Penvir (Famciclovir 250mg) Tablets

Penvir general information

What is Penvir used for?

A virus is a piece of genetic material, either DNA or RNA, wrapped up in a protein coat.  A virus cannot replicate itself and can only survive by invading a host cell and using the host cell’s equipment to reproduce its genetic material and synthesise its protein coat.  New fully formed virus particles are released from the host cell to infect new cells.  Viruses cause many diseases, some of which are mild, while others can prove fatal. 

The Herpesvirus family of viruses (also called Herpesviridae) is a large family of double-stranded DNA viruses that cause several diseases.  These include Herpes simplex virus (HSV) type 1 (HSV-1) and type 2 (HSV-2) that causes cold sores and genital herpes, and Varicella zoster virus (VZV) that causes chickenpox and shingles.  Penvir tablets 250mg are used to treat infections of the skin and mucous membranes caused by HSV and VZV and help relieve painful symptoms, heal blisters and sores, and help prevent infection recurrence.

Herpesvirus life cycle

A Herpesvirus such as HSV and VZV can only replicate by getting inside a host cell nucleus and becoming integrated into the host cell DNA.  The infected cell then replicates the virus DNA and produces the proteins needed for the virus to complete its life cycle.  Infectious virus particles called virions are then released to infect more cells.  Both HSV and VZV can enter a latent state in the cells of their host.  They do this by migrating to sensory ganglia (bundle of nerve cells), where they can lie dormant until activated again.  HSV migrates to the sensory ganglia of the nerves that supply sensation to the skin, and VZV migrates to the dorsal root ganglia of the spine.  The virus can become reactivated by various factors, including pressure on the nerve roots, stress, infection, minor trauma, and ultraviolet radiation from the sun.  The virus then travels back up the nerves and re-infects the skin cells at the end of the nerve. 

Infection with herpes simplex virus

Cold sores, also known as herpes labialis, are caused by infection of the lips and face by Herpes simplex virus type 1 (HSV-1).  Cold sores are spread by direct physical contact, and the virus replicates within the epidermis, which is the outer layer of the skin.  A tingling sensation on the lips or face is the warning sign the virus has been activated.  Once the cold sore has developed, it forms blisters on the skin, which join up to create a weeping sore.  This is when the infection is contagious and can spread to form more cold sores.  Direct physical contact with others at this infectious stage can spread the virus to them. 

Genital herpes can be caused by HSV-1 or HSV-2 and is a sexually transmitted disease spread by direct sexual contact.  Symptoms vary from mild to severe and include irritation, burning, or itching around the genitals.  Painful blisters and sores can develop, and you may feel unwell, with headache, fever, and general aching.  Eventually, after a few weeks, the blisters heal and disappear.

If treated at the early stages of symptoms appearing, blisters can be prevented from developing.  Once infected with HSV-1 or HSV-2, the infection cannot be cured.  The virus lies dormant in the sensory nerves that supply the skin until reactivated by a trigger such as stress, sunlight, or if the immune system is compromised.  

Shingles

Shingles are caused by varicella zoster Virus (VZV), which is the same virus that causes chickenpox.  If you have had chickenpox, which is a common childhood disease, the virus can lie dormant for years in the dorsal root ganglia.  These are nerve cells that carry sensory messages from the rest of the body to the spinal cord.  When VZV is activated, it travels back up the nerves to infect the skin cells and causes a painful blistering rash known as herpes zoster.  This can happen on any part of the body, depending on which sensory nerve the virus travels along.  Shingles are more common in older people or anyone with a weakened immune system. 

How does Penvir work?

Penvir tablets 250mg contain famciclovir, an antiviral medication that is used to treat an infection with herpesvirus, including HSV-1, HSV-2, and VZV.  Famciclovir in Penvir tablets 250mg is a prodrug of penciclovir.  It is rapidly converted to penciclovir inside virus-infected cells. 

Penciclovir is a nucleoside analogue of guanosine, which is a building block of DNA needed by the virus to replicate.  Penciclovir is activated by a viral enzyme called thymidine kinase that converts penciclovir to a form that is in turn, converted to penciclovir triphosphate by the host cellular kinases (enzymes that transfers phosphate groups).  Penciclovir triphosphate becomes incorporated into viral DNA and inhibits viral DNA polymerase enzyme, which is the enzyme that synthesises the viral DNA, without affecting normal cellular processes.  Viral DNA synthesis is blocked, which inhibits the replication of viral DNA and stops the growth and spread of the virus.  Inhibition of viral replication relieves symptoms, reduces the amount of latent virus in the neural ganglia, and allows the immune system to fight the infection. 

Penciclovir triphosphate persists in virus-infected cells for about 10 hours and blocks the transcription of the virus by DNA polymerase.  Since the activation of famciclovir in Penvir tablets 250mg depends on a viral enzyme, cells that are not infected with the virus are not affected.

What does Penvir contain?

Penvir tablets 250mg contains the active ingredient famciclovir an antiviral medication that is used to treat infections with herpesvirus, including HSV-1, HSV-2, and VZV, that cause cold sores, genital herpes and shingles. 

What are the side effects of Penvir?

Most medications have some side effects, but they are not experienced by everyone.  Some side effects are commonly experienced when taking Penvir, but others are not so common, and you should discuss any problems or concerns with your primary care physician. 

Common side effects when taking Penvir include headache, nausea, vomiting, diarrhoea, abdominal pain, dizziness, rash, itching.

When should Penvir not be used?

Have a talk with your primary healthcare physician before taking Penvir tablets 250mg so that you have a full understanding of what this medicine is for and how to use it.  There are some reasons for not taking a medication; these are called contraindications, and for Penvir you should consider the following before taking Penvir:

• Have you ever had an unusual reaction or an allergy when taking Penvir?
• Are you pregnant or breastfeeding?
• Do you have any problems with your kidneys or your liver?
• Do you have a weakened immune system?

What medications interact with Penvir?

Some medicines interact with Penvir tablets 250mg and may affect the way it works, or are affected by Penvir or increase side effects; you should discuss possible interactions with your primary care physician.  These may include probenecid for gout, diuretics for fluid retention, raloxifene for osteoporosis.

If other medications may interact with Penvir, your doctor will discuss these with you. 

How should Penvir be taken and for how long?

You should take your Penvir tablets 250mg swallowed whole with a glass of water, with or without food, two to three times daily for five-seven days, depending on what you are being treated for and your doctor’s recommendation.  You should start your treatment as soon as possible after the first signs of symptoms and continue to take your Penvir tablets 250mg for as long as recommended by your doctor

Missed dose of Penvir

If you miss a dose of Penvir tablets 250mg take it as soon as you remember, unless it is time to take the next dose, then skip the missed dose.  Do not take a double dose.

How should Penvir be stored?

You should store your Penvir tablets 250mg below 25°C in a cool dry place.