Is a test dose required when starting imipenem (a beta-lactam antibiotic) in patients with a history of allergy to beta-lactam antibiotics?

Test Dose for Starting Imipenem

No test dose is required when starting imipenem in patients with a history of beta-lactam allergy. Patients with a history of penicillin or cephalosporin allergy may receive carbapenems (including imipenem) without testing or additional precautions, irrespective of whether the prior reaction was anaphylactic. 1

Evidence-Based Approach to Imipenem Administration

For Patients with Penicillin or Cephalosporin Allergy

• Carbapenems can be administered directly without skin testing or graded challenge in patients with any history of penicillin or cephalosporin allergy, including those with prior anaphylaxis. 1

• The cross-reactivity rate between penicillins and carbapenems is less than 1%, far lower than historically believed. 2

• This recommendation represents a significant evolution from older practices that avoided carbapenems in beta-lactam allergic patients based on a single outdated study reporting 47.4% cross-reactivity with imipenem. 2

When Desensitization IS Required

Desensitization protocols should only be used in the rare circumstance of a patient with a confirmed IgE-mediated allergy specifically to imipenem itself (positive skin test to imipenem), when imipenem is absolutely necessary and no alternative exists. 3, 4

• Rapid intravenous desensitization can be performed over 4 hours using a continuous infusion protocol in intensive care settings for life-threatening infections. 3

• This scenario is extremely uncommon, as most patients labeled as "beta-lactam allergic" have reactions to penicillins or cephalosporins, not carbapenems. 5

Clinical Algorithm

1. Obtain detailed allergy history to identify the specific beta-lactam that caused the reaction (penicillin, cephalosporin, or carbapenem). 1

2. If history indicates penicillin or cephalosporin allergy: Administer imipenem directly without testing or precautions. 1

3. If history indicates prior reaction specifically to imipenem: Consider skin testing with imipenem; if positive and imipenem is essential, perform desensitization. 2

4. If multiple drug allergies or severe allergy history exists: A conservative approach may include drug challenge or tolerance induction, but this is not standard for carbapenem administration. 1

Important Caveats

• Avoid all beta-lactams (including carbapenems) in patients with a history of severe delayed reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS syndrome, or other severe cutaneous adverse reactions (SCARs). 1

• The recommendation to give carbapenems without testing applies to immediate and non-severe delayed hypersensitivity reactions to other beta-lactams, not to severe delayed reactions. 1

• Approximately 90% of patients reporting penicillin allergy are not truly allergic and could safely receive beta-lactams, making the liberal use of carbapenems in these patients particularly safe. 5

• Do not confuse cross-reactivity patterns: The minimal cross-reactivity between penicillins/cephalosporins and carbapenems is due to different core ring structures, unlike the R1 side chain similarities that drive cross-reactivity within the penicillin and cephalosporin classes. 1