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GERICLINICS

GeriQBank · Paper III · Q13

Mechanisms of Drug-Induced Thrombocytopenia

Moderate YieldAsked ×17-mark note
Topic
Haematology, Oncology & Screening
Chapter
Haematology
Years asked
Not recorded in the source
Frequency
Set 1× in Paper III (2009–2025)

As set in the university paper

  • What are the mechanisms of drug-induced thrombocytopenia?

    Paper III · Haematology & Oncology · asked ×1 · 7-mark note · see in paper list

Detailed answer

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Attempt it firstOutline your answer as a 7-mark note before revealing it — definition, causes, evaluation, management and the geriatric angle.Reveal answer

Covered briefly: Pathy's Ch. 24 gives the two-mechanism framework and HIT in detail; the six-antibody subdivision below is externally sourced.

High-Yield Points

1.

Pathy's rule: "Prescription drugs should ALWAYS be considered as a possible cause in any case of thrombocytopenia."

2.

Two broad mechanisms: direct marrow suppression, or induction of an immune response.

Non-Immune Mechanisms

3.

Dose-dependent marrow suppression (cytotoxics, alcohol, chloramphenicol).

4.

Idiosyncratic marrow aplasia (gold, phenylbutazone, carbamazepine, thiazides).

5.

Direct platelet/megakaryocyte toxicity (linezolid, valproate, daptomycin, bortezomib).

6.

Drug-induced thrombotic microangiopathy (quinine, gemcitabine, clopidogrel).

Immune Mechanisms — Six Types

Mechanism How it works Prototype drugs

1.

Hapten- Covalent binding → neo-antigen Penicillins, cephalosporins dependent

2.

Quinine-type Tri-molecular complex — drug alters antibody CDR → binds Quinine, quinidine, sulfonamides, GPIIb/IIIa or GPIb/IX vancomycin, rifampicin

3.

Fiban-type Binds RGD site → exposes LIBS neoepitope; onset within HOURS Tirofiban, eptifibatide 4. Chimeric Antibody against murine CDR3 Abciximab antibody

5.

Autoantibody True autoantibody, drug-independent, may persist Gold, procainamide, checkpoint inhibitors induction

6.

Immune complex PF4–drug complex → IgG → FcγRIIa → platelet ACTIVATION Heparin (HIT), VITT HIT — The Special Case

9.

Unlike other DIT causing bleeding, HIT causes THROMBOSIS via platelet activation. Mortality ~30% if untreated. More common with UFH than LMWH.

10.

Management: stop heparin, start argatroban (acute) then fondaparinux. Warfarin worsens acute HIT.

Timing Clues

Mechanism Onset

Classic (quinine-type) DITP 5–10 days first exposure; hours on re-exposure Fiban/abciximab-type Within hours, even first exposure HIT 5–10 days (or hours if heparin in prior 100 days)

Latest Updates (2023–Present)

HIT now part of a family of "anti-PF4 disorders": classic HIT, autoimmune HIT, spontaneous HIT (no heparin exposure, post-infection/surgery), and VITT (adenoviral-vector COVID vaccines). DOACs (rivaroxaban, apixaban) now accepted alternatives to argatroban/fondaparinux in stable HIT. VITT treatment: non-heparin anticoagulation + high-dose IVIg. Immune checkpoint inhibitors (pembrolizumab, nivolumab) recognised as an important autoantibody-type cause — may persist after stopping, often needs steroids/IVIg. Refined "antibody-first" model for quinine-type binding confirmed structurally.

Current Practice Update

Domain Pathy's (2022) Current evidence

GPIIb/IIIa inhibitors Not mentioned Fiban-type and abciximab-type mechanisms — hours to onset MD Geriatrics – Haematology Compendium Page 26 of 34 HIT Heparin-triggered only Part of anti-PF4 spectrum including VITT; DOACs accepted Culprit drugs Aspirin, paracetamol, quinine, quinidine Expanded — linezolid, checkpoint inhibitors, ADCs MD Geriatrics – Haematology Compendium Page 27 of 34

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