Antiplatelet drugs (Antithrobocytic drugs)

SYNTHESIS AND DRUG PROFILE

Antiplatelet drugs (Antithrobocytic drugs)

Platelets provide the initial haemostatic plug at the sites of vascular injury. Platelet aggregation is implicated in thrombus formation in arterial systems and pathogenesis of atherosclerosis. Thus, agents that inhibit platelet aggregation should be able to modify or prevent atherosclerotic disease and thrombosis.

Drugs interfering with platelet functions are as follows:

i. Aspirin

Mode of action: Aspirin inhibits the enzyme cycloxygenase and thromboxane synthetase (TxA₂) by binding irreversibly and interfering with the platelet aggregation.

Synthesis and drug profile of Aspirin is discussed in under sec I, Chapter NSAIDs.

ii. Dipyridamole (Persantine, Cardiwell)

Synthesis

Properties and uses: Dipyridamole is a bright yellow crystalline powder, practically insoluble in water, soluble in acetone, ethanol, and dilute solutions of mineral acids. It is an adenosine reuptake inhibitor, inhibitor of platelet aggregation, and useful in transient ischaemic attacks and secondary prevention of myocardial infarction.

Assay: Dissolve the sample in methanol and titrate against 0.1 M perchloric acid. Determine the end point potentiometrically.

Dose: 50–75 mg 8 hrly in combination with aspirin.

Dosage forms: Dipyridamole tablets B.P.

iii. Ticlopidine HCl (Tyklid, Ticlid)

Properties and uses: Ticlopidine hydrochloride is a white crystalline powder, sparingly soluble in water and ethanol, and very slightly soluble in ethyl acetate. Ticlopidine is a thieno pyridines used for thrombosis prevention in patients with atherosclerotic disease. It acts as an inhibitor of adenosine diphosphate (ADP)mediated platelet aggregation, and hence, used as an antiplatelet drug.

Synthesis

Dosage: The oral dose is 250 mg twice a day.

Assay: Dissolve the sample in anhydrous acetic acid and add acetic anhydride. Titrate against 0.1 M perchloric acid and determine the end point potentiometrically.

iv. Sulphinpyrazone (Anturane)

Properties and uses: Sulphinpyrazone is a white powder, very slightly soluble in water, sparingly soluble in alcohol, but soluble in dilute solutions of alkali hydroxides. It has antiplatelet and potent uricosuric effects, and hence, used in the treatment of gout.

Synthesis

Assay: Dissolve the sample in acetone and titrate against 0.1 M sodium hydroxide using bromothymol blue as indicator until the colour changes from yellow to blue.

Dose: The dose is 300 mg four times a day.

Dosage forms: Sulphinpyrazone tablets B.P.

v. Picotamide Monohydrate

Properties and uses: Picotamide monohydrate is a white crystalline powder, slightly soluble in water, soluble in ethanol, methylene chloride, and dilute mineral acids. It acts as thromboxane synthetase inhibitor and thromboxane receptor antagonist; used as antiplatelet agent.

Assay: Dissolve the sample in a mixture of anhydrous acetic acid and acetic anhydride (1:1) and titrate against 0.1 M perchloric acid. Determine the end point potentiometrically.