Oral Antiviral Drugs

Antiviral drugs are a class of medication used specifically for treating viral infections such as influenza, herpes virus infections, viral hepatitis and human immunodeficiency virus (HIV) (to be described under a separate article). Antibiotics are not useful for treating viral infections unlike specific antivirals which are targeted for specific viruses. Antiviral drugs do not destroy their target pathogen, instead, they inhibit their replication by inactivating the enzymes.

They help to stop infections from getting worse and reduce the chance of the return of an infection. They are sometimes used to prevent people whom the immune systems are not working properly from infections. However, vaccination might be a better and safer option to prevent some of the viral infections, like seasonal influenza and hepatitis. The following are typical examples of viral infections:-

Influenza is a viral infection that attacks respiratory system including nose, throat and lungs. Influenza and its complications can be serious. People at higher risk of developing influenza complications include young children, elderly, pregnant women, people with impaired immune system or chronic illnesses.

Herpes virus infections are commonly caused by herpes simplex virus and varicella–zoster virus, which are well known for causing cold sores or genital herpes, and chickenpox or shingles respectively.

The most common types of viral hepatitis are hepatitis A, B and C, which are caused by hepatitis A, B and C virus respectively. Hepatitis A is transmitted by contaminated food and water, whereas hepatitis B and C are transmitted by blood or body fluids.

Viral infections can cause illnesses vary from minor ailments like common cold to severe diseases like acquired immunodeficiency syndrome (AIDS). Most of the time, people are diagnosed viral infections with no specific information about the type of causative viruses. Usually, the symptoms are relatively mild, with recovery without any treatment, especially in persons with normal immunity. Examples are common cold, and viral gastroenteritis caused by Rotavirus infection.

There are different types of oral antivirals drugs for specific viral infections, particularly for the immunocompromised. These are all prescription-only medicines and should be administered strictly under doctor’s instruction and recommendation.

Oseltamivir (neuraminidase inhibitor) reduces replication of influenza A and B viruses by inhibiting viral neuraminidase. It is indicated for use within 48 hours of the first symptoms of influenza. In otherwise healthy individuals, the duration of symptoms may be reduced by 1–1.5 days.

Oseltamivir is indicated for post-exposure prophylaxis of influenza when influenza is circulating in the community. It is also indicated for use in exceptional circumstances (e.g. when vaccination does not cover the infective strain) to prevent influenza in an epidemic.

Severe infection, neonatal herpes infection or infection in immunocompromised individuals requires treatment with a systemic antiviral drug. Primary or recurrent genital herpes simplex infection is treated with an oral antiviral drug. Treatment of herpes simplex infection should start as early as possible and usually within the first few days of the appearance of the infection.

Chickenpox in otherwise healthy children between 1 month and 12 years is usually mild and antiviral treatment is not usually required. However, it is more severe in adolescents and adults than in children; antiviral treatment started within 24 hours of the onset of rash may reduce the duration and severity of symptoms in otherwise healthy adults and adolescents. Antiviral treatment is generally recommended in immunocompromised patients and those at special risks (e.g. because of severe cardiovascular or respiratory disease or chronic skin disorder).

In herpes zoster (shingles) systemic antiviral treatment can reduce the severity and duration of pain, complications, and viral shedding. Treatment with the antiviral should be started within 72 hours of the onset of rash and is usually continued for 7 – 10 days.

Examples used to treat the above viral infections include aciclovir and famciclovir (nucleoside analogues of guanine).

Treatment for viral hepatitis should be initiated by a specialist. The management of uncomplicated acute viral hepatitis is largely symptomatic. Hepatitis B and hepatitis C viruses are major causes of chronic hepatitis.

For chronic hepatitis B, the initial treatment options include entecavir (nucleoside reverse transcriptase inhibitor (NRTI)) or tenofovir (nucleotide reverse transcriptase inhibitor (NtRTI)). Other drugs indicated for the treatment of chronic hepatitis B include adefovir (NtRTI), lamivudine (NRTI), or telbivudine, (nucleoside analogue of thymidine with specific activity against the hepatitis B virus).

For the treatment of chronic hepatitis C, usually a combination of drugs are used. A combination of ribavirin (nucleoside analogue) and peginterferon alfa (immunomodulating drug available in injectable form only), or together with either boceprevir or telaprevir (protease inhibitor, which inhibits the replication of hepatitis C virus genotype 1, but are less effective against other genotypes of the virus).

Common side effects and Precautions

• Follow doctor’s advice on the use of your medicine.  Do not stop or change the regimen by yourself.
  
  
• Build up good body immunity to prevent viral infections by having a balanced diet, regular exercise and adequate rest, reducing stress and avoiding smoking.
  
  
• As some viral infections are contagious, avoid contact with persons with weakened immunity e.g. infants, young children, the elderly and pregnant women when you are ill.
  
  

• Always seek medical advice on the best treatment option.  Your doctor will prescribe the most appropriate drugs for you after considering your condition and response to the drugs.
  
  
• You may be prescribed more than one medication for treating the infection, make sure that you are clear about the purpose and the usage of each preparation and consult your doctor if you have any doubts.
  
  
• Inform your doctor if you are suffering from chronic diseases or on any medications, as these may warrant special precautions when deciding treatment plan.
  
  
• Seek medical advice as soon as possible if you experience any symptoms or side effects suspected to be related to antiviral drugs.  Your doctor may review the type and dosage of your medications.
  
  
• Have regular medical follow-ups as advised by your doctor if you need to use antiviral drugs on a long-term basis.
  
  

Oral antiviral drugs should be kept in a cool and dry place. Unless specified on the label, medicines should not be stored in refrigerators. Furthermore, drugs should be kept properly in places where unreachable of children to prevent accidental ingestion.