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PH8.1-11 | Antimicrobial and Chemotherapy Pharmacology — PBL Case

CLINICAL SETTING

Gopal Marandi, a 48-year-old tribal farmer from Jharkhand's Palamu district, is brought to the district hospital by his wife after three weeks of worsening fatigue, drenching night sweats, and a lump in his neck. His work involves growing rice paddy in waterlogged fields. He has no chronic illnesses and takes no regular medications. He has not seen a doctor in years. His family sold livestock to afford the bus fare to this hospital. On examination: Temperature 38.8°C, pulse 110/min, BP 100/70 mmHg. There is a non-tender 4×5 cm matted cervical lymph node mass on the right side. Spleen tip palpable 2 cm below left costal margin. Abdomen soft. No jaundice. Skin shows several hypopigmented anaesthetic patches on the forearms. The admitting resident notes that Gopal's presentation does not fit a single diagnosis — he has several findings pointing in different directions.

Trigger 1: The Matted Node and the Anaesthetic Patches

The resident orders: CBC (Hb 9.4g/dL, WBC 12,400 with 18% lymphocytes, platelets 280,000), ESR 88 mm/h, peripheral smear (normochromic normocytic anaemia, no blast cells). Random blood glucose 98 mg/dL. Chest X-ray: hilar adenopathy, no parenchymal lesion. Sputum AFB smear: requested. The dermatologist is consulted for the skin lesions. She examines 4 hypopigmented patches on both forearms, each with loss of sensation to light touch and absent sweating. She also finds thickening of the left ulnar nerve. Slit-skin smear is sent. The surgeon notes the cervical nodes: the largest is 4.5 cm, firm, non-fluctuant, without overlying skin changes.

DISCUSSION POINTS

  • What are the possible diagnoses for the cervical lymphadenopathy in a tribal farmer from Jharkhand? Prioritise them by pre-test probability and explain your reasoning.
  • The skin lesions have anaesthesia and nerve thickening. What is the most likely diagnosis and how would you classify it (paucibacillary vs multibacillary)?
  • Could these two sets of findings (lymph nodes + skin lesions) be part of a single unifying diagnosis, or are they independent? How would each answer change your investigation plan?
Click to reveal Trigger 2: Results Arrive — But New Problems Emerge (discuss previous trigger first!)

Trigger 2: Results Arrive — But New Problems Emerge

Results return over the next 48 hours: - Sputum AFB smear: 3+ positive (at least 10 AFB per field) - Slit-skin smear: BI 2+ (multibacillary leprosy confirmed) - FNAC of cervical node: granulomatous lymphadenitis, AFB seen - Malaria rapid diagnostic test (RDT): Positive for Plasmodium vivax antigen - Stool microscopy (sent on admission): Hookworm ova ++, Ascaris lumbricoides ova + Gopal now has confirmed simultaneous infections: pulmonary tuberculosis, multibacillary leprosy, vivax malaria, and hookworm/ascariasis — contributing to his profound anaemia (Hb 9.4g/dL). The senior physician asks the team: 'Which infection do we treat first? Can we treat all of them simultaneously? And what specific drug interaction hazards exist in this patient?'

DISCUSSION POINTS

  • Prioritise the treatment sequence for this patient. Which condition is immediately life-threatening? Which can wait 48 hours? Which requires long-term treatment?
  • Rifampicin is a component of both TB (HRZE) and leprosy (WHO MDT). Can you use a single rifampicin-containing regimen to cover both? If not, why not — and what does this mean for drug interaction risks?
  • Identify all potential drug-drug and drug-disease interactions in this patient who will be on: ATT (HRZE) + MDT (rifampicin + clofazimine + dapsone) + antimalarial + anthelmintic. Specifically: (a) chloroquine-dapsone interaction; (b) primaquine G6PD concern; (c) rifampicin CYP450 effects on co-medications.
Click to reveal Trigger 3: Unexpected Finding and an Ethical Dilemma (discuss previous trigger first!)

Trigger 3: Unexpected Finding and an Ethical Dilemma

On Day 5, a peripheral blood film sent to rule out concurrent falciparum co-infection is negative. G6PD testing: NORMAL. Gopal improves with chloroquine + primaquine for vivax malaria, albendazole for STH infections. ATT is started (HRZE). MDT is deferred for 1 week to allow clinical stabilisation. However, on Day 7, the nurse reports Gopal is becoming drowsy and his wife states he has taken 'his full week's supply of tablets' in one sitting because he thought it would 'cure him faster.' Serum drug levels cannot be measured at this district hospital. Immediate exam: confused (GCS 12), tachycardia 118/min, BP 88/60 mmHg, no focal neurology. Liver function is checked urgently — pending. The district team must act with available resources. They also learn this is Gopal's only chance at getting treatment — his family cannot afford a second hospital visit if he is discharged without a complete treatment plan.

DISCUSSION POINTS

  • What is the most likely acute toxicity from overdose of the current drug combination (HRZE + chloroquine + albendazole)? Which single drug is most dangerous in overdose and why?
  • Describe the immediate pharmacological management that can be initiated at a district hospital level without drug level monitoring. What is the antidote, if any, for the most dangerous toxicity?
  • This patient is from a marginalised tribal community with limited healthcare access. His wife cannot read. Using the principles of antibiotic stewardship and patient-centred prescribing from PH8.2, design a practical adherence support strategy for Gopal's 6-month ATT + 12-month MDT course that could realistically be implemented at district hospital level.

Group Task Assignments

Group 1: Antimicrobial Resistance and Rational Use

  • Research the current prevalence of MDR-TB in Jharkhand district hospitals and explain what changes to Gopal's ATT regimen would be required if RNTCP DST returned rifampicin resistance.
  • Identify the top 3 AMR stewardship failures that would occur if this patient's complex multi-drug regimen were prescribed without proper counselling and monitoring.

Competencies: PH8.1, PH8.2

Group 2: Antibacterial Pharmacology — TB and Drug Interactions

  • Create a mechanistic drug interaction table for this patient's full regimen (HRZE + MDT + chloroquine + albendazole), identifying CYP450 substrates, inducers, and inhibitors.
  • Explain the kinetics of isoniazid in fast vs slow acetylators and how this determines toxicity risk in Gopal.

Competencies: PH8.3, PH8.5

Group 3: Leprosy — MDT and Lepra Reactions

  • Prepare a patient-friendly explanation (as if speaking to Gopal's wife, who cannot read) of why MDT must continue even if a lepra reaction occurs, what the reaction looks like, and when to return to hospital immediately.
  • Explain clofazimine's dual role in MDT — antibacterial mechanism AND anti-inflammatory mechanism in Type 2 (ENL) reactions.

Competencies: PH8.6

Group 4: Tropical and Parasitic Pharmacology

  • Explain why Gopal's vivax malaria requires primaquine after chloroquine and what the G6PD testing result means for long-term management.
  • For the hookworm + ascariasis co-infection, calculate the albendazole regimen required and explain why the standard single dose differs in efficacy for the two species.

Competencies: PH8.7, PH8.9

Group 5: Stewardship and Health Advocacy

  • Design a 12-month adherence support plan for a tribal patient with limited literacy and healthcare access — incorporating WHO/DOTS principles, simplified dosing calendars, and community health worker integration.
  • Calculate the total number of tablets Gopal will take in 6 months of ATT + 12 months of MDT. Identify which days have the highest pill burden and propose a strategy to minimise confusion.

Competencies: PH8.2, PH8.5, PH8.6

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [PH8.1] What are the four principal mechanisms of antimicrobial resistance? For each mechanism, give one example of a specific pathogen-drug pair from India's current AMR burden.
  2. [PH8.2] What are the core components of an antibiotic stewardship programme at a district hospital level? What unique challenges exist for implementing ASP in low-resource tribal district hospitals?
  3. [PH8.3] Explain the mechanism, spectrum, and key adverse effect of each first-line ATT drug (H, R, Z, E). Why must these four drugs be used in combination rather than sequentially?
  4. [PH8.5] What are the RNTCP/NSP TB treatment categories and the treatment regimens for each? Under what circumstances does Category I treatment fail, and what regimen follows?
  5. [PH8.6] Compare WHO MDT regimens for paucibacillary and multibacillary leprosy. What distinguishes Type 1 from Type 2 lepra reactions in clinical presentation and pharmacological management?
  6. [PH8.7] Explain the life-cycle stage specificity of antimalarial drugs. Why does P. vivax malaria require primaquine in addition to a blood schizonticide? What are the absolute contraindications to primaquine?
  7. [PH8.9] Compare the mechanisms and clinical spectrum of albendazole and praziquantel. For which helminth species is each drug the drug of choice, and why?