doxycycline
Brand: Vibramycin, Doryx, Oracea, Monodox
Prototype: tetracycline
Drug Class: antibiotic
Drug Family: antibiotic
Subclass: tetracycline
Organ Systems: infectious-disease
Mechanism of Action
Binds reversibly to the 30S ribosomal subunit, blocking binding of aminoacyl-tRNA to the acceptor (A) site; prevents peptide chain elongation; bacteriostatic; also has anti-inflammatory properties; broader spectrum than older tetracyclines.
30S ribosomal subunit
Indications
- community-acquired pneumonia (atypical organisms)
- chlamydia (drug of choice)
- Lyme disease (early localized — drug of choice)
- rickettsial diseases (Rocky Mountain spotted fever — drug of choice)
- malaria prophylaxis
- acne vulgaris
- anthrax (alternative to ciprofloxacin)
- rosacea
Contraindications
- children <8 years (permanent tooth discoloration)
- pregnancy (second/third trimester)
- severe hepatic impairment
Adverse Effects
Common
- esophagitis/esophageal ulceration (if not taken with adequate water)
- nausea
- vomiting
- photosensitivity
- tooth discoloration (children <8 years)
Serious
- hepatotoxicity (high doses)
- pseudotumor cerebri (intracranial hypertension)
- C. difficile colitis
- Jarisch-Herxheimer reaction (spirochete infections)
Pharmacokinetics (ADME)
| Absorption | ~93% oral bioavailability; reduced by divalent cations but less so than older tetracyclines |
| Distribution | Protein binding 80–90%; Vd ~0.75 L/kg; concentrates in liver, kidney, bone, skin |
| Metabolism | Not significantly metabolized |
| Excretion | Biliary/fecal (50%); renal (40%); does NOT require dose adjustment in renal failure (unlike older tetracyclines) |
| Half-life | 18–22 hours — allows once-daily dosing (100–200 mg qd for most infections) |
| Onset | 1–4 hours |
| Peak | 1.5–4 hours |
| Duration | 12–24 hours |
| Protein Binding | 80–90% |
| Vd | ~0.75 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| divalent cations (antacids, calcium, iron, dairy, sucralfate) | chelation reduces absorption; separate by 2 hours | major |
| isotretinoin | additive pseudotumor cerebri risk | major |
| warfarin | may increase INR via gut flora alteration | moderate |
Nursing Considerations
- Instruct patient to take with a full glass of water and remain upright for 30–60 minutes after ingestion to prevent esophagitis and ulceration — a significant and preventable adverse effect
- Separate doxycycline administration from antacids, calcium, iron, magnesium, or dairy products by at least 2 hours; these chelate and reduce absorption
- Counsel patients about photosensitivity — use sunscreen, protective clothing; avoid prolonged sun exposure during therapy
- Doxycycline does not require renal dose adjustment (unlike older tetracyclines which accumulate in CKD due to renal elimination) — an important advantage
Clinical Pearls
- Doxycycline is the drug of choice for Rocky Mountain Spotted Fever (RMSF) even in children <8 years when RMSF is suspected — the risk of untreated RMSF (30% mortality) far outweighs the risk of dental staining from a short course
- Doxycycline is uniquely safe in renal failure among tetracyclines because it uses biliary/fecal elimination — it actually replaces older tetracyclines in CKD patients
Safety Profile
Pregnancy safe
Lactation avoid
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.