Antimicrobials · Tetracyclines
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Doxycycline is the first-line treatment for Lyme disease (Borrelia burgdorferi), Rocky Mountain spotted fever (Rickettsia rickettsii), and Chlamydia trachomatis infections.
Doxycycline acts by binding to the 30S ribosomal subunit, effectively inhibiting bacterial protein synthesis.
Doxycycline is the preferred tetracycline in patients with renal impairment because it is primarily eliminated via the fecal route rather than the kidneys.
Common adverse effects include esophageal ulceration (pill esophagitis), photosensitivity, and gastrointestinal distress.
Doxycycline is contraindicated in pregnant women and children under 8 years old due to the risk of permanent tooth discoloration and enamel hypoplasia.
Absorption of doxycycline is significantly reduced when administered concurrently with divalent or trivalent cations, such as calcium, magnesium, aluminum, or iron supplements.
Doxycycline is the drug of choice for community-acquired pneumonia in outpatient settings when covering for atypical pathogens like Mycoplasma pneumoniae.
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A 24-year-old female presents to the clinic complaining of a fever, headache, and a maculopapular rash that began on her wrists and ankles before spreading to her trunk. She reports a recent hiking trip in North Carolina where she recalls removing a tick from her leg. Physical examination reveals petechiae on the palms and soles. Laboratory studies show thrombocytopenia and hyponatremia.
What is the most appropriate pharmacologic treatment for this patient?
Doxycycline
The patient's presentation is classic for Rocky Mountain spotted fever, for which doxycycline is the gold-standard treatment regardless of age, as the benefits outweigh the risks of dental staining.
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High yield triage
Classification
Tetracycline antibiotic; bacteriostatic protein synthesis inhibitor.
Indications
Lyme disease, Chlamydia, RMSF, CAP, and MRSA skin infections.
Mechanism of Action
Binds 30S ribosomal subunit to inhibit tRNA binding to mRNA.
Side Effects
Photosensitivity, esophagitis; teratogenic, tooth discoloration.
Contraindications / Monitoring
Pregnancy, children <8 years; monitor for esophageal ulceration.
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