Pharmacology
Summary
Tetracyclines--- such as doxycycline and minocycline--- are a class of broad-spectrum antibiotics that inhibit bacterial protein synthesis by binding to the bacterial ribosome, thus impeding the growth and proliferation of a wide range of pathogens. These drugs enter the bacteria and accumulate in the cell, where they bind reversibly to the 30S ribosomal subunit to block tRNA binding and halt peptide formation, thereby inhibiting bacterial protein synthesis.
Tetracyclines are broad spectrum antibiotics that demonstrate activity against numerous gram-positive and gram-negative bacteria, including MRSA, rickettsiae, and atypical bacteria. Furthermore, they treat a variety of atypical pathogens, including diseases transmitted by ticks like Rocky Mountain spotted fever and Lyme disease, as well as zoonotic diseases like Brucellosis, Q fever, and the plague. They also treat sexually transmitted infections such as chlamydia urethritis and cervicitis, bronchitis, and community-acquired pneumonia caused by atypical bugs. Oral tetracyclines, which are primarily absorbed in the proximal small intestine and stomach, are used to treat moderate to severe inflammatory acne and should not be given alongside multivalent cations like calcium, iron, and magnesium to avoid impaired absorption. Tetracyclines should not be used in children less than 8 years old or during pregnancy due to their propensity to bind with the calcium deposited in newly formed bone or teeth, which can cause harm to the growing fetus or child. Other notable side effects include nausea, vomiting, diarrhea, skin photosensitivity and, in rare cases, Fanconi syndrome.
Lesson Outline
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FAQs
Tetracyclines, such as doxycycline and minocycline, work by acting on the bacterial ribosome to inhibit translation. They bind reversibly to the bacterial 30S ribosomal subunit, leading to the cessation of protein synthesis and thus, the growth of the bacteria. As they are bacteriostatic in nature, they don't directly kill bacteria but instead halt their growth. Tetracyclines are broad-spectrum antibiotics, so they can target a wide variety of bacteria.
Tetracyclines, such as doxycycline or minocycline, are effective against a variety of infections, making them versatile antibiotics. They can treat MRSA infections, culture-negative endocarditis caused by Coxiella, Yersinia infections, and Brucella infections. Furthermore, they can treat various diseases caused by Chlamydia species, including cervicitis, urethritis, pelvic inflammatory disease, and certain forms of pneumonia. They can also be used against tick-borne bacteria like Rickettsia, Ehrlichia, Francisella, Borrelia and to treat acne vulgaris.
Tetracyclines may cause a range of side effects, the most common of which include nausea, vomiting, and diarrhea. They can also lead to skin photosensitivity, making the skin more sensitive to sunlight and increasing the risk of sunburn. Additionally, tetracyclines can cause discoloration of teeth in young children and are considered teratogenic due to their potential to deposit in fetal teeth and bone, which can lead to deformities. Also, they are associated with Fanconi syndrome (type 2 RTA) when expired tetracyclines are used.
Tetracyclines tend to decrease absorption of multivalent cations such as calcium (Ca2+), magnesium (Mg2+), and iron (Fe2+). This happens because tetracyclines bind to these ions in the gastrointestinal tract, forming insoluble complexes that cannot be absorbed efficiently into the body. Therefore, this may reduce the effective levels of these cations in the body and can interfere with the effectiveness of the antibiotics themselves.
One of the primary ways that bacteria develop resistance to tetracyclines is through the use of efflux pumps. These are proteins that function to remove foreign substances, including antibiotics, out of the bacterial cells. This mechanism decreases the concentration of the antibiotic within the bacteria, thereby reducing its effect. Also, tetracyclines are eliminated through feces, which limits their time in the body and can potentially contribute to the development of bacterial resistance.
