(D) is the true statement here. Drug interactions are a major concern for bosentan. It is a substrate of 3A4 (many, many drugs) and 2C9. On top of that, it is an autoinducer, meaning that it induces its own metabolism. There are contraindcations for bosentan including cyclosporine (3A4) and glyburide due to hepatotoxicity. Warfarin also has a decreased effect due to the autoinduction of 3A4.
(A) is a false statement. Remember: endothelin-1 is a receptor to promote vasoconstriction, so you want to ANTAGONIZE the receptor. Indeed, bosentan is an ET-1 ANTagonist.
(B) is false. Bosentan is pregnancy category X. Hepatotoxicity is such a concern with this drug that LFTs are monitored at baseline AND monthly.
(C) is false because it is NOT selective. It antagonizes ETa and ETb (though ETa to a greater extent. Selective ET-1 antagonists will be discussed later.
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