Vardenafil (INN) is a PDE5 inhibitor used in the treatment of erectile dysfunction (impotence). It can assist men with this disorder in achieving and maintaining an erection during sexual activity. It is commonly marketed under the trade name Levitra (Bayer AG). It is a phosphodiesterase inhibitor that is similar to sildenafil (Viagra) and tadalafil (cialis).

History

Vardenafil was co-marketed by Bayer Pharmaceuticals and GSK under the trade name Levitra. As of 2005, the co-promotion rights of GSK on Levitra have been “transferred back” to Bayer in many markets outside of the United States. In Italy, Bayer markets the product as Levitra and GSK markets the product as Vivanza. Due to European Union trade rules, parallel imports may result in the Vivanza branded packs being seen alongside Levitra packs in pharmacies in other EU member states.

Chemical structure and presentation

Vardenafil HCl is designated chemically as piperazine, 1-[[3-(1,4-dihydro-5-methyl-4-oxo-7-propylimidazo[5,1-f][1,2,4]triazin-2-yl)-4-ethoxyphenyl]sulfonyl]-4-ethyl-, monohydrochloride and has the following structural formula:

Vardenafil HCl is a nearly colorless, solid substance with a molecular weight of 579.1 g/mol and a solubility of 0.11 mg/mL in water. LEVITRA is formulated as orange, round, film-coated tablets with “BAYER” cross debossed on one side and “2.5″, “5″, “10″, and “20″ on the other side corresponding to 2.5 mg, 5 mg, 10 mg, and 20 mg of vardenafil, respectively. In addition to the active ingredient, vardenafil HCl, each tablet contains microcrystalline cellulose, crospovidone, colloidal silicon dioxide, magnesium stearate, hypromellose, polyethylene glycol, titanium dioxide, yellow ferric oxide, and red ferric oxide.

Mechanism of Action

Penile erection is a hemodynamic process initiated by the relaxation of smooth muscle in the corpus cavernosum and its associated arterioles. During sexual stimulation, nitric oxide is released from nerve endings and endothelial cells in the corpus cavernosum. Nitric oxide activates the enzyme guanylate cyclase resulting in increased synthesis of cyclic guanosine monophosphate (cGMP) in the smooth muscle cells of the corpus cavernosum. The cGMP in turn triggers smooth muscle relaxation, allowing increased blood flow into the penis, resulting in erection. The tissue concentration of cGMP is regulated by both the rates of synthesis and degradation via phosphodiesterases (PDEs). The most abundant PDE in the human corpus cavernosum is the cGMPspecific phosphodiesterase type 5 (PDE5); therefore, the inhibition of PDE5 enhances erectile function by increasing the amount of cGMP. Because sexual stimulation is required to initiate the local release of nitric oxide, the inhibition of PDE5 has no effect in the absence of sexual stimulation.
In vitro studies have shown that vardenafil is a selective inhibitor of PDE5. The inhibitory effect of vardenafil is more selective on PDE5 than for other known phosphodiesterases (>15-fold relative to PDE6, >130-fold relative to PDE1, >300-fold relative to PDE11, and >1,000-fold relative to PDE2, 3, 4, 7, 8, 9, and 10).

Pharmacokinetics

The pharmacokinetics of vardenafil are approximately dose proportional over the recommended dose range. Vardenafil is eliminated predominantly by hepatic metabolism, mainly by CYP3A4 and to a minor extent, CYP2C isoforms. Concomitant use with strong CYP3A4 inhibitors such as ritonavir, indinavir, ketoconazole, itraconazole as well as moderate CYP3A inhibitors such as erythromycin results in significant increases of plasma levels of vardenafil.

Absorption

Vardenafil is rapidly absorbed with absolute bioavailability of approximately 15%. Maximum observed plasma concentrations after a single 20 mg dose in healthy volunteers are usually reached between 30 minutes and 2 hours (median 60 minutes) after oral dosing in the fasted state. Two foodeffect studies were conducted which showed that high-fat meals caused a reduction in Cmax by 18%-50%.

Distribution

The mean steady-state volume of distribution (Vss) for vardenafil is 208 L, indicating extensive tissue distribution. Vardenafil and its major circulating metabolite, M1, are highly bound to plasma proteins (about 95% for parent drug and M1). This protein binding is reversible and independent of total drug concentrations.
Following a single oral dose of 20 mg vardenafil in healthy volunteers, a mean of 0.00018% of the administered dose was obtained in semen 1.5 hours after dosing.

Metabolism

Vardenafil is metabolized predominantly by the hepatic enzyme CYP3A4, with contribution from the CYP3A5 and CYP2C isoforms. The major circulating metabolite, M1, results from desethylation at the piperazine moiety of vardenafil. M1 is subject to further metabolism. The plasma concentration of M1 is approximately 26% that of the parent compound. This metabolite shows a phosphodiesterase selectivity profile similar to that of vardenafil and an in vitro inhibitory potency for PDE5 28% of that of vardenafil. Therefore, M1 accounts for approximately 7% of total pharmacologic activity.

Excretion

The total body clearance of vardenafil is 56 L/h, and the terminal half-life of vardenafil and its primary metabolite (M1) is approximately 4-5 hours. After oral administration, vardenafil is excreted as metabolites predominantly in the feces (approximately 91-95% of administered oral dose) and to a lesser extent in the urine (approximately 2-6% of administered oral dose).

Pharmacodynamics

Effects on Blood Pressure

In a clinical pharmacology study of patients with erectile dysfunction, single doses of vardenafil 20 mg caused a mean maximum decrease in supine blood pressure of 7 mm Hg systolic and 8 mm Hg diastolic (compared to placebo), accompanied by a mean maximum increase of heart rate of 4 beats per minute. The maximum decrease in blood pressure occurred between 1 and 4 hours after dosing. Following multiple dosing for 31 days, similar blood pressure responses were observed on Day 31 as on Day 1. Vardenafil may add to the blood pressure lowering effects of antihypertensive agents.

Effects on Blood Pressure and Heart Rate When LEVITRA is Combined with Nitrates

A study was conducted in which the blood pressure and heart rate response to 0.4 mg nitroglycerin (NTG) sublingually was evaluated in 18 healthy subjects following pretreatment with LEVITRA 20 mg at various times before NTG administration. LEVITRA 20 mg caused an additional time-related reduction in blood pressure and increase in heart rate in association with NTG administration. The blood pressure effects were observed when LEVITRA 20 mg was dosed 1 or 4 hours before NTG and the heart rate effects were observed when 20 mg was dosed 1, 4, or 8 hours before NTG. Additional blood pressure and heart rate changes were not detected when LEVITRA 20 mg was dosed 24 hours before NTG.

Electrophysiology

The effect of 10 mg and 80 mg vardenafil on QT interval was evaluated in a single-dose, double-blind, randomized, placebo- and active-controlled (moxifloxacin 400 mg) crossover study in 59 healthy males (81% White, 12% Black, 7% Hispanic) aged 45-60 years. The QT interval was measured at one hour post dose because this time point approximates the average time of peak vardenafil concentration. The 80 mg dose of LEVITRA (four times the highest recommended dose) was chosen because this dose yields plasma concentrations covering those observed upon co-administration of a low-dose of LEVITRA (5 mg) and 600 mg BID of ritonavir. Of the CYP3A4 inhibitors that have been studied, ritonavir causes the most significant drug-drug interaction with vardenafil. Table 1 summarizes the effect on mean uncorrected QT and mean corrected QT interval (QTc) with different methods of correction (Fridericia and a linear individual correction method) at one hour post-dose. No single correction method is known to be more valid than the other. In this study, the mean increase in heart rate associated with a 10 mg dose of LEVITRA compared to placebo was 5 beats/minute and with an 80 mg dose of LEVITRA the mean increase was 6 beats/minute.

Effects on Vision

Single oral doses of phosphodiesterase inhibitors have demonstrated transient dose-related impairment of color discrimination (blue/green) using the Farnsworth-Munsell 100-hue test and reductions in electroretinogram (ERG) b-wave amplitudes, with peak effects near the time of peak plasma levels. These finding are consistent with the inhibition of PDE6 in rods and cones, which is involved in phototransduction in the retina. The findings were most evident one hour after administration, diminishing but still present 6 hours after administration. In a single dose study in 25 normal males, LEVITRA 40 mg, twice the maximum daily recommended dose, did not alter visual acuity, intraocular pressure, fundoscopic and slit lamp findings.

Dosing

For most individuals, the recommended dose of vardenafil is 10 mg per day taken 60 minutes before intercourse. If there is no response or side effects, the dose may be increased to 20 mg or, if there are side effects, it may be reduced to 5 mg. Individuals 65 years of age or older should begin therapy with 5 mg. Individuals who are taking medications that increase the blood levels of vardenafil should start treatment with 2.5 to 5 mg of vardenafil.

Side effects

Vardenafil may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • headache
  • upset stomach
  • heartburn
  • dizziness
  • flushing
  • stuffy or runny nose
  • flu-like symptoms

Some side effects can be serious. If you experience any of the following symptoms , call your doctor immediately:

  • erection that lasts longer than 4 hours
  • sudden severe loss of vision (see below for more information)
  • blurred vision
  • changes in color vision (seeing blue tinge on objects, difficulty telling the difference between blue and green, or difficulty seeing at night)
  • swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs
  • hoarseness
  • difficulty breathing or swallowing
  • fainting
  • hives
  • rash

Vardenafil may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Some patients experienced a sudden loss of some or all of their vision after they took vardenafil or other medications that are similar to vardenafil. The vision loss was permanent in some cases. It is not known if the vision loss was caused by the medication. If you experience a sudden loss of vision while you are taking vardenafil, call your doctor immediately. Do not take any more doses of vardenafil or similar medications such as sildenafil (Viagra) or tadalafil until you talk to your doctor.

Drug Interactions

Cytochrome P450 Inhibitors

Cimetidine (400 mg b.i.d.) had no effect on vardenafil bioavailability (AUC) and maximum concentration (Cmax) of vardenafil when co-administered with 20 mg LEVITRA in healthy volunteers. Erythromycin (500 mg t.i.d) produced a 4-fold increase in vardenafil AUC and a 3-fold increase in Cmax when co-administered with LEVITRA 5 mg in healthy volunteers. It is recommended not to exceed a single 5 mg dose of LEVITRA in a 24-hour period when used in combination with erythromycin. Ketoconazole (200 mg once daily) produced a 10-fold increase in vardenafil AUC and a 4-fold increase in Cmax when co-administered with LEVITRA (5 mg) in healthy volunteers. A 5-mg LEVITRA dose should not be exceeded when used in combination with 200 mg once daily ketoconazole. Since higher doses of ketoconazole (400 mg daily) may result in higher increases in Cmax and AUC, a single 2.5 mg dose of LEVITRA should not be exceeded in a 24-hour period when used in combination with ketoconazole 400 mg daily.

HIV Protease Inhibitors

Indinavir (800 mg t.i.d.) co-administered with LEVITRA 10 mg resulted in a 16-fold increase in vardenafil AUC, a 7-fold increase in vardenafil Cmax and a 2-fold increase in vardenafil half-life. It is recommended not to exceed a single 2.5 mg LEVITRA dose in a 24-hour period when used in combination with indinavir.
Ritonavir (600 mg b.i.d.) co-administered with LEVITRA 5 mg resulted in a 49-fold increase in vardenafil AUC and a 13-fold increase in vardenafil Cmax. The interaction is a consequence of blocking hepatic metabolism of vardenafil by ritonavir, a highly potent CYP3A4 inhibitor, which also inhibits CYP2C9. Ritonavir significantly prolonged the half-life of vardenafil to 26 hours. Consequently, it is recommended not to exceed a single 2.5 mg LEVITRA dose in a 72-hour period when used in combination with ritonavir.

Effects of LEVITRA on other drugs

Nitrates

The blood pressure lowering effects of sublingual nitrates (0.4 mg) taken 1 and 4 hours after vardenafil and increases in heart rate when taken at 1, 4 and 8 hours were potentiated by a 20 mg dose of LEVITRA in healthy middle-aged subjects. These effects were not observed when LEVITRA 20 mg was taken 24 hours before the NTG. Potentiation of the hypotensive effects of nitrates for patients with ischemic heart disease has not been evaluated, and concomitant use of LEVITRA and nitrates is contraindicated.

Nifedipine

Vardenafil 20 mg, when co-administered with slow-release nifedipine 30 mg or 60 mg once daily, did not affect the relative bioavailability (AUC) or maximum concentration (Cmax) of nifedipine, a drug that is metabolized via CYP3A4. Nifedipine did not alter the plasma levels of LEVITRA when taken in combination. In these patients whose hypertension was controlled with nifedipine, LEVITRA 20 mg produced mean additional supine systolic/diastolic blood pressure reductions of 6/5 mm Hg compared to placebo.

Alpha-blockers

When LEVITRA 10 or 20 mg was given to healthy volunteers either simultaneously or 6 hours after a 10 mg dose of terazosin, significant hypotension developed in a substantial number of subjects. With simultaneous dosing of LEVITRA 10 mg and terazosin 10 mg, 6 of 8 subjects experienced a standing systolic blood pressure of less than 85 mm Hg. With simultaneous dosing of LEVITRA 20 mg and terazosin 10 mg, 2 of 9 subjects experienced a standing systolic blood pressure of less than 85 mm Hg. When LEVITRA dosing was separated from terazosin 10 mg by 6 hours, 7 of 28 subjects who received 20 mg of LEVITRA experienced a decrease in standing systolic blood pressure below 85 mm Hg. In a similar study with tamsulosin in healthy volunteers, 1 of 24 subjects dosed with LEVITRA 20 mg and tamsulosin 0.4 mg separated by 6 hours experienced a standing systolic blood pressure below 85 mm Hg. Two of 16 subjects dosed simultaneously with LEVITRA 10 mg and tamsulosin 0.4 mg experienced a standing systolic blood pressure below 85 mm Hg. The administration of lower doses of LEVITRA with alpha blockers has not been completely evaluated to determine if they can be safely administered together. Based on these data, LEVITRA should not be used in patients on alpha-blocker therapy.

Ritonavir and Indinavir

Upon concomitant administration of 5 mg of LEVITRA with 600 mg BID ritonavir, the Cmax and AUC of ritonavir were reduced by approximately 20%. Upon administration of 10 mg of LEVITRA with 800 mg TID indinavir , the Cmax and AUC of indinavir were reduced by 40% and 30%, respectively.

Alcohol

Alcohol (0.5 g/kg body weight: approximately 40 mL of absolute alcohol in a 70 kg person) and vardenafil plasma levels were not altered when dosed simultaneously. LEVITRA (20 mg) did not potentiate the hypotensive effects of alcohol during the 4-hour observation period in healthy volunteers when administered with alcohol (0.5 g/kg body weight).

Aspirin

LEVITRA (10 mg and 20 mg) did not potentiate the increase in bleeding time caused by aspirin (two 81 mg tablets). Other interactions: LEVITRA had no effect on the pharmacodynamics of glyburide (glucose and insulin concentrations) and warfarin (prothrombin time or other pharmacodynamic parameters).

Carcinogenesis, Mutagenesis, Impairment of Fertility

Vardenafil was not carcinogenic in rats and mice when administered daily for 24 months. In these studies systemic drug exposures (AUCs) for unbound (free) vardenafil and its major metabolite were approximately 400- and 170- fold for male and female rats, respectively, and 21 and 37-fold for male andfemale mice, respectively, the exposures observed in human males given the Maximum Recommended Human Dose (MRHD) of 20 mg. Vardenafil was not mutagenic as assessed in either the in vitro bacterial Ames assay or the forward mutation assay in Chinese hamster V79 cells. Vardenafil was not clastogenic as assessed in either the in vitro chromosomal aberration test or the in vivo mouse micronucleus test. Vardenafil did not impair fertility in male and female rats administered doses up to 100 mg/kg/day for 28 days prior to mating in male, and for 14 days prior to mating and through day 7 of gestation in females. In a corresponding 1-month rat toxicity study, this dose produced an AUC value for unbound vardenafil 200 fold greater than AUC in humans at the MRHD of 20 mg. There was no effect on sperm motility or morphology after single 20 mg oral doses of vardenafil in healthy volunteers.

Overdosage

The maximum dose of LEVITRA for which human data are available is a single 120 mg dose administered to eight healthy male volunteers. The majority of these subjects experienced reversible back pain/myalgia and/or “abnormal vision”. In cases of overdose, standard supportive measures should be taken as required. Renal dialysis is not expected to accelerate clearance because vardenafil is highly bound to plasma proteins and is not significantly eliminated in the urine.

FDA ALERT [7/2005]

A small number of men have lost eyesight in one eye some time after taking Levitra, Viagra, or Cialis. This type of vision loss is called non-arteritic anterior ischemic optic neuropathy (NAION). NAION causes a sudden loss of eyesight because blood flow is blocked to the optic nerve.
We do not know at this time if Levitra, Viagra, or Cialis cause NAION. NAION also happens in men who do not take these medicines. People who have a higher chance for NAION include those who:

  • have heart disease
  • are over 50 years old
  • have diabetes
  • have high blood pressure
  • have high cholesterol
  • smoke
  • have certain eye problems

FDA has approved new labels for Levitra, Viagra, and Cialis to include information on possible eyesight loss (NAION).

Stop using Levitra, Viagra, or Cialis if you have a loss in your eyesight. Get medical help right away.

Sources: fda (pdf), wikipedia, medlineplus, medicinenet

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