Penicillin Group. Penicillin G, the most popularly used antibiotic because it is the cheapest, safest, and most effective antibacterial treatments available. Although penicillins are extremely safe, patients can occasionally develop an immune reaction to them and become allergic. In such cases the availability of alternative antibiotics is critical.
• Penicillin G and V remain the drugs of choice for treating many gram-positive bacterial infections. Penicillin G and V are used to treat infections caused by gram-positive Staphylococcus pyogenes (strep throat), and Streptococcus pneumoniae (respiratory tract infections). These are also used to treat the sexually transmitted diseases gonorrhea and syphilis. Penicillin V is similar in its activity to penicillin G, but because it is not destroyed by stomach acid it is a better drug for oral dose.
Methicillin was the first penicillin to have activity against the staphylococcus strains that were resistant to penicillin G.
• Ampicillin and amoxycillin are similar antibiotics with a broader spectrum of activity than earlier penicillins, it is active against common gram-negative bacteria as well as gram positive bacteria. But they are not active against penicillin G-resistant staphylococci. Both are effective on oral administration and are active against the gram-negative bacterium Escherichia coli (a common cause of urinary tract infections), Haemophilus influenzae (an important cause of ear infections and meningitis in infants), and Salmonella typhi (responsible for typhoid fever).
• Carbenicillin was the first penicillin synthesized to possess useful activity against Pseudomonas aeruginosa. This bacterium is normally only responsible for infections in hospitalized patients and had proved particularly difficult to treat.
Cephalosporin Group - injectable forms of this group are generally broad-spectrum, bactericidal agents that are restricted to hospital use for the treatment of serious infections.
Tetracycline Group - are broad-spectrum antibiotics that have been used to treat a wide range of infections, are orally active, and are bacteriostatic. It is used in the treatment of gonorrhea (caused by Neisseria gonorrhea) and urinary tract infections caused by Escherichia coli. Drugs belonging to this group can cause pigmentation of the teeth in childre
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. Around 300-500 people die each year from an allergy to a beta lactum antibiotic. 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.
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. Sometimes, chavulanic acid is added to a synthetic penicillin to extend the life of the drug. Here are 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.
Bacitracin is an antibiotic produced by a Bacillus species. It prevents the growth of the cell wall. Because of its high toxicity, it is not systemically used. It is used in topic antibiotics, and to sterilize the bowel before surgery, since it is not absorbed by the digestive tract.
Polymyxin is an antibiotic produced by Bacillus polymyxis. It works by inhibiting cell membrane growth. It is rather toxic to humans, so is therefore usually used only as a topical antibiotic. Occasionally, it is used to treat urinary tract infections, however it must be used under close hospital supervision, for it will easily damage the kidney and other organs.
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.
Chloramphenicol is produced by Streptomyces venezuelae. It works by inhibiting translation during protein synthesis. It is effective against both Gram-positive and Gram-negative bacteria. It is currently produced by chemical synthesis. Chloramphenicol causes aplastic anemia in a small percentage of patients, and ever since that was discovered, chloramphenicol has been used very little in non life-threatening situitions.
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
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.
Nalidixic acid is a synthetic chemotheraputic agent effective against Gram-negative bacteria. It binds to DNA gyrase enzyme (topoisomerase) and inhibits DNA duplication. It is a member of a group of compounds called the quinolones. It is mainly used in the treatment of urinary tract infections, and will kill several types of Gram-negative bacteria such as E. coli, Enterobacteriaceae aerogenes, K. pneumoniae, and Proteus species, which are common causes of urinary tract infections. It is not effective against Pseudomonas aeruginosa, and Gram-positive bacteria are usually resistant.
Rifamycins are produced by Streptomyces mediterranei. They inhibit transcription in eubacterial RNA polymerase. A synthetic derivative of rifamycin is:
• Rifampicin is active against Gram-positive and Gram-negative bacteria. It is often used against Mycobacterium tuberculosis. It has a greater effect on the bacteria that causes tuberculosis than most other antibiotics. It has replaced isoniazid as the front-line drug to treat tuberculosis, especially where isoniazid resistance is present. It is also used to meningitis, caused by Neisseria meningitidis. It can be taken orally.
Sulfonamides were introduced in 1935 by Domagk. He discovered that these chemicals could cure mice with beta-hemolytic Streptococci infections. Sulfonamides are derived from the compound sulfanilamide. They are effective against Streptococcus pneumoniae, beta-hemolytic streptococci, and E. coli. The sulfonamides are used in treatment for urinary tract infections caused by E. coli and in treatment of meningococcal meningitis. Some examples of sulfonamides are:
• Prontosil
• Gantrisin
• Trimethoprim
Isoniazid (INH) is primarily used in the treatment of tuberculosis. It works by inhibiting synthesis of mycolic acid. It is usually given together with rifampicin. It prevents the growth of bacteria resistant to rifampicin.
Paraaminosalicylic acid (PAS), is a chemotheraputic agent once used as the primary agent in tuberculosis treatment. Paraaminosalicylic acid is an anti-folate. It is used only as a secondary anti-tuberculosis agent, having been replaced by ethambutol.
Ethambutol, a chemotheraputic agent used in the treatment of tuberculosis, works by inhibiting the incorporation of mycolic acids into the mycobacterial cell wall.
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