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1. ABoth drugs are renally excreted by the same transporter, causing accumulation of each drug when combined together
2. BNitrates are said to block phosphodiesterase type 5, so combining them with sildenafil produces unpredictable enzyme competition
3. CSildenafil inhibits hepatic metabolism of nitrates, causing nitrate plasma levels to rise into a toxic range
4. DBoth drugs raise cyclic GMP, and their combined vasodilation can cause severe, life-threatening hypotension
5. ESildenafil displaces nitrates from plasma protein binding, sharply increasing the free circulating fraction of the nitrate