Is ampicillin effective for treating non-typhoidal Salmonella bacteremia?

Ampicillin for Non-Typhoidal Salmonella Bacteremia

Ampicillin is not recommended as first-line therapy for non-typhoidal Salmonella bacteremia due to high rates of resistance (up to 60%), but may be used if susceptibility is confirmed. 1, 2, 3

First-Line Treatment Recommendations

• Ciprofloxacin is the primary drug of choice for non-typhoidal Salmonella bacteremia in adults, typically administered at 500 mg twice daily for 14 days 4
• For severe infections or in immunocompromised patients, initial combination therapy with ceftriaxone (2 g once daily IV) plus ciprofloxacin is recommended until susceptibility results are available 5, 4
• After susceptibility testing, therapy can be de-escalated to a single appropriate agent based on results 4

Role of Ampicillin

• Ampicillin is FDA-approved for treating infections caused by susceptible strains of Salmonella, including gastrointestinal tract infections and bacteremia 6
• However, high rates of ampicillin resistance (32-60%) have been documented in non-typhoidal Salmonella isolates 1, 2, 3
• Ampicillin should only be used if susceptibility testing confirms that the isolate is sensitive 5
• When used for susceptible organisms, the typical dose is 500 mg three times daily 5

Alternative Treatment Options

• Trimethoprim-sulfamethoxazole (TMP-SMZ) can be used if the organism is susceptible 5, 4
• Ceftriaxone is effective against most strains, including ampicillin-resistant isolates 5, 7
• All isolates typically remain susceptible to cefotaxime and ciprofloxacin, making these more reliable empiric choices 1, 2

Special Populations

Immunocompromised Patients

• HIV-infected persons with Salmonella bacteremia require long-term therapy to prevent recurrence 5
• Fluoroquinolones (ciprofloxacin) are usually the drugs of choice for susceptible organisms in HIV patients 5

Children

• In children, ampicillin may be used if the organism is susceptible 5
• Other options for children include TMP-SMZ, cefotaxime, and ceftriaxone 5
• Fluoroquinolones should be used with caution in children and only if no alternatives exist 5

Pregnant Women

• Ampicillin is considered safe during pregnancy and can be used if the organism is susceptible 5
• Other safe options include cefotaxime, ceftriaxone, or TMP-SMZ 5
• Fluoroquinolones should be avoided during pregnancy 5

Clinical Implications of Resistance

• Patients receiving antibiotics that are inactive in vitro (discordant therapy) experience more days of fever and longer hospital stays compared to those receiving effective antibiotics 3
• Antimicrobial-resistant non-typhoidal Salmonella infections are associated with higher rates of bloodstream infection and hospitalization 7
• Resistance to ampicillin has been increasing over time (from 12.9% to 52.5% in some studies) 2

Monitoring and Follow-up

• Blood cultures should be obtained in all patients with suspected Salmonella bacteremia 3
• Susceptibility testing should be performed promptly to guide appropriate antibiotic selection 3, 8
• For immunocompromised patients, consider long-term suppressive therapy to prevent recurrence 5

Common Pitfalls

• Empiric use of ampicillin without susceptibility testing may lead to treatment failure due to high resistance rates 1, 2, 7
• Delaying effective antimicrobial therapy in high-risk patients (immunocompromised, elderly, infants) may increase risk of complications 5, 4
• Household contacts of patients with Salmonella should be evaluated for asymptomatic carriage to prevent recurrent transmission, especially to immunocompromised individuals 5