most likely to occur when a habitual user ingests a 100-mg dose of secobarbital at a social gathering?
- Disorientation
- Mild euphoria (correct)
- Significant sedation
- Severe toxicity
How does increasing the number of carbons in a compound affect its lipophilicity and toxicity?
How does increasing the number of carbons in a compound affect its lipophilicity and toxicity?
- Increases lipophilicity and decreases toxicity
- Has no effect on lipophilicity or toxicity
- Decreases both lipophilicity and toxicity
- Increases both lipophilicity and toxicity (correct)
What pharmacological property does thiopental exhibit compared to phenobarbital?
What pharmacological property does thiopental exhibit compared to phenobarbital?
- Shorter duration of action (correct)
- Slower movement into the CNS
- Longer duration of action
- Lower lipid solubility
Which of the following barbiturates is more likely to be rapidly metabolized due to its lipid solubility?
Which of the following barbiturates is more likely to be rapidly metabolized due to its lipid solubility?
What is the primary site of metabolism for oxybarbiturates?
What is the primary site of metabolism for oxybarbiturates?
What transformation occurs during Phase I reactions for oxybarbiturates?
What transformation occurs during Phase I reactions for oxybarbiturates?
How does the presence of polar side chains affect the duration of action of barbiturates?
How does the presence of polar side chains affect the duration of action of barbiturates?
Which of the following statements is true regarding the pharmacokinetics of barbiturates?
Which of the following statements is true regarding the pharmacokinetics of barbiturates?
What is the primary role of benzodiazepines in modern therapy?
What is the primary role of benzodiazepines in modern therapy?
Which drug class includes compounds that produce sedation and hypnosis through CNS depression?
Which drug class includes compounds that produce sedation and hypnosis through CNS depression?
What has largely replaced the use of barbiturates in medicinal practices?
What has largely replaced the use of barbiturates in medicinal practices?
What has caused the decline in barbiturate use since the 1940s?
What has caused the decline in barbiturate use since the 1940s?
What are the primary components required for the synthesis of barbiturates?
What are the primary components required for the synthesis of barbiturates?
Which side chains contribute to the pharmacological classification of barbiturates?
Which side chains contribute to the pharmacological classification of barbiturates?
How many accidental and intentional poisonings are attributed to barbiturates per year?
How many accidental and intentional poisonings are attributed to barbiturates per year?
The duration of effect of barbiturates is influenced by which of the following factors?
The duration of effect of barbiturates is influenced by which of the following factors?
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Study Notes
Central Nervous System Depressants
- Central nervous system depressants are used for sedation, hypnosis, and anesthesia
- The type of depressant used depends on the desired outcome
- Sedatives calm individuals who are anxious or restless
- Hypnotics cause drowsiness and aid in inducing sleep
- Examples of depressants include barbiturates, benzodiazepines, and chloral hydrate
History and Classification
- Bromides were widely used as sedatives in the early 20th century
- Barbiturates were introduced in the 1940s, replacing bromides in use and becoming popular as sedatives and for treating pain, anxiety, hypertension, epilepsy, and psychiatric disorders
- Chloral hydrate and meprobamate emerged as alternative, comparable sedative-hypnotics
- Benzodiazepines replaced traditional sedative-hypnotics as more effective, less toxic, and less addictive anxiolytics
- Today, buspirone (Buspar) and zolpidem (Ambien) are widely used agents for anxiety, sleep, and anesthesia
- Benzodiazepines are still frequently used
Barbiturates
- Barbiturates are malonylurea derivatives synthesized from malonic acid and urea
- Structure determines the duration of action of the barbiturate
- Longer and bulkier aliphatic and allocyclic side chains produce barbiturates with longer durations of action
- Methylbutyl (1-mb) side chain and replacement of the C2 with a sulfur group create more lipid-soluble, less acidic barbiturates with shorter durations of action
- Examples of barbiturates with different durations of action include:
- Ultrashort-acting (thiopental): used as a preoperative sedative/hypnotic
- Short-acting (pentobarbital)
- Intermediate-acting (secobarbital)
- Long-acting (phenobarbital)
Pharmacology and Clinical Use
- Barbiturates produce sedation, hypnosis, or anesthesia through CNS depression
- The effects depend on various factors:
- Dose
- Mental state of the individual
- Duration of action
- Physical environment
- Tolerance
- These factors determine whether the response is therapeutic or euphoric
- Examples of Effects:
- A 100mg dose of secobarbital at bedtime induces sleep
- The same dose taken by a habitual user at a social gathering may only cause euphoria and mild sedation
Toxicokinetics and Metabolism
- The lipid solubility of barbiturates determines the duration of action and toxicity
- Increased carbon chains and bulkier side chains increase lipid solubility and toxicity
- Thiopental is an example of a highly lipid-soluble barbiturate with rapid onset and short duration of action
- Barbiturates are nonionic, lipid-soluble compounds with pKa between 7.2 and 7.9
- Rapid movement into and out of CNS determines the onset and duration of action
- Barbiturates with the slowest onset and longest duration of action contain the most polar side chains (ethyl and phenyl)
- Metabolism of barbiturates occurs primarily in the liver, but also in the kidney and brain for thiobarbiturates
- Phase I reactions introduce polar groups at the C5 position of oxybarbiturates, transforming them into inactive metabolites
- Thiobarbiturates undergo desulfuration and ring opening
- Oxidation at the C5 position is the key biotransformation reaction for drug detoxification
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