Barbiturates and Benzodiazepines

CNS Depressants: Barbiturates and Benzodiazepines

Overview of CNS Depressants

• CNS depressants vary in their level of inhibition, influenced by drug type and dosage. They are used to transition patients from a tense state to calmness.

• Tranquilizers, also known as anti-anxiety medications or anxiolytics, help achieve this calming effect. Sedatives further reduce physical activity for recovery purposes, such as post-heart attack care.

Types of CNS Depressants

• The video focuses on barbiturates and benzodiazepines among other CNS depressants like alcohol and miscellaneous hypnotics (e.g., Ambien). These drugs can induce sleep or sedation based on their classification.

Mechanism of Action

• GABA is a key neurotransmitter responsible for 50% of inhibitory activity in the brain; it binds to receptors on chloride channels, leading to hyperpolarization and reduced action potential likelihood. Barbiturates and benzodiazepines enhance GABA's effects by binding to these channels.

Barbiturates: Characteristics and Effects

• Barbiturates cause dose-dependent CNS depression; low doses serve as hypnotics while higher doses can lead to general anesthesia. There is no ceiling effect, making them particularly dangerous due to potential respiratory depression at high doses.

• Withdrawal from barbiturates can result in REM rebound—an increase in dreaming and anxiety—as the brain compensates for lost REM sleep during treatment discontinuation. This may manifest as nightmares.

Drug Interactions and Tolerance

• Barbiturate use leads to liver enzyme induction, resulting in faster breakdown of both the drug itself and other medications metabolized by the same enzymes, increasing the risk of drug-drug interactions. Tolerance develops over time due to this enzyme induction process.

Specific Barbiturate Examples

• Common barbiturates include:

• Phenobarbital (Luminal): Long-acting (6–12 hours), may cause next-day drowsiness.

• Pentobarbital (Nembutal): Intermediate duration (4–6 hours).

• Secobarbital (Seconal): Short-acting (2–4 hours), typically used for difficulty falling asleep but not staying asleep.

Barbiturates have various medical applications including insomnia treatment, pre-anesthetic use, neonatal seizures management, etc.

Benzodiazepines: Overview and Uses

• Benzodiazepines are primarily anti-anxiety drugs but also function as sedatives, muscle relaxants, anti-convulsants, and are effective against alcohol withdrawal symptoms like agitation or seizures. They can be utilized for conscious sedation procedures as well.

Mechanism of Action for Benzodiazepines

• These drugs bind specifically to benzodiazepine receptors on GABA-chloride channels which increases chloride influx into neurons leading to enhanced inhibitory effects that promote sedation or hypnosis while reducing anxiety through limbic system inhibition. Additionally, they lower motor neuron excitation causing muscle relaxation effects beneficial in seizure treatments.

Benzodiazepines: Uses, Risks, and Effects

Overview of Benzodiazepines

• Benzodiazepines are utilized for various central nervous system (CNS) effects, exhibiting both beneficial and adverse outcomes. They disrupt the normal sleep cycle by increasing stage two non-REM sleep while decreasing stage four.

Pregnancy Considerations

• The use of benzodiazepines during pregnancy is contraindicated as they fall under category D and X. Potential risks include floppy infant syndrome characterized by hypotonia, hypothermia, lethargy, and difficulties in breathing and feeding. There is also a slight risk of cleft palate in newborns.

Metabolism and Tolerance

• Unlike barbiturates, benzodiazepines do not induce metabolic tolerance due to their lack of enzyme induction. They possess a ceiling effect that limits CNS depression potential but can still be dangerous if misused.

Dependency and Usage Guidelines

• Mixing benzodiazepines with other CNS depressants like alcohol is discouraged. Users should avoid operating machinery or driving while on these medications due to dependency risks and drug-seeking behavior.

Variability Among Benzodiazepines

• Benzodiazepines vary in duration (short-, intermediate-, long-acting), onset (rapid acting within 15 minutes; slow acting takes 30 to 60 minutes), half-life, potency, and peak onset times.

Next-Day Drowsiness Concerns

• Fluorazepam has a longer half-life (40-100 hours), making it likely to cause next-day drowsiness compared to temazepam (10-40 hours). Triazolam's short action (1.5 to 3 hours) may lead to early morning awakenings.

Tolerance Compared to Barbiturates

• While benzodiazepines can lead to tolerance and dependence, this effect is less pronounced than with barbiturates. Additionally, an antidote for overdose exists—flumazenil—unlike barbiturate overdoses which lack specific treatment options.