Contents 1 Pinyin 2 Instructions for sildenafil 2.1 Drug name 2.2 English name 2.3 Alias ??of Viagra 2.4 Classification 2.5 Dosage form 2.6 Pharmacological effects of sildenafil 2.7 Pharmacokinetics of sildenafil 2.8 West Indications of denafil 2.9 Contraindications of sildenafil 2.10 Precautions 2.11 Adverse reactions of sildenafil 2.12 Usage and dosage of sildenafil 2.13 Interactions of Viagra with other drugs This is a redirect entry, ** *Enjoyed the content of sildenafil. For the convenience of reading, sildenafil in the following text has been automatically replaced by Viagra. You can click here to restore the original appearance, or use the note method to display 1 Pinyin

wàn ài kě 2 Viagra Instructions 2.1 Drug Name

English name of Viagra 2.2

Sildenafil 2.3 Alias ??of Viagra

Sildenafil; Hidenafine Citrate; Viagra 2.4 Classification

Urinary system Drugs> Drugs for the treatment of male erectile dysfunction

2.5 Dosage Forms

Tablets: Each tablet contains 25mg, 50mg or 100mg of Viagra. 2.6 Pharmacological effects of Viagra

Viagra is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5) and is an oral drug for the treatment of ED. The physiological mechanism of erection in normal people involves the release of nitric oxide (NO) in the body during sexual intercourse. Nitric oxide activates guanylyl cyclase in the smooth muscle cells of the corpus cavernosum, leading to an increase in cGMP levels, causing the smooth muscles in the corpus cavernosum to relax, the cavernous sinus to expand, and blood to flow in, causing erection of the penis. Patients with erectile dysfunction are mainly due to the relaxation disorder of cavernous smooth muscle. Viagra has no direct relaxing effect on the isolated human corpus cavernosum, but it can inhibit the decomposition of cGMP by PDE5 in the corpus cavernosum, thereby enhancing the effect of nitric oxide. When sexual intercourse causes local release of nitric oxide, Viagra can inhibit PDE5, increase the level of cGMP in the corpus cavernosum, relax the smooth muscle of the corpus cavernosum, and allow blood to flow into the corpus cavernosum. Some studies have shown that the erectile response increases with increasing dose and plasma concentration, and the drug effect can last up to 4 hours (but is weaker than at 2 hours). In vitro experiments show that Viagra has high selectivity for PDE5. This selectivity is more than 80 times that of PDE1, more than 700 times that of PDE2 and PDE4, and 4,000 times that of PDE3. Since PDE3 is related to the control of myocardial contractility and PDE5 does not exist in myocardium, Viagra has no positive inotropic effect and does not directly affect myocardial contractile function. However, Viagra can dilate blood vessels in the systemic circulation. When taken orally in large doses (100 mg), it can cause a decrease in supine blood pressure [the average maximum decrease is 1.12/0.73kPa (8.4/5.5mmHg)], and the blood pressure decreases most significantly 1 to 2 hours after taking the drug, so blood pressure At peak drug concentrations, sexual activity may induce cardiac events. Viagra's selective effect on PDE5 is only 10 times that of PDE6, and PDE6 is an enzyme present in the retina. Therefore, Viagra may cause abnormal color vision at high doses or high blood concentrations. In addition to human cavernous smooth muscle, low concentrations of PDE5 are also found in platelets, blood vessels, visceral smooth muscle, and skeletal muscle. Viagra may enhance anti-platelet aggregation (in vitro experiments), inhibit platelet thrombosis (in vivo experiments), and relax peripheral blood vessels (in vivo experiments) by inhibiting PDE5 in these tissues. 2.7 Pharmacokinetics of Viagra

Viagra is rapidly absorbed after oral administration, takes effect in 10 to 40 minutes, and has an absolute bioavailability of approximately 40%. Peak plasma concentration (cmax) is reached after 30 to 120 minutes of oral administration on an empty stomach, and cmax is reached after 90 to 180 minutes of oral administration after meals. Healthy volunteers take a single oral dose of 100mg. After 24 hours, the plasma concentration is approximately 2ng/ml, and the cmax is 440ng/ml.

The area under the curve (AUC) increases after use in patients with abnormal liver function, severe renal insufficiency, or elderly people over 65 years of age. Viagra and its main circulating metabolite (N-demethylate) are approximately 96% bound to plasma proteins, and the protein binding rate has nothing to do with the total drug concentration. The tissue is well distributed and the volume of distribution (Vd) is 105L. Viagra is cleared primarily by the hepatic microsomal enzymes cytochrome P450 3A4 (CYP 3A4, primary pathway) and cytochrome P450 2C9 (CYP 2C9, secondary pathway). Its main metabolite (N-demethylate) has PDE selectivity similar to Viagra, and its plasma concentration is about 40% of Viagra. Therefore, approximately 20% of Viagra's pharmacological effects come from its metabolites. The elimination half-life of Viagra and its metabolites is approximately 4 hours. 80% of the administered dose is mainly excreted in the feces in the form of metabolites, and 13% is excreted via the kidneys. 90 minutes after healthy volunteers took the drug, the amount of Viagra measured in the blood was less than 0.001% of the administered dose. 2.8 Indications of Viagra

It is used to treat *** erectile dysfunction (ED). 2.9 Contraindications of Viagra

1. Those who are allergic to Viagra.

2. Those who are using nitroglycerin, sodium nitroprusside or other organic nitrates. 2.10 Precautions

1. Use with caution (1) Patients with retinitis pigmentosa or other retinal malformations (because a small number of patients may have hereditary genetic abnormalities of retinal phosphodiesterase). (2) Patients who have had myocardial infarction, stroke, shock or fatal arrhythmia in the past 6 months. (3) Patients with hypotension or hypertension, heart failure, and ischemic heart disease. (4) Patients with bleeding disorders or active peptic ulcers. (5) Patients with diseases that can cause priapism (such as sickle cell anemia, multiple myeloma, leukemia). (6) Patients with *** anatomical deformities (such as *** curvature, *** cavernous fibrosis or induration).

2. Effects of drugs on children Viagra is not suitable for children (especially newborns).

3. Effects of drugs on the elderly: Studies have shown that the clearance rate of Viagra in healthy elderly volunteers (not less than 65 years old) is reduced, and the area under the curve increases by 40%. Since higher plasma concentrations may increase adverse reactions, the starting dose of Viagra should be reduced.

4. The impact of drugs on pregnancy The U.S. Drug and Food Administration (FDA) classifies Viagra’s pregnancy safety as level B.

5. The impact of drugs on breastfeeding It is not clear whether Viagra is excreted in breast milk.

6. Viagra is not suitable for women.

7. While giving Viagra to treat ED, its related causes should be treated. Additionally, the recommended dosage of Viagra does not work in the absence of sexual intercourse.

8. The transient reduction in supine blood pressure caused by Viagra can usually be ignored for most patients, but it is still necessary to carefully consider whether this vasodilation effect will cause adverse effects on patients with hypotension or other cardiovascular diseases. Consequences, especially during sexual activity (which is potentially dangerous to the heart in the presence of existing cardiovascular risk factors). Therefore, patients with existing cardiovascular disease should not use Viagra to treat erectile dysfunction.

9. If symptoms such as angina, dizziness, and nausea occur at the beginning of sexual activity, sexual activity must be terminated.

10. If the penis continues to have an erection for more than 4 hours after taking the drug, appropriate treatment should be given; if priapism is not treated in time, the penis tissue may be damaged and lead to permanent loss of erectile function.

11. The safety and effectiveness of other methods for treating erectile dysfunction combined with Viagra have yet to be studied, so combined use is not recommended for the time being.

12. It is unclear when patients can safely take nitrates after taking Viagra.

13. Some studies have shown that when healthy volunteers increase the single dose to 800mg, the adverse reactions are similar to those at low doses, but the incidence rate increases. When overdose occurs, routine supportive care should be administered as needed. Because Viagra is highly bound to plasma proteins and is not eliminated in the urine, hemodialysis does not increase its clearance.

2.11 Adverse reactions of Viagra

1. Cardiovascular system: Myocardial infarction, sudden cardiac death, heart failure, arrhythmia, hypotension, cerebral hemorrhage, cerebral thrombosis, and transient ischemia may occur Cardiovascular adverse events such as sexual shock and hypertension have been reported. Most of them occur during or just after sexual activity. Some of them occur within hours to days after taking medication or sexual activity. There are even a few that occur shortly after taking medication and before sexual intercourse. When active. It has not yet been determined whether these reactions are caused directly by Viagra or by a combination of factors such as sexual activity and the patient's cardiovascular status.

2. Digestive system: Indigestion (7%), diarrhea (3%) may occur; dry mouth, vomiting, dysphagia, glossitis, gingivitis, stomatitis, esophagitis, gastritis, Colitis, abnormal liver function, and rectal bleeding have been reported.

3. Blood: There are case reports of anemia and leukopenia.

4. Metabolic/endocrine system: Gout, diabetes, peripheral edema, hyperuricemia, hypoglycemic reactions, hypernatremia, etc. have been reported.

5. Respiratory system: Nasal congestion (4%) may occur; there are case reports of asthma, pharyngitis, sinusitis, bronchitis, phlegm, cough, dyspnea, etc.

6. Genitourinary system: Urinary tract infection (3%) may occur; cystitis, increased nocturia, frequent urination, urinary incontinence, abnormal vaginal discharge, genital edema, lack of sexual intercourse, etc. have been reported ; There are also case reports of prolonged erection (more than 4 hours), priapism (painful erection more than 6 hours), and hematuria.

7. Central nervous system: headache (16%), dizziness (2%) may occur; ataxia, hypertonia, tremor, neuralgia, neuropathy, abnormal sensation, Case reports of dizziness, depression, anxiety, insomnia, drowsiness, dreaminess, slow reflexes, hypoesthesia, epileptic seizures, etc.

8. Musculoskeletal system: There are case reports of joint diseases, muscle pain, tendon rupture, tenosynovitis, bone pain, muscle weakness, synovitis, etc.

9. Skin: facial flushing (10%), rash (2%) may occur, and there are case reports of urticaria, herpes simplex, pruritus, skin ulcers, contact dermatitis, exfoliative dermatitis, etc.

10. Eyes: Dilated pupils, conjunctivitis, eye bleeding, cataracts, dry eyes, eye pain, photophobia, red eyes or eye congestion, eye burning, eye swelling and pressure, Increased intraocular pressure, retinal vasculopathy or hemorrhage, vitreous detachment, and perimacular edema have been reported. Mild transient visual abnormalities (3%) may also occur, mainly manifesting as pale vision, enhanced light perception, blurred vision, diplopia, temporary visual loss or vision loss, etc.

11. Ears: There are reports of tinnitus and deafness.

12. Others: Systemic reactions may also occur, such as shock, fatigue, pain (such as chest pain), chills, allergic reactions, etc. 2.12 Usage and dosage of Viagra

1. For most patients, the recommended dose is 50mg, taken as needed about 1 hour before sexual activity, and sexual intercourse is required after taking the drug. However, it can be taken at any time within 0.5 to 4 hours before sexual activity. Based on the efficacy and tolerance, the daily dose can be adjusted between 25 and 100 mg. Do not take the drug more than once a day. (1) Dosage in patients with renal insufficiency: The recommended starting dose for patients with severe renal insufficiency (when the creatinine clearance is less than or equal to 30ml/min, AUC and cmax is almost doubled) is 25 mg. (2) Dosage in case of hepatic insufficiency: The recommended starting dose for patients with hepatic impairment (such as cirrhosis, AUC and cmax increase by 84% and 47% respectively) is 25 mg.

2. Dosage for the elderly: The recommended starting dose for people over 65 years old is 25mg.

3. Dosage for other diseases (1) The appropriate starting dose for those taking potent cytochrome P4503A4 inhibitors and erythromycin at the same time is 25 mg. (2) It is recommended that patients taking HIV protease inhibitors (such as ritonavir) should take no more than 25 mg of Viagra every 48 hours.

2.13 Drug interactions

1. (1) With CYP450 3A4 enzyme inhibitors (such as ketoconazole, itraconazole, erythromycin) and non-specific inhibitors of CYP450 (such as cimetidine ) when used together, the AUC of Viagra increases and the clearance rate decreases. (2) When combined with HIV protease inhibitors [such as saquinavir, ritonavir (Ritonavir)], the cmax and AUC of Viagra increase, while the steady-state pharmacokinetics of saquinavir and ritonavir are inconsistent. affected. (3) Combined use with loop diuretics, potassium-sparing diuretics and non-selective β-blockers can increase the AUC of Viagra’s active metabolite (N-desmethyl Viagra) by 62% and 102% respectively, but this This effect has no clinical significance. (4) Combination with drugs that induce CYP4503A4 (such as rifampicin) may reduce the plasma level of Viagra. (5) No obvious interaction is seen when combined with CYP450 2C9 inhibitors (such as tolbutamide, warfarin). (6) Combined with CYP450 2D6 enzyme inhibitors (such as selective serotonin reuptake inhibitors, tricyclic antidepressants), thiazide drugs and thiazide diuretics, angiotensin-converting enzyme inhibitors, calcium channel blockers The combined use of lagants, etc. has no effect on the pharmacokinetics of Viagra.

2. When patients with hypertension take Viagra (100mg) and amlodipine (5mg or 10mg) at the same time, the systolic blood pressure in the supine position is further reduced by an average of 1.06kPa (8mmHg), and the diastolic blood pressure is further reduced by an average of 0.93kPa (7mmHg). ).

3. Combined use with α-receptor blockers (such as doxazosin) may cause hypotension symptoms in some patients. Therefore, if the dose of Viagra exceeds 25 mg, it should not be taken within 4 hours of taking alpha-blockers.

4. When used in combination with organic nitrates, Viagra can inhibit PDE5 and thus affect the degradation of cGMP, which may cause an extreme drop in blood pressure and should be prohibited from combined use.

5. In vitro experiments found that Viagra can enhance the anti-human platelet aggregation effect of sodium nitroprusside.

6. When used with heparin, it has a superimposed effect on prolonging the bleeding time of anesthetized rabbits, but no similar human studies have been conducted.

7. Combined use with aspirin has no effect on bleeding time.