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PH3.1-9 | Central Nervous System Pharmacology — PBL Case

CLINICAL SETTING

It is a Sunday morning at a medical college hostel in Pune. A group of final-year MBBS students has gathered at the common room after receiving an emergency WhatsApp message from their batchmate Rohan's roommate: 'Something is very wrong with Rohan. He won't wake up and his breathing is slow.' When four of them reach the room, they find Rohan (23 years old) lying on his bed, deeply drowsy but rousable with loud calling. He has slow, shallow breathing (rate: 10/min), miotic pinpoint pupils, and there is a faint smell of alcohol. On the desk: three empty beer cans, a blister pack of diazepam 5 mg with three tablets missing, and an unlabelled bottle of small white tablets. His medical history is significant: he has been on sertraline 50 mg for depression for 6 weeks, and his mother mentions over the phone that he was also seen taking alprazolam tablets from a friend 'to sleep' over the past two months. The hostel warden calls the campus ambulance. As the attending team arrives at the hostel, you are the student-on-call accompanying the intern.

Trigger 1: First Assessment — What Is Wrong With Rohan?

On rapid assessment: GCS = 12/15 (E3V4M5). Vital signs: BP 108/70 mmHg, HR 68/min (regular), RR 10/min, SpO₂ 91% on room air, temperature 36.8°C. Pupils: 2 mm bilaterally, equal, react slowly to light. The three missing diazepam tablets and beer can suggest multi-substance ingestion. The intern places Rohan in recovery position and applies supplemental oxygen via facemask.

DISCUSSION POINTS

  • What is the most likely primary diagnosis based on the clinical presentation? List all substances that may have contributed to the current state.
  • Which pharmacological mechanism explains the combination of miosis, respiratory depression, and sedation? Name the receptor type mediating each feature.
  • Is the clinical picture consistent with opioid toxidrome, BZD toxidrome, or combined CNS depression? How would you differentiate them clinically before any investigation?
  • What immediate pharmacological intervention, if any, is indicated before transport to the casualty department?
Click to reveal Trigger 2: In the Casualty — Investigation Results and a New Finding (discuss previous trigger first!)

Trigger 2: In the Casualty — Investigation Results and a New Finding

In the casualty, blood is drawn and urine drug screen sent. The unlabelled white tablets are identified by the clinical pharmacologist on call as tramadol 50 mg — 4 tablets are missing from a strip of 10. The urine drug screen confirms: benzodiazepines positive, opiates negative (tramadol may not be detected on standard opiate screens), ethanol positive (blood alcohol level 120 mg/dL). 30 minutes after arrival, Rohan begins to recover spontaneously. However, he develops sudden agitation, whole-body tremor, and profuse sweating. His temperature rises to 38.9°C. His heart rate increases to 112/min. The treating physician looks concerned.

DISCUSSION POINTS

  • Tramadol inhibits serotonin reuptake (SERT) and Rohan has been taking sertraline for 6 weeks. What syndrome has just developed? What is the mechanism?
  • Why did tramadol give a NEGATIVE result on the standard urine opiate screen? What pharmacological principle explains this?
  • Rank the following interventions in order of priority for the new presentation: IV cyproheptadine, IV lorazepam for agitation, IV paracetamol for fever, IV naloxone, stopping sertraline and tramadol.
  • Ethanol and diazepam both enhance GABA-A. Would their combination produce additive, synergistic, or antagonistic CNS depression? Explain using the concept of receptor mechanisms.
Click to reveal Trigger 3: Recovery and the Underlying Problem (discuss previous trigger first!)

Trigger 3: Recovery and the Underlying Problem

Rohan recovers over 24 hours with supportive management. Sertraline and tramadol are stopped; the treating team manages the serotonin syndrome with IV diazepam for agitation and active cooling. On Day 2, Rohan is medically fit but refuses to leave. He confides to the intern that he has been taking alprazolam every day for 2 months from a friend's prescription and that he is terrified to stop — he tried once and developed severe tremors. He says he is also still low in mood, and that the sertraline was not helping. The consultant psychiatrist reviews him and makes a diagnosis of major depressive disorder with co-occurring benzodiazepine use disorder.

DISCUSSION POINTS

  • Rohan has been taking alprazolam daily for 2 months. If alprazolam were stopped abruptly, what is the pharmacodynamic mechanism that would produce his withdrawal symptoms, and why can this cause seizures?
  • Devise a pharmacological de-escalation plan for Rohan's BZD use: which BZD would you switch to before tapering, at what taper rate, and over what duration?
  • Sertraline was reportedly 'not helping' after 6 weeks. The treating psychiatrist must decide whether to switch or augment. Apply pharmacological reasoning — what is the minimum therapeutic trial duration, and what augmentation strategy could be used while keeping his seizure-risk context in mind?
  • What long-term prescribing principles would you emphasise to Rohan's parents and the college counsellor to prevent a similar episode in future? Include at least one pharmacological and one behavioural strategy.

Group Task Assignments

Group 1: CNS Depressant Pharmacology — Mechanism of Combined Toxicity

  • Map the molecular mechanisms of diazepam, ethanol, and tramadol (opioid component) at their respective CNS receptor targets
  • Explain why the combination of BZD + ethanol causes more than additive CNS depression with reference to GABA-A receptor pharmacology
  • Prepare a table comparing GCS findings and vital signs in pure BZD toxidrome vs pure opioid toxidrome vs the combined presentation in this case

Competencies: PH3.2, PH3.4

Group 2: Serotonin Syndrome — Recognition, Mechanism, and Management

  • List all the serotonergic drugs in Rohan's history and classify each by the mechanism through which it increases synaptic serotonin
  • Compare serotonin syndrome vs neuroleptic malignant syndrome — tabulate onset, causative drugs, neuromuscular signs, autonomic signs, and treatment
  • Prepare a clinical algorithm for emergency management of moderate serotonin syndrome (as occurred in Rohan)

Competencies: PH3.4, PH3.5

Group 3: Benzodiazepine Dependence and Safe Withdrawal

  • Explain the GABA-A receptor changes that cause physical dependence after 2 months of daily alprazolam use
  • Design a structured BZD withdrawal protocol for Rohan: which drug, what starting dose equivalent, what taper schedule (with pharmacokinetic rationale for BZD selection)
  • Compare alprazolam vs diazepam pharmacokinetically (half-life, active metabolites) and explain why a switch before taper is safer

Competencies: PH3.2, PH3.6

Group 4: Antidepressant Management — Selection, Timeline, and Augmentation

  • Evaluate whether 6 weeks of sertraline constitutes an adequate antidepressant trial and explain the pharmacological basis for the antidepressant response delay
  • Recommend an antidepressant switch or augmentation strategy for Rohan that accounts for his seizure-risk context (note: which antidepressants lower seizure threshold?)
  • Draft a patient education sheet for Rohan explaining the importance of antidepressant adherence and what to expect in the first 4-8 weeks of treatment

Competencies: PH3.5

Group 5: Drug Misuse and De-Addiction — Opioid/BZD/Alcohol

  • Classify alcohol, benzodiazepines, and tramadol (opioid component) by their dependence-producing properties (reward pathway, physical dependence potential, withdrawal severity)
  • Research naltrexone's role in alcohol use disorder and explain the pharmacological mechanism and evidence basis for its use
  • Prepare a brief for the college counsellor: what pharmacological and non-pharmacological interventions are available for a medical student with co-occurring depression and BZD use disorder?

Competencies: PH3.8, PH3.9

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [PH3.2] What are the differences between benzodiazepines and barbiturates in their mechanism at GABA-A receptors, and why is BZD overdose less lethal than barbiturate overdose?
  2. [PH3.3] Which antiseizure drugs are contraindicated in absence and myoclonic epilepsy, and what is the pharmacological mechanism of this worsening?
  3. [PH3.4] Why is pethidine (and tramadol) specifically contraindicated with SSRIs and MAOIs? Which opioids are safe in a patient on serotonergic drugs?
  4. [PH3.5] What is the mechanism of the 2-4 week delay in antidepressant response, and how does this guide clinical management when a patient reports early non-response?
  5. [PH3.6] Describe the pharmacodynamic and pharmacokinetic basis of benzodiazepine withdrawal, and why does it require gradual taper rather than abrupt cessation?
  6. [PH3.8] How does ethanol interact pharmacokinetically and pharmacodynamically with CNS depressants, and why must thiamine be given before glucose in alcoholic patients?
  7. [PH3.9] What is the role of buprenorphine/naloxone in opioid use disorder management, and why must buprenorphine induction begin only when a patient is already in moderate withdrawal?