ANTIBIOTIC CLASSIFICATION AND SIDE EFFECTS

 

Antibiotics classification

Although there are several classification schemes for antibiotics, based on bacterial spectrum (broad versus narrow) 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.

The main classes of antibiotics are:

• Beta-Lactams
  • Penicillins
  • Cephalosporins
• Macrolides
• Fluoroquinolones
• Tetracyclines
• Aminoglycosides

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.

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. Penicillins are used to treat skin infections, dental infections, ear infections, respiratory tract infections, urinary tract infections, gonorrhea.

There are four types of penicillins:

• 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 meningococcus.
• Penicillinase-resistant penicillins, notably methicillin and oxacillin, 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 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 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 includes:
  • cephalothin
  • cefazolin
  • cephapirin
  • cephradine
  • cephalexin
  • cefadroxil
• 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 includes:
  • cefaclor
  • cefamandole
  • cefonicid
  • ceforanide
  • cefuroxime
• 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 includes:
  • cefcapene
  • cefdaloxime
  • cefditoren
  • cefetamet
  • cefixime
  • cefmenoxime
  • cefodizime
  • cefoperazone
  • cefotaxime
  • cefpimizole
  • cefpodoxime
  • ceftibuten
  • ceftriaxone
• 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 includes:
  • cefclidine
  • cefepime
  • cefluprenam
  • cefozopran
  • cefpirome
  • cefquinome

Cephalosporins side effects

Cephalosporins generally cause few side effects. Common side effects associated these drugs include: diarrhoea, nausea, mild stomach cramps or upset. Approximately 5–10% of patients with allergic hypersensitivity to penicillins will also have cross-reactivity with cephalosporins. Thus, cephalosporin antibiotics are contraindicated in people with a history of allergic reactions (urticaria, anaphylaxis, interstitial nephritis, etc) to penicillins or cephalosporins. Cephalosporin antibiotics are classed as pregnancy category B.

Fluroquinolones

Fluoroquinolones (fluoridated quinolones) are the newest class of antibiotics. Their generic name often contains the root "floxacin". They are synthetic antibiotics, and not derived from bacteria. Fluoroquinolones belong to the family of antibiotics called quinolones. The older quinolones are not well absorbed and are used to treat mostly urinary tract infections. The newer fluroquinolones are broad-spectrum bacteriocidal drugs that are chemically unrelated to the penicillins or the cephaloprosins. Because of their excellent absorption fluroquinolones can be administered not only by intravenous but orally as well.

Fluoroquinolones are used to treat most common urinary tract infections, skin infections, and respiratory infections (such as sinusitis, pneumonia, bronchitis).

Fluoroquinolones inhibit bacteria by interfering with their ability to make DNA. This activity makes it difficult for bacteria to multiply. This effect is bacteriocidal.

Fluoroquinolone grope includes:

• ciprofloxacin
• levofloxacin
• lomefloxacin
• norfloxacin
• sparfloxacin
• clinafloxacin
• gatifloxacin
• ofloxacin
• trovafloxacin

Fluoroquinolones side effects

Fluoroquinolones are well tolerated and relatively safe. The most common side effects include nausea, vomiting, diarrhea, abdominal pain. Other more serious but less common side effects are central nervous system effects (headache, confusion and dizziness), phototoxicity (more common with lomefloxacin and sparfloxacin). All drugs in this class have been associated with convulsions. Fluoroquinolones are classed as pregnancy category C.

Tetracyclines

Tetracyclines got their name because they share a chemical structure that has four rings. They are derived from a species of Streptomyces bacteria. Tetracycline antibiotics are broad-spectrum bacteriostatic agents, that inhibit bacterial protein synthesis. Tetracyclines may be effective against a wide variety of microorganisms, including rickettsia and amebic parasites.

Tetracyclines are used in the treatment of infections of the respiratory tract, sinuses, middle ear, urinary tract, skin, intestines. Tetracyclines also are used to treat Gonorrhoea, Rocky Mountain spotted fever, Lyme Disease, typhus. Their most common current use is in the treatment of moderately severe acne and rosacea.

Tetracycline antibiotics are:

• tetracycline
• doxycycline
• minocycline
• oxytetracycline

Tetracyclines side effects

Drugs in the tetracycline class become toxic over time. Expired drugs can cause a dangerous syndrome resulting in damage to the kidneys.

Common side effects associated with tetracyclines include cramps or burning of the stomach, diarrhea, sore mouth or tongue. Tetracyclines can cause skin photosensitivity, which increases the risk of sunburn under exposure to UV light. This may be of particular importance for those intending to take on holidays long-term doxycyline as a malaria prophylaxis. Rarely, tetracyclines may cause allergic reactions. Very rarely severe headache and vision problems may be signs of dangerous secondary intracranial hypertension.

Tetracycline antibiotics should not be used in children under the age of 8, and specifically during periods of tooth development. Tetracyclines are classed as pregnancy category D. Use during pregnancy may cause alterations in bone development.

Macrolides

The macrolide antibiotics are derived from Streptomyces bacteria, and got their name because they all have a macrocyclic lactone chemical structure. The macrolides are bacteriostatic, binding with bacterial ribosomes to inhibit protein synthesis. Erythromycin, the prototype of this class, has a spectrum and use similar to penicillin. Newer members of the group, azithromycin and clarithyromycin, are particularly useful for their high level of lung penetration. Macrolide antibiotics are used to treat respiratory tract infections (such as pharyngitis, sinusitis, and bronchitis), genital, gastrointestinal tract, and skin infections.

Macrolide antibiotics are:

• erythromycin
• clarithromycin
• azithromycin
• dirithromycin
• roxithromycin
• troleandomycin

Macrolides side effects

Side effects associated with macrolides include nausea, vomiting, and diarrhea; infrequently, there may be temporary auditory impairment. Azithromycin has been rarely associated with allergic reactions, including angioedema, anaphylaxis, and dermatologic reactions. Oral erythromycin may be highly irritating to the stomach and when given by injection may cause severe phlebitis. Macrolide antibiotics should be used with caution in patients with liver dysfunction. Pregnancy category B: Azithromycin, erythromycin. Pregnancy category C: Clarithromycin, dirithromycin, troleandomycin.

Aminoglycosides

Aminoglycosides are derived from various species of Streptomyces.

In 1943, Selman Waksman, together with his co-workers, discovered that a fungus Streptomyces griseus produced an antibiotic substance which they named "streptomycin." Selman Waksman was awarded the Nobel Prize in Physiology or Medicine in 1952 for his discovery of streptomycin.

Aminoglycoside antibiotics are used to treat infections caused by gram-negative bacteria. Aminoglycosides may be used along with penicillins or cephalosporins to give a two-pronged attack on the bacteria. Aminoglycosides work quite well, but bacteria can become resistant to them. Since aminoglycosides are broken down easily in the stomach, they can't be given by mouth and must be injected. Generally, aminoglycosides are given for short time periods.

The aminoglycosides are drugs which stop bacteria from making proteins. This effect is bacteriocidal.

Aminoglycoside grope includes:

• amikacin
• gentamicin
• kanamycin
• neomycin
• streptomycin
• tobramycin

Aminoglycosides side effects

The major irreversible toxicity of aminoglycosides is ototoxicity, that is damage to the ear and hearing. Among them, streptomycin and gentamicin are primarily vestibulotoxic, whereas amikacin, neomycin, dihydrosterptomycin, and kanamicin are primarily cochleotoxic.

Another important concern with aminoglycoside antibiotics is nephrotoxicity, that is kidney damage.