All these four medications are available only through prescription. They help in prevention as well as treatment of the influenza disease. In prevention mode, the drugs are to be taken a minimum of two weeks before the onset of the flu outbreak or flu season in the community. In treatment mode, the drugs help in lowering the flu symptoms significantly and also the duration matters.

Flu shot or vaccine is the nest known preventive measure against influenza, but there are also some drugs which can do the same job at times. The first three drugs namely Tamiflu, Symmetrel and Flumadine can be used from the age of just one year, meaning that even children can take it.

Symmetrel and Flumadine were the two medicines initially approved by the US FDA (Food and Drug Administration). These drugs are capable are fighting against influenza A viruses alone but not influenza B viruses. These two drugs can stop the function of the M2 protein of the flu virus. The M2 protein is responsible for producing a channel on the outer membrane of the virus, to initiate the replication. Hence the flu viruses cannot replicate though it is able to enter the cell.

Tamilflu and Relenza were approved later in 1999 by the FDA. These were the first drugs which belonged to a new class called neuraminidase inhibitors. The outer membranes or surfaces of flu viruses are lined by neuraminidase (NA) proteins. It is an enzyme which helps in splitting the bonds which hold the newly formed viral particles outside the infected cell. After the breakage of this bond, the viral particles are free to move and infect any new cells nearer. Likewise, the infection spreads from one cell to another. Neuraminidase inhibitors hinder the activity of neuraminidase enzyme and do not permit the release of newly formed viral particles, thus stopping the infection to a single cell or so.

By such functions, the above drugs help in the treatment of flu. These medications are able to prevent flu by the following.
• Consumption of drugs 2 weeks earlier to the season
• In case of close contact with an infected member (unavoidable) since it is a member of the family.
• In case of close contact with a vaccinated person to provide better protection against flu.
• In case of flu epidemic, drug usage immediately after vaccination during the formation of antibodies provides better protection. Antibodies are proteins formed against any foreign body by the immune system for protection.
•  In case of flu epidemic, drug usage is recommended if the vaccine has not included the current prevailing viral strain.

But before the usage of any of these drugs, it is good to consult the doctor to choose the best medicine apt for you.

Tamiflu and Relenza
Tamilflu is prescribed for adults and infants who are elder than 1 year and Relenza is meant for adults as well as children elder than 7 years. These drugs are meant for people those affected with uncomplicated flu and have been experiencing flu for less than 2 days. These drugs help in the treatment for both type A and B influenza. 
 
Flumadine
Flumadine is prescribed especially for type A influenza. This drug has no effect on type B influenza infections.

Symmetrel
Symmetrel can be given to adults and children elder than 1 year for type A influenza treatment alone. This drug can be used for prevention purposes also. Though both Flumadine and Symmetrel are used in the treatment of type A influenza, Symmetrel has been found to have more side-effects comparatively. The most commonly caused side-effects are lightheadedness and sleeplessness.

Proper Dosages
Tamilflu is available in the pill form and can be taken twice in a day for 5 days in the case of adults. In the case of children, the dosage depends on the weight of the child. If the patient is unable to swallow the pill, Tamilflu can be taken in the form of a liquid suspension.
Symmetrel and Flumadine are also available in the pill form and taken orally. Relenza alone is available in the powder form and is taken by inhaling through a device called diskhaler. The suggested dosage is two inhalations twice, once in morning and once in night for a period of 5 days.
Precautions to be taken

There are some people who may be allergic to flu medications or some of its ingredients if not the whole drug. Such people are advised not to take them. Relenza is one such drug which is not prescribed for people affected with chronic respiratory diseases like asthma, COPD, etc. it has been found through studies that people with these diseases had wheezing as a side-effect after consuming Relenza. Hence if such an affected person is prescribed Relenza, the doctor must also prescribe a fast-acting bronchodilator which can be inhaled soon after the drug is taken in order to avoid wheezing. Tamilflu dosage must also be altered based on the variety of kidney disease that the patient has.

All these drugs are harmful during the periods of pregnancy and nursing and are not prescribed for routine use at such times. Research is still under process for the drug’s effect on the unborn child when taken by pregnant women. There are evidences for neuraminidase inhibitors interacting with other drugs. Hence it is essential to consult the healthcare provider before taking medication for flu treatment.

Viral Resistance to Drugs
Drug-resistant influenza viruses might occur in nearly one-third of the patients who are prescribed Symmetrel or Flumadine for flu treatment. There are studies confirming the resistance development for the drugs Relenza and Tamilflu. Hence the research on neuraminidase inhibitor-resistance is being carried out.

The first influenza virus was discovered in 1930s. Scientists have categorized those viruses from that time into three main types, as already mentioned, depending on the composition of proteins they possess.

Type A virus have been discovered in many animals like pigs, ducks, chickens, whales and humans. Type B is found mostly in humans alone and type C is found in pigs, dogs and humans. Type C is responsible only for mild infections unlike types A and B. Type C do not lead to epidemics.
Type A viruses can still be subdivided into subgroups depending on the two surface proteins, namely HA and NA. Research has subdivided into 16 HA types and 9 NA types of the influenza type A virus. The subtypes are based on a naming system including the place and year of discovery of the strain, type of HA, NA proteins and lab identification number.

An apt example is A/Hong Kong/156/97 (H5N1), where A represents the type A virus, Hong Kong is the place of discovery of the subtype, 156 is the lab identification number, 97 is the time of discovery, H5N1 represents the virus has 5 HA proteins and 1 NA protein. If the flu virus infects animals other than humans, it is represented by A/Chicken/Hong Kong/G9/97 (H9N2). Type B and C have no subdivisions.

The flu viruses are naturally found in wild ducks, shore birds, etc. Though the virus has been in such birds for several millions of years, it does not harm them. The flu virus can easily jump the species barrier and infect domesticated animals in an order like ducks, chickens, pigs, etc. Pigs are affected by both avian flu and human flu. Hence in a farm where these animals and birds live in close proximity, pigs do represent flu virus-mixing bowl. When a pig is affected by both the human and avian flu at the same time, the viruses can exchange genes. Such a virus can infect human from pigs.
Based on the range of bird-type flu surface proteins that get exchanged into the humans, the influenza disease may vary from mild to severe. In 1997, this step has been surpassed and the bird flu can affect humans directly without the pigs acting as bowls. Such an outbreak in 1997 was assumed to turn into a pandemic but luckily the virus was unable to pass between humans.

The flu symptoms that appear soon after infection are fever, dry coughs, sore throat, chills, runny/ stuffy nose, muscle aches, headache, and excessive fatigue. The fever starts to decline normally on the second day or sometimes the third day after the illness shows up the symptoms.

There is also something called stomach flu. In stomach flu, the influenza symptoms occur along with nausea, diarrhea and vomiting, mostly in children. In rare cases, gastrointestinal symptoms may occur. Stomach flu is not influenza. 

In adults, influenza is accompanied by some complications if bacterial infection occurs simultaneously. This can lead to pneumonia in persons with weak lungs. Yet the flu virus without the bacterial association can cause pneumonia. Unlike other diseases, these complications appear after the common symptoms of influenza subside and the infected person feels far better in health.

After a short period of improvement, symptoms like high fever, severe chest pain that can be felt in each breath, shaking chills and cough that forms thick, yellowish green mucus, etc may occur all of a sudden. Pneumonia can be a life-threatening disease at times. If any of the above symptoms exist, it is highly recommended to meet the healthcare specialist as soon as possible.

In children or young adults, the same complications can occur in addition to the risk of Reye’s syndrome. It is a condition affecting the nerves. It can develop during recovery from flu. It just starts with nausea and vomiting, but mental changes like confusion and delirium may progress. It can frequently occur in younger adults after the intake of aspirin for fever. This occurs rarely but it is recommended to consult a doctor before taking aspirin or similar products. It is good to rely on the doctor for any of the medications to be taken.

Children are more prone to flu complications especially when their immune system is weak. Very young children whose immune system has not yet developed fully and older people whose immune system is weak are unable to fight against influenza and its complications. Hence flu can affect them more easily than people with a good immune system. The other complications in children are croup, ear infections like otitis media, and convulsions due to fever. New born babies who are just out of ICU are more likely to develop flu complications.