Cialis substitutes

In clinical practice, in addition to Tadalafil (Cialis), its analogues Vardenafil (Levitra) and Sildenafil (Viagra) are widely used to correct potency disorders in men.

The drugs "Viagra" and "Levitra" are in many ways similar to the drug "Cialis" in action, but there are some differences in the pharmacokinetics of these drugs and the dosages recommended for use. There are also differences in the frequency of some side effects.

Mechanism of action and clinical effects

The drugs Viagra (Sildenafil) and Levitra (Vardenafil) belong to the same group of drugs (selective phosphodiesterase blockers of the fifth type) as Cialis (Tadalafil), so their mechanism of action is similar. During sexual stimulation, nitric oxide is released in the cavernous bodies of the penis, which is a relaxing factor for the muscular wall of the vessels, which leads to an increase in the volume of blood flowing to the cavernous bodies and, accordingly, the onset of an erection. Nitric oxide causes the expansion of blood vessels by stimulating the production of cyclic guanosine monophosphate (c-GMP), which is destroyed by the enzyme phosphodiesterase type 5. Blockade of this enzyme (PDE-5) leads to the accumulation of c-GMP and the development of pharmacological effects.

Pharmacokinetics of Viagra and Levitra

Both drugs are well absorbed from the gastrointestinal tract. The time to obtain the maximum concentration of the drug in the blood of Sildenafil and Vardenafil is one hour and thirty minutes, respectively. The pharmacological effect of Vardenafil occurs after fifteen minutes and lasts about twelve hours. Sildenafil's effects develop in an average of twenty-five minutes and last for about four to five hours. These indicators are significantly worse for Viagra and Levitra than for Tadenafil (Cialis). The development time and duration of the effect of Tadenafil is 16 minutes and 36 hours, respectively.

Taking Vardenafil ("Levitra") with fatty foods lowers the maximum concentration of the drug in the blood by an average of 18-50 percent. The binding to blood proteins is 95 percent, which must be taken into account when prescribing concomitant therapy. The half-life of Vardenafil is about four to five hours, which is significantly less than that of Tadenafil (Cialis). Vardenafil and its metabolites are excreted as much as possible in the feces (91-95%), the rest (smaller) part is excreted in the urine. Taking Sildenafil with food also reduces the absorption of the drug. The percentage of binding to blood proteins is the same as that of Vardenafil with Tadenafil and is equal to 95-96 percent. Sildenafil metabolism occurs in the liver with the participation of cytochrome P450 enzymes. The half-life of Sildenafil is identical to the half-life of Vardenafil and is three to five hours. This drug is also predominantly excreted in the feces (80%) and slightly in the urine.

Indications for use in the clinic of drugs Viagra and Levitra

Correction of impaired erection in men. The drugs are not used in women.

Drug administration and dosage

Sexual stimulation is needed for the effects. Sildenafil is used in dosages of 25 to 100 milligrams once every 24 hours, depending on tolerability and effectiveness. It is taken one hour before sexual intercourse. Vardenafil is prescribed initially at a dosage of 10 milligrams. The maximum dose is 20 milligrams. It is also used before intercourse one hour, but it is allowed to take it four hours before contact.

Drug contraindications

Contraindications to the use of Viagra and Levitra are similar to Cialis. These include:

• drug intolerance
• simultaneous administration of drugs, nitric oxide donors
• severe pathologies of the liver, kidneys and cardiovascular system
• diseases of the retina< / li>

Side effects

Since these are drugs of the same group, their side effects are similar. Most often observed: