Doxycycline – Uses, Effects and Side Effects

What is Doxycycline?

Doxycycline is an antibiotic belonging to the tetracycline class of drugs. First developed in the 1960s, it has become one of the most widely used antibiotics worldwide. Doxycycline is effective against a broad spectrum of bacteria and is used both for the treatment and prevention of various infectious diseases.

Mechanism of Action

Doxycycline inhibits bacterial protein synthesis by binding to the 30S subunit of the bacterial ribosome. This prevents the attachment of aminoacyl-tRNA to the ribosome-mRNA complex, blocking the production of essential proteins within bacterial cells. Without these proteins, the bacteria cannot replicate and are eliminated by the body immune system. This mechanism is described as bacteriostatic, meaning the drug inhibits bacterial growth rather than killing bacteria directly.

Indications and Uses

Doxycycline is used to treat a wide variety of infectious diseases, including:

• Respiratory tract infections: such as pneumonia caused by atypical organisms like Chlamydophila pneumoniae or Mycoplasma pneumoniae
• Skin infections: particularly inflammatory acne vulgaris
• Sexually transmitted infections: such as chlamydia and syphilis (in patients with penicillin allergy)
• Lyme disease: first-line therapy in the early stages
• Malaria prophylaxis and treatment: especially in regions with chloroquine-resistant strains
• Rickettsial infections and Q fever: caused by intracellular bacteria
• Eye infections: such as trachoma (caused by Chlamydia trachomatis)
• Anthrax: as a second-line agent or in combination therapy

Dosage and Administration

Doxycycline is available as tablets, capsules, and intravenous infusion solutions. The standard adult dose is 100 to 200 mg per day, depending on the type and severity of the infection. It should always be taken with plenty of fluid (at least a full glass of water) and in an upright position to prevent esophageal irritation. Taking doxycycline with food may improve tolerability; however, dairy products, and supplements containing calcium, magnesium, or iron can reduce absorption and should be taken at a separate time.

Side Effects

Like all antibiotics, doxycycline can cause side effects. Common side effects include:

• Gastrointestinal complaints: nausea, vomiting, diarrhea, and abdominal pain
• Photosensitivity: increased sensitivity to sunlight and higher risk of sunburn; direct sun exposure should be avoided during treatment
• Esophagitis: inflammation of the esophagus if the medication is not taken correctly
• Disruption of gut flora: which may lead to fungal infections such as oral thrush
• Allergic reactions: rare but possible

In children under 8 years of age, doxycycline can cause permanent tooth discoloration and impair bone development, making it contraindicated in this age group. It should also be avoided during pregnancy and breastfeeding.

Drug Interactions

Doxycycline can interact with various other substances and medications:

• Antacids, dairy products, calcium, magnesium, and iron: reduce absorption of doxycycline in the intestine
• Anticoagulants (e.g., warfarin): doxycycline may enhance their blood-thinning effect
• Oral contraceptives: in rare cases, doxycycline may reduce contraceptive effectiveness
• Vitamin A supplements: increased risk of elevated intracranial pressure

Contraindications

Doxycycline should not be used in patients with:

• known hypersensitivity to tetracyclines
• children under 8 years of age
• pregnancy and breastfeeding
• severe hepatic impairment (consult a physician)

References

1. World Health Organization (WHO): WHO Model List of Essential Medicines, 23rd Edition, 2023. Available at: https://www.who.int/publications/i/item/WHO-MHP-HPS-EML-2023.02
2. Brunton L.L. et al.: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th Edition. McGraw-Hill Education, 2022.
3. Centers for Disease Control and Prevention (CDC): Doxycycline – Antibiotic Use and Resistance. Available at: https://www.cdc.gov/antibiotic-use