Neuromuscular and skeletal: Back pain (5%) Respiratory: Epistaxis (6%), dyspnea (5%), cough (4%) Hypersensitivity, including angioedema Interactions Prasugrel has a low potential for interactions. It may, for example, be used with proton pump inhibitors to reduce the risk of gastrointestinal bleeding without loss of its antiplatelet effect. Pharmacology Mechanism of action 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. Prasugrel inhibits platelet aggregation more rapidly, more consistently, and to a greater extent than clopidogrel. The TRITON-TIMI 38 study compared prasugrel with clopidogrel, and showed that prasugrel reduced rates of ischaemic events, but increased bleeding risk. Overall mortality rates were similar for each drug. 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 individual with the exception in patients over the age of 75, weight under 60 kg, and patients with a history of stroke or TIA due to increased risk of bleeding, although several cases have been reported of decreased responsiveness to prasugrel. It has been suggested that the decreased responsiveness observed in prasugrel is likely due to its low but significant frequency of High Platelet Reactivity (HPR). 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