Prasugrel

Medical uses

Prasugrel is used in combination with low dose aspirin to prevent thrombosis in patients with ACS, including unstable angina pectoris, non-ST elevation myocardial infarction (NSTEMI), and ST elevation myocardial infarction (STEMI), who are planned for treatment with PCI. In studies, prasugrel was more effective than the related clopidogrel but also caused more bleeding. Overall mortality was the same.

Prasugrel does not change the risk of death when given to people who have had a STEMI or NSTEMI. Prasugrel does however increase the risk of bleeding and may decrease the risk of further cardiovascular problems. Thus routine use in NSTEMI patients is of questionable value.

Contraindications

Prasugrel should not be given to patients with active pathological bleeding, such as peptic ulcer or a history of transient ischemic attack or stroke, because of higher risk of stroke (thrombotic stroke and intracranial hemorrhage).

Adverse effects

Adverse effects include:

Interactions

As opposed to clopidogrel, proton pump inhibitors do not reduce the antiplatelet effects of prasugrel and hence it is relatively safe to use these medications together.

Pharmacology

Prasugrel is a member of the thienopyridine class of ADP receptor inhibitors, like ticlopidine (trade name Ticlid) and clopidogrel (trade name Plavix). These agents reduce the aggregation ("clumping") of platelets by irreversibly binding to P2Y₁₂ receptors. Compared to clopidogrel, prasugrel inhibits adenosine diphosphate–induced platelet aggregation more rapidly, more consistently, and to a greater extent than do standard and higher doses of clopidogrel in healthy volunteers and in patients with coronary artery disease, including those undergoing PCI. Clopidogrel, unlike prasugrel, was issued a black box warning from the FDA on March 12, 2010, as the estimated 2–14% of the US population who have low levels of the CYP2C19 liver enzyme needed to activate clopidogrel may not get the full effect. Tests are available to predict if a patient would be susceptible to this problem or not. Unlike clopidogrel, prasugrel is effective in most individuals, although several cases have been reported of decreased responsiveness to prasugrel.

Pharmacodynamics

Prasugrel produces inhibition of platelet aggregation to 20 μM or 5 μM ADP, as measured by light transmission aggregometry. Following a 60-mg loading dose of the drug, about 90% of patients had at least 50% inhibition of platelet aggregation by one hour. Maximum platelet inhibition was about 80%. Mean steady-state inhibition of platelet aggregation was about 70% following three to five days of dosing at 10 mg daily after a 60-mg loading dose. Platelet aggregation gradually returns to baseline values over five to 9 days after discontinuation of prasugrel, this time course being a reflection of new platelet production rather than pharmacokinetics of prasugrel. Discontinuing clopidogrel 75 mg and initiating prasugrel 10 mg with the next dose resulted in increased inhibition of platelet aggregation, but not greater than that typically produced by a 10-mg maintenance dose of prasugrel alone. Increasing platelet inhibition could increase bleeding risk. The relationship between inhibition of platelet aggregation and clinical activity has not been established.

Pharmacokinetics

Prasugrel is a prodrug and is rapidly metabolized by esterases in the intestine and blood serum to a likewise inactive thiolactone, which is then converted, via CYP450-mediated (primarily CYP3A4 and CYP2B6) oxidation, to a pharmacologically active metabolite (R-138727). R-138727 has an elimination half-life of about 7 hours (range 2 h to 15 h). Healthy subjects, patients with stable atherosclerosis, and patients undergoing PCI show similar pharmacokinetics.

Chemistry

Prasugrel has one chiral atom. It is used in racemic form as the hydrochloride salt, which is a white powder.

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