CNS depressants include a broad category of drugs such as benzodiazepines, barbiturates, alcohols, and some sleep medications. These agents slow brain activity and are commonly used for anxiety, insomnia, and seizure control. Overdose can result in significant respiratory depression, coma, and life-threatening complications. Early identification and supportive management are central to patient outcomes.
Common CNS Depressants
- Benzodiazepines (diazepam, lorazepam)
- Barbiturates (phenobarbital)
- Z-drugs (zolpidem, zopiclone)
- Alcohols (ethanol, methanol, ethylene glycol)
- Opioids – though classified separately, they cause CNS depression
Mechanism of Action
Benzodiazepines
- Enhance GABA-A receptor activity
- Increase frequency of chloride channel opening
Barbiturates
- Prolong duration of chloride channel opening at GABA-A receptors
- High doses: direct GABA-mimetic effect → profound CNS depression
Z-Drugs
- Act on benzodiazepine site of GABA-A receptor
Clinical Features of CNS Depressant Overdose
CNS Effects
- Drowsiness and slurred speech
- Ataxia
- Lethargy
- Coma in severe cases
Respiratory Depression
- Slow, shallow breathing
- Hypoventilation and hypoxia
Cardiovascular Effects
- Hypotension (more common with barbiturates)
- Bradycardia
Other Findings
- Hypothermia
- Decreased reflexes
Complications
- Respiratory arrest
- Aspiration pneumonia
- Hypoxic brain injury
- Shock (barbiturates)
- Rhabdomyolysis from prolonged immobility
Diagnosis
- Clinical examination
- Blood gases showing respiratory acidosis
- Urine drug screen
- Electrolytes and renal/liver function
Management
1. Supportive Care (Most Important)
- Maintain airway and breathing
- Oxygen therapy
- IV fluids for hypotension
- Monitor vital signs closely
2. Decontamination
- Activated charcoal within 1 hour for large ingestions
- Not useful for alcohol poisoning
3. Specific Antidote: Flumazenil
Flumazenil is a benzodiazepine receptor antagonist.
- Useful in pure benzodiazepine overdose
- Contraindicated in chronic benzodiazepine users (risk of seizures)
- Avoid if co-ingestion of TCA or pro-convulsant drugs
4. Enhanced Elimination
- Barbiturates: alkalinization of urine may help
- Hemodialysis for phenobarbital poisoning
5. Management of Complications
- Mechanical ventilation for respiratory failure
- Treat aspiration pneumonia with antibiotics
- Address rhabdomyolysis with aggressive IV fluids
Differences Between Benzodiazepine and Barbiturate Toxicity
- Benzodiazepines: safer, rarely fatal alone
- Barbiturates: deep coma, hypotension, higher mortality
Detailed Notes:
For PDF style full-color notes, open the complete study material below:
PATH: PHARMD/ PHARMD NOTES/ PHARMD FOURTH YEAR NOTES/ CLINICAL TOXICOLOGY/ CNS DEPRESSANTS.