Antibiotics / Antibacterials

Antibiotics are life-saving medicines that can stop some infections and save lives. Antibiotic drugs help your body fight bacteria either by directly killing the offending bugs or by weakening them so that your own immune system can fight and kill them more easily. However, Antibiotics o nly work against infections caused by germs. They do not work against infections caused by viruses. Viruses cause colds, the flu, and most coughs and sore throats.

Antibiotics kill or inhibit bacterial growth in these ways.

• Interference with Cell Wall Synthesis : The first antibiotic, Penicillin, and many others work by preventing the germs from repairing their cell walls. The cell walls weaken and eventually burst, leading to the cell's death.

• Disruption of Cellular Processes : Erythromycin and Tetracycline prevent cells from making proteins or other essential components. This prevents the cells from growing and multiplying, making it easier for the body's immune system to destroy them.

• Blocking of Metabolism : Antibiotics known as polymyxins prevent germs from taking in nutrients and expelling their own metabolic waste products. This leads to a combination of starving the germ and accumulating toxins that kill it.

• Blocking DNA Synthesis : Ciprofloxacin, Levofloxacin, and other antibiotics in this class prevent the germs from multiplying by interfering with their ability to make DNA.

• Competition with Nutrients : Some germs require the vitamin-like substance para-aminobenzoic acid (PABA) to survive. Sulfa antibiotics are chemically very close in structure to PABA. The germs that require PABA are fooled into picking up the antibiotic rather than the PABA. This inhibits their growth, making it easier for the body's immune system to kill them.

The Problem of Antibiotic Resistance

Antibiotics can do more harm than good if they are not used the right way. You can protect yourself and your family by knowing when you should use antibiotics and when you should not.

When germs are exposed to the same antibiotic again and again, the antibiotic stops working. Being exposed to the same antibiotic for a long time can make some germs change. These changes make the germs so strong that they can fight back against antibiotics. Then these germs are said to be "resistant" to this antibiotic. Resistant germs grow faster when antibiotics are used too often or are not used the right way.

Bacteria become resistant by changes in the bacteria's genes by several different ways:

• Bacterial genes mutate : Just like the genes of larger organisms mutate, bacterial genese mutate; some of these changes happen because of chemical or radiation exposure and some just happen randomly. If bacteria with a changed gene is less susceptible to an antibiotic, and that antibiotic is around, the less susceptible (and more resistant) version of the bacteria is more likely to survive the antibiotic and continue to multiply.
  
  This is particularly likely to happen if the amount of antibiotic around isn't quite enough to kill all of the bacteria quickly -- as can happen if you don't take enough of the antibiotic to keep its level in your body high, or if you stop taking the antibiotic too early. This is why when you are prescribed an antibiotic you must take it exactly as prescribed, and for as long as it was prescribed. You may feel better after a short time of starting the course, but you may still have some bacteria left in you and those bacteria left include the ones that are partly resistant to the antibiotic already and likely to become more resistant.
  
  Possible cultivation of Bacterial resistance is also why we shouldn't take an antibiotic for an illness like a cold that isn't likely to be bacterial: the antibiotic will kill off the susceptible bacteria, leaving bacteria that are resistant to that antibiotic.

• Bacterial Gene Trading : Although there are many different species of bacteria, some bacteria can "trade" genes with other bacteria. If you have a relatively harmless bacteria in you, e.g. in your mouth or your intestines, and you've used, overused or misused antibiotics some of those harmless bacteria will become resistant to the antibiotics you've taken. They can then pass on the resistance genes they have developed to other harmful bacteria.

• Virual-induced Gene Replication : There are viruses around that attack bacteria rather than plants, animals, or people. Most of these viruses just kill the bacteria, but sometimes the viruses can copy genes from one kind of bacteria to another. In this process, the virus can end up copying the the antibiotic resistance genes to other bacteria.

As we have seen Antibiotic Resistance is a major problem today in the worldwide fight against infection.

Basic Guidelines in determining need for Antibiotics

These are some basic guidelines to determine if you need Antibiotics:

• Colds and flu are caused by viruses. They cannot be cured with antibiotics.

• Cough and bronchitis are almost always caused by viruses. But if these problems do not go away, germs may be the cause.

• A sore throat is usually caused by a virus and cannot be cured with an antibiotic. But strep throat is caused by germs. Your doctor will do a lab test before prescribing an antibiotic for strep throat.

• Ear infections can be caused by viruses or germs. Antibiotics sometimes are used for ear infections, but they are not always needed since they do not work for ear infections caused by viruses.

• Sinus infections can be caused by viruses or germs. Antibiotics sometimes are used to treat sinus infections. But a runny nosewith yellow or green mucus does not always mean you need to take an antibiotic.

Antiviral Agents

Antivirals are used to treat infections caused by viruses. Unlike antibacterial drugs, which may cover a wide range of pathogens, antiviral agents tend to be narrow in spectrum, and have limited efficacy. As a class, the antivirals are not curative, and must be used either prophylactically or early in the development of an infection. Their mechanism of action is typically to inactivate the enzymes needed for viral replication. This will reduce the rate of viral growth, but will not inactive the virus already present.

Exclusive of the antiretroviral agents used in HIV (AIDS) therapy, there are currently only 11 antiviral drugs available, covering four types of virus. A category of antiviral drugs is known as the antiretroviral drugs. These drugs target those viruses of clinical significance called retroviruses that use the mechanism of reverse transcription to manufacture the genetic material needed for their replication. The prime example of a retrovirus is the Human immunodeficiency virus (HIV), which is the viral agent of acquired immunodeficiency syndrome (AIDS). The development of antiviral drugs has been stimulated by the efforts to fight HIV. Some anti-HIV drugs have also shown promise against Hepatitis B virus, Herpes Simplex virus, and Varicella-Zoster virus.

The recent spread of highly pathogenic strains of avian influenza has highlighted the threat posed by pandemic influenza. In the early phases of a pandemic, the only treatment available would be neuraminidase inhibitors, which many countries are considering stockpiling for pandemic use. A number of intervention strategies can reduce the impact of influenza pandemics. During interpandemic years, influenza vaccination is used to reduce deaths and disease. However, vaccine is unlikely to be available in time or in sufficient quantities for use during a pandemic and other, nontherapeutic, disease control options will have to be used.

Two groups of antiviral drugs are available for the treatment and prophylaxis of influenza. These are the adamantanes (amantadine and rimantadine) and the neuraminidase inhibitors (oseltamivir and zanamivir). The adamantanes may be effective against pandemic strains, but concern exists about adverse reactions and the development of antiviral resistance.

Advances in Antiviral Drug Therapy during the past 20 years have led to increased understanding of the pathogenicity of viruses. As a result, potential pharmacologic agents have been identified with the ability to stop viral propagation by interfering with any one of a number of necessary steps for a virus to enter and replicate itself within a host cell. The agents include drugs that inhibit attachment, penetration and uncoating of certain viruses, as well as compounds that block the viral DNA replicative process. The challenge has been to identify those agents that affect viral DNA preferentially over host cell DNA, producing effective toxicity for the virus but minimal toxicity for the host cell. This article discusses the most frequently used antiviral chemotherapy.

Antiviral agents usually work in one of the following ways:

• Antiviral drugs can replace the nucleoside thymidine in the virus cell, and its incorporation produces a nonfunctional DNA. However, the same thing happens to the DNA of the host cells. So, this class of antiviral drugs is also an anti-host drug. Blockage of the viral replicative pathway by mimicking nucleosides can be successful, but because the virus utilizes the host's genetic machinery, stopping the viral replication usually affects the host cell adversely.

• Antiviral drugs block a viral enzyme whose activity is crucial for replication of the viral genetic material. This approach has been successfully exploited by the drug Acyclovir. The drug is converted in the host cell to a compound that can out compete another compound for the binding of the viral enzyme, DNA polymerase, which is responsible for building DNA. The incorporation of the Acyclovir derivative exclusively into the viral DNA stops the formation of the DNA. Acyclovir has shown considerable success against herpes simplex viruses and Epstein-Barr virus. Another drug that acts in a similar fashion is Famiciclovir.

• Antiviral drugs can be directed at the "translation process", whereby the information from the viral genome that has been made into a template is read to produce the protein product. Antiviral drugs of this class can block this "translation process" of viruses. For example, the drug ribavirin inhibits the formation of messenger ribonucleic acid.

• Antiviral agents can be directed at earlier steps in the viral replication pathway. Amantadine and rimantadine block the influenza A virus from penetrating into the host cell and releasing the nuclear material.

• Antiviral therapy also includes molecular approaches. Oligonucleotides are sequences of nucleotides that are specifically synthesized to be complimentary with a target sequence of viral ribonucleic acid. By binding to the viral RNA, the Oligonucleotide blocks the RNA from being used as a template to manufacture protein.