Tetracyclines Flashcards
What is the mechanism of action of tetracyclines (Doxycycline, Minocycline, Tetracycline)?
Tetracyclines bind to the 30S ribosomal subunit and prevent attachment of aminoacyl-tRNA to the A site of the ribosome, halting protein synthesis (bacteriostatic). They enter bacteria via passive diffusion and active transport; uptake is decreased in anaerobes.
Describe the spectrum of activity of tetracyclines (Doxycycline, Minocycline, Tetracycline).
Tetracyclines are broad-spectrum, covering atypicals and zoonotic organisms like Rickettsia, Borrelia, Mycoplasma pneumoniae, Chlamydia, and some protozoa. They also act against Gram-positives and some Gram-negatives but are not very effective against most anaerobes.
How do bacteria develop resistance to tetracyclines (Doxycycline, Minocycline, Tetracycline)?
Resistance occurs via increased efflux pumps that expel the drug or via ribosomal protection proteins that allow translation to proceed despite tetracyclines. Enzymatic inactivation is less common.
Outline key pharmacokinetic features of tetracyclines (Doxycycline, Minocycline, Tetracycline).
Tetracyclines are well absorbed orally but absorption is decreased by dairy, antacids, or iron supplements. Doxycycline and minocycline are more lipophilic with high bioavailability. Doxycycline is excreted fecally, while others are renally excreted.
What major drug interactions involve tetracyclines (Doxycycline, Minocycline, Tetracycline)?
Divalent or trivalent cations will chelate tetracyclines and prevent absorption. Tetracyclines can enhance warfarin’s effect and should not be given with retinoids due to risk of pseudotumor cerebri.
What are common clinical uses for tetracyclines (Doxycycline, Minocycline, Tetracycline)?
Doxycycline is used for tick-borne diseases, atypical pneumonia, STIs, acne, and MRSA skin infections. Tetracycline is used in H. pylori regimens and acne. Minocycline is used in acne and meningococcal carrier state eradication.
In which patients are tetracyclines contraindicated or to be avoided (Doxycycline, Minocycline, Tetracycline)?
Contraindicated in children under 8, pregnant women, and breastfeeding mothers due to tetracyclines’ (Doxycycline, Minocycline, Tetracycline) ability to discolor teeth and inhibit bone growth. Use with caution in renal impairment and avoid expired tetracyclines due to risk of Fanconi syndrome.
List major adverse effects of tetracyclines (Doxycycline, Minocycline, Tetracycline).
Common adverse effects include GI irritation (esophagitis), tooth enamel dysplasia, photosensitivity, and vestibular toxicity. Rarely, they may cause benign intracranial hypertension and Fanconi syndrome with outdated tetracyclines.
What is a helpful mnemonic to recall tetracycline uses (Doxycycline, Minocycline, Tetracycline)?
“VACUuM THe BedRoom” lists organisms treated by tetracyclines: Vibrio cholerae, Acne, Chlamydia, Ureaplasma urealyticum, Mycoplasma pneumoniae, Tularemia, H. pylori, Borrelia, Rickettsia. Avoid taking with milk, antacids, or iron.
