What are the uses and dosing of doxycycline (antibiotic)?

Doxycycline: Clinical Uses and Dosing

Doxycycline is a broad-spectrum tetracycline antibiotic with established uses in treating sexually transmitted infections (STIs), respiratory tract infections, skin/soft tissue infections, and as prophylaxis for malaria and bacterial STI prevention, with dosing varying from 100 mg twice daily for treatment to 200 mg single-dose for post-exposure prophylaxis.

Primary Antimicrobial Uses

Sexually Transmitted Infections

• First-line treatment for Chlamydia trachomatis: 100 mg orally twice daily for 7 days 1, 2, 3
• Alternative treatment for syphilis in penicillin-allergic non-pregnant patients:
  • Early syphilis: 100 mg orally twice daily for 2 weeks 3
  • Late syphilis (>1 year duration): 100 mg orally twice daily for 4 weeks 3
• Effective against many Neisseria gonorrhoeae strains, though not first-line due to increasing resistance 1, 2
• Nongonococcal urethritis (NGU) caused by C. trachomatis or U. urealyticum: 100 mg orally twice daily for 7 days 3
• Acute epididymo-orchitis: 100 mg orally twice daily for at least 10 days 3

Respiratory and Other Infections

• Skin and soft tissue infections (including MRSA): 100 mg orally twice daily 2
• Effective against intracellular pathogens, mycoplasmas, rickettsias, and certain protozoa 4, 5
• Inhalational anthrax post-exposure prophylaxis: 100 mg orally twice daily for 60 days 3

Malaria Prophylaxis

• Adults: 100 mg daily starting 1-2 days before travel, continued during travel and for 4 weeks after leaving malarious area 3
• Children >8 years: 2 mg/kg once daily (up to adult dose) 3

Post-Exposure Prophylaxis for Bacterial STIs (Doxy PEP)

The CDC strongly recommends offering doxy PEP to gay, bisexual, and other men who have sex with men (MSM) and transgender women (TGW) with at least one bacterial STI (syphilis, chlamydia, or gonorrhea) in the past 12 months 6, 1.

Dosing Protocol

• 200 mg (any formulation) taken as a single dose within 72 hours after oral, vaginal, or anal sex 6, 1
• Maximum dose: 200 mg per 24-hour period 6, 2
• Take as soon as possible after sexual exposure for optimal efficacy 6

Efficacy Data

• Reduces syphilis and chlamydia infections by >70% 1
• Reduces gonococcal infections by approximately 50% 1
• Combined reduction in bacterial STI acquisition of approximately two-thirds in high-risk populations 7

Population-Specific Recommendations

• Strong recommendation (AI quality evidence) for MSM and TGW with recent bacterial STI history 6
• May be considered for MSM and TGW without recent STI diagnosis but engaging in high-risk sexual activities 6
• No recommendation can be made for cisgender women, cisgender heterosexual men, transgender men, or other queer/nonbinary persons due to insufficient evidence 6

Monitoring Requirements

• Assess ongoing need for doxy PEP every 3-6 months 6, 1
• Perform bacterial STI screening at baseline and every 3-6 months 6, 1, 2
• Screen for gonorrhea and chlamydia at all anatomic sites of exposure (pharyngeal, rectal, urogenital) 6
• Serologic testing for syphilis at each visit 6
• HIV screening every 3-6 months for HIV-negative individuals not on PrEP 6, 1

Standard Dosing Regimens

Adults

• Initial dose: 200 mg on day 1 (given as 100 mg every 12 hours) 3
• Maintenance: 100 mg daily 3
• Severe infections (including chronic urinary tract infections): 100 mg every 12 hours 3

Pediatric Dosing (Children >8 years old)

• ≤100 lbs: 2 mg/lb divided into two doses on day 1, then 1 mg/lb daily (single or divided doses) 2, 3
• Severe infections: up to 2 mg/lb may be used 3
• >100 lbs: use adult dosing 2, 3

Pharmacologic Properties

• Long elimination half-life of approximately 12 hours, allowing once or twice daily dosing 1, 4
• High bioavailability with excellent tissue penetration due to lipophilicity 4, 5
• Therapeutic serum activity persists for 24 hours following recommended dosing 3
• Absorption not significantly affected by food or milk 3, 4
• Does not accumulate excessively in renal impairment 3

Administration Guidelines

To Minimize Adverse Effects

• Take with a full glass of liquid and adequate fluid 3
• Avoid lying down for 1 hour after administration to prevent esophagitis 6
• May be taken with food or milk if gastric irritation occurs 3

Adverse Effects and Precautions

Common Side Effects

• Photosensitivity (most common) 6, 1, 2
• Gastrointestinal symptoms: nausea, vomiting, diarrhea 6, 1, 2
• Esophagitis, esophageal discomfort, and ulceration 6, 1, 2
• Most adverse effects resolve with discontinuation 1

Antimicrobial Resistance Concerns

• Potential for development of antimicrobial resistance in other pathogens and commensal organisms 6
• Unknown long-term effects on microbiome 6
• Providers who commonly treat STIs generally believe benefits outweigh resistance risks for appropriate populations 8

Contraindications

• Pregnancy 2
• Children under 8 years of age 2, 3

Comprehensive Sexual Health Approach for Doxy PEP

When prescribing doxy PEP, implement within a broader prevention strategy 6, 1:

• Risk reduction counseling including condom use 6
• Discussion of reducing number of partners 6
• Linkage to HIV PrEP for HIV-negative individuals 6
• Linkage to HIV care for those living with HIV 6
• Vaccination as indicated 6
• Shared decision-making discussing both benefits and potential harms 6

Non-Infectious Dermatologic Uses

• Treatment of acne and rosacea at sub-antimicrobial doses 4, 9
• Anti-inflammatory properties useful for hair follicle diseases, granulomatous diseases, and vascular proliferation 9
• Inhibits molecular pathways beyond antimicrobial activity 9