What is the recommended prophylactic dose of doxycycline (antibiotic)?

Doxycycline Prophylactic Dosing

The prophylactic dose of doxycycline depends on the indication: 100 mg daily for malaria prophylaxis, or 200 mg as a single dose within 72 hours after sexual exposure for bacterial STI prevention. 1, 2

STI Post-Exposure Prophylaxis (Doxy PEP)

For prevention of bacterial sexually transmitted infections, prescribe doxycycline 200 mg as a single dose to be taken as soon as possible within 72 hours after oral, vaginal, or anal sex, with a maximum of 200 mg per 24-hour period. 1

• This regimen is specifically recommended for men who have sex with men (MSM) and transgender women (TGW) with at least one bacterial STI (syphilis, chlamydia, or gonorrhea) diagnosed in the past 12 months 1
• The prescription should account for enough doses based on anticipated sexual activity until the next visit 1
• Reassess ongoing need for doxy PEP every 3-6 months 1
• No recommendation can be made for cisgender women, cisgender heterosexual men, transgender men, or other queer and nonbinary persons due to insufficient evidence 1

Malaria Prophylaxis

For malaria prevention, prescribe doxycycline 100 mg orally once daily. 1, 2

• Begin prophylaxis 1-2 days before travel to malarious areas 1, 2
• Continue daily during travel in malarious areas 1, 2
• Continue for 4 weeks after leaving the malarious area 1, 2
• For children over 8 years: 2 mg/kg once daily up to the adult dose of 100 mg 2

Anthrax Post-Exposure Prophylaxis

For inhalational anthrax exposure, prescribe doxycycline 100 mg orally twice daily for 60 days. 1

• For children weighing less than 100 lb (45 kg): 2.2 mg/kg orally twice daily for 60 days 1
• For children weighing 100 lb or more: use adult dose of 100 mg twice daily 1

Critical Administration Instructions

Patients must take doxycycline with a full glass of water (at least 100-200 mL) on a full stomach with non-dairy food and remain upright for at least 1 hour after administration to prevent esophagitis. 3, 4, 5

• Separate doxycycline from all dairy products (milk, yogurt, cheese, calcium-fortified juice) by at least 2 hours before AND after taking the medication to prevent chelation and reduced absorption 3, 5
• Separate from antacids and supplements containing calcium, iron, magnesium, or sodium bicarbonate by at least 2 hours 3, 5
• Counsel patients on photosensitivity risk and recommend sun protection measures 1

Common Pitfalls to Avoid

• Do not confuse prophylactic dosing with treatment dosing: Treatment of established chlamydia infection requires 100 mg twice daily for 7 days, not the 200 mg single-dose prophylaxis regimen 3, 2
• The 2-hour dairy separation applies both before AND after doxycycline administration—many patients miss this critical detail 5
• Suboptimal drug levels from dairy interaction can lead to treatment failure and antimicrobial resistance development 3, 5
• For STI prophylaxis, patients should not exceed 200 mg per 24 hours even with multiple sexual encounters 1