Sildenafil , commonly known as Viagra, is known for treating male erectile dysfunction (ED), and was originally developed as a drug for the treatment of cardiovascular disease. At present, not only the therapeutic effect of sildenafil on ED is verified, but also sildenafil has a therapeutic effect on diseases such as pulmonary hypertension.
I. Clinical use of sildenafil
1. Erectile dysfunction
Sildenafil increases the level of cyclic guanosine monophosphate (cGMP) in the corpus cavernosum by inhibiting phosphodiesterase 5 (PDE5), relaxes the smooth muscle of the cavernous body, and the blood flows into the corpus cavernosum, improving the erectile response caused by sexual stimulation. 4 hours.
Dosage: sildenafil, oral, 25~100mg each time, once a day, about 1 hour before sex.
2. Pulmonary hypertension
The US FDA has approved sildenafil for the treatment of pulmonary hypertension. Low-oxygen pulmonary hypertension associated with high altitudes may also be effective with sildenafil.
Dosage: sildenafil, oral, 5~25mg each time, three times a day, 4 to 6 hours interval.
3. Female infertility
The uterine artery and ovarian arterial blood supply disorders are one of the causes of infertility in women.
Sildenafil can expand uterine artery blood flow and ovarian artery blood flow, improve endometrial development, improve pregnancy success rate, and reduce the abortion rate of infertility patients with thin endometrium.
4. Benign prostatic hyperplasia
The occurrence of benign prostatic hyperplasia (BPH) is closely related to sexual dysfunction. Sildenafil can inhibit the proliferation of prostatic interstitial cells, and can relax the smooth muscles of the prostate, bladder, urethra, etc., and improve the symptoms of lower urinary tract.
Need to be reminded that if you take α-blockers (such as doxazosin) and sildenafil at the same time, it can cause orthostatic hypotension.
II. Adverse reactions of sildenafil
The most common adverse reactions to sildenafil are headache (16%), flushing (10%) and indigestion (7%). More serious adverse reactions are visual impairment, sudden deafness, and sudden cardiac death.
1. Visual impairment
Main manifestations: light color, enhanced light perception, blurred vision, double vision, short-sighted vision or decreased vision, and even permanent blindness.
The main mechanism: sildenafil has high selectivity for phosphodiesterase 5 (PDE5), but when it is used in a large amount, it can inhibit phosphodiesterase 6 (PDE6) in the retina and cause visual abnormalities.
2. Sudden deafness
Most of the reports of sudden deafness have been reported as hearing loss in one ear, and about one-third in temporary deafness.
Medication: It can cause sudden deafness, and seek medical attention if there is hearing loss.
3. Sudden cardiac death
Phosphodiesterase 3 (PDE3) is present in the myocardium, so amrinone has a positive inotropic effect; phosphodiesterase 5 (PDE5) is absent in the myocardium, and sildenafil has no positive inotropic effect.
However, myocardial infarction, sudden cardiac death, cerebral hemorrhage, and cerebral thrombosis have been reported after taking sildenafil. There are no cardiovascular risk factors, and the risk of serious cardiovascular events is low, but there are also cases of myocardial infarction without cardiovascular risk factors.
III. Interaction of sildenafil
1. Interaction with food
On the fasting oral sildenafil, the peak concentration can be reached in 0.5 hour to 2 hours; with the high-fat diet, the sildenafil peak time is delayed by 1 hour, and the peak concentration is reduced by about 30%.
Grapefruit juice can increase the bioavailability of sildenafil and increase the blood concentration of sildenafil. Try to avoid taking it.
Sildenafil does not enhance the antihypertensive effect of alcohol, but both can cause hypotension.
2. Interaction with anti-angina drugs
Anti-angina drugs such as sildenafil with nitroglycerin, isosorbide dinitrate, isosorbide mononitrate can cause fatal hypotension. Organic nitrates are banned (at least) within 24 hours of taking sildenafil.
Some studies have found that the quick-acting rescue pills have a certain antihypertensive effect, and those taking silidafil should also use the quick-acting rescue pills.
3. Interaction with antihypertensive drugs
With sildenafil alone, blood pressure can be reduced by about 10/5 mmHg.
Patients taking antihypertensive drugs may suffer from hypotension if taking sildenafil.
4. Interaction with erythromycin
Sildenafil is mainly metabolized by CYP3A4 (the main pathway) and CYP2C9 (secondary pathway), and the half-life is eliminated by about 4 hours.
CYP3A4 inhibitors: erythromycin, clarithromycin, cimetidine, itraconazole, fluconazole, etc., inhibit the metabolism of sildenafil, increase the blood concentration of sildenafil, can cause severe hypotension .