Penicillin allergy
Don't miss
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Anaphylaxis now | IM epinephrineThe only effective treatment to prevent anaphylactic shock and serious complications, including death.
Dose by age and weight: PHAC table opens in a new tab. INESSS tool, p. 22 opens in a new tabPHAC table, French opens in a new tab |
| Very severe history | Avoid penicillins after anaphylactic shock with intubation or cardiac arrest, or SJS/TEN, DRESS or AGEP.Refer promptly to allergology, without waiting for an emergency that needs a beta-lactam. |
| Provocation test | Only under medical supervision, where IM epinephrine is available. |
Diagnose
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| History | Document eight items:Which penicillin Confirmed by an allergologist or not Re-exposure since, without reaction A picture that does not suggest allergy Factors that call for special caution Immediate or delayed reaction How long ago Type of skin lesion |
| Immediate | Onset under 1 h after the first dose, gone within 24 hRare IgE reactions may start up to 6 h after an oral dose. Urticaria, angioedema, bronchospasm, hypotension, anaphylaxis. A minority of reported reactions. |
| Delayed | Hours to days after exposure (up to 6 weeks for DRESS).Maculopapular rash, AGEP, DRESS, SJS/TEN. Most reported reactions. The majority are para-infectious, not allergic. |
| Not an allergy | Any beta-lactam without precaution when the history is only:Isolated digestive symptoms (nausea, vomiting, diarrhea)
Non-specific symptoms (headache, fatigue, chills, worsening fever)
|
| Not a risk factor | Family history of penicillin allergy, atopy, food allergy |
| PEN-FAST | Optional, when the history is thin or unclear0–2: low risk; reintroduce a beta-lactam without skin testing.
3 or more: further workup or precautions before reintroducing; follow the INESSS algorithm.
Not for age 12 or under, serum sickness, interstitial nephritis, drug-induced hepatitis or cytopenias. INESSS tool, p. 10 opens in a new tabMDCalc PEN-FAST opens in a new tab |
| Risk tier | Low, moderate or high risk of recurrenceSet by severity, reaction type and how long ago. |
Investigate
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Provocation test, immediate history | Mainly to rule out an immediate reactionObtain informed consent first. One, two or three steps as the risk of recurrence rises; observe 60 min. High risk (very severe reaction): Avoid penicillins Different cephalosporin: with precautions, 2-step test Identical or similar cephalosporin: only if necessary, 3-step test Allergology consultation highly recommended |
| Provocation test, delayed history | One step (full dose) or two steps (one tenth, then the rest)Observe 48–72 h after each step, in clinic or at home. The person stops the antibiotic if symptoms appear. |
| Reading it | Subjective symptoms with no objective sign may be a nocebo effect: reassure and continue if the person agrees. Probable IgE-mediated reaction: stop and treat. No reaction confirms tolerance. |
Treat
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Allergist already confirmed | Follow the allergologist's adviceA reassessment may be needed, especially if testing was more than 5 years ago. |
| Low risk | Re-exposeAllergology consultation not needed. |
| Moderate or high risk | Permission depends on the drug class:Without precaution With precautions Only if necessary Avoid |
| Drug classes | Similar cephalosporins: Cefadroxil and Cefprozil (same side chain as Amoxicillin) Cephalexin (same side chain as Ampicillin) Different cephalosporins: Cefazolin, Cefuroxime, Cefixime, Ceftriaxone and the rest of the tool's list |
| Different cephalosporins, carbapenems | Do not avoid them on a penicillin labelCarbapenems are a last resort or for a specific indication. Prescribe them without caution, except after a very severe reaction. |
| Within the penicillins | Some people truly allergic to Amoxicillin may tolerate other penicillins, except Ampicillin. |
| Only if necessary | When a beta-lactam is essential (for example syphilis) and allergology is unavailable, decide on: Clinical judgment Your comfort level The person's preference |
H. pylori eradication with a penicillin label: see Dyspepsia and H. pylori.
Follow-up
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Tolerated | Tell the person, their community pharmacy and their treating cliniciansIdeally give the person a written note. |
| Label | Remove it only when the tolerated drug answers the labelUnspecified penicillin label and another penicillin tolerated: remove the label. Same penicillin tolerated: remove that label. A different beta-lactam tolerated: keep the culprit's label and chart the tolerance. |
| Reaction | Stop the antibiotic and treatComplete the new drug-allergy reaction declaration form (AH-707 in French, AH-707A in English).
Update the chart and the hospital and community pharmacy records.
Tell the person the diagnosis, the reaction type and the drug.
Assess the need for allergology. INESSS tool, p. 14 opens in a new tabDeclaration forms opens in a new tab |
| Refer to allergology | Severe history and no reintroduction done. Very severe history: promptly. Infection that needs a penicillin (syphilis, neurosyphilis). Frequent expected use (recurrent infections, COPD at high risk of exacerbation, cystic fibrosis, immunodeficiency, cancer, transplant). Multidrug-resistant infection that needs a penicillin. Polypharmacy with limited safe choices. Penicillin label plus a fluoroquinolone, macrolide or TMP-SMX label. |
| Short of referral | Conseil numérique for a specialist's advice on the reaction, the management or the need for allergology. INESSS tool, p. 15 opens in a new tabMSSS conseil numérique opens in a new tab |
Children, pregnancy, organ-specific reactions
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Children | Rashes on a penicillin can last several weeks and are generally not allergic. No PEN-FAST at age 12 or under. Refer when outpatient re-exposure is not feasible or parents refuse. Confirmed allergy: periodic reassessment by a pediatric allergologist, for example every 5 years. |
| Pregnancy | Same management as the general populationProvocation test any time if indicated, ideally in the second trimester. |
| Organ-specific reactions | After a cytopenia, hemolytic anemia, drug-induced hepatitis or interstitial nephritis: Penicillin or identical or similar cephalosporin possible on risk-benefit, with close lab monitoring Different cephalosporins and carbapenems without special precautions |
Reviewed 17 October 2026 against the official sources below.
Sources
Blue square: Québec. The code names the body; each section's key gives its full name.