What is the first‑line treatment regimen for uncomplicated brucellosis in an otherwise healthy adult?

First-Line Treatment for Uncomplicated Brucellosis

The optimal first-line treatment for uncomplicated brucellosis in an otherwise healthy adult is doxycycline 100 mg orally twice daily for 6 weeks combined with streptomycin 15 mg/kg intramuscularly daily for 2–3 weeks, which achieves the lowest relapse rate of approximately 5%. 1

Primary Recommended Regimen (AI – Highest Evidence)

• Doxycycline-streptomycin is the gold standard combination, consisting of doxycycline 100 mg orally twice daily for 6 weeks plus streptomycin 15 mg/kg intramuscularly daily for 2–3 weeks (typically 14–21 days). 1, 2
• This regimen carries an AI recommendation (strong evidence from randomized controlled trials) and delivers the lowest relapse rate at approximately 5%. 1
• Meta-analysis confirms superiority over other regimens, with an odds ratio of 3.17 (95% CI 2.05–4.91) favoring doxycycline-streptomycin over doxycycline-rifampicin. 3

Alternative First-Line Regimen (AI – When Injections Are Impractical)

• Doxycycline-rifampicin consists of doxycycline 100 mg orally twice daily for 6 weeks plus rifampicin 600–900 mg once daily (single morning dose) for 6 weeks. 1, 2
• This regimen also carries an AI recommendation but has a significantly higher relapse rate of approximately 16% compared to 5% with doxycycline-streptomycin. 1
• Choose this regimen only when intramuscular injections are not feasible or streptomycin is unavailable, as it offers the convenience of all-oral therapy. 1
• Avoid rifampicin-based regimens in regions with endemic tuberculosis due to the risk of promoting mycobacterial resistance. 1, 2

Alternative Aminoglycoside Regimen (BI – When Streptomycin Unavailable)

• Doxycycline-gentamicin consists of doxycycline 100 mg orally twice daily for 6 weeks plus gentamicin 5 mg/kg parenterally once daily for 7 days. 1
• This regimen carries a BI recommendation (moderate evidence) and offers comparable efficacy to doxycycline-streptomycin with wider availability of gentamicin. 1
• Relapse rates are slightly higher at 10–20% compared to the primary regimen. 1
• Use weight-based dosing (5 mg/kg daily), not fixed 500 mg doses, and ensure the full 7-day course is completed. 1
• Meta-analysis shows no significant difference between doxycycline-streptomycin and doxycycline-gentamicin (OR 1.89,95% CI 0.81–4.39). 3

Critical Treatment Principles

Combination Therapy Is Mandatory

• Never use monotherapy for brucellosis, as historical data show relapse rates of 13% with monotherapy versus 4.8% with combination therapy. 1
• Monotherapy promotes bacterial resistance and unacceptably high treatment failure. 4

Six-Week Duration Is Essential

• Do not shorten treatment below 6 weeks for uncomplicated disease, as courses shorter than 4 weeks result in relapse rates of approximately 22%. 1
• Even with optimal therapy, expect overall relapse rates of 5–15% in uncomplicated cases. 1, 2

Aminoglycoside Duration Matters

• Streptomycin requires 14–21 days (2–3 weeks) for optimal outcomes. 1
• Gentamicin requires a minimum of 7 days; shorter courses (5 days) show failure/relapse rates of 10–20%. 1

Second-Line Options (Lower-Quality Evidence)

Trimethoprim-Sulfamethoxazole (CII Recommendation)

• TMP-SMX 800 mg/160 mg twice daily for 6 weeks carries a CII recommendation (poor evidence, optional use). 1
• Never use as monotherapy, as relapse rates reach 46% when used alone for 45 days. 1
• May be considered as a cost-effective alternative in resource-limited settings when combined with rifampicin, though this combination still shows inferior outcomes. 1

Quinolone-Containing Regimens (CII Recommendation)

• Ofloxacin or ciprofloxacin should be reserved for second- or third-line use in combination regimens only. 1
• These agents carry a CII recommendation due to higher cost, potential to foster antimicrobial resistance, and higher relapse rates compared to standard regimens. 1
• Efficacy is comparable to doxycycline-rifampicin but with no advantage over established first-line options. 1

Common Pitfalls to Avoid

• Do not choose doxycycline-rifampicin as first-line when streptomycin is available, as relapse rates are three times higher (16% vs 5%). 1
• Do not discontinue therapy early based on symptom resolution alone, as microbiological cure lags behind clinical improvement. 1
• Do not use fixed-dose gentamicin (500 mg); always calculate weight-based dosing at 5 mg/kg daily. 1
• Do not shorten aminoglycoside courses: gentamicin requires 7 days minimum and streptomycin requires 14–21 days. 1
• Do not use TMP-SMX as monotherapy under any circumstances due to 46% relapse rates. 1

Algorithmic Approach to Regimen Selection

1. Is intramuscular injection feasible and streptomycin available?

   • Yes → Use doxycycline-streptomycin (lowest relapse rate, 5%). 1
   • No → Proceed to step 2.

2. Is gentamicin available?

   • Yes → Use doxycycline-gentamicin (relapse rate 10–20%). 1
   • No → Proceed to step 3.

3. Is the patient in a tuberculosis-endemic region?

   • No → Use doxycycline-rifampicin (relapse rate 16%). 1
   • Yes → Avoid rifampicin; consider doxycycline-TMP-SMX or refer for streptomycin/gentamicin access. 1, 2

4. Ensure 6-week total duration for all regimens. 1, 2