PRADAXA 75MG, HARD CAPSULE

Indication

Dabigatran is indicated for the prevention of venous thromboembolic events in patients who have undergone elective hip or knee replacement surgery (based on RE-NOVATE, RE-MODEL, and RE-MOBILIZE trials). In 2010, it was approved in the US and Canada for prevention of stroke and systemic embolism in patients with atrial fibrillation (approval based on the RE-LY trial). Contraindications: severe renal impairment (CrCL < 30 ml/min); haemorrhagic manifestations, bleeding diathesis or spontaneous or pharmacologic impairment of haemostasis; lesions at risk of clinically significant bleeding (e.g. extensive cerebral infarction (haemorrhagic or ischemic) in the last 6 months, active peptic ulcer disease); concomitant treatment with P-glycoprotein inhibitors (e.g. oral ketoconazole, verapamil); and those with known hypersensitivity to dabigatran, dabigatran etexilate or any ingredient used in the formulation or component of the container. As of December 2012, dabigatran is contraindicated in patients with mechanical prosthetic heart valves.

Mechanism of Action

Dabigatran etexilate is an inactive pro-drug that is converted to dabigatran, the active form, by esterase-catalyzed hydrolysis in the plasma and liver. Dabigatran, the main active principle in plasma, is a rapid-acting competitive and reversible direct inhibitor of thrombin. Thrombin, a serine protease, is responsible for the conversion of fibrinogen to fibrin in the coagulation cascade. Inhibition of thrombin consequently prevents thrombus development. Dabigatran inhibits free thrombin, fibrin-bound thrombin and thrombin-induced platelet aggregation.

Pharmacokinetics

Absorption

Peak plasma concentrations were achieved in 6 hours in post surgical patients. In healthy patients, maximum concentrations were achieved in 0.5 to 2 hours. The absolute bioavailability of dabigatran in the body after administration of dabigatran etexilate was 6.5%. Food does not affect the bioavailability of dabigatran etexilate, but it delays the time to peak plasma concentrations by 2 hours. Oral bioavailability may increase by up to 75% when pellets are taken out of the hydroxypropylmethylcellulose (HPMC) capsule. Therefore, capsules should not be opened and pellets taken alone. Furthermore, although absorption of dabigatran etexilate is independent of gastrointestinal acidity, coadministration of pantoprazole (proton pump inhibitor) may reduce the bioavailability of dabigatran. Despite this finding, dose adjustment is not required.

Distribution

Moderate tissue distribution with a Vd of 60-70L. Accumulation factor, twice daily dosing = 2

Metabolism

CYP450 enzymes are not involved in the metabolism of dabigatran thus is not expected to interact with drugs metabolized by CYP isoenzymes. Dabigatran is typically metabolised by esterases and microsomal carboxylesterases. Pharmacologically active acylglucoronides are formed via conjugation. Four positional isomers, 1-O, 2-O, 3-O, and 4-O, acylglucuronides exist, each accounting for less than 10% of total plasma dabagatran.

Elimination

Toxicity

The most common adverse reactions include dyspepsia or gastritis-like symptoms. The approximate lethal dose (LD50) in rats and mice was observed at single oral doses of > 2000 mg/kg. Oral doses of 600 mg/kg did not induce any toxicologically meaningful changes in dogs and Rhesus monkeys. Dabigatran was well-tolerated in rats and Rhesus monkeys during repeat-dose toxicity studies. No evidence of mutagenic potential.

Active Ingredient/Synonyms

Ethyl 3-[[[4-[[[(hexyloxyl)carbonyl]amino]iminomethyl]phenyl]amino]methyl]-1-methyl-1H-benzimidazol-5-yl]carbonyl](pyridin-2-yl)amino] propanoate | Dabigatran etexilate |