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Pharmacotherapeutic Group: Endothelin Receptor Antagonist; Vasodilator.
Pharmacology: Pharmacodynamics: Mechanism of Action: Endothelian receptor antagonist that blocks endothelin receptors on endothelium and vascular smooth muscle (stimulation of these receptors is associated with vasoconstriction). Bosentan blocks both ETA and ETB receptors, with a slightly higher affinity for the A subtype.
Pharmacokinetics: Distribution: Vd: ~18 L (does not distribute into RBCs).
Protein binding, plasma: >98% primarily to albumin.
Metabolism: Hepatic via CYP2C9 and 3A4 to three primary metabolites (one contributing ~10% to 20% pharmacologic activity); steady-state plasma concentrations are 50% to 65% of those attained after single dose (most likely due to autoinduction of liver enzymes); steady-state is attained within 3 to 5 days.
Bioavailability: ~50%
Half-life elimination: ~5 hours; prolonged with heart failure, possibly in PAH.
Time to peak, plasma: 3 to 5 hours.
Excretion: Feces (as metabolites); urine (<3% as unchanged drug).
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