Dr. Saba Abdi1

Selective toxicity with minimal side effects to host

Easy to tolerate without a complex drug regimen

Bactericidal rather than bacteriostatic Narrow spectrum Low cost Stable(shelf life) Adequate bioavailability

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Antibiotics can be :• Antibacterial• Antiviral• Antifungal• Antiprotozoal• Cancerostatic• Coccidiostatic• Antihelmintic• Insecticidal• Herbicidal• Immunosuppressive• Diabetogenic

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• Beta lactum antibiotics are chemicals that contain the 4-membered beta lactum ring. They are produced by the fungus molds Penicillium and Cephalosporium. These antibiotics inhibit the last step in the bacterium's cell wall synthesis. Beta lactum antibiotics are useful against Gram-positive bacteria.

There are several kinds of beta lactum antibiotic: • Natural Penicillins are produced by fermentation

of the fungus Penicillium notatum chrysogenum. They include Pencillin G and Penicillin V. They will kill streptococcus, gonococcus and staphylococcus. They are usually not effective against Gram-negative rod-shaped bacteria.

• Cephalolsporins are similar to penicillins and are made from a species of Cephalosporium. They are used as penicillin substitutes, and in surgical prophylaxis.

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• Semisynthetic penicillins were first used in 1959. A mold produces the main part of the molecule, which is then altered chemically. These antibiotics are usually constructed to have certain advantages over natural penicillins.

Some types of semisynthetic penicillin:• Amoxycillin and Ampicillin are useful not only

on Gram-positive bacteria, but also on some Gram-negative bacteria.

• Clavamox, also called augmentin, is prepared by adding chavulanic acid to amoxycillin. Clavulanic acid is made from Streptomyces clavuligerus.

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Aminoglycosides are products of Spectromyces griseus. They are protein synthesis inhibitors binding to bacterial

ribosomes to prevent the initiation of protein synthesis. They can be used against a wide variety of both Gram-positive

and Gram-negative bacteria. Aminoglycoside usage has been limited because prolonged use

has been found to cause kidney damage and injury to the auditory nerves, leading to deafness.

Some examples of Aminoglycosides are: Streptomycin has its primary use for treating tuberculosis patients.

Gentamicin is used against many strains of Grma-positive and Gram-negative bacteria, including Pseudomonas aeruginosa

Kanamycin is a complex of three different antibiotics. It is effective against many gram-positive bacteria, including penicillin-resistant staphlococci, even at low concentrations.

Tombramycin, along with gentamicin, are the principal antibiotics used for treatments against Pseudomonas infections.

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Tetracyclines are a family of eight antibiotics, all products of Sptromyces. Some of these can now be produced synthetically.

Tetracyclines block protein synthesis on isolated ribosomes. It concentrates in certain types of ribosomes possesed only by bacteria, so it is not toxic to the animal. Because of their extremely low toxicity, they were overused in the medical community, and now there is widespread resistance to tetracyclines. However, they are still useful in treatment of some diseases, such as Lyme disease.

Some examples of tetracyclines are: Tetracycline Chlortetracycline Doxycycline is a semisynthetic tetracycline

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• Macrolides are produced by Streptomyces erythreus.

• Their chemical structures contain large lactone rings linked through glycoside bonds with amino sugars.

• Macrolides are inhibitors of protein synthesis. They are effective against Gram-positive bacteria and most Gram-negative bacteria, Neissera, Legionella, and Haemophilus, but not Enterobacteriaceae.

• The most important macrolides are: Erythromycin Oleandomycin

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Polyenes Variotin Griseofulvin

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Actinomycin Mitocin C Daunomycin Adriamycin Carminomycin

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Antibiotic Disease

Fusaric acid Parkinson’s disease

D-penicillamine Rheumatoid artheritis, multiple sclerosis, chronic active hepatitis, pulmonary fibrosis and heavy metal poisoning

Candicidin Hypercholesterolaemia

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Indirect effect: Alteration of ecological balance of the normal microflora or induction of allergic or hypersensitivity reaction.

Direct effects(toxicity): ototoxicity, neuromuscular blockade, neurological toxicity, nephrotoxicity , haematological toxicity, hepatotoxicity , gastrointestinal toxicity, cutaneous toxicity.

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• Used to treat infections, to increase growth and to improve feed utilization.

• Examples:1.Penicilline and streptomycin are used to

prevent infection during artificial insemination of cattle.

2.Monensin is added to cattle feed to cause growth increase and improve feed utilization.

3.Tetracycline is added to fish feed to prevent bacterial infection.

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• Antibiotics are used as pesticides, herbicides, growth regulators and for short term conservation of food.

• Examples:1.Thuringin- it is a nucleoside exotoxin is an

insecticidal antibiotic2.Polunactin is used as an acaricide

(pesticide).3.Herbimycin is used as a herbicide

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