Vigabase

Uses

Vigabase Citrate is used for the treatment of Erectile Dysfunction.

Vigabase is also used to associated treatment for these conditions: Erectile Dysfunction, NYHA Functional Class II-III Pulmonary arterial hypertension, Premature Ejaculation, Symptomatic pulmonary arterial hypertension (PAH)

How Vigabase works

Vigabase is an oral therapy for erectile dysfunction . In the natural setting, i.e. with sexual stimulation, it restores impaired erectile function by increasing blood flow to the penis .

The physiological mechanism responsible for the erection of the penis involves the release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation . Nitric oxide then activates the enzyme guanylate cyclase, which results in increased levels of cyclic guanosine monophosphate (cGMP), producing smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood .

Vigabase is a potent and selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5) in the corpus cavernosum, where PDE5 is responsible for degradation of cGMP . Vigabase has a peripheral site of action on erections . Vigabase has no direct relaxant effect on isolated human corpus cavernosum but potently enhances the relaxant effect of NO on this tissue . When the NO/cGMP pathway is activated, as occurs with sexual stimulation, inhibition of PDE5 by sildenafil results in increased corpus cavernosum levels of cGMP . Therefore sexual stimulation is required in order for sildenafil to produce its intended beneficial pharmacological effects .

Moreover, apart from the presence of PDE5 in the corpus cavernosum of the penis, PDE5 is also present in the pulmonary vasculature . Vigabase, therefore, increases cGMP within pulmonary vascular smooth muscle cells resulting in relaxation . In patients with pulmonary arterial hypertension, this can lead to vasodilation of the pulmonary vascular bed and, to a lesser degree, vasodilatation in the systemic circulation .

Dosage

Vigabase dosage

The usual starting dose of Vigabaseis 50 mg once daily. lt should be taken before 30-40 minutes of intercourse. Depending on effectiveness and tolerance; the dose may be increased to a maximum recommended dose of 100 mg or decreased to 25 mg. The maximum dosing frequency is once per day.

Some factors are associated with increased plasma levels of sildenafil: age>65, hepatic impairment, severe renal impairment and concomitant use of ketoconazole, itraconazole, erythromycin. Since higher plasma levels may increase both the efficacy and incidence of adverse events, a starting dose of 25 mg should be considered in these patients.

Vigabase may takes longer time to work if you take it with a heavy meal.

Side Effects

Like all medicines, Vigabase can cause side effects although not everybody gets them.The side effects reported in association with the use of Vigabase are usually mild to moderate and of a short duration. All medicines including Vigabase can cause allergic reactions.

Contact with doctors immediately if experiences any of the following symptoms after taking Vigabase: sudden wheeziness, difficulty in breathing or dizziness, swelling of the eyelids, face, lips or throat. Common side effect includes headache, facial flushing, indigestion, effects on vision, light sensitivity, blurred vision or reduced, stuffy nose and dizziness. Uncommon side effect includes vomiting, skin rash, bleeding at the back of the eye, red eyes, eye pain, double vision, abnormal sensation in the eye, irregular or rapid heartbeat, muscle pain, feeling sleepy, reduced sense of touch, vertigo, ringing in the ears, nausea, dry mouth, chest pain & feeling tired.

Toxicity

In single-dose volunteer studies of doses up to 800 mg, adverse reactions were similar to those seen at lower doses, but the incidence rates and severities were increased . Doses of 200 mg did not result in increased efficacy but the incidence of adverse reaction (headache, flushing, dizziness, dyspepsia, nasal congestion, altered vision) was increased .

Due to the lack of data on the effect of sildenafil indicated for the treatment of pulmonary arterial hypertension (PAH) in pregnant women, sildenafil is not recommended for women of childbearing potential unless also using appropriate contraceptive measures .

The safety and efficacy of sildenafil indicated for treating PAH in a woman during labor and delivery have not been studied . Caution should ultimately be exercised when sildenafil is administered to nursing women as it is not known if sildenafil or its metabolites are excreted in human breast milk .

The safety and efficacy of sildenafil for the treatment of PAH in children below 1 year of age has not been established as no data is available .

Clinical experience with the elderly population in the use of sildenafil for the treatment of PAH has been varied. Some reports suggest that there are no identified differences in responses between elderly and younger patients while others have documented that clinical efficacy as measured by 6-minute walk distance could be less in elderly patients . In general, dose selection for an elderly patient should be cautious, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy .

Conversely, when sildenafil was used to treat erectile dysfunction in healthy elderly volunteers (65 years or over), a reduced clearance of sildenafil was observed . This reduction resulted in about 90% higher plasma concentrations of sildenafil and the active N-desmethyl metabolite compared to those seen in healthy younger volunteers (18-45 years) . Due to age-differences in plasma protein binding, the corresponding increase in free sildenafil plasma concentration was approximately 40% .

Vigabase was not carcinogenic when administered to rats for 24 months at a dose resulting in total systemic drug exposure (AUCs) for unbound sildenafil and its major metabolite of 29- and 42- times, for male and female rats, respectively, the exposures observed in human males given the Maximum Recommended Human Dose (MRHD) of 100 mg . Vigabase was not carcinogenic when administered to mice for 18-21 months at dosages up to the Maximum Tolerated Dose (MTD) of 10 mg/kg/day, approximately 0.6 times the MRHD on a mg/m2 basis .

Vigabase was negative in in vitro bacterial and Chinese hamster ovary cell assays to detect mutagenicity, and in vitro human lymphocytes and in vivo mouse micronucleus assays to detect clastogenicity .

There was no impairment of fertility in rats given sildenafil up to 60 mg/kg/day for 36 days to females and 102 days to males, a dose producing an AUC value of more than 25 times the human male AUC .

Precaution

Warnings: In patients with preexisting cardiovascular disease, there is a potential risk in sexual activity. Vigabase should not be generally used in men for whom sexual activity is inadvisable because of their underlying cardiovascular status. Vigabase has systemic vasodilatory properties (mean maximum decrease of 8.4/5.5 mmHg). Patients with left ventricular outflow obstruction (e.g. aortic stenosis, idiopathic hypertrophic subaortic stenosis) and those with severely impaired autonomic control of blood can be particularly sensitive to the actions of vasodilators including Vigabase.There is no controlled clinical data on the safety or efficacy of Vigabase in Patients who have suffered from a myocardial infarction, stroke, or life-threatening arrhythmia within the last 6 months. Caution should be taken in patients with resting hypotension (BP <90/50) or hypertension (BP >170/110), cardiac failure or coronary artery disease causing unstable angina, retinitis pigmentosa. Prolonged erection greater than 4 hours and priapism (painful erections greater than 6 hours in duration) have been reported infrequently since market approval of Vigabase. In this situation, patient should seek immediate medical assistance.

Precautions: Please tell your doctor or pharmacist if you are taking or have recently taken other medicines, including medicines obtained without prescription. Vigabase tablets may interfere with some medicines, especially those used to treat chest pain. In the event of a medical emergency, you should tell the healthcare professional treating your condition that you have taken Vigabase and if you did, do not take Vigabase with other medicines unless your doctor tells you can.You should not take Vigabase if you are taking medicines called nitrates as the combination of these products may cause a potentially dangerous decrease in your blood pressure. Always tell your doctor or pharmacist if you are taking any of these medicines that are often used for the relief of angina pectoris (or chest painJ.You should not take Vigabase if you are using any of the drugs known as nitric oxide donors such as amyl nitrite as the combination may also lead to potentially dangerous decrease in your blood pressure. If you are taking medicines known as protease inhibitors, such as for the treatment of HIV, your doctor may start you on the lowest dose (25 mg) of Vigabase. Some patients who take alpha-blocker therapy for the treatment of high blood pressure or prostate enlargement may experience dizziness or light-headedness, which may be caused by low blood pressure upon sitting or standing up quickly. Certain patients have experienced these symptoms when taking Vigabase with alpha-blocker. This is most likely to occur within 4 hours after taking Vigabase. In order to reduce the likelihood of these symptoms occur,you should be on a regular daily dose of your alpha-blocker before you start Vigabase. Your doctor may start you on a lower dose (2S mg) of Vigabase if you have hypotension (avoid if systolic blood pressure below 90 mmHg), recent stroke, unstable angina & myocardial infarction. Drinking alcohol can temporally impair your ability to get an erection, to get the maximum benefit from your medicine; you are advised not to drink excessive amounts of alcohol before taking Vigabase.

Interaction

Inhibitors of CYP3A4 such as cimetidine and erythromycin are likely to reduce sildenafil clearance. CYP3A4 inducers such as rifampicin may decrease the plasma concentrations of sildenafil. Symptomatic hypotension when used with α-blockers. Plasma concentrations are increased by ritonavir.

Food Interaction

• Take with or without food. If taken with a high-fat meal the medicine may take a little longer to start working.

[Moderate] GENERALLY AVOID: Coadministration with grapefruit juice may slightly increase the oral bioavailability and delay the onset of action of sildenafil.

The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits.

In a randomized, crossover study with 24 healthy male volunteers, ingestion of 250 mL of grapefruit juice one hour before and concurrently with a 50 mg dose of sildenafil increased the mean area under the plasma concentration-time curve (AUC) of sildenafil and its pharmacologically active N-desmethyl metabolite by 23% and 24%, respectively, compared to water.

Peak plasma concentrations (Cmax) were unaltered, but the time to reach sildenafil Cmax was prolonged by 0.25 hour.

The observed increase in sildenafil bioavailability is unlikely to be of clinical significance in most individuals.

However, pharmacokinetic interactions involving grapefruit juice are often subject to a high degree of interpatient variability and may be significant in the occasional susceptible patient.

Indeed, one subject in the study had a 2.6-fold increase in sildenafil concentrations.

MANAGEMENT: It may be advisable to avoid administration of sildenafil with grapefruit juice to prevent potential toxicity and delay in onset of action.

Vigabase Alcohol interaction

[Moderate] GENERALLY AVOID:

Additive hypotensive effects may occur when phosphodiesterase-5 (PDE5) inhibitors are used with alcohol, as both are mild systemic vasodilators.

In clinical pharmacology studies, more subjects administered alcohol at a dose of 0.7 g/kg (equivalent to approximately 6 ounces of 80-proof vodka in an 80-kg male; consumed within 10 minutes in study subjects, providing blood alcohol levels of 0.08%) in combination with tadalafil 10 or 20 mg single doses had clinically significant decreases in blood pressure than with alcohol alone.

There were reports of postural dizziness, and orthostatic hypotension was observed in some.

When tadalafil 20 mg was administered with alcohol at a lower dose of 0.6 g/kg (equivalent to approximately 4 ounces of 80-proof vodka in an 80-kg male), orthostatic hypotension was not observed, dizziness occurred with similar frequency relative to alcohol alone, and the hypotensive effects of alcohol were not potentiated.

Neither tadalafil nor alcohol affected the plasma concentrations of the other.

Administration of avanafil 200 mg with alcohol at a dose of 0.5 g/kg (equivalent to approximately 3 ounces of 80-proof vodka in a 70-kg male; consumed within 15 minutes in study subjects, providing blood alcohol levels of 0.057%) resulted in additional maximum supine systolic/diastolic blood pressure decreases of 3.5/4.5 mm Hg and additional maximum pulse rate increase of 9.3 bpm compared to alcohol alone, but did not cause orthostatic hypotension or dizziness.

The plasma concentrations of alcohol were not affected.

Vigabase 50 mg and vardenafil 20 mg reportedly did not potentiate the hypotensive effect of alcohol in healthy volunteers with mean maximum blood alcohol levels of 0.08% and in healthy volunteers administered alcohol at a dose of 0.5 g/kg, respectively.

Alcohol and vardenafil plasma levels were not altered when dosed simultaneously.

Patients taking PDE5 inhibitors should avoid consuming large amounts of alcohol, which may increase the potential for orthostatic signs and symptoms including increase in heart rate, decrease in standing blood pressure, dizziness, and headache.

Vigabase Drug Interaction

Major: tadalafilModerate: metoprolol, metoprololUnknown: amphetamine / dextroamphetamine, aspirin, aspirin, ubiquinone, rosuvastatin, apixaban, omega-3 polyunsaturated fatty acids, fluticasone nasal, atorvastatin, pregabalin, acetaminophen, cyanocobalamin, ascorbic acid, cholecalciferol, alprazolam, rivaroxaban, cetirizine

Vigabase Disease Interaction

Major: cardiovascular disease, renal dysfunction, pulmonary diseaseModerate: priapism, alcoholism, hearing loss, liver disease, retinitis pigmentosa, seizure disorders

Volume of Distribution

The mean steady-state volume of distribution documented for sildenafil is approximately 105 L - a value which suggests the medication undergoes distribution into the tissues .

Elimination Route

Vigabase is known to be quickly absorbed, with maximum plasma concentrations being observed within 30-120 minutes (with a median of 60 minutes) of oral administration in a fasting patient . Moreover, the mean absolute bioavailability observed for sildenafil is about 41% (from a range of 25-63%) . In particular, after oral three times a day dosing of sildenafil, the AUC and Cmax increase in proportion with dose over the recommended dosage range of 25-100 mg .

When used in pulmonary arterial hypertension patients, however, the oral bioavailability of sildenafil after a dosing regimen of 80 mg three times a day, was on average 43% greater than compared to the lower doses .

Finally, if sildenafil is administered orally with food, the rate of absorption is observed to be decreased with a mean delay in Tmax of about 60 minutes and a mean decrease in Cmax of approximately 29% . Regardless, the extent of absorption is not observed to be significantly affected as the recorded AUC decreased by only about 11 % .

Half Life

The terminal phase half-life observed for sildenafil is approximately 3 to 5 hours .

Clearance

The total body clearance documented for sildenafil is 41 L/h .

Elimination Route

After either oral or intravenous administration, sildenafil is excreted as metabolites predominantly in the feces (approximately 80% of the administered oral dose) and to a lesser extent in the urine (approximately 13% of the administered oral dose) .

Pregnancy & Breastfeeding use

Vigabase is not indicated for use in newborns, children & women.

Contraindication

Vigabase was shown to potentiate the hypotensive effects of nitrates and its administration to patients who are using organic nitrates, either regularly and or intermittently, in any form is therefore contraindicated.

Acute Overdose

In studies with healthy volunteers of single doses up to 800 mg, adverse events were similar to those seen at lower doses but incidence rates and severities were increased. In cases of overdose, standard supportive measures should be adopted as required. Renal dialysis is not expected to accelerate clearance as sildenafil is highly bound to plasma proteins and it is not eliminated in the urine.

Storage Condition

Store below 30° C. Protect from light and moisture. Keep out of reach of children.

Innovators Monograph

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