Tadalafil should not be given with:
**Core Concept**
Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor used in the treatment of erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). It works by increasing the levels of cyclic guanosine monophosphate (cGMP) in the smooth muscle, leading to vasodilation and improved blood flow.
**Why the Correct Answer is Right**
The correct answer is **C. Nitroglycerin**. Tadalafil should not be given with nitroglycerin because both substances lower blood pressure, and combining them can cause a significant drop in blood pressure, leading to dizziness, fainting, or even heart attack. This is because both tadalafil and nitroglycerin inhibit the phosphodiesterase enzyme, leading to an accumulation of cGMP and subsequent vasodilation.
**Why Each Wrong Option is Incorrect**
* **Option A:** **Ritonavir**. While ritonavir is a cytochrome P450 3A4 (CYP3A4) inhibitor that can increase the levels of tadalafil, it is not a contraindication for their combination. In fact, ritonavir is used to boost the levels of tadalafil in patients with HIV.
* **Option B:** **Aspirin**. Aspirin is not a contraindication for tadalafil. In fact, low-dose aspirin is often used to prevent cardiovascular events in patients with PAH.
* **Option D:** **Warfarin**. Warfarin is an anticoagulant that does not interact with tadalafil in a clinically significant way. There is no contraindication for their combination.
**Clinical Pearl / High-Yield Fact**
When prescribing PDE5 inhibitors like tadalafil, it's essential to ask about the use of nitrates, such as nitroglycerin, as they can cause a significant drop in blood pressure. Patients should be advised to avoid the use of nitrates for 48 hours after taking tadalafil.
**Correct Answer:** C. Nitroglycerin