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Antibiotics


Antibiotics a substance produced by bacteria that destroys microorganisms or inhibits their growth and reproduction, although at present many antibiotics are chemically synthesized. Antibiotics are extensively used to treat infectious diseases of man and other animals. In 1928 the British scientist Sir Alexander Fleming discovered a substance produced by a mould which had the ability to inhibit growth of bacteria in culture media. The substance was given the name antibiotic. In later years the substance was purified and tested as to its potential for therapeutic use in the treatment of diseases caused by microbes. It turned out that the substance could cure many human infectious diseases without any harmful side effects to the patient. This rapidly led to widespread therapeutic use of the substance to which the name penicillin was given, since the mould that produced it was identified as the fungus Penicillium notatum. By 1940 the efficacy of penicillin in the treatment of infectious diseases was so well founded that it stimulated scientists to search for new substances with similar properties.

The number of antibiotic substances that has been discovered so far exceeds 10,000 and the inventory is not yet complete as new substances are added to the list every year. The term antibiotics usually refers to substances of microbial origin that act against bacterial pathogens. Certain drugs have an antibiotic-like action, but their target organisms are not bacteria. For example, agents acting against viruses are antiviral drugs, those acting against protozoan parasites, such as malarial parasites, are anti-malarial drugs, those against fungal pathogens, anti-fungal drugs, etc. These substances also exert selective toxicity like the antibiotics, but are not classified as antibiotics, although they are often termed as such.

Antibiotics are secondary metabolites (metabolites not essential for growth and reproduction of the producing organisms) whose production is restricted to limited groups of microorganisms. The most prolific producers of antibiotic substances are the soil bacteria called actinobacteria that are quite harmless to humans or other animals. This group of mycelial bacteria produces over three-quarters of the known antibiotics, although unicellular bacteria and imperfect fungi also produce quite a large number of antibiotics. Since World War II, the use of antibiotics has been increasing steadily with consequent saving of millions of lives all over the world. Although the number of antibiotic substances discovered to date is large, most of those are toxic to man and animals, and thus have no therapeutic use. Only about 160 antibiotics are currently in clinical use for treatment of human and animal diseases. These include antibiotics naturally produced by bacteria, their derivatives produced by chemical modification in order to enhance efficacy and circumvent the problem of antibiotic resistance which most bacteria develop as a result of prolonged use of antibiotics, and a small number of synthetic antibiotics. Antibiotics are mainly classified on the basis of their mode of action and their chemical structure.

All antibiotics that are in clinical use in the industrialised world are found in Bangladesh. Government policy in general is liberal with antibiotic import, admittedly because the need is great due to a high prevalence of infectious diseases and heavy germ load in the environment. The bulk of the antibiotics used in Bangladesh is for humans; farm use of antibiotics in poultry and livestock sectors is still marginal in this country. All antibiotics used in Bangladesh are imported from foreign pharmaceutical companies. The relatively expensive brands that are not used extensively are imported in finished marketable form, but the commonly used antibiotics are imported in bulk. The local pharmaceutical companies of which there are about half a dozen large and over 50 or so smaller units, are all packaging units. There are some pharmaceutical companies registered as such but their product range is narrow and their production volume and market share insignificant.

No industrial unit has yet undertaken antibiotic production locally. One or two companies have, however, undertaken antibiotic raw materials production in bulk. This is essentially restricted to the penicillin group of antibiotics. Ampicillin and amoxycillin are among the commonest antibiotics prescribed in the country. There is no research and development (R&D) activity in the pharmaceutical sector with respect to antibiotic production locally, not to speak of development of new antibiotics which, of course, is costly and beyond our technical expertise and financial means at the present time. The reason for low research and development (R&D) interest in the pharmaceutical sector is said to be the lack of incentive and the fact that profit earning from packaging and marketing antibiotics is sufficiently rewarding for most pharmaceutical companies. This effectively subdues any venture initiatives towards local production since the risk involved outweighs potential gains in the short term. However, with expanding globalisation the issues of local production and investments in R&D activity will assume greater importance.

Rational use of antibiotics is a serious issue in the context of Bangladesh. Bacteria are so well armoured that frequently they develop an array of biochemical mechanisms by which they can resist the antibiotic. Thus, the greater an antibiotic is in use the faster will be the development of resistance. With its 160 million people and a very heavy infectious disease load, in Bangladesh huge quantities of antibiotics are used annually. But a very large portion of this is used unfortunately under conditions of inadequate or no medical supervision and in most cases without prior tests on identification of the disease-causing organism and determination of its sensitivity to the antibiotic prescribed. The sale of antibiotics without proper medical prescription or on a quack 'prescription' or simply on verbal demand of the buyer is common both in cities and rural areas. Even in those cases where a qualified doctor prescribes an antibiotic, patient compliance regarding using the full course of the drug is not always satisfactory largely due to ignorance. All of these contribute to rapid emergence of resistant types of bacteria soon after a new antibiotic is introduced. This is happening even with the newer types of antibiotics against which laboratory studies indicate that there should not be rapid development of resistance. [Zia Uddin Ahmed]

See also drug, health and health sciences.