Doxycycline Dosage for Adults
The standard dosage of doxycycline for adults is 100 mg orally twice daily for most infections, with a loading dose of 200 mg on the first day (100 mg every 12 hours) recommended for more rapid therapeutic effect. 1
General Dosing Guidelines
The FDA-approved dosing for doxycycline in adults follows a consistent pattern:
- Initial dose: 200 mg on day 1 (given as 100 mg every 12 hours)
- Maintenance dose: 100 mg daily, either as a single dose or divided into two 50 mg doses 1
- For severe infections: 100 mg every 12 hours is recommended 1
Specific Infection-Based Dosing
Doxycycline dosing varies slightly based on the type of infection being treated:
Bacterial Infections
- Standard bacterial infections: 100 mg twice daily for 7-14 days 2
- Outpatient MRSA skin infections: 100 mg twice daily for 5-10 days 2, 3
- More severe infections: 100 mg every 12 hours for the duration of treatment 1
Sexually Transmitted Infections
- Chlamydia: 100 mg twice daily for 7 days 2
- Nongonococcal urethritis: 100 mg twice daily for 7 days 2, 1
- Uncomplicated gonococcal infections: 100 mg twice daily for 7 days 1
- Alternative single-visit dosing: 300 mg followed by another 300 mg one hour later 1
Tick-Borne Diseases
- Lyme disease treatment: 100 mg twice daily for 10-21 days 3, 2
- Lyme disease prophylaxis: 200 mg as a single dose 2
- Human Granulocytic Anaplasmosis: 100 mg twice daily for 10 days 3, 2
Other Specific Indications
- Malaria prophylaxis: 100 mg daily 1
- Post-exposure inhalational anthrax: 100 mg twice daily for 60 days 1
- Syphilis (early): 100 mg twice daily for 2 weeks 1
- Syphilis (>1 year duration): 100 mg twice daily for 4 weeks 1
Administration Considerations
To maximize effectiveness and minimize side effects:
- Take with adequate fluid to reduce esophageal irritation 2
- Remain upright for 30-60 minutes after taking 2
- Can be taken with food if gastric irritation occurs 2, 1
- Avoid taking within 2 hours of antacids, iron, calcium, magnesium supplements, or dairy products 2
Special Considerations
Duration of Treatment
Treatment duration varies by condition but typically ranges from 7-21 days for most infections. For certain conditions like post-exposure anthrax prophylaxis, treatment extends to 60 days 1.
Contraindications and Cautions
- Pregnancy: Generally contraindicated, especially after 6 months gestation 2
- Breastfeeding: Use with caution; azithromycin may be preferred 2
- Renal impairment: Standard dosing generally does not require adjustment 1
Common Side Effects
- Gastrointestinal: nausea, vomiting, diarrhea, esophageal irritation
- Dermatological: photosensitivity
- Gynecological: vaginal yeast infections 2
Clinical Pearls
- The therapeutic antibacterial serum activity typically persists for 24 hours following recommended dosage 1
- For streptococcal infections, therapy should continue for at least 10 days 1
- Low-dose doxycycline (20-40 mg/day) may be used for anti-inflammatory effects in certain conditions 4, but standard antimicrobial dosing should be used for infections