Pharmacology Made Simple : Antibiotics : Tetracyclines

Pharmacology Made Simple : Antibiotics : Tetracyclines

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Tertracycline:

Tetracycline is in the tetracyclines family of medications. 

It works by blocking the ability of bacteria to make proteins.

Tetracycline was originally made from bacteria of the Streptomyces type.

Mechanism of action:

Tetracycline inhibits protein synthesis by blocking the attachment of charged aminoacyl-tRNA to the A site on the ribosome. Tetracycline binds to the 30S subunit of microbial ribosomes. 

Thus, it prevents introduction of new amino acids to the nascent peptide chain.

The action is usually inhibitory and reversible upon withdrawal of the drug. Mammalian cells are less vulnerable to the effect of tetracyclines, despite the fact that tetracycline binds to the small ribosomal subunit of both prokaryotes and eukaryotes (30S and 40S, respectively). 

This is because bacteria actively pump tetracycline into their cytoplasm, even against a concentration gradient, whereas mammalian cells do not. This accounts for the relatively small off-site effect of tetracycline on human cells.

Clinical Uses :

Tetracycline is an antibiotic used to treat a number of infections.

This includes acne, cholera, brucellosis, plague, malaria, and syphilis.

It is taken by mouth.

Side Effects :

Common side effects include vomiting, diarrhea, rash, and loss of appetite.

Other side effects include poor tooth development if used by children less than eight years of age,

kidney problems, and sunburning easily.

Use during pregnancy may harm the baby.

Medical uses:

It is first-line therapy for Rocky Mountain spotted fever (Rickettsia),

Lyme disease (B. burgdorferi),

Q fever (Coxiella), psittacosis, and

Mycoplasma pneumoniae and to eradicate nasal carriage of meningococci.

Tetracycline tablets were used in the plague outbreak in India in 1994.

Spectrum of bacterial susceptibility

Tetracyclines have a broad spectrum of antibiotic action.

Originally, they possessed some level of bacteriostatic activity against almost all medically relevant aerobic and anaerobic bacterial genera, both Gram-positive and Gram-negative, with a few exceptions, such as Pseudomonas aeruginosa and Proteus spp., which display intrinsic resistance.

However, acquired (as opposed to inherent) resistance has proliferated in many pathogenic organisms and greatly eroded the formerly vast versatility of this group of antibiotics.

Resistance amongst Staphylococcus spp., Streptococcus spp., Neisseria gonorrhoeae, anaerobes, members of the Enterobacteriaceae, and several other previously sensitive organisms is now quite common.

Tetracyclines remain especially useful in the management of infections by certain obligately intracellular bacterial pathogens such as Chlamydia, Mycoplasma, and Rickettsia.

They are also of value in spirochaetal infections, such as syphilis, leptospirosis, and Lyme disease. Certain rare or exotic infections, including anthrax, plague and brucellosis, are also susceptible to tetracyclines. These agents also have activity against certain eukaryotic parasites, including those responsible for diseases such as malaria and balantidiasis.

Precautions:

Discolor permanent teeth (yellow-gray-brown), from prenatal period through childhood and adulthood.

Be inactivated by Ca2+ ions, so are not to be taken with milk, yogurt, and other dairy products.

Be inactivated by aluminium, iron, and zinc, not to be taken at the same time as indigestion remedies (common antacids and over-the-counter heartburn medicines).

Cause skin photosensitivity, so exposure to the sun or intense light is not recommended.

Cause drug-induced lupus, and hepatitis.

Cause microvesicular fatty liver.

Cause tinnitus.

Interfere with methotrexate by displacing it from the various protein-binding sites.

Cause breathing complications, as well as anaphylactic shock, in some individuals.

Affect bone growth of the fetus, so should be avoided during pregnancy.

Fanconi syndrome may result from ingesting expired tetracyclines.

Caution should be exercised in long-term use when breastfeeding. Short-term use is safe.