Drug-induced immunological reaction leading to drug-induced immune thrombocytopenia.

Drug-induced thrombocytopenia


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is any disorder in which there is an abnormally low amount(below 100,000
cells/mm3) of platelets. Platelets are parts of the blood
that help blood to clot.


Drug-Induced Thrombocytopenia:

When a drugs causes
reduction in platelet count, it is called drug-induced thrombocytopenia.


Types of Drug-Induced Thrombocytopenia:

Drug-induced immune thrombocytopenia.

Drug-induced nonimmune thrombocytopenia.

immune thrombocytopenia

Drug causes
production of antibodies
and destroys the platelets, due to immunological reaction leading to drug-induced
immune thrombocytopenia. Heparin causes drug-induced immune thrombocytopenia in
most of the cases.


Mechanism :

Hapten type

The offending
drug binds covalently to certain platelet Glyco Proteins (GPs). Antibodies are
generated that bind to these drug-bound GP epitopes. After the binding of
antibodies to the platelet surface, lysis occurs through complement activation
or through clearance from the circulation by macrophages. Hapten-mediated
immune thrombocytopenia usually occurs at least 7 days after the initiation of
the drug, although it can occur much sooner if the exposure is actually a
reexposure to a previously administered drug.

Antibody binding:

Antibodies exist
in the blood that recognize an epitope on the platelet GP.( Quinine,
anticonvulsants, vancomycin and nonsteroidal anti-inflammatory)


Most serious
type of heparin-induced thrombocytopenia (HIT) type II is by formation of
immune complex.




type I:

 More common, mild, reversible, non-immune-mediated  reaction that usually occurs within the first
2 days of therapy, often asymptomatic.

HIT type II:

Less common but
more severe and more complicated. The platelet count generally begins to
decline 5 to 10 days after the start of heparin therapy. Patients undergone  a recent surgery , patients receiving heparin
for thrombosis prophylaxis, cardiac surgery, orthopedic surgery are at high


Diagnosis of HIT:

Clinical based
and supported by laboratory testing. Several types of assays are available
platelet activation assays, platelet aggregation studies and enzyme-linked immune
sorbent assay method.


Drug-induced non-immune thrombocytopenia:

Drug causes
direct toxicity or bone marrow suppression. Chemotherapy drugs
and antiepileptic drugs cause drug-induced non-immune thrombocytopenia.


Decreased Platlets


Bleeding when
you brush your teeth

Easy bruising

Pinpoint red
spots on the skin (petechiae)




Stop the offending drug and treat symptomatically.

For people who have
life-threatening bleeding, treatments may include:

therapy (IVIG) Plasma
exchange (plasmapheresis)Platelet


Kamakshi V. Rao.Drug-Induced Hematologic
Disorders: Pharmacotherapy: A Pathophysiologic Approach. Joseph T. DiPiro, etal



K.Bharathi Priya

Assistant Professor

Department of Pharmacy Practice