Useful components of the medical history1,4,7,15
| What was the time frame of the reaction? | Allergic reactions to medications have characteristic times of onset, with some (such as IgE-mediated reactions) occurring within a few hours after a dose, and others (such as DRESS) being delayed in onset. Most drug allergies occur within the first two weeks of taking the drug; however, there are some exceptions (such as drug-induced lupus erythematosus and DRESS). |
| What cutaneous symptoms occurred? | Knowledge of the type of skin eruption aids in determining type of testing and prognosis (for example, urticaria is suggestive of an IgE-mediated reaction, whereas a maculopapular rash is suggestive of a type IV reaction). |
| Were any other medications being used concurrently? | It is possible that a newly prescribed medication, such as an antibiotic, is blamed for a reaction that was instead caused by another medication (such as nonsteroidal anti-inflammatory drugs). |
| Has the medication been used in the past? | Most drug-induced allergic reactions require a period of sensitization before a reaction, although some (such as DRESS) can occur on first exposure after several weeks of use. |
| Were there any patient-specific or drug-specific risk factors for a reaction? | Drug-specific risk factors include route of administration (parenteral and cutaneous routes of administration are associated with a higher degree of sensitization than oral administration), prolonged duration of dose associated with increased risk, repetitive exposure to the medication and concurrent virus (such as Epstein–Barr virus, which causes rash 100% of the time when amoxicillin is used concurrently). Host-specific risk factors include sex (female), older age, some genetic polymorphisms (such as HLA-B5701, which increases the risk of abacavir hypersensitivity) and underlying conditions (systemic lupus erythematosus, HIV) which increase the risk of allergic reactions. |
| Has this reaction occurred before? | Some cutaneous reactions, such as urticaria, may be due to another etiology (such as chronic urticaria), instead of a drug allergy. In addition, if the reaction has occurred in the past with a particular or related drug, this increases the likelihood of drug allergy. |
| How long ago was the reaction? | There is a high rate of outgrowing drug-induced allergic reactions to some medications (e.g., penicillin; within 10 years after an allergic reaction, most patients will be pencillin tolerant). |
Note: DRESS = drug reaction with eosinophilia and systemic symptoms, IgE = immunoglobulin E.