Viasil

Viasil is indicated for the treatment of pulmonary arterial hypertension (WHO Group I) in adults to improve exercise ability and delay clinical worsening. The delay in clinical worsening was demonstrated when Viasil was added to background epoprostenol therapy.

Studies establishing effectiveness were short-term (12 to 16 weeks), and included predominately patients with New York Heart Association (NYHA) Functional Class II–III symptoms and idiopathic etiology (71%) or associated with connective tissue disease (CTD) (25%).

Limitation of Use: Adding Viasil to bosentan therapy does not result in any beneficial effect on exercise capacity.

Viasil is used to treat men who have erectile dysfunction (also called sexual impotence). Viasil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where this enzyme works.

Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection. When a man is sexually stimulated, his body's normal response is to increase blood flow to his penis to produce an erection. By controlling the enzyme, Viasil helps to maintain an erection after the penis is stroked. Without physical action to the penis, such as that occurring during sexual intercourse, Viasil will not work to cause an erection.

Viasil is also used in both men and women to treat the symptoms of pulmonary arterial hypertension. This is a type of high blood pressure that occurs between the heart and the lungs. When hypertension occurs in the lungs, the heart must work harder to pump enough blood through the lungs. Viasil works on the PDE5 enzyme in the lungs to relax the blood vessels. This will increase the supply of blood to the lungs and reduce the workload of the heart.

Viasil is available only with your doctor's prescription.

Viasil Tablets And

Oral Suspension

The recommended dose of Viasil is 5 mg or 20 mg three times a day. Administer Viasil doses 4-6 hours apart.

In the clinical trial no greater efficacy was achieved with the use of higher doses. Treatment with doses higher than 20 mg three times a day is not recommended.

Viasil Injection

Viasil injection is for the continued treatment of patients with PAH who are currently prescribed oral Viasil and who are temporarily unable to take oral medication.

The recommended dose is 2.5 mg or 10 mg administered as an intravenous bolus injection three times a day. The dose of Viasil injection does not need to be adjusted for body weight.

A 10 mg dose of Viasil injection is predicted to provide pharmacological effect of Viasil and its N-desmethyl metabolite equivalent to that of a 20 mg oral dose.

Reconstitution Of The Powder For

Oral Suspension

1. Tap the bottle to release the powder.
2. Remove the cap.
3. Accurately measure out 60 mL of water and pour the water into the bottle. (Figure 1)
4. Replace the cap and shake the bottle vigorously for a minimum of 30 seconds. (Figure 2)
5. Remove the cap.
6. Accurately measure out another 30 mL of water and add this to the bottle. You should always add a total of 90 mL of water irrespective of the dose prescribed. (Figure 3)
7. Replace the cap and shake the bottle vigorously for a minimum of 30 seconds. (Figure 4)
8. Remove the cap.
9. Press the bottle adaptor into the neck of the bottle (as shown on Figure 5, below). The adaptor is provided so that you can fill the oral syringe with medicine from the bottle. Replace the cap on the bottle.
10. Write the expiration date of the constituted oral suspension on the bottle label (the expiration date of the constituted oral suspension is 60 days from the date of constitution).

Incompatibilities

Do not mix with any other medication or additional flavoring agent.

How supplied

Dosage Forms And Strengths

Viasil Tablets

White, film-coated, round tablets engraved with “RVT20” containing Viasil citrate equivalent to 20 mg of Viasil.

Viasil Injection

Single use vial containing 10 mg/12.5 mL of Viasil.

Viasil for

Oral Suspension

White to off-white powders containing 1.57 g of Viasil citrate (equivalent to 1.12 g of Viasil) in a bottle intended for constitution. Following constitution with 90 mL of water, the volume of the oral suspension is 112 mL and the oral suspension contains 10 mg/mL Viasil. A 2 mL oral syringe (with 0.5 mL and 2 mL dose markings) and a press-in bottle adaptor are also provided.

Storage And Handling

Viasil tablets are supplied as white, film-coated, round tablets containing Viasil citrate equivalent to the nominally indicated amount of Viasil as follows:

Recommended Storage for Viasil Tablets: Store at controlled room temperature 20°C - 25°C (68°F - 77°F); excursions permitted to 15°C - 30°C (59°F -86°F).

Viasil injection is supplied as a clear, colorless, sterile, ready to use solution containing 10 mg Viasil/12.5 mL presented in a single-use glass vial.

Recommended Storage for Viasil Injection: Store at controlled room temperature 20°C - 25°C (68°F -77°F); excursions permitted to 15°C - 30°C (59°F - 86°F).

Viasil powder for oral suspension is supplied in amber glass bottles. Each bottle contains white to off-white powders containing 1.57 g of Viasil citrate (equivalent to 1.12 g Viasil). Following constitution, the volume of the oral suspension is 112 mL (10 mg Viasil/mL). A 2 mL oral dosing syringe (with 0.5 mL and 2 mL dose markings) and a press-in bottle adaptor are also provided.

Recommended storage for Viasil for oral suspension: Store below 30°C (86°F) in the original package in order to protect from moisture.

Constituted

Oral Suspension

Store below 30°C (86°F) or in refrigerator at 2°C to 8°C (36° F - 46°F). Do not freeze. The shelf-life of the constituted oral suspension is 60 days. Any remaining oral suspension should be discarded 60 days after constitution.

Distributed by: Pfizer Labs, Division of Pfizer Inc., NY, NY 10017. Revised: Apr 2015

See also:
What is the most important information I should know about Viasil?

Do not take Viasil if you are also using a nitrate drug for chest pain or heart problems. This includes nitroglycerin (Nitrostat, Nitrolingual, Nitro-Dur, Nitro-Bid, and others), isosorbide dinitrate (Dilatrate-SR, Isordil, Sorbitrate), and isosorbide mononitrate (Imdur, ISMO, Monoket). Nitrates are also found in some recreational drugs such as amyl nitrate or nitrite ("poppers"). Taking Viasil with a nitrate medicine can cause a sudden and serious decrease in blood pressure.

During sexual activity, if you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw, stop and call your doctor right away. You could be having a serious side effect of Viasil.

Do not take Viasil more than once a day. Allow 24 hours to pass between doses. Do not take Viasil while also taking Viasil, unless your doctor tells you to.

Contact your doctor or seek emergency medical attention if your erection is painful or lasts longer than 4 hours. A prolonged erection (priapism) can damage the penis.

Viasil can decrease blood flow to the optic nerve of the eye, causing sudden vision loss. This has occurred in a small number of people taking Viasil, most of whom also had heart disease, diabetes, high blood pressure, high cholesterol, or certain pre-existing eye problems, and in those who smoke or are over 50 years old. It is not clear whether Viasil is the actual cause of vision loss.

Stop using Viasil and get emergency medical help if you have sudden vision loss.

Use Viasil suspension as directed by your doctor. Check the label on the medicine for exact dosing instructions.

• An extra patient leaflet with detailed instructions for use is available with Viasil suspension. Talk to your pharmacist if you have questions about this information.
• Take Viasil suspension by mouth with or without food. Take your doses 4 to 6 hours apart unless your doctor tells you otherwise.
• Shake well for at least 10 seconds before each use.
• Use the oral dosing syringe that comes with Viasil suspension to measure your dose. Ask your pharmacist for help if you are unsure of how to measure your dose.
• Do not mix Viasil suspension with other medicine or flavoring.
• Wash and dry the dosing syringe after each use.
• Take Viasil suspension on a regular schedule to get the most benefit from it. Take it at the same times each day.
• Continue to take Viasil suspension even if you feel well. Do not miss any doses.
• Do not suddenly stop taking Viasil suspension or change your dose without talking to your doctor.
• If you miss a dose of Viasil suspension, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.

Ask your health care provider any questions you may have about how to use Viasil suspension.

Use: Labeled Indications

Erectile dysfunction: Viasil: Treatment of erectile dysfunction.

Pulmonary arterial hypertension: Viasil: Treatment of pulmonary arterial hypertension (WHO group I; efficacy established predominately in patients with WHO/NYHA functional class II and III) in adults to improve exercise ability and delay clinical worsening.

Off Label Uses

High-altitude pulmonary edema

Based on the 2019 Wilderness Medical Society consensus guidelines for the prevention and treatment of acute altitude illness, Viasil is a recommended option for the prevention and treatment of high-altitude pulmonary edema (as an adjunct to descent, oxygen, or portable hyperbaric therapy). Supplemental oxygen and descent are the mainstays of treatment. For prevention, Viasil should only be considered for patients with a history of high-altitude pulmonary edema, especially multiple episodes.

Raynaud phenomenon

Data from a meta-analysis and small controlled trials support the use of Viasil for Raynaud phenomenon related to systemic sclerosis, demonstrating a decrease in the frequency and severity of attacks.

See also:
What other drugs will affect Viasil?

Effects of Other Drugs on Viasil Viasil Citrate

In Vitro Studies: Viasil Viasil metabolism is principally mediated by the cytochrome P450 (CYP) isoforms 3A4 (major route) and 2C9 (minor route). Therefore, inhibitors of these isoenzymes may reduce Viasil clearance.

In Vivo Studies: Cimetidine (800 mg), a nonspecific CYP inhibitor, caused a 56% increase in plasma Viasil concentrations when coadministered with Viasil citrate (50 mg) to healthy volunteers.

When a single 100 mg dose of Viasil citrate was administered with erythromycin, a specific CYP3A4 inhibitor, at steady state (500 mg bid for 5 days), there was a 182% increase in Viasil systemic exposure (AUC). In addition, coadministration of the HIV protease inhibitor saquinavir, also a CYP3A4 inhibitor, at steady state (1200 mg tid) with Viasil citrate (100 mg single dose) resulted in a 140% increase in Viasil C_max and a 210% increase in Viasil AUC. Viasil Viasil citrate had no effect on saquinavir pharmacokinetics. Stronger CYP3A4 inhibitors such as ketoconazole or itraconazole would be expected to have still greater effects, and population data from patients in clinical trials did indicate a reduction in Viasil clearance when it was coadministered with CYP3A4 inhibitors (such as ketoconazole, erythromycin, or cimetidine).

Coadministration with the HIV protease inhibitor ritonavir, which is a highly potent P450 inhibitor, at steady state (400 mg bid) with Viasil citrate (100 mg single dose) resulted in a 300% (4-fold) increase in Viasil C_max and a 1000% (11-fold) increase in Viasil plasma AUC. At 24 hours the plasma levels of Viasil were still approximately 200 ng/mL, compared to approximately 5 ng/mL when Viasil was dosed alone. This is consistent with ritonavirs marked effects on a broad range of P450 substrates. Viasil Viasil citrate had no effect on ritonavir pharmacokinetics.

It can be expected that concomitant administration of CYP3A4 inducers, such as rifampin, will decrease plasma levels of Viasil.

Single doses of antacid (magnesium hydroxide/aluminum hydroxide) did not affect the bioavailability of Viasil citrate.

Pharmacokinetic data from patients in clinical trials showed no effect on Viasil pharmacokinetics of CYP2C9 inhibitors (such as tolbutamide, warfarin), CYP2D6 inhibitors (such as selective serotonin reuptake inhibitors, tricyclic antidepressants), thiazide and related diuretics, ACE inhibitors, and calcium channel blockers. The AUC of the active metabolite, N-desmethyl Viasil, was increased 62% by loop and potassium-sparing diuretics and 102% by nonspecific beta-blockers. These effects on the metabolite are not expected to be of clinical consequence.

Effects of Viasil Viasil Citrate on Other Drugs

In Vitro Studies: Viasil Viasil is a weak inhibitor of the cytochrome P450 isoforms 1A2, 2C9, 2C19, 2D6, 2E1 and 3A4 (IC50 >150 mM). Given Viasil peak plasma concentrations of approximately 1 mcM after recommended doses, it is unlikely that Viasil citrate will alter the clearance of substrates of these isoenzymes.

In Vivo Studies: When Viasil citrate 100 mg oral was coadministered with amlodipine, 5 mg or 10 mg oral, to hypertensive patients, the mean additional reduction on supine blood pressure was 8 mmHg systolic and 7 mmHg diastolic.

No significant interactions were shown with tolbutamide (250 mg) or warfarin (40 mg), both of which are metabolized by CYP2C9.

Viasil Viasil citrate (50 mg) did not potentiate the increase in bleeding time caused by aspirin (150 mg).

Viasil Viasil citrate (50 mg) did not potentiate the hypotensive effect of alcohol in healthy volunteers with mean maximum blood alcohol levels of 0.08%.

Viasil Viasil (100 mg) did not affect the steady state pharmacokinetics of the HIV protease inhibitors, saquinavir and ritonavir, both of which are CYP3A4 substrates.

See also:
What are the possible side effects of Viasil?

The following serious adverse events are discussed elsewhere in the labeling:

• Mortality with pediatric use
• Hypotension
• Vision loss
• Hearing loss
• Priapism
• Vaso-occlusive crisis

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Safety data of Viasil in adults were obtained from the 12-week, placebo-controlled clinical study (Study 1) and an open-label extension study in 277 Viasil-treated patients with PAH, WHO Group I.

The overall frequency of discontinuation in Viasil-treated patients on 20 mg three times a day was 3% and was the same for the placebo group.

In Study 1, the adverse reactions that were reported by at least 3% of Viasil-treated patients (20 mg three times a day) and were more frequent in Viasil-treated patients than in placebo-treated patients are shown in Table 1. Adverse reactions were generally transient and mild to moderate in nature.

Table 1: Most Common Adverse Reactions in Patients with PAH in Study 1 (More Frequent in Viasil-Treated Patients than Placebo-Treated Patients and Incidence ≥ 3% in Viasil-Treated Patients)

At doses higher than the recommended 20 mg three times a day, there was a greater incidence of some adverse reactions including flushing, diarrhea, myalgia and visual disturbances. Visual disturbances were identified as mild and transient, and were predominately color-tinge to vision, but also increased sensitivity to light or blurred vision.

The incidence of retinal hemorrhage with Viasil 20 mg three times a day was 1.4% versus 0% placebo and for all Viasil doses studied was 1.9% versus 0% placebo. The incidence of eye hemorrhage at both 20 mg three times a day and at all doses studied was 1.4% for Viasil versus 1.4% for placebo. The patients experiencing these reactions had risk factors for hemorrhage including concurrent anticoagulant therapy.

In a placebo-controlled fixed dose titration study (Study 2) of Viasil (starting with recommended dose of 20 mg and increased to 40 mg and then 80 mg all three times a day) as an adjunct to intravenous epoprostenol in patients with PAH, the adverse reactions that were more frequent in the Viasil + epoprostenol group than in the epoprostenol group (greater than 6% difference) are shown in Table 2.

Table 2: Adverse Reactions (%) in patients with PAH in Study 2 (incidence in Viasil + Epoprostenol group at least 6% greater than Epoprostenol group)

Viasil Injection

Viasil injection was studied in a 66-patient, placebo-controlled study in patients with PAH at doses targeting plasma concentrations between 10 and 500 ng/mL (up to 8 times the exposure of the recommended dose). Adverse events with Viasil injection were similar to those seen with oral tablets.

Postmarketing Experience

The following adverse reactions have been identified during post approval use of Viasil (marketed for both PAH and erectile dysfunction). Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Cardiovascular Events

In postmarketing experience with Viasil at doses indicated for erectile dysfunction, serious cardiovascular, cerebrovascular, and vascular events, including myocardial infarction, sudden cardiac death, ventricular arrhythmia, cerebrovascular hemorrhage, transient ischemic attack, hypertension, pulmonary hemorrhage, and subarachnoid and intracerebral hemorrhages have been reported in temporal association with the use of the drug. Most, but not all, of these patients had preexisting cardiovascular risk factors. Many of these events were reported to occur during or shortly after sexual activity, and a few were reported to occur shortly after the use of Viasil without sexual activity. Others were reported to have occurred hours to days after use concurrent with sexual activity. It is not possible to determine whether these events are related directly to Viasil, to sexual activity, to the patient's underlying cardiovascular disease, or to a combination of these or other factors.

Nervous system

Seizure, seizure recurrence

Each film-coated tablet contains Sildenafil citrate equivalent to 50 mg Viasil.

Each film-coated tablet contains Sildenafil citrate equivalent to 100 mg Viasil.

Each orodispersible tablet contains Sildenafil citrate equivalent to 50 mg Viasil.

Excipients/Inactive Ingredients: Film-Coated Tablets: In addition to the active ingredient, Viasil citrate, each tablet contains the following inactive ingredients: Microcrystalline cellulose, calcium hydrogen phosphate (anhydrous), croscarmellose sodium, magnesium stearate, hydroxypropyl methylcellulose (hypromellose), titanium dioxide (E171), lactose, triacetin, and FD & C Blue #2 aluminum lake [indigo carmine aluminum lake (E132)].

Orodispersible Tablets: In addition to the active ingredient, Viasil citrate, each orodispersible tablet contains the following inactive ingredients: Microcrystalline cellulose, silica hydrophobic colloidal, croscarmellose sodium, magnesium stearate, indigo carmine aluminium lake (E132), sucralose, mannitol, crospovidone, polyvinyl acetate, povidone, flavouring (contains: Maltodextrin and dextrin), natural flavouring (contains: Maltodextrin, E422 glycerol and E1520 propylene glycol), lemon flavouring (contains: Maltodextrin and E307 alpha tocopherol).