Depressants: Alcohol & Sedatives

Introduction

Biological Basis

Genetic predisposition accounts for 40-60% of the vulnerability to addiction, highlighting its nature as a medical condition.

Environmental Influence

Factors like early exposure, trauma, and socioeconomic conditions play critical roles in the development of SUD.

Central nervous system (CNS) depressants slow brain activity, producing sedation, anxiolysis, and at higher doses, anesthesia and respiratory depression. This class includes alcohol—humanity's oldest and most widely used intoxicant—as well as benzodiazepines, barbiturates, and related sedative-hypnotics. These substances share mechanisms of action, cross-tolerance, and importantly, potentially life-threatening withdrawal syndromes.

Learning Objectives

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

Alcohol: Pharmacology and Effects

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

Alcohol Use Disorder

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.

Alcohol Withdrawal

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)

Benzodiazepines

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:

Bind to benzodiazepine site on GABA-A receptor
Increase frequency of chloride channel opening
Enhance inhibitory effect of GABA
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.

Alcohol-Benzodiazepine Interactions

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

Other Sedative-Hypnotics

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

Case Study: Combined Depressant Use

Vijay, 45, is brought to the emergency department after being found unresponsive at home. His wife reports he has been drinking heavily for years and also takes alprazolam (Xanax) 1mg three times daily that he obtained from multiple doctors. On exam, he is somnolent, respiratory rate 8/min, BP 90/60. Empty bottles of alcohol and pill bottles are found nearby.

Discussion Questions:

4What pharmacological mechanisms explain his presentation?
5What is the immediate management priority?
6What complications should you anticipate over the next 48-72 hours if he survives?
7How would you manage potential withdrawal from both substances?
8What systems issues enabled his polypharmacy?

Key Takeaways

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

Next Module: The Opioid Crisis: From Morphine to Fentanyl →