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 Name | Manufacturer | Price (USD) |
---|---|---|
Vibramycin | Pfizer | $50–80 (30 tablets, 100 mg) |
Doryx | Mayne Pharma | $40–70 (30 tablets, 100 mg) |
Generic Doxycycline | Various | $10–30 (30 tablets, 100 mg) |
18. FAQs (15 Questions)
- What is doxycycline used for?
It is used to treat bacterial infections, acne, malaria prevention, and other conditions like Lyme disease. - How does doxycycline work?
It inhibits bacterial protein synthesis, stopping bacterial growth. - Can doxycycline be taken with food?
Yes, but avoid taking it with dairy products, as they can reduce absorption. - 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. - Can doxycycline cause sunburn?
Yes, it can increase sensitivity to sunlight, so use sunscreen and avoid prolonged sun exposure. - Is doxycycline safe for children?
It is not recommended for children under 8 years due to the risk of teeth discolouration. - Can doxycycline be used during pregnancy?
It should be avoided unless absolutely necessary, as it can harm the foetus. - What are the common side effects of doxycycline?
Nausea, diarrhoea, abdominal pain, and photosensitivity are common side effects. - How should doxycycline be taken?
Take it with plenty of water and avoid lying down for at least 30 minutes after dosing. - Can doxycycline interact with other medications?
Yes, it interacts with antacids, iron supplements, warfarin, and oral contraceptives. - 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. - Can doxycycline cause diarrhoea?
Yes, it may cause diarrhoea. Persistent or severe diarrhoea could indicate a serious condition like Clostridioides difficile infection. - Can doxycycline be used for acne?
Yes, it is commonly used for long-term management of moderate to severe acne. - What should I avoid while taking doxycycline?
Avoid dairy products, antacids, and iron supplements close to your dosing time. - How should doxycycline be stored?
Store at room temperature, away from light and moisture.