Doxycycline
Doxyferm · Doxycyklin EQL Pharma · Vibranord
The tetracycline that covers both respiratory pathogens and the intracellular organisms that beta-lactams miss — Mycoplasma pneumoniae, Chlamydophila, and Borrelia. Near-complete oral absorption and a long half-life make once-daily dosing possible. It is the standard choice in pneumonia in penicillin-allergic patients and in atypical pneumonia, but the age limit of 8 years and pregnancy significantly restrict use.
Not given to children under 8 years or in the second half of pregnancy — tetracyclines bind to mineralising tooth substance and cause enamel hypoplasia and permanent discoloration. In these patients, amoxicillin or phenoxymethylpenicillin is used for Borrelia and erythromycin for atypical pneumonia.
Dosing in adults
| Indication | Regimen | Comment |
|---|---|---|
| Pneumonia in penicillin-allergic patients | 200 mg × 1 orally for 3 days, then 100 mg × 1 — total 7 days | covers both pneumococci and atypical organisms |
| Atypical pneumonia (Mycoplasma, Chlamydophila) | 200 mg × 1 orally days 1–3, then 100 mg × 1 — total 7–10 days | first-line choice in adults and children over 8 years |
| Erythema migrans | 100 mg × 2 orally for 10 days | for solitary EM, phenoxymethylpenicillin 1 g × 3 for 10 days is first-line choice |
| Multiple erythema migrans, Borrelia lymphocytoma, neuroborreliosis | 200 mg × 1 orally for 10–14 days | oral doxycycline is equivalent to intravenous ceftriaxone in early neuroborreliosis |
| COPD exacerbation with treatment indication | 200 mg × 1 orally day 1, then 100 mg × 1 — total 5–7 days | covers Haemophilus influenzae and Moraxella |
No dose adjustment at any level of renal function — largely eliminated via the gut and does not accumulate. This is a practical advantage in patients with renal failure where other alternatives require dose modification.
Use with caution in severe hepatic failure and avoid concurrent hepatotoxic drugs. No established dose reduction.
Children 8 years and older: 4 mg/kg × 1 day 1 (maximum 200 mg), then 2 mg/kg × 1 (maximum 100 mg). In neuroborreliosis 4 mg/kg × 1 for 10–14 days. Contraindicated below age 8.
Wrong choice for lower urinary tract infection — urinary concentration is low and E. coli resistance is high. Also avoid in pregnancy and in children under 8 years, and never take the tablet lying down or without fluid: doxycycline is one of the most common causes of drug-induced oesophageal ulceration.
Pharmacokinetics
- BIOAVAIL.
- approximately 93 % orally
- t½
- 18–22 hours
- PROTEIN BINDING
- 80–90 %
- METABOLISM
- Negligible
- EXCRETION
- Renal approximately 40 %, remainder via the gut
- FOOD EFFECT
- Calcium, iron, and antacids chelate and abolish absorption
- CNS PENETRATION
- Good — adequate for neuroborreliosis
- ONSET
- Therapeutic level within 30 minutes