How Levitra and Viagra Work
More than half the incidences of impotence (erectile dysfunction) are considered to arise from medical (physical) causes, such as diabetes and circulatory, neurological, or urological conditions. The rest are considered to be caused bypsychological problems. Levitra and Viagra treat the physical limitation that reduces blood flow to the penis. An erection occurs when blood flow into the penis increases while outflow decreases. With sexual stimulation, the body produces and releases nitric oxide in the penis. This activates an enzyme known as guanylate cyclase and causes the production of cyclic guanosine monophosphate (cGMP). The monophosphate cGMP directly affects erections by altering blood flow rates into and out of a penis.
Viagra and Levitra both inhibit the presence of phosphodiesterase-5 (PDE5), an enzyme that breaks down cGMP. This allows the cGMP to accumulate in larger quantities and have a longer-lasting effect, increasing the potential and persistence of an erection.
The following video features a physician explaining how PDE5 inhibitor drugs like Cialis, Viagra, and Levitra work and how they differ:
Efficacy
Vardenafil and sildenafil are effective in treating erectile dysfunction and pulmonary arterial hypertension. They are well-tolerated by patients, with few suffering from serious side effects. Additionally, Viagra (sildenafil) has recently been found to treat the symptoms of several other health conditions.
Levitra vs. Viagra Studies
Levitra very slightly outperformed Viagra in one study of men with erectile dysfunction and risk factors for cardiovascular disease, with more men preferring Levitra over Viagra (39% to 35%). Neither drug caused significant side effects.[1]
A 2011 comparison of studies of Cialis, Levitra, and Viagra concluded that there was "insufficient data" to decide which drug was best at treating erectile dysfunction. The researchers suggested doctors have patients try all three drugs to decide which works best for them personally.
Levitra Studies
A meta-analysis of eight randomized, double-blinded, placebo-controlled clinical trials found Levitra greatly improved erectile function in men who also suffered from hypertension.
In a randomized, double-blinded study of Japanese men suffering from erectile dysfunction, 90% of patients on Levitra saw significant improvements in achieving an erection. Furthermore, patients experienced no serious side effects. Mild side effects, such as flushing and headaches, were reported, however, and were more common on higher doses of the drug.
A combination of Levitra, the antidepressant Zoloft (sertraline), and behavioral psychosexual therapy were found to moderately improve the symptoms of men suffering from premature ejaculation.
Levitra improved erectile function in men with renal transplants, a demographic that frequently suffers from erectile dysfunction. Side effects experienced from taking Levitra were relatively mild and did not alter the results of renal function tests.
Viagra Studies
In a study of 979 men who were taking Viagra, over 94% of participants reported improved erectile function over the course of 4 years of using the drug. Side effects and discontinuation of the drug due to "insufficient response" were rare. Long-term use of Viagra was shown to be effective and safe.
An overview of clinical studies of Viagra found the drug to be safe and effective, even in some "difficult-to-treat" populations, such as patients with diabetes mellitus. Furthermore, the drug appears to have "beneficial effects" on the symptoms of several other chronic conditions, including some forms of premature ejaculation.
While Viagra has not been found to treat sexual dysfunction in women, at least one study has found the drug is effective in treating symptoms associated with interstitial cystitis (bladder pain syndrome) in women.
Side Effects
The common side effects of Viagra are usually mild and last a few hours, and may include facial flushing, an upset stomach, and headaches. Less common side effects are blurred vision, or perceiving a bluish tint in one's vision, and sensitivity to light. Levitra has shown additional common and usually mild side effects, including dizziness and nasal congestion.
Most side effects experienced from taking these drugs are temporary. Clinical studies have revealed that the frequency of these side effects decreases over time. However, a rare side effect, vision loss, has been reported with people who have used PDE5 inhibitors, including Viagra, Levitra, and Cialis. This loss of vision could be permanent and thus any vision-related side effects require an immediate visit to a doctor or medical facility. There is no evidence as yet that PDE5 inhibitors are the direct cause of vision loss.
The dependence or addiction liability of Viagra and Levitra is low. Many patients are able to have erections without these medications, though often not as easily or frequently.
Warnings
Those wanting to take Viagra or Levitra should get a prescription for the medication, based on a complete medical history. A person should reveal if he has an allergy to sildenafil or vardenafil, or any other medication, and report any incident of allergic reactions, such as a rash, hives, itching, shortness of breath, wheezing, coughing, or swelling of face, lips, tongue and throat.
Cardiovascular conditions should also be mentioned to doctors, as well as any renal or hepatic condition. Past and current drug use or addiction should be shared as well.
Viagra and Levitra can interact with other medications, so other prescribed treatments need to be discussed. A person should not take Viagra or Levitra with alcohol (liquor, beer, or wine) or in conjunction with Isosorbide dinitrate, isosorbide mononitrate, nitroglycerin, or drugs called "poppers", like amyl nitrate and butyl nitrate. If a person has been told not to have sex by a healthcare provider, this recommendation needs to be discussed with a doctor before using Viagra or Levitra. As neither drug prevents sexually transmitted diseases, use of a condom for protection is advised.
Drug Interactions
Patients taking medication to lower blood pressure should use Viagra and Levitra under medical advice and with caution, Both medications enhance the effects of lowering blood pressure, so patients with hypertension and angina who are taking nitrates such as isosorbide dinitrate (Isordil), isosorbide mononitrate (Imdur, Ismo, Monoket), and nitroglycerin (Nitro-Dur, Transderm-Nitro), as well as alpha-blocking drugs such as terazosin (Hytrin), should avoid Viagra and Levitra, unless cleared by a doctor. A common side effect of Viagra and Levitra in these patients is chest pain and lowered blood pressure, conditions that require prompt medical attention.
Other medications, such as Cimetidine (Tagamet), erythromycin, ketoconazole (Nizoral), itraconazole (Sporanox), and mibefradil (Posicor), can cause significant increases in the amount of sildenafil and vardenafil in the body, leading to a sudden drop in blood pressure. Patients on these medications should be observed carefully when taking Viagra or Levitra. Similarly, Rifampin decreases the blood levels of sildenafil and can reduce its effectiveness.
Vardenafil excretion is inhibited by erythromycin, ketoconazole (Nizoral), itraconazole (Sporanox), indinavir (Crixivan) and ritonavir (Norvir), so these drugs increase the concentration of vardenafil in the blood. To avoid potential complications, the dose of vardenafil should be reduced. Vardenafil reduces the concentration of ritonavir and indinavir in the blood, and can reduce the effect of these drugs.
Storage
Viagra and Levitra should be stored at room temperature and away from rooms with excessive moisture (e.g., bathroom, kitchen). Neither drug should be exposed to direct sunlight.
Generic Viagra
Revatio, a drug used to treat pulmonary arterial hypertension, has the same active ingredient as Viagra i.e., sildenafil. Both drugs are manufactured by Pfizer, who sued Teva in 2013 to block a generic variant of Viagra. While Teva is slated to launch a generic for Viagra in December 2017, ED patients who are looking for a cheaper generic right now can consult their doctor and get a prescription for Revatio.
Revatio costs about $0.70 per 20mg pill of sildenafil. Viagra pills are available in 25-, 50- and 100-mg doses, and doctors often prescribe the higher 50 or 100mg dose. Your doctor may be able to prescribe a dose of 5 Revatio 20mg pills, which would cost about $3.50 compared with Viagra's cost of upwards of $50 per pill.
Chemistry
Sildenafil citrate is a powder, white to off-white in color, soluble in water at 3.5 mg/ml. The molecular weight is 666.7 g/mol. Viagra tablets combine sildenafil citrate with inactive ingredients such as microcrystalline cellulose, anhydrous dibasic calcium phosphate, croscarmellose sodium, magnesium stearate, hypromellose, titanium dioxide, lactose, triacetin, and FD & C Blue #2 aluminum lake. Tablets are formed as rounded blue diamonds, coated in soluble film, in doses of 25 mg, 50 mg and 100 mg. Tablets are to be taken orally.
Vardenafil, the main ingredient in Levitra, is a pale solid with a solubility in water of 0.11 mg/ml. The molecular weight is 579.1 g/mol. A Levitra tablet blends vardenafil primarily with these inactive ingredients: crospovidone, microcrystalline cellulose, colloidal silicon dioxide, hypromellose, polyethylene glycol, magnesium stearate, yellow ferric oxide, titanium dioxide, and red ferric oxide. The end result is an orange tablet in 2.5 mg, 5 mg, 10 mg and 20 mg doses. Tablets are to be taken orally.
0 التعليقات