Doxycycline

1. Introduction

Doxycycline is a broad-spectrum tetracycline antibiotic used to treat bacterial infections, including respiratory, urinary, and skin infections. It also has anti-inflammatory and antiprotozoal properties, making it effective for acne, malaria prophylaxis, and some parasitic infections. It works by inhibiting bacterial protein synthesis, stopping bacterial growth.

2. Indications

  • Approved Indications:
    • Respiratory tract infections (e.g., pneumonia, bronchitis).
    • Skin and soft tissue infections (e.g., cellulitis, abscesses).
    • Sexually transmitted infections (e.g., chlamydia, gonorrhoea).
    • Lyme disease.
    • Acne vulgaris (long-term management).
    • Malaria prophylaxis.
    • Rickettsial infections (e.g., Rocky Mountain spotted fever).
    • Anthrax (including post-exposure prophylaxis).
  • Off-Label Uses:
    • Rosacea (management of inflammatory lesions).
    • Treatment of multidrug-resistant bacterial infections (specific cases).

3. Dosage

  • Adults:
    • Infections: 100 mg twice daily on day one, then 100 mg once daily (or twice daily if severe).
    • Acne: 50–100 mg once daily for long-term use.
    • Malaria prophylaxis: 100 mg once daily, starting 1–2 days before travel and continuing for 4 weeks after leaving the malaria-endemic area.
  • Children (≥8 years):
    • Infections: 2.2 mg/kg twice daily on day one, then 2.2 mg/kg once daily (maximum: 100 mg daily).
  • Elderly:
    • No specific dose adjustment required, but monitor closely for gastrointestinal side effects.

4. Administration

  • Take orally with a full glass of water to minimise the risk of oesophageal irritation or ulcers.
  • Take with food to reduce gastrointestinal upset, but avoid dairy products, as they may reduce absorption.
  • Avoid lying down for at least 30 minutes after taking doxycycline.

5. Forms Available

  • Tablets: 50 mg, 100 mg.
  • Capsules: 50 mg, 100 mg.
  • Oral suspension: 25 mg/5 mL.
  • Injectable solution: 100 mg/vial.

6. Side Effects

6.1. Common Side Effects

  • Nausea and vomiting.
  • Diarrhoea.
  • Abdominal pain.
  • Photosensitivity (increased sensitivity to sunlight).

6.2. Less Common Side Effects

  • Headache.
  • Dry mouth.
  • Skin rash.

6.3. Rare but Serious Side Effects

  • Oesophageal irritation or ulceration.
  • Hepatotoxicity (rare liver injury).
  • Intracranial hypertension (pseudotumour cerebri).
  • Severe allergic reactions (e.g., Stevens-Johnson syndrome).

7. Warnings

  • Photosensitivity: Avoid excessive sun exposure and use sunscreen while on doxycycline.
  • Oesophageal Irritation: Take with plenty of water and avoid lying down immediately after dosing.
  • Teeth Discolouration: Avoid in children under 8 years and during pregnancy unless no alternatives are available.

8. Precautions

  • Use cautiously in patients with liver impairment, as the drug is metabolised in the liver.
  • Avoid in patients with known hypersensitivity to tetracyclines.
  • Avoid using outdated doxycycline, as it may cause Fanconi syndrome (renal toxicity).

9. Interactions

  • Drug-Drug Interactions:
    • Antacids containing aluminium, magnesium, or calcium: Decreased absorption of doxycycline.
    • Iron supplements: Reduced absorption of doxycycline.
    • Warfarin: Increased risk of bleeding; monitor INR.
    • Oral contraceptives: May reduce contraceptive efficacy.
  • Drug-Food Interactions:
    • Avoid taking doxycycline with milk or dairy products, as they can reduce absorption.

10. Monitoring Parameters

  • Symptom improvement in infections.
  • Monitor for gastrointestinal side effects, including oesophageal irritation.
  • Watch for signs of hepatotoxicity or severe skin reactions.

11. Use in Children

  • Approved for children over 8 years in specific conditions like Lyme disease and rickettsial infections. Avoid in younger children due to the risk of teeth discolouration and enamel hypoplasia.

12. Use in Pregnancy

  • Category D: Avoid unless necessary, as doxycycline can harm the foetus (e.g., tooth discolouration, delayed skeletal development).

13. Use in Elderly

  • Generally safe but monitor for gastrointestinal side effects and ensure adequate hydration to minimise the risk of oesophageal irritation.

14. Use in Kidney Disease

  • No dose adjustment required, as doxycycline is not renally excreted to a significant extent.

15. Use in Liver Disease

  • Use with caution in patients with hepatic impairment. Monitor liver function if used long-term.

16. Patient Counselling Points

  • Take doxycycline with a full glass of water and avoid lying down for at least 30 minutes to prevent oesophageal irritation.
  • Use sunscreen and avoid prolonged sun exposure, as doxycycline can make your skin more sensitive to sunlight.
  • Avoid dairy products, antacids, and iron supplements within 2 hours of taking doxycycline.
  • Inform your doctor if you develop severe diarrhoea, persistent headache, or vision changes.
  • If taking doxycycline for malaria prevention, complete the full course, even after leaving the malaria-endemic area.

17. Table of Brand Names, Manufacturers, and Prices

Brand NameManufacturerPrice (USD)
VibramycinPfizer$50–80 (30 tablets, 100 mg)
DoryxMayne Pharma$40–70 (30 tablets, 100 mg)
Generic DoxycyclineVarious$10–30 (30 tablets, 100 mg)

18. FAQs (15 Questions)

  1. What is doxycycline used for?
    It is used to treat bacterial infections, acne, malaria prevention, and other conditions like Lyme disease.
  2. How does doxycycline work?
    It inhibits bacterial protein synthesis, stopping bacterial growth.
  3. Can doxycycline be taken with food?
    Yes, but avoid taking it with dairy products, as they can reduce absorption.
  4. How long does it take for doxycycline to work?
    Symptom improvement may be seen within a few days, but complete the full course as prescribed.
  5. Can doxycycline cause sunburn?
    Yes, it can increase sensitivity to sunlight, so use sunscreen and avoid prolonged sun exposure.
  6. Is doxycycline safe for children?
    It is not recommended for children under 8 years due to the risk of teeth discolouration.
  7. Can doxycycline be used during pregnancy?
    It should be avoided unless absolutely necessary, as it can harm the foetus.
  8. What are the common side effects of doxycycline?
    Nausea, diarrhoea, abdominal pain, and photosensitivity are common side effects.
  9. How should doxycycline be taken?
    Take it with plenty of water and avoid lying down for at least 30 minutes after dosing.
  10. Can doxycycline interact with other medications?
    Yes, it interacts with antacids, iron supplements, warfarin, and oral contraceptives.
  11. What should I do if I miss a dose of doxycycline?
    Take it as soon as you remember, but skip it if it’s close to the next dose. Do not double up.
  12. Can doxycycline cause diarrhoea?
    Yes, it may cause diarrhoea. Persistent or severe diarrhoea could indicate a serious condition like Clostridioides difficile infection.
  13. Can doxycycline be used for acne?
    Yes, it is commonly used for long-term management of moderate to severe acne.
  14. What should I avoid while taking doxycycline?
    Avoid dairy products, antacids, and iron supplements close to your dosing time.
  15. How should doxycycline be stored?
    Store at room temperature, away from light and moisture.