Doxycycline. What diseases does it treat?

For most adult bacterial infections, start doxycycline 100 mg orally twice daily (after a 200 mg loading dose if rapid attainment of levels is desired) and tailor duration to the diagnosis. For mild skin infections or acne you may use lower or modified-release dosing; for severe or systemic infections follow organism-specific guidance and consult local antibiograms.

Treat common indications with these typical regimens: uncomplicated community-acquired pneumonia – 100 mg twice daily for 7–10 days; uncomplicated urogenital chlamydia – 100 mg twice daily for 7 days; early Lyme disease (erythema migrans) – 100 mg twice daily for 10–21 days depending on clinical response; rickettsial infections (e.g., RMSF) – 100 mg twice daily until at least 3 days after fever subsides, usually 5–7 days total; acne and rosacea – subantimicrobial or low-dose formulations such as 40 mg once daily for extended courses measured in months.

Use doxycycline for prevention and special indications with specific instructions: malaria prophylaxis – 100 mg once daily starting 1–2 days before travel, daily during exposure, and for 4 weeks after return; anthrax post-exposure prophylaxis – commonly 100 mg twice daily for 60 days per public health guidance; certain zoonotic and intracellular infections (e.g., brucellosis, tularemia, Q fever) often include doxycycline as a core agent combined with other drugs as recommended.

Administer doxycycline with a full glass of water and remain upright for 30 minutes to reduce risk of esophageal irritation. Separate dosing from calcium, iron, magnesium and aluminum supplements or antacids by at least 2–4 hours to avoid reduced absorption. Expect photosensitivity – advise broad-spectrum sun protection and avoid prolonged sun exposure. Monitor for severe diarrhea and stop the drug if you suspect C. difficile colitis.

Avoid use in pregnancy and in children under 8 years because of risks to fetal and developing teeth and bone; weigh risks versus benefits when breastfeeding. Watch for uncommon adverse reactions such as intracranial hypertension (report new severe headache or vision changes) and drug interactions that can increase anticoagulant effect (monitor INR) or reduce absorption with cation-containing products. When resistance or unusual pathogens are suspected, obtain cultures and adjust therapy based on susceptibility results.

Acne Vulgaris: Doxycycline Dosing, Duration, Side Effects, and When to Switch Therapies

Dosing and duration

For moderate inflammatory acne, initiate doxycycline 100 mg orally twice daily; for patients who cannot tolerate twice-daily dosing, 100 mg once daily is an acceptable alternative. Use doxycycline 40 mg delayed-release (Oracea) once daily when the goal is anti-inflammatory control with lower antibacterial pressure.

Reassess at 6–8 weeks for early response and at 12 weeks for meaningful clinical improvement. Plan a primary antibiotic course of up to 12 weeks; extend to a maximum of 6 months only if lesions respond and a clear transition to maintenance (topical retinoid ± benzoyl peroxide, hormonal options for females) is underway. If disease improves, stop antibiotics and continue maintenance therapy rather than prolonging systemic therapy indefinitely.

Side effects, precautions, and monitoring

Common adverse effects: gastrointestinal upset (take with food to reduce nausea), photosensitivity (use broad-spectrum sunscreen and protective clothing), and esophagitis (take with a full glass of water and remain upright for 30 minutes). Separate doxycycline from antacids, calcium, iron and multivitamins by at least 2–3 hours to preserve absorption.

Serious but uncommon risks: intracranial hypertension (new severe headache or vision changes requires immediate discontinuation and evaluation), hepatotoxicity (stop and evaluate with unexplained jaundice or severe abdominal pain), and drug-related hypersensitivity. Avoid doxycycline during pregnancy and in children under 8 years due to permanent tooth discoloration and effects on bone. For women of childbearing potential, confirm non-pregnancy and discuss contraception; if pregnancy is planned or confirmed, stop doxycycline and switch therapy.

Routine laboratory monitoring is not required for short courses, but check liver enzymes if symptoms suggest hepatic injury or if therapy will be prolonged beyond 3 months. Advise patients to report severe adverse events, persistent GI intolerance, or visual disturbances immediately.

When to switch therapies

Switch or escalate therapy if: no meaningful improvement by 12 weeks despite adherence and concurrent topical therapy; new or progressive nodules, cysts, or scarring; intolerable adverse effects; pregnancy or planning pregnancy; or patient preference to avoid prolonged antibiotics. For treatment failure with inflammatory nodulocystic acne or scarring, refer for oral isotretinoin evaluation. For females with hormonally driven acne, consider combined oral contraceptives or spironolactone (typically 50–200 mg/day) as alternatives or adjuncts.

If intolerance is the issue, options include switching to low-dose 40 mg doxycycline for anti-inflammatory benefit, using topical regimens (benzoyl peroxide plus topical retinoid and topical antibiotic or clindamycin), or selecting an alternative systemic agent under dermatology guidance. For suspected antibiotic resistance or atypical infection, obtain cultures and tailor therapy based on results.

Community-Acquired Pneumonia: Indications, Dose Adjustments, and Managing Treatment Failure

Use doxycycline 100 mg PO twice daily (or 100 mg IV q12h when IV therapy is required) as an outpatient option for uncomplicated adult community-acquired pneumonia (CAP) in patients without contraindications.

Indications and patient selection

• Appropriate when treating mild outpatient CAP caused or suspected to be caused by typical pathogens (Streptococcus pneumoniae) or atypicals (Mycoplasma, Chlamydophila).
• Reasonable alternative for patients with immediate-type beta-lactam allergy or when macrolide use is undesirable (local macrolide resistance or drug interactions).
• Do not use as monotherapy for severe CAP requiring hospitalization, for suspected Pseudomonas or MRSA, or in pregnancy and children <8 years (risk of tooth discoloration and bone effects).

Dosing, adjustments, and interactions

• Typical adult dosing:
  • Oral: 100 mg twice daily; optional single loading dose 200 mg once followed by 100 mg twice daily.
  • IV: 100 mg every 12 hours (switch to oral when clinically stable and able to tolerate oral intake).
  • Duration: usually 5–7 days if clinically stable for 48–72 hours (afebrile and improving respiratory status); extend if slow resolution or complications present.
• Renal function: no dose adjustment for renal impairment or dialysis.
• Hepatic impairment: use caution with severe hepatic dysfunction; consider lower cumulative dosing and monitor liver tests during prolonged therapy.
• Obesity: standard dosing applies; reassess clinically and consider specialist input if response is suboptimal.
• Key drug interactions and administration tips:
  • Separate doxycycline and multivalent cation products (antacids, iron, calcium, sucralfate, dairy if high-calcium meal) by ≥2 hours to preserve absorption.
  • Monitor INR if patient on warfarin; doxycycline can potentiate anticoagulation.
  • Avoid concomitant isotretinoin or other retinoids due to increased intracranial hypertension risk.
  • Photosensitivity risk–counsel on sun protection.

Follow-up and monitoring: arrange clinical reassessment at 48–72 hours after starting therapy; check symptom trajectory, temperature, oxygenation, and adherence. Obtain baseline liver tests if prolonged therapy anticipated.

Managing treatment failure

• Define failure: clinical deterioration or lack of meaningful improvement by 48–72 hours (persistent fever, hypoxia, worsening dyspnea or radiographic progression).
• Immediate steps:
  1. Verify adherence and proper administration (timing relative to antacids, vomiting, absorption issues).
  2. Reassess diagnosis: repeat chest radiograph or chest CT if worsening, evaluate for complications (pleural effusion, empyema, lung abscess), and consider alternate diagnoses (pulmonary embolism, heart failure, noninfectious inflammation).
  3. Obtain microbiology: sputum Gram stain and culture, blood cultures (if febrile or systemically ill), and consider PCR/respiratory viral testing.
• Escalation of antimicrobial therapy:
  • If doxycycline failure without risk factors for resistant gram-negatives: switch to a beta-lactam (amoxicillin-clavulanate) plus doxycycline or add a macrolide, depending on allergy profile and local resistance patterns.
  • For patients with comorbidities or more severe disease, use a respiratory fluoroquinolone (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) or beta-lactam plus macrolide based on allergy status and risk of adverse effects.
  • If risk factors for Pseudomonas or MRSA exist (recent hospitalization, prior cultures, structural lung disease), broaden coverage to include anti-pseudomonal beta-lactams or anti-MRSA agents guided by local susceptibility and infectious diseases consultation.
• When to hospitalize: hemodynamic instability, hypoxemia (SpO2 <90% on room air or requiring supplemental oxygen), altered mental status, or inability to take oral meds–admit and obtain broader diagnostic testing and IV therapy.
• Consult infectious diseases or pulmonology for repeated failure, unusual pathogens, immunocompromised hosts, or complicated pleuropulmonary disease.

Lyme Disease and Tick-Bite Prophylaxis: Timing, Adult and Pediatric Regimens

Administer a single 200 mg dose of doxycycline to eligible adults within 72 hours of removing an Ixodes tick that was likely attached ≥36 hours and in regions where ≥20% of local ticks carry Borrelia burgdorferi.

Use prophylaxis only when the tick is clearly identified as an Ixodes species (or highly suspected), attachment time is estimated at ≥36 hours (engorged appearance or known exposure interval), doxycycline is not contraindicated, and the patient has not received doxycycline in the preceding 28 days. A randomized trial reported roughly an 87% reduction in development of erythema migrans with a single 200 mg dose compared with placebo.

Adult regimens and follow-up

Prophylaxis: doxycycline 200 mg PO once, given within 72 hours of tick removal. Do not repeat the single-dose strategy.

Treatment of early localized Lyme (erythema migrans): doxycycline 100 mg PO twice daily for 10–21 days (commonly 10–14 days for uncomplicated single EM). For neurologic (e.g., meningitis, cranial neuropathy) or cardiac (e.g., high-grade AV block) manifestations, use parenteral ceftriaxone and tailor duration to clinical response and specialty guidance.

Advise patients about side effects (photosensitivity, GI upset, risk of esophagitis); recommend taking doxycycline with a full glass of water and remaining upright for 30 minutes. If a rash or systemic symptoms develop within 30 days, initiate a full therapeutic course rather than additional prophylactic dosing.

Pediatric and pregnancy considerations

Children ≥8 years: prophylaxis dose 4.4 mg/kg PO once (single dose), maximum 200 mg, given within 72 hours and under the same eligibility criteria as adults. Treatment for early Lyme: doxycycline 4.4 mg/kg/day divided twice daily (2.2 mg/kg/dose), maximum 100 mg twice daily, for 10–21 days.

Children <8 years and pregnant or breastfeeding patients: avoid doxycycline for prophylaxis and routine treatment because of risks to tooth and bone development and fetal exposure. For prophylaxis in these groups, do not substitute an equivalent single-dose antibiotic; instead observe and start treatment if signs of Lyme disease appear. For confirmed early Lyme or symptomatic infection use amoxicillin (children: 50 mg/kg/day divided TID, max 500 mg TID; adults: 500 mg PO TID) for 14–21 days or cefuroxime axetil (children: ~30 mg/kg/day divided BID; adults: 500 mg PO BID) if penicillin allergy or intolerance to amoxicillin is present.

Malaria Chemoprophylaxis and Treatment: Indications, Travel Dosing, and Contraindications

Use doxycycline 100 mg orally once daily for malaria prevention in adults: start 1–2 days before entering the endemic area, continue daily during exposure, and stop 28 days (4 weeks) after leaving.

For treatment of uncomplicated malaria, give doxycycline 100 mg orally twice daily for 7 days only as an adjunct to a rapidly acting schizonticide (for example, combine with quinine for chloroquine-resistant P. falciparum or use after parenteral artesunate in severe cases); do not use doxycycline alone to treat acute severe malaria because it acts slowly against blood stages.

Avoid doxycycline in pregnancy and in children younger than 8 years because of fetal and permanent dental/bone effects; select alternative agents (e.g., mefloquine or atovaquone–proguanil for non-pregnant adults and appro­priate pediatric options per guidelines). Do not prescribe to anyone with a known tetracycline hypersensitivity.

Reduce absorption by divalent cations: separate doses from calcium, iron, magnesium, aluminum-containing antacids and sucralfate by at least 2–4 hours. Take doxycycline with a full glass of water and remain upright for 30–60 minutes to lower esophagitis risk; taking with food reduces GI upset and does not substantially impair efficacy.

Warn patients about photosensitivity–use high-SPF sunscreen and protective clothing. Stop medication and seek evaluation for severe diarrhea (risk of Clostridioides difficile), new severe headache or visual disturbance (possible intracranial hypertension), or signs of allergic reaction. Monitor INR if the patient is taking warfarin; adjust anticoagulation based on lab results.

Indication	Adult dosing	Pediatric / Special notes	Key contraindications & cautions
Chemoprophylaxis (travel)	100 mg PO once daily; start 1–2 days pre-travel, continue daily during exposure, stop 28 days after return	Not recommended for children <8 years; for children ≥8 follow pediatric product labeling or local public health guidance	Pregnancy, allergy to tetracyclines, significant hepatic disease; caution with breastfeeding
Adjunct treatment of uncomplicated malaria	100 mg PO twice daily for 7 days when given with a fast-acting antimalarial (e.g., quinine)	Use with pediatric dosing guidance for children ≥8; not a sole agent for acute therapy	Not for monotherapy in severe or complicated malaria; avoid concurrent isotretinoin (risk of intracranial hypertension)
When prophylaxis fails (symptoms while traveling)	Obtain prompt diagnostic testing (blood smear or rapid test); treat based on species and severity–do not rely on prophylaxis alone	Seek pediatric evaluation rapidly for febrile children regardless of prophylaxis	Any fever in a returning traveler from endemic areas requires urgent assessment

Choose doxycycline when adherence to a daily regimen is likely, when the traveler is not pregnant and is aged ≥8 years, and when local resistance patterns and drug availability favor a tetracycline-containing strategy. Offer alternatives for pregnant travelers, for young children, or for those with contraindications.

Sexually Transmitted Infections: Doxycycline for Chlamydia, Rectal Infections, and Partner Management

Recommend doxycycline 100 mg orally twice daily for 7 days for uncomplicated urogenital Chlamydia trachomatis in nonpregnant adults and adolescents who can adhere to a multi-day regimen.

For rectal chlamydia, prescribe doxycycline 100 mg PO twice daily for 7 days; randomized data show higher microbiologic cure rates versus a single 1 g azithromycin dose, so doxycycline is the preferred first-line agent for rectal infection in nonpregnant patients.

Treat lymphogranuloma venereum (LGV; serovars L1–L3) with doxycycline 100 mg PO twice daily for 21 days; arrange surgical drainage of fluctuant buboes when indicated and screen for co-infections (HIV, syphilis, gonorrhea).

If pregnancy or age <8 years prevents doxycycline use, substitute azithromycin 1 g PO single dose for chlamydia (follow obstetric/pediatric guidance for dosing and follow-up). Do not use doxycycline in pregnancy; consult obstetrics for LGV alternatives.

Offer expedited partner therapy (EPT) where legal: provide either azithromycin 1 g single dose or doxycycline 100 mg PO twice daily for 7 days for partners unable to access prompt clinical care. Prefer azithromycin for EPT when adherence is uncertain and avoid doxycycline for partners who are pregnant or children.

Advise patient and partners to abstain from sexual activity until treatment is completed and for 7 days after treatment completion (for single-dose azithromycin, wait 7 days after the dose). Treat sexual partners exposed during the previous 60 days or the most recent partner if exposure exceeds 60 days.

Test-of-cure with NAAT is recommended at 3–4 weeks after treatment only for pregnant persons and when symptoms persist or reinfection is suspected. Perform repeat screening at approximately 3 months after treatment to detect reinfection.

Counsel on adherence and adverse effects: take doxycycline with food or a large glass of water and remain upright for 30 minutes to reduce esophagitis risk; expect gastrointestinal upset and photosensitivity–use sunscreen and avoid prolonged sun exposure. Review drug interactions and allergy history before prescribing.

If NAAT remains positive at 3–4 weeks or symptoms continue, evaluate adherence, re-exposure, and alternate pathogens (including Mycoplasma genitalium); obtain targeted testing and consider retreatment per local guidelines or specialist consultation.