Doxycycline: Uses, Dosage, Side Effects, and More
1. Drug Name
Generic Name: Doxycycline
Brand Name(s):
- Pakistan: Doxylin, Vibramycin
- India: Doxy-1, Doxicip
- United States: Vibramycin, Oracea
- United Kingdom: Doryx, Efracea
2. Pharmacological Class
Class: Antibiotic
Subclass: Tetracycline
3. Mechanism of Action
Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing the addition of amino acids to growing peptide chains. This action halts bacterial growth and replication.
4. Indications
Primary Indications:
- Treatment of various bacterial infections including respiratory tract infections, urinary tract infections, skin infections, and certain sexually transmitted infections.
- Prevention of malaria.
Off-label Uses:
- Treatment of acne.
- Chronic prostatitis.
5. Dosage and Administration
Standard Dosage:
- Adults: 100 mg twice daily on the first day, followed by 100 mg once daily. For more severe infections, 100 mg twice daily may be used.
Route of Administration: Oral (tablets, capsules) and intravenous.
Special Populations:
- Pediatric: Not recommended for children under 8 years due to the risk of tooth discoloration and enamel hypoplasia.
- Geriatric: No specific dose adjustment required, but caution advised due to potential for increased sensitivity.
6. Pharmacokinetics
Absorption: Doxycycline is well absorbed from the gastrointestinal tract, with a bioavailability of 90-100%.
Distribution: It is widely distributed in body tissues and fluids.
Metabolism: Minimal hepatic metabolism.
Excretion: Primarily excreted unchanged in the urine and feces.
Half-life: Approximately 18-22 hours.
7. Contraindications
Doxycycline is contraindicated in patients with a history of allergic reactions to doxycycline or other tetracyclines. It is also contraindicated during pregnancy and in children under 8 years of age due to the risk of tooth discoloration.
8. Warnings and Precautions
Use with caution in patients with hepatic impairment or those at risk of esophageal irritation and ulceration. Avoid excessive sunlight or artificial UV light exposure due to the risk of photosensitivity reactions.
9. Side Effects
Common Side Effects: Nausea, vomiting, diarrhea, and photosensitivity.
Serious Side Effects: Severe allergic reactions, intracranial hypertension, and esophageal ulceration.
10. Drug Interactions
Major Interactions: Anticoagulants (increased risk of bleeding), isotretinoin (increased risk of intracranial hypertension).
Moderate Interactions: Antacids, calcium, iron, and magnesium supplements (reduced absorption of doxycycline).
Minor Interactions: Oral contraceptives (reduced efficacy).
11. Pregnancy and Lactation
Pregnancy Category: Category D - Positive evidence of risk.
Breastfeeding Considerations: Doxycycline is excreted in breast milk. Use with caution and only if clearly needed, as it may affect bone and tooth development in the nursing infant.
12. Patient Counseling Information
Key Points for Patients:
- Take doxycycline exactly as prescribed, even if you feel better before completing the course.
- Avoid taking doxycycline with dairy products or calcium-fortified juices alone, but it can be taken with meals that include these products.
- Report any signs of severe headaches, visual disturbances, or skin reactions to your doctor immediately.
Administration Tips:
- Take with a full glass of water. Drink plenty of fluids while taking doxycycline.
- Do not lie down for at least 30 minutes after taking doxycycline to prevent esophageal irritation.