Depressants: Alcohol & Sedatives

By the end of this module, you will be able to:

• Explain the biphasic effect of alcohol
• Describe the GABAergic mechanism shared by CNS depressants
• Recognize the signs and dangers of alcohol withdrawal, including delirium tremens
• Identify the synergistic risks of combining depressants
• Apply appropriate clinical management strategies

Mechanism of Action

Alcohol affects multiple neurotransmitter systems:

| System | Effect | Clinical Manifestation | |--------|--------|------------------------| | GABA-A | Enhanced (agonist-like) | Sedation, anxiolysis, muscle relaxation | | Glutamate (NMDA) | Inhibited | Impaired memory, coordination | | Dopamine | Increased (indirect) | Reward, reinforcement | | Serotonin | Modulated | Mood effects | | Opioid | Endorphin release | Euphoria |

The Biphasic Effect

Alcohol produces different effects at different blood alcohol concentrations (BAC):

Ascending Limb (Rising BAC):

• Euphoria, sociability, disinhibition
• Increased energy, talkativeness
• Stimulant-like effects predominate
• This phase reinforces drinking

Descending Limb (Falling BAC):

• Sedation, fatigue, impairment
• Depression, irritability
• Depressant effects predominate
• Often drives continued drinking to "maintain the buzz"

Clinical Significance: People often drink to stay on the ascending limb, leading to escalating consumption.

Blood Alcohol Concentration Effects

| BAC (%) | Effects | |---------|---------| | 0.02-0.03 | Relaxation, slight mood elevation | | 0.05-0.06 | Lowered inhibitions, impaired judgment | | 0.08-0.10 | Legal intoxication (most jurisdictions), impaired coordination | | 0.15-0.20 | Significant motor impairment, slurred speech | | 0.25-0.30 | Severe impairment, risk of blackout | | 0.35-0.40 | Risk of coma, life-threatening | | 0.40+ | Potential fatal respiratory depression |

Alcohol Metabolism

Pathway:

Alcohol → (ADH) → Acetaldehyde → (ALDH) → Acetate → CO2 + H2O

Key Enzymes:

• Alcohol Dehydrogenase (ADH): Converts alcohol to acetaldehyde (toxic)
• Aldehyde Dehydrogenase (ALDH): Converts acetaldehyde to acetate (harmless)

Genetic Variations:

• ALDH2*2 variant (common in East Asia): Slow acetaldehyde metabolism
• Results in "flush reaction": Facial flushing, nausea, headache
• Protective against alcoholism (drinking is unpleasant)

Metabolism Rate:

• Average: 0.015% BAC per hour
• Cannot be accelerated by coffee, food, or exercise
• Individual variation exists

Diagnostic Criteria

DSM-5 criteria (same as other SUDs): 2+ of 11 criteria in 12 months

Specific to Alcohol:

• High tolerance (able to drink large amounts)
• Characteristic withdrawal syndrome
• Using alcohol in hazardous situations (driving)
• Continued use despite physical consequences (liver disease)

Health Consequences

Acute:

• Injuries (falls, accidents, violence)
• Alcohol poisoning
• Blackouts (anterograde amnesia)
• Risky sexual behavior

Chronic:

• Liver disease (fatty liver → hepatitis → cirrhosis)
• Pancreatitis
• Cardiovascular disease
• Multiple cancers (mouth, throat, liver, breast, colon)
• Neurological damage (Wernicke-Korsakoff syndrome)
• Fetal Alcohol Spectrum Disorders (if pregnant)

Fetal Alcohol Spectrum Disorders (FASD)

No safe amount of alcohol during pregnancy is established.

Features:

• Facial abnormalities (smooth philtrum, thin upper lip)
• Growth deficiencies
• CNS damage, intellectual disability
• Behavioral problems, learning difficulties

Prevention Message: Abstinence from alcohol throughout pregnancy is the only way to prevent FASD.

Pathophysiology

Chronic alcohol exposure causes adaptive changes:

• GABA-A receptor downregulation (reduced inhibition)
• NMDA receptor upregulation (increased excitation)
• When alcohol is removed: Hyperexcitability

Timeline and Symptoms

6-12 hours: Minor withdrawal

• Tremor ("the shakes")
• Anxiety, irritability
• Nausea, vomiting
• Tachycardia, hypertension
• Insomnia

12-24 hours: Withdrawal seizures

• Generalized tonic-clonic seizures
• May occur without other symptoms
• Usually self-limited but can be recurrent

24-72 hours: Alcoholic hallucinosis

• Visual, auditory, or tactile hallucinations
• Sensorium otherwise clear (unlike DT)
• Patient may recognize hallucinations as unreal

48-96 hours: Delirium Tremens (DT)

• Medical emergency
• Altered mental status, confusion, disorientation
• Autonomic instability (fever, tachycardia, hypertension)
• Hallucinations
• Agitation, tremor
• 5-15% mortality if untreated

Risk Factors for Severe Withdrawal

• History of withdrawal seizures or DT
• Heavy, prolonged use
• Concurrent medical illness
• Older age
• Concurrent benzodiazepine use
• Previous severe withdrawals (kindling effect)

Clinical Assessment

CIWA-Ar (Clinical Institute Withdrawal Assessment for Alcohol-Revised):

• 10-item scale assessing withdrawal severity
• Scores range 0-67
• Guides medication dosing
• Items: Nausea, tremor, sweating, anxiety, agitation, tactile/auditory/visual disturbances, headache, orientation

| CIWA-Ar Score | Severity | Management | |---------------|----------|------------| | 0-9 | Minimal | Observation, supportive care | | 10-19 | Mild-Moderate | Pharmacotherapy typically needed | | 20+ | Severe | Intensive treatment required |

Management

Benzodiazepines (First-line):

• Cross-tolerant with alcohol (same GABA-A mechanism)
• Prevent seizures, reduce withdrawal severity
• Common agents: Diazepam, chlordiazepoxide, lorazepam

Dosing Approaches:

• Symptom-triggered: Dose based on CIWA-Ar score (preferred)
• Fixed-schedule: Regular dosing with taper (for severe cases or when monitoring limited)

Supportive Care:

• Thiamine (prevent Wernicke's encephalopathy)
• IV fluids, electrolyte correction
• Quiet environment
• Frequent monitoring

Adjunctive Medications:

• Anticonvulsants (if seizure risk)
• Beta-blockers (for autonomic symptoms)
• Antipsychotics (for hallucinations—use with caution)

Common Benzodiazepines

| Drug | Trade Name | Half-life | Clinical Use | |------|------------|-----------|--------------| | Diazepam | Valium | Long (20-100 hrs) | Anxiety, alcohol withdrawal | | Lorazepam | Ativan | Intermediate (10-20 hrs) | Anxiety, seizures | | Alprazolam | Xanax | Short (6-12 hrs) | Anxiety, panic | | Clonazepam | Klonopin | Long (30-40 hrs) | Seizures, panic | | Midazolam | Versed | Ultra-short (1-4 hrs) | Sedation for procedures |

Mechanism

Benzodiazepines enhance GABA-A receptor function:

1. Bind to benzodiazepine site on GABA-A receptor
2. Increase frequency of chloride channel opening
3. Enhance inhibitory effect of GABA
4. Do not directly open channel (unlike barbiturates)

This mechanism confers relative safety compared to barbiturates (less respiratory depression alone).

Risks

Dependence:

• Physical dependence develops with chronic use
• Even therapeutic doses for weeks can cause dependence
• Withdrawal can be severe, prolonged

Withdrawal (similar to alcohol):

• Anxiety, insomnia
• Tremor, sweating
• Seizures (can be life-threatening)
• Prolonged course (weeks to months for long-acting)

Cognitive Effects:

• Anterograde amnesia
• Impaired attention and reaction time
• Falls in elderly

The Benzodiazepine-Opioid Crisis

Combination of benzodiazepines with opioids dramatically increases overdose risk:

Mechanism: Both cause respiratory depression through different pathways

• Opioids: Direct brainstem respiratory center depression
• Benzodiazepines: Enhance GABA, reduce respiratory drive

Statistics:

• 30% of opioid overdose deaths involve benzodiazepines
• Risk of overdose 10x higher with combination

FDA Black Box Warning: Concurrent use of opioids and benzodiazepines increases risk of sedation, respiratory depression, coma, and death.

Synergistic CNS Depression

Both enhance GABA transmission → additive/synergistic effects:

• Profound sedation
• Respiratory depression
• Increased overdose risk

Cross-Tolerance

Chronic alcohol users are cross-tolerant to benzodiazepines:

• May require higher doses for sedation/anxiolysis
• Benzodiazepines can substitute during alcohol withdrawal

Clinical Implications

Never combine alcohol and benzodiazepines recreationally Benzodiazepines are treatment of choice for alcohol withdrawal (controlled, medical setting) Patients on benzodiazepines should be counseled about alcohol risks

Barbiturates

Mechanism: Directly open GABA-A chloride channels (more dangerous than benzos)

Historical Use: Anxiety, seizures, anesthesia (largely replaced by benzos)

Current Use: Phenobarbital (seizures, alcohol withdrawal), thiopental (anesthesia)

Risks: Narrow therapeutic index, severe respiratory depression, high abuse potential

Z-Drugs (Zolpidem, Zaleplon, Eszopiclone)

Mechanism: Selective GABA-A modulation (similar to benzos)

Use: Insomnia (short-term)

Risks:

• Complex sleep behaviors (sleep-driving, sleep-eating)
• Dependence potential (though less than benzos)
• Next-day impairment

GHB (Gamma-Hydroxybutyrate)

Mechanism: GABA-B agonist, GHB receptor agonist

Medical Use: Narcolepsy (Xyrem)

Abuse: "Date rape drug," club drug

Risks: Rapid onset, steep dose-response, respiratory depression

• Alcohol enhances GABA and inhibits glutamate, producing biphasic effects
• Alcohol withdrawal can be life-threatening (seizures, delirium tremens)
• Benzodiazepines are the treatment of choice for alcohol withdrawal
• Benzodiazepines enhance GABA function and carry significant dependence risk
• Combining depressants (alcohol + benzos + opioids) dramatically increases overdose risk
• Medical management of depressant withdrawal requires careful monitoring and appropriate pharmacotherapy
• FASD is 100% preventable through abstinence during pregnancy

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