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although there are several classification schemes for antibiotics, based on bacterial spectrum (broad versus narrow) or route of administration (injectable versus oral versus topical), or type of activity (bactericidal vs. 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: aminoglycosides, penicillins, fluoroquinolones, cephalosporins, macrolides, and tetracyclines. while each class is composed of multiple drugs, each drug is unique in some way.
the penicillins are the oldest class of antibiotics. penicillins have a common chemical structure which they share with the cephalosporins. penicillins are generally bactericidal, inhibiting formation of the cell wall. penicillins are used to treat skin infections, dental infections, ear infections, respiratory tract infections, urinary tract infections, gonorrhea.
there are four types of penicillins:
penicillins side effects
- the natural penicillins 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 meningococcal.
- penicillinase-resistant penicillins, notably methicillin and amoxicillin, are active even in the presence of the bacterial enzyme that inactivates most natural penicillins.
- aminopenicillins such as ampicillin and amoxicillin have an extended spectrum of action compared with the natural penicillins. extended spectrum penicillins are effective against a wider range of bacteria.
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 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 have a beta-lactam ring structure that interferes with synthesis of the bacterial cell wall and so are bactericidal. cephalosporins are derived from cephalosporin c which is produced from cephalosporium acremonium.
cephalosporins are used to treat pneumonia, strep throat, staph infections, tonsillitis, bronchitis, otitis media, various types of skin infections, gonorrhea, urinary tract infections cephalosporin antibiotics are also commonly used for surgical prophylaxis. cephalexin can also be used to treat bone infections.
cephalosporins are among the most diverse classes of antibiotics, they are grouped into "generations" by their antimicrobial properties. each newer generation has a broader spectrum of activity than the one before.
- the first generation cephalosporins include: 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 first generation cephalosporins include:
- the second generation cephalosporins. 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. enough variation exists between the second generation cephalosporins in regard to their spectrums of activity against most species of gram negative bacteria, that susceptibility testing is generally required to determine sensitivity. the second generation cephalosporins include:
- the third generation cephalosporins have much expanded gram negative activity. however, some members of this group have decreased activity against gram-positive organisms. they have the advantage of convenient dosing schedules, but they are expensive. the third generation cephalosporins include:
- 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 than the third generation cephalosporins. many fourth generation cephalosporins can cross blood brain barrier and are effective in meningitis. the fourth generation cephalosporins include:
the article continues to explain the how and why antibiotics are choosen. it should help you.