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PH9.1-7 | Miscellaneous Therapeutics — PBL Case

CLINICAL SETTING

It is Monday morning at a 50-bed District Hospital in rural Maharashtra. Dr Priya, the medical officer on duty, receives two patients within the same hour — a situation familiar in harvest season. **Patient 1 — Bay 1, Emergency:** Ramesh, a 42-year-old farmer, is carried in by his son. He is semi-conscious, drooling profusely, sweating through his shirt, and making laboured, wheezing breaths. His son found him collapsed in the field after he had been manually spraying an organophosphate pesticide for several hours without protective equipment. His pupils are pinpoint; his muscles twitch intermittently. Pulse 52/min, BP 90/60 mmHg, SpO₂ 76% on air. **Patient 2 — Waiting Area:** Siddhi, a 19-year-old student, sits accompanied by her mother. She has had severe cystic acne for three years — multiple large, painful nodules and scarring on her face, jaw, and chest that have not responded to six months of oral antibiotics and topical benzoyl peroxide. She is distressed and says the acne has affected her ability to attend college. Dr Priya notes she is of childbearing age.

Trigger 1: The Emergency Unfolds

Dr Priya attends to Ramesh first. The ward nurse asks: 'Doctor, what do we give him?' Dr Priya recognises the toxidrome immediately. She orders airway support and turns to the drug cupboard. The hospital stocks atropine sulphate (0.6 mg/mL ampoules), pralidoxime chloride (1 g vials), and activated charcoal. Meanwhile in the waiting area, Siddhi's mother asks the junior doctor: 'We read online that there is a very strong tablet for severe acne — isotretinoin. Can she just start it today?' The junior doctor recalls it is not so simple.

DISCUSSION POINTS

  • What toxidrome is Ramesh presenting with? Name five clinical signs you would actively look for and explain the receptor-level mechanism producing each sign.
  • What is the first drug to give Ramesh, and what is the correct titration endpoint? Why is 'heart rate normalising' an incorrect endpoint?
  • What information must the junior doctor gather about Siddhi BEFORE isotretinoin can even be considered? Why is this information pharmacologically critical?
Click to reveal Trigger 2: Ramesh Stabilises — Siddhi's Full Assessment (discuss previous trigger first!)

Trigger 2: Ramesh Stabilises — Siddhi's Full Assessment

After large doses of atropine (his secretions are finally drying — it took 14 mg over 90 minutes), Ramesh is more stable. His oxygen saturation is now 94%. Dr Priya adds pralidoxime IV. His son mentions he also had a seizure in the field. Meanwhile, the junior doctor completes Siddhi's assessment: her last menstrual period was 10 days ago, a pregnancy test is negative, she is not currently using any contraception. She has no prior psychiatric history. Her LFTs and fasting lipids come back: ALT slightly elevated at 48 U/L (normal <40), total cholesterol 5.2 mmol/L, triglycerides 2.1 mmol/L. Dr Priya explains isotretinoin to Siddhi and her mother. She also checks if Siddhi has had her HPV vaccine series — she has not.

DISCUSSION POINTS

  • Why is pralidoxime given to Ramesh in addition to atropine? Explain the mechanism — which receptor system does pralidoxime address that atropine cannot? What is the critical timing constraint and why?
  • Given Siddhi's blood results, is she immediately eligible to start isotretinoin? What specific pre-treatment requirements must be fulfilled, and why does the pharmacy/prescribing protocol require dual contraception (not just one method)?
  • Regarding Siddhi's HPV vaccination: classify the HPV vaccine by type and explain why it is appropriate to give a live vs recombinant vs other type for this indication.
Click to reveal Trigger 3: One Month Later (discuss previous trigger first!)

Trigger 3: One Month Later

Ramesh recovers and is discharged after 5 days. His wife comes a month later for a check-up and mentions that their 8-year-old son, who played in the same field, has been 'slow to learn' at school recently. A blood test reveals a lead level of 58 µg/dL — the field soil was contaminated from a nearby illegal battery recycling unit that also used the water source. The child has no neurological symptoms. Siddhi returns for her first monthly isotretinoin review. She is tolerating the drug but reports very dry lips and eyes. Her repeat triglycerides are now 3.8 mmol/L (markedly elevated). She has been compliant with dual contraception.

DISCUSSION POINTS

  • The child has lead poisoning without encephalopathy (BLL 58 µg/dL). Select the appropriate chelating agent, state its mechanism of action, the route of administration, and one important monitoring parameter during treatment.
  • For Siddhi: (i) Are the triglyceride elevation and mucocutaneous effects expected? Explain the mechanism of each. (ii) What threshold would prompt you to stop isotretinoin for triglycerides? (iii) Is dose reduction or addition of a fibrate appropriate here?
  • Siddhi asks: 'My cousin just received a kidney transplant and is on cyclosporine — can I share some of my Dettol antiseptic with her for wound care?' What counsel would you give, and is there a pharmacological interaction concern between topical antiseptics and cyclosporine's adverse effect profile?

Group Task Assignments

Group 1: Organophosphate poisoning — mechanism and antidote pharmacology

  • Draw and explain the acetylcholine accumulation cascade in OP poisoning — label muscarinic vs nicotinic sites
  • Construct a table comparing atropine (mechanism, target receptor, dose endpoint, signs of over-atropinisation) vs pralidoxime (mechanism, enzyme ageing, timing window)
  • Identify the sequence of drug administration in the emergency scenario with justification

Competencies: PH9.2

Group 2: Isotretinoin — mechanism, safety, and prescribing protocol

  • Explain isotretinoin's mechanism in severe acne linking to the four pathogenic steps (hyperkeratinisation, sebum, C. acnes, inflammation)
  • List every pre-treatment requirement and the pharmacological rationale for each (teratogenicity, lipid, LFT, psychiatric)
  • Write a patient-friendly one-page counselling note in simple English

Competencies: PH9.6

Group 3: Paediatric lead poisoning and chelation

  • Explain the mechanism by which lead impairs haem synthesis and neurological development
  • Compare the chelating agents for lead (BAL, CaNa₂EDTA, DMSA) — indication, route, adverse effects, and context
  • Explain the '4-hour BAL-before-EDTA' rule for lead encephalopathy and why EDTA alone worsens CNS status

Competencies: PH9.3

Group 4: Vaccines — types, cold chain, and contraindications

  • Classify BCG, OPV, MMR, HPV, and hepatitis B vaccines by type with immunological rationale
  • Explain why live vaccines are contraindicated in severely immunocompromised patients — using the transplant patient as a concrete example
  • Describe the cold chain requirements for each vaccine type and the consequences of cold chain failure

Competencies: PH9.4

Group 5: Antiseptics + glaucoma pharmacology

  • Apply the Spaulding classification to: stethoscope, flexible endoscope, surgical instrument, and skin wound — recommend the correct agent for each
  • Compare chlorhexidine vs alcohol for hand antisepsis — speed of kill, residual activity, spectrum, and appropriate clinical context
  • For Dr Priya's glaucoma patient (hypothetical follow-up): explain the FP-receptor mechanism of latanoprost vs the beta-2 mechanism of timolol and which is contraindicated in a patient with COPD

Competencies: PH9.5, PH9.7

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [PH9.2] What is the pathophysiology of organophosphate poisoning? Describe the SLUDGE toxidrome, explain atropine's mechanism and correct dosing endpoint, and describe the time-critical mechanism of pralidoxime.
  2. [PH9.6] How does isotretinoin work in severe acne? What are the mandatory pre-treatment safety requirements, and what are the key adverse effects (teratogenicity, dyslipidaemia, mucocutaneous) with monitoring parameters?
  3. [PH9.3] How does lead cause toxicity in children (haem synthesis + neurological)? What chelating agent is used for non-encephalopathic paediatric lead poisoning and why? How does the management differ in lead encephalopathy?
  4. [PH9.4] Classify BCG, OPV, HPV, and MMR vaccines by type. Explain why live vaccines are contraindicated in immunocompromised patients, and describe the combined active-passive immunisation approach for hepatitis B post-exposure prophylaxis.
  5. [PH9.5] What is the Spaulding classification and how does it guide antiseptic/disinfectant selection? Compare chlorhexidine (residual activity, mechanism) vs alcohol (no residual) for surgical hand antisepsis.
  6. [PH9.7] How do prostaglandin analogues (latanoprost) reduce IOP mechanistically? List three local adverse effects. Why are topical beta-blockers contraindicated in COPD/asthma?
  7. [PH9.1] Compare cyclosporine and tacrolimus: binding proteins, mechanism, potency, and adverse effect profile differences (gingival hyperplasia, hirsutism, PTDM). Why do both require TDM?