What is the recommended dose of doxycycline (tetracycline antibiotic) for adults?

Doxycycline Dosing for Adults

For most adult bacterial infections, the standard doxycycline dose is 200 mg on the first day (given as 100 mg every 12 hours), followed by 100 mg daily as maintenance therapy. 1

Standard Adult Dosing Regimen

• Loading dose: 200 mg on day 1, administered as 100 mg every 12 hours 1
• Maintenance dose: 100 mg once daily thereafter 1
• Severe infections: 100 mg every 12 hours may be continued throughout the treatment course 1

The FDA-approved labeling establishes this as the foundational dosing strategy across most indications, with therapeutic serum activity typically persisting for 24 hours following recommended dosing 1.

Condition-Specific Dosing

Tick-Borne Infections

• Lyme disease prophylaxis (post-tick bite): Single 200 mg dose within 72 hours of tick removal 2
• Early Lyme disease treatment: 100 mg twice daily for 10-21 days 2
• Human granulocytic anaplasmosis: 100 mg twice daily for 10 days 3
• Rickettsial diseases: 100 mg twice daily, continuing at least 3 days after fever subsides, typically 5-7 days minimum 4

The Infectious Diseases Society of America emphasizes that for anaplasmosis, treatment should be extended to 10-14 days if concurrent Lyme disease is suspected 4.

Sexually Transmitted Infections

• Chlamydia (urethral, endocervical, or rectal): 100 mg twice daily for 7 days 1
• Nongonococcal urethritis: 100 mg twice daily for 7 days 1
• Uncomplicated gonorrhea: 100 mg twice daily for 7 days 1
• Acute epididymo-orchitis: 100 mg twice daily for at least 10 days 1
• Early syphilis: 100 mg twice daily for 2 weeks (penicillin-allergic patients) 1
• Late syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1
• STI post-exposure prophylaxis: Single 200 mg dose within 72 hours after sexual exposure (not to exceed 200 mg per 24 hours) 2

Skin and Soft Tissue Infections

• MRSA skin infections: 100 mg twice daily for 7-14 days based on clinical response 4
• Acne vulgaris: 100 mg daily as maintenance (after 200 mg loading dose on day 1) 3
• Subantimicrobial dosing for acne: 20 mg twice daily may be used for anti-inflammatory effects without antimicrobial activity 5, 6

The American Academy of Dermatology guidelines specify that doxycycline should not be used as monotherapy for acne 3.

Respiratory Infections

• Community-acquired pneumonia: 100 mg twice daily, with some experts recommending 200 mg as the first dose to achieve adequate serum levels more rapidly 4
• Inhalational anthrax (post-exposure): 100 mg twice daily for 60 days 1

Other Infections

• Q fever (acute): 100 mg twice daily for 14 days 2
• Q fever (chronic): 100 mg twice daily plus hydroxychloroquine 200 mg three times daily for ≥18 months 2
• Malaria prophylaxis: 100 mg once daily, starting 1-2 days before travel and continuing for 4 weeks after leaving malarious area 1

Administration Guidelines

Critical administration considerations to optimize efficacy and minimize adverse effects:

• Fluid intake: Administer with adequate fluid (8 ounces) to reduce esophageal irritation and ulceration risk 1, 7
• Food/milk: May be given with food or milk if gastric irritation occurs; absorption is not markedly affected 1
• Upright positioning: Patients should avoid lying down for 1 hour after taking doxycycline to prevent esophagitis 4
• Drug interactions: Separate dosing by at least 2 hours from dairy products, antacids, and supplements containing calcium, iron, magnesium, or sodium bicarbonate 4

Special Populations

Renal Impairment

• No dose adjustment required: Studies indicate that usual recommended doses do not lead to excessive accumulation in patients with renal impairment 1
• Hemodialysis: Doxycycline is not significantly removed during dialysis; maintain standard dosing 8

The pharmacokinetic data demonstrate that in chronic renal failure, doxycycline half-life varies between 10-24 hours, but no accumulation occurs with repeated 100 mg daily dosing 8.

Geriatric Patients

• Standard dosing applies: Serum levels and tissue distribution in elderly patients are not significantly different from young adults 8
• No dose adjustment needed based on age alone 8

Hepatic Impairment

• Stable hepatitis B carriers: A single 200 mg dose appears safe in inactive HBV carriers with normal liver enzymes and no cirrhosis 2
• Severe hepatic impairment: Use with caution, though specific dosing adjustments are not well-established in guidelines

Common Pitfalls and Caveats

Key errors to avoid in doxycycline prescribing:

• Exceeding recommended dosage: May result in increased incidence of side effects 1
• Inadequate treatment duration: For streptococcal infections, therapy must continue for 10 days 1
• Delayed treatment in rickettsial diseases: Do not wait for laboratory confirmation; delay can lead to severe disease and death 4
• Photosensitivity: Advise all patients to avoid sun exposure due to significant photosensitivity risk 7, 2
• Pregnancy: Generally contraindicated; alternative agents should be considered except for life-threatening infections 2

Clinical Response Monitoring

• Expected response time: Fever should subside within 24-48 hours of treatment initiation 4
• Failure to respond: If no improvement within 24-48 hours, reevaluate for alternative diagnoses 3, 4

Dosing Summary by Severity

Mild to moderate infections: 200 mg day 1 (as 100 mg q12h), then 100 mg daily 1

Severe infections: 100 mg every 12 hours throughout treatment course 1

Life-threatening infections (anthrax, severe rickettsial disease): 100 mg every 12 hours for extended duration (60 days for anthrax) 1