PDE 5 inhibitors Drug Interactions Flashcards
What can happen if a patient takes phosphodiesterase type 5 inhibitors and organic nitrates?
They may experience sudden and severe low blood pressure (hypotension).
Why does taking both phosphodiesterase type 5 inhibitors and organic nitrates lead to low blood pressure?
Organic nitrates can cause low blood pressure on their own, and they are also nitric oxide donors, which can further lower blood pressure.
What is the main reason why phosphodiesterase type 5 inhibitor use is contraindicated in patients taking nitrates?
Because the combination can cause severe hypotension
How long should nitrates be withheld after taking phosphodiesterase type 5 inhibitors?
24 hours after sildenafil, vardenafil, or avanafil; and 48 hours after tadalafil.
What kind of agents should be used for treating angina in a patient who has taken a phosphodiesterase type 5 inhibitor?
Non-nitrate-containing agents like calcium channel blockers, beta-adrenergic antagonists, or morphine.
Do dietary sources of nitrates, nitrites, or L-arginine interact with phosphodiesterase type 5 inhibitors?
No, they do not interact because they do not increase circulating or tissue levels of nitric oxide in humans.
What are the factors that influence the degree of hypotension when taking phosphodiesterase type 5 inhibitors and α-adrenergic antagonists?
a) Stability of patient’s blood pressure prior to taking both drugs; b) Dose of the α-adrenergic antagonist used; c) Particular α-adrenergic antagonist used; d) Particular phosphodiesterase type 5 inhibitor used; e) Timing of administration of both drugs.
What factors help reduce the risk of hypotension in the interaction between phosphodiesterase type 5 inhibitors and α-adrenergic antagonists?
a) Stable blood pressure before taking both drugs; b) Low dose of α-adrenergic antagonist; c) Uroselective or extended-release α-adrenergic antagonist; d) Preferential use of tadalafil; e) 4 to 6 hours interval between doses.
What effect do potent CYP3A4 inhibitors have on plasma levels of phosphodiesterase type 5 inhibitors?
They may increase plasma levels by threefold or more, necessitating lower starting doses to minimize dose-related adverse effects.
How do CYP3A4 inducers, such as rifampin or phenytoin, carbamazepine affect plasma levels of phosphodiesterase type 5 inhibitors?
They can decrease plasma levels, requiring higher starting doses of the inhibitors.
Which phosphodiesterase type 5 inhibitor can prolong the QT interval when used with certain antiarrhythmics?
Vardenafil. If used with type 1A antiarrhythmics (eg, quinidine or procainamide) or type 3 antiarrhythmics (eg, sotalol, amiodarone), vardenafil can prolong the QT
interval. This is a unique drug interaction of vardenafil and not a pharmacologic class effect
vardenafil can prolong the QT
interval. This is a unique drug interaction of vardenafil and not a pharmacologic class effect. What’s “not a pharmacologic effect”
it means that this effect is specific to vardenafil and not a general characteristic of all phosphodiesterase type 5 (PDE5) inhibitors.
