Doxycycline
A tetracycline taken by mouth for chlamydia, rickettsial infections, Lyme disease, atypical pneumonia and acne, and to prevent malaria.
Drug card
- Class
- Tetracycline
- How it works
- Binding the 30S ribosomal subunit so tRNA cannot bring in new amino acids
- Used for
- Chlamydia and nongonococcal urethritis
- Rickettsial infections, such as spotted fevers and typhus
- Early Lyme disease
- Atypical pneumonia (Mycoplasma)
- Known for
- Photosensitivity (exaggerated sunburn)
- Esophagitis and esophageal ulcers
- Tooth discoloration if given during tooth development
- Its name
- -cycline means a tetracycline antibiotic
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does doxycycline work?
Doxycycline binds the 30S ribosomal subunit (perhaps the 50S too) and blocks aminoacyl-tRNA binding, halting protein synthesis; its bacteriostatic action spans Gram-positive as well as Gram-negative organisms. It is absorbed almost completely, so it upsets the lower bowel less often, and it also inhibits collagenase.
Like other tetracyclines: Tetracyclines bind the bacterial 30S ribosomal subunit and stop aminoacyl-tRNA from docking on the mRNA-ribosome complex, so no further amino acids are added. They are mainly bacteriostatic and broad-spectrum, including Chlamydia, Rickettsia and Mycoplasma. They form stable calcium complexes in growing bone, and metal ions in antacids and iron block their absorption.
Uses
What is doxycycline used for?
- Chlamydia and nongonococcal urethritis
- Rickettsial infections, such as spotted fevers and typhus
- Early Lyme disease
- Atypical pneumonia (Mycoplasma)
- Malaria prevention for travelers
- Severe acne (adjunct therapy)
Side effects
Side effects of doxycycline
- Photosensitivity (exaggerated sunburn)Known for
- Esophagitis and esophageal ulcersKnown forSerious
- Tooth discoloration if given during tooth developmentKnown for
- Nausea and vomiting
- Diarrhea
- Headache
- Rash
- Raised pressure in the skull (pseudotumor cerebri)Serious
- Vaginal thrush
- Severe skin reactions, including DRESSSerious
- Liver toxicitySerious
- PancreatitisSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Children under 8 and late pregnancy: avoid unless the infection is serious, as in RMSF; CDC found short courses did not stain teeth.
- Antacids, iron, calcium, magnesium and bismuth reduce its absorption.
- Carbamazepine, phenytoin and barbiturates shorten its half-life; it can increase warfarin's effect.
- Avoid with isotretinoin, which also raises intracranial pressure.
Good to know: CDC calls it the treatment of choice for Rocky Mountain spotted fever at any age, and WHO lists it as a first choice for cholera and chlamydia.
Remember it
A way to remember it
TEETH
- T
- Tooth discoloration in children under 8
- E
- Esophageal ulcers if taken just before lying down
- E
- Exaggerated sunburn (photosensitivity)
- T
- Thrush from Candida overgrowth
- H
- High pressure in the skull (pseudotumor cerebri)
TEETH fits a class best known for staining developing teeth; tetracyclines also bind calcium wherever bone is forming.
Written for biofideX
Its name
-cycline means tetracycline antibiotic
Doxycycline, minocycline and tigecycline share it. Anthracycline anticancer drugs such as doxorubicin end in -rubicin instead.
- Every drug name stem
Its class
Tetracyclines
Other tetracyclines with a card:
Easily mixed up with aminoglycosides, macrolides and fluoroquinolones.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Doxycycline hyclate delayed-release tablets: label (DailyMed)
- Doxycycline (NCI Thesaurus)
- Doxycycline (NHS)
- Clinical Care of Rocky Mountain Spotted Fever (CDC)
- Clinical Treatment of Erythema Migrans Rash (CDC)
- WHO Model List of Essential Medicines, 24th list (2025) (WHO)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Antibiotics: protein synthesis
Doxycycline is one of 10 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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