Viagra (Sildenafil) Interactions – Introduction
Sildenafil, among other brands, which is widely used to treat erectile dysfunction in men, is an erectile dysfunction medicine that stimulates blood flow to the penis and thus promotes a tighter and more durable erection. But, like any drug, drugs must be managed carefully to avoid interaction with other substances. On this page, we will discuss 6 clinically relevant Viagra interactions.
Viagra (Sildenafil) Interactions
Viagra belongs to the class of phosphodiesterase 5 inhibitors. The other medications in this category are Cialis and Levitra. They all work in exactly the same way, and they shouldn’t be taken together. Combination therapy with these drugs increases the likelihood of low blood pressure, dizziness and priapism (pain in an extended erection). -Please note that you may only take one PDE5 inhibitor at a time, adhering to the prescribed dose.
1. Nitrates:
Nitrates, which are used to treat angina pectoris and hypertension, act by exuding nitric oxide (NO) in the body, which in turn stimulates production of cGMP and vasodilatation. A combination of Viagra and nitrates can cause a dramatic drop in blood pressure, resulting in hypotension and even death (Dean et al., 2017). This type of interaction can be dangerous, particularly in patients with coronary artery disease, who will develop myocardial ischemia from a drop in blood pressure.
Use of Viagra together with nitrates is not recommended because of their similar vasodilating properties. Nitrates are discouraged for at least 24 to 48 hours after taking Viagra, according to the United States Food and Drug Administration (FDA) (Drug Safety Communication, 2017). Patients should be educated about the signs and symptoms of nitrate-related side effects, and seek emergency medical attention if required.
2. Alpha-blockers:
The drugs include the alpha-blockers terazosin, doxazosin, and prazosin, which are used to treat hypertension, BPH, and Raynaud’s phenomenon. These medications act by blocking 1-adrenergic receptors found in smooth muscle vessels, decreasing peripheral resistance and lowering blood pressure.
The combination of Viagra and alpha-blockers increases your risk of orthostatic hypotension, dizziness and syncope. They are caused by a common mode of action that causes them to lower blood pressure. Yet doctors can avoid this interaction by prescribing patients with the lowest possible alpha-blocker dose, and directing them to take Viagra at least four hours after taking their alpha-blocker dose (Jayaraman et al., 2015). This single-dose delivery results in a slow blood pressure decrease and can prevent adverse reactions.
3. Protease Inhibitors:
Protease Inhibitors (PIs) are antiviral medications prescribed to treat Human Immunodeficiency Virus (HIV) infection. PIs act by preventing the HIV protease enzyme, which the virus requires to replicate, from working. Studies have found that when PIs are administered with Viagra, the plasma levels of Viagra’s active component, sildenafil, can jump dramatically (Schiff et al., 2004). This increase in plasma concentration increases the drug’s pharmacological activity, and can lead to hypotension and other side effects. Therefore, PI-prescribed patients should be given a reduced dose of Viagra and closely monitored to ensure their safety and protection.
4. Riociguat:
Riociguat is a medication used to treat PAH, which is caused by high blood pressure in the pulmonary arteries. Riociguat works by stimulating production of cGMP, a vasodilatory signalling molecule. Viagra also stimulates cGMP because it blocks its metabolism, and so causes vasodilation. This means that the combination of riociguat and Viagra can lead to potentially fatal hypotension due to vasodilation. Consequently, simultaneous administration of these drugs is not recommended and patients are advised to cease taking Viagra or any other PDE5 inhibitor while taking riociguat.
5. Grapefruit Juice:
Grapefruit juice acts as an inhibitor of CYP3A4, the enzyme that controls the metabolism of Sildenafil. In this way, grapefruit juice administered alongside or a day after taking Viagra might alter the activity of this enzyme inhibitor and raise Sildenafil plasma levels. Mayo Clinic, 2021. This increased plasma concentration in particular magnifies the drug’s pharmacological effects, including hypotension, and its side effects. As reported by Liu et al. (2008), the AUC of grapefruit juice combined with Sildenafil was 2.4 times higher than that of Sildenafil taken by itself. Thus, Viagra users should avoid grapefruit juice in order to avoid unwanted side effects, such as a spike in plasma levels.
6. Alcohol
Another Viagra-compatible drug is alcohol. Alcohol is a CNS depressant, and Viagra enhanced the vasodilatory effects of alcohol. Alcohol, like grapefruit juice, disables the process of decomposition. It is reflected by the high Viagra concentration in blood. This interaction increases the risk of adverse reactions such as slurred speech, blood pressure and headache. Frye et al. (2007) found that drinking alcohol and taking Sildenafil resulted in higher systolic and diastolic blood pressure when compared with taking Sildenafil alone. This makes Viagra to be used with a small dose of alcohol; additionally, such therapy should be done according to the dosage advised.
Conclusion: Viagra (Sildenafil) Interactions
The point is, even though Viagra is an effective and safe drug to use for ED, you need to consider a host of factors including drug interactions, food, and alcohol when giving this drug. Before using Viagra, tell your doctor about all your medicines and medical conditions. Not only that, you should use the dose recommended and not take Viagra with other PDE5 inhibitors and nitrates. Knowing and acting wisely will make the usage of Viagra in ED-treatment safe and effective.
