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Antibiotics Types And Side Effects
What are Antibiotics? The word "antibiotics" comes from the Greek anti ("against") and bios ("life"). Antibiotics are drugs that either destroy bacteria or prevent their reproduction. Antibiotics that kill bacteria are called "bactericidal" and the ones that stop the growth of bacteria are called "bacteriostatic".
Since penicillin's introduction during the 1940s, scientists developed numerous other antibiotics. Today, over 100 different antibiotics are available. About 90% of antibiotics are made from living organisms such as bacteria, others are produced synthetically, either in whole or in part.
Antibiotics classification
Although there are several classification schemes for antibiotics, based on bacterial spectrum (broad, narrow) or route of administration (injectable, oral, topical), or type of activity (bactericidal, bacteriostatic), the most useful is based on chemical structure. Antibiotics within a structural class will generally have similar patterns of effectiveness, toxicity, and allergic potential.
Most commonly used types of antibiotics are: Penicillins, Fluoroquinolones, Cephalosporins, Macrolides, and Tetracyclines. While each class is composed of multiple drugs, each drug is unique in some way.
Penicillins
The penicillins are the oldest class of antibiotics. Penicillins have a common chemical structure which they share with the cephalopsorins. Penicillins are generally bactericidal, inhibiting formation of the cell wall.
There are four types of penicillins:
* The natural pencillins are based on the original penicillin-G structure. Penicillin-G types are effective against gram-positive strains of streptococci, staphylococci, and some gram-negative bacteria such as meningococcus.
*Penicillinase-resistant penicillins are active even in the presence of the bacterial enzyme that inactivates most natural penicillins.
*Extended spectrum penicillins which are effective against a wider range of bacteria.
*Aminopenicillins such as ampicillin and amoxicillin have an extended spectrum of action compared with the natural penicillins.
Penicillins side effects
Penicillins are among the least toxic drugs known. The most common side effect of penicillin is diarrhea. Nausea, vomiting, and upset stomach are also common. In rare cases penicillins can cause immediate and delayed allergic reactions - specifically, skin rashes, fever, and anaphylactic shock. Penicillins are classed as category B during pregnancy.
Cephalosporins
Cephalosporins have a mechanism of action identical to that of the penicillins. However, the basic chemical structure of the penicillins and cephalosporins differs in other respects, resulting in some difference in the spectrum of antibacterial activity. Like the penicillins, cephalosporins interfere with synthesis of the bacterial cell wall and so are bactericidal.
Cephalosporins are among the most diverse classes of antibiotics, they are grouped into "generations" by their antimicrobial properties. Each generation has a broader spectrum of activity than the one before.
The first generation cephalosporins include: cephalothin, cefazolin, cephapirin, cephradine, cephalexin, cefadroxil. Their spectrums of activity are quite similar. They possess generally excellent coverage against most gram-positive pathogens and variable to poor coverage against most gram negative pathogens.
The second generation cephalosporins include: cefaclor, cefamandole, cefonicid, ceforanide, cefuroxime. In addition to the gram-positive spectrum of the first generation cephalosporins, these agents have expanded gram-negative spectrum. Cefoxitin and cefotetan also have good activity against Bacteroides fragilis.
The third generation cephalosporins have much expanded gram-negative activity. However, some members of this group have decreased activity against gram-positive organisms. The third generation cephalosporins include: cefcapene, cefdaloxime, cefditoren, cefetamet, cefixime, cefmenoxime, cefodizime, cefoperazone, cefotaxime, cefpimizole, cefpodoxime, ceftibuten, ceftriaxone. They have the advantage of convenient dosing schedules, but they are expensive.
The fourth generation cephalosporins are extended-spectrum agents with similar activity against gram-positive organisms as first-generation cephalosporins. They also have a greater resistance to beta-lactamases (bacterial enzymes that may destroy antibiotic before it can do its work) than the third generation cephalosporins. Many fourth generation cephalosporins can cross blood brain barrier and are effective in meningitis. The fourth generation cephalosporins include: cefclidine, cefepime, cefluprenam, cefozopran, cefpirome, cefquinome.