Doxycycline

Generic Name

Doxycycline

Brand Names

Vibramycin

Doryx

Doxylin

Monodox

Oracea

Adoxa

Periostat

Acticlate

Alodox

Available as capsules, tablets, dispersible tablets, suspension, and intravenous formulations

Drug Class

Tetracycline antibiotic

Broad-spectrum bacteriostatic agent

Second-generation tetracycline derivative

Mechanism of Action

Doxycycline inhibits bacterial protein synthesis by binding reversibly to the 30S ribosomal subunit

This prevents the attachment of aminoacyl-tRNA to the ribosomal acceptor (A) site, blocking translation

It acts as a bacteriostatic agent by arresting bacterial growth rather than killing bacteria directly

Also exhibits anti-inflammatory effects via inhibition of matrix metalloproteinases and neutrophil chemotaxis

Effective against both gram-positive and gram-negative bacteria, intracellular pathogens, and atypical organisms

Indications

Infectious Diseases

Respiratory tract infections (bronchitis, pneumonia, sinusitis)

Acne vulgaris and rosacea (topical and systemic use)

Chlamydia trachomatis infections (urethritis, cervicitis, pelvic inflammatory disease)

Rickettsial infections (Rocky Mountain spotted fever, typhus, Q fever)

Mycoplasma pneumoniae

Brucellosis (with rifampin or streptomycin)

Plague (Yersinia pestis, with aminoglycoside)

Anthrax (including post-exposure prophylaxis of inhalational anthrax)

Malaria prophylaxis and treatment (especially Plasmodium falciparum)

Leptospirosis (treatment and prophylaxis)

Cholera and traveler’s diarrhea caused by Vibrio cholerae

Sexually transmitted infections (e.g., lymphogranuloma venereum)

Lyme disease (early and late stages)

Tularemia

Syphilis (alternative for penicillin-allergic patients)

Scrub typhus

Cellulitis (particularly MRSA-suspected)

Relapsing fever

Helicobacter pylori eradication (as part of combination therapy)

Non-Infectious Indications

Acne vulgaris (long-term low-dose anti-inflammatory effect)

Ocular rosacea and blepharitis

Periodontitis (as low-dose Periostat formulation)

Rheumatoid arthritis (rare, off-label)

Prevention of malaria in travelers

Treatment of filarial diseases and onchocerciasis (in mass drug administration programs)

Dosage and Administration

Adults

Standard infections

100 mg twice daily or 200 mg once daily

May give loading dose of 200 mg on first day followed by 100 mg once daily

Acne vulgaris

50–100 mg once or twice daily

Low-dose subantimicrobial regimens (e.g., 40 mg daily for anti-inflammatory effect)

Malaria prophylaxis

100 mg once daily

Begin 1–2 days before travel and continue for 4 weeks after leaving endemic area

Malaria treatment

100 mg twice daily for 7 days (with quinine or artesunate)

Chlamydia and nongonococcal urethritis

100 mg twice daily for 7 days

May extend up to 14 days for pelvic inflammatory disease

Lyme disease (early localized)

100 mg twice daily for 10–21 days

Single 200 mg dose for post-tick bite prophylaxis within 72 hours

Children over 8 years and ≥45 kg

Dose similar to adult (100 mg twice daily)

Avoid use in children under 8 due to risk of permanent tooth discoloration and bone growth suppression unless in life-threatening infections (e.g., Rocky Mountain spotted fever)

Administration Notes

Take with full glass of water

Remain upright for 30 minutes after ingestion to avoid esophageal irritation or ulceration

Can be taken with food to reduce GI upset but may slightly reduce absorption

Avoid antacids, iron, calcium, magnesium, or zinc supplements within 2–3 hours of dosing

Enteric-coated or delayed-release formulations minimize GI side effects

Pharmacokinetics

Bioavailability: 90–100% orally

Peak plasma level: 1.5–4 hours after dose

Half-life: ~18–22 hours (longer than tetracycline)

Widely distributed, including into respiratory tract, genital tract, and CNS (limited)

Primarily excreted via feces (non-biliary route), less dependent on renal function

Highly protein-bound (~80–90%)

Not significantly removed by dialysis

Contraindications

Hypersensitivity to doxycycline or any tetracycline-class antibiotic

Children under 8 years old (except for life-threatening infections)

Pregnancy, particularly second and third trimesters (risk to fetal bone and teeth)

Breastfeeding, especially for long-term use

Warnings and Precautions

Photosensitivity reactions—exaggerated sunburn possible

Esophageal ulceration risk—administer with caution

Benign intracranial hypertension (especially in young women or when used with isotretinoin or other retinoids)

Superinfection including fungal or resistant bacterial overgrowth with long-term use

Pseudomembranous colitis due to Clostridioides difficile

Discoloration of teeth and enamel hypoplasia in children and fetus

May interfere with bone development in fetus and growing children

Autoimmune hepatitis, lupus-like syndrome, and hemolytic anemia (rare)

Monitor for hypersensitivity reactions, including Stevens-Johnson syndrome and anaphylaxis

Long-term use for acne requires periodic evaluation of benefit-risk balance

Adverse Effects

Common

Nausea

Vomiting

Diarrhea

Abdominal pain

Photosensitivity

Rash

Esophagitis/esophageal ulceration

Tooth discoloration (if used in children)

Uncommon

Headache

Fatigue

Dizziness

Allergic reactions (urticaria, pruritus)

Candidiasis (oral or vaginal)

Anorexia

Hepatotoxicity (dose-related, especially in high IV doses)

Rare and Serious

Pseudotumor cerebri (benign intracranial hypertension)

Pancreatitis

Anaphylaxis

Thrombocytopenia

Eosinophilia

Hepatic failure

Stevens-Johnson syndrome

Jarisch-Herxheimer reaction in spirochetal infections

Pregnancy and Lactation

Pregnancy Category D (US FDA)

Crosses placenta

Use only if clearly needed for life-threatening infections (e.g., rickettsial disease)

Risks include permanent discoloration of teeth, inhibition of bone growth, and hepatotoxicity

Breastfeeding

Excreted in human milk

Short-term use may be acceptable but long-term use not recommended

American Academy of Pediatrics considers doxycycline compatible with breastfeeding when used short term

Drug Interactions

Antacids containing magnesium, calcium, or aluminum

Reduce absorption—separate by 2–3 hours

Iron supplements and multivitamins

Chelate doxycycline—reduce absorption

Oral contraceptives

Possible reduced efficacy—backup contraception recommended

Warfarin

Potentiates anticoagulant effect—monitor INR

Penicillins

Antagonistic effect when used concurrently—avoid in serious infections

Barbiturates, phenytoin, carbamazepine

May reduce doxycycline serum levels due to hepatic enzyme induction

Isotretinoin

Increased risk of pseudotumor cerebri—avoid combination

Methotrexate

May increase methotrexate toxicity—caution advised

Monitoring Parameters

Symptomatic response in infection or acne

Signs of gastrointestinal intolerance or esophageal irritation

Sun sensitivity and skin reactions

Periodic liver and renal function tests in prolonged therapy

CBC in long-term or high-dose use

Pregnancy status in women of childbearing potential

Counseling Points

Take with water and remain upright for 30 minutes to avoid throat irritation

Avoid sunlight and use sunscreen due to risk of photosensitivity

Complete entire course as prescribed

Use backup contraception if on oral contraceptives

Report any persistent headaches, vision changes, or severe GI pain

Do not use expired doxycycline due to risk of nephrotoxicity from degradation products

Avoid dairy products within 1–2 hours of dosing in some formulations

Do not self-medicate with antibiotics without proper indication

Comparative Notes

Doxycycline vs Minocycline

Minocycline has better CNS penetration and more vestibular side effects

Doxycycline is preferred for malaria prophylaxis and most systemic infections

Doxycycline has less hepatic metabolism than minocycline

Doxycycline vs Tetracycline

Doxycycline is longer-acting, better absorbed, and causes fewer GI side effects

More effective and preferred in current clinical guidelines

Doxycycline vs Azithromycin

Azithromycin has fewer GI side effects and is often preferred in pregnancy

Doxycycline is more effective in some STIs and rickettsial infections

Both are used in combination for PID and respiratory infections

Legal and Regulatory Status

Prescription-only

Approved by FDA, EMA, MHRA, and other regulatory agencies worldwide

Listed on WHO Model List of Essential Medicines

Included in guidelines for STI treatment, malaria prophylaxis, acne management, and rickettsial diseases