Brucellosis Treatment: Gold Standard Regimen

Brucellosis is a zoonotic infection caused by intracellular gram-negative coccobacilli of the genus Brucella, typically acquired from unpasteurized dairy products or contact with infected livestock. Because the organism survives within macrophages, treatment requires prolonged combination antibiotic therapy with agents that achieve good intracellular penetration; monotherapy is associated with unacceptably high relapse rates.

Correct Answer: Streptomycin and Doxycycline

The World Health Organization (WHO) recommends Doxycycline (100 mg twice daily for 6 weeks) combined with Streptomycin (an aminoglycoside, given intramuscularly for the first 2–3 weeks) as the classic and most efficacious regimen for adult brucellosis. This doxycycline–streptomycin combination has consistently shown the lowest relapse rates in comparative trials and is regarded as the gold standard against which all other regimens are measured.

• Doxycycline: A tetracycline with excellent intracellular penetration, directly targeting Brucella organisms sequestered within host cells.
• Streptomycin: An aminoglycoside that provides potent bactericidal synergy during the initial weeks of therapy, significantly reducing relapse compared to doxycycline monotherapy or doxycycline paired with oral agents alone.

Where streptomycin is impractical (e.g., due to injection requirements, nephrotoxicity, or ototoxicity concerns), doxycycline plus rifampin for 6 weeks is used as an acceptable oral alternative — but this combination is considered slightly inferior in efficacy to the doxycycline–streptomycin regimen and is not the true gold standard.

Why the Other Options Are Incorrect

• Azithromycin and Rifampin: Not a standard first-line regimen for brucellosis; azithromycin is not a preferred agent in established international guidelines for this infection and lacks the robust efficacy data of the doxycycline-based regimens.
• Trimethoprim and Sulfamethoxazole: Cotrimoxazole is used mainly as an alternative in children, pregnant women, or in combination with other agents for neurobrucellosis, but it is not the gold-standard regimen for the general adult population.
• Amikacin and Ciprofloxacin: This combination has been studied but is not established as first-line or gold-standard therapy; fluoroquinolone-based regimens have shown higher relapse rates compared to the doxycycline–streptomycin combination.

Therefore, the correct and internationally accepted gold-standard treatment for brucellosis in adults is Streptomycin and Doxycycline.