What questions should be asked when evaluating a patient with drug hypersensitivity?

Key Questions to Ask When Evaluating a Patient with Drug Hypersensitivity

When evaluating a patient with suspected drug hypersensitivity, a detailed and structured clinical history is the most important diagnostic tool to determine causality and prevent future reactions. 1

Essential Questions About the Reaction

Temporal Relationship and Drug Exposure

• Complete medication history: List all medications (including over-the-counter preparations) taken within 2 months prior to symptom onset 1
• Timeline for each drug: When was each drug started and stopped? 1
  • Create a detailed timeline using tools like www.drugrash.co.uk
• Latency period: How long after starting the drug did symptoms begin?
  • Most reactions occur 5-28 days after drug initiation (shorter if previously exposed) 1
  • Reactions occurring >3 months after starting therapy are rarely due to that drug 1

Reaction Characteristics

• Detailed description of symptoms: What exactly happened? 2
• Progression pattern: How did symptoms evolve? Did they occur in crops over days/weeks? 1
• Severity: Were hospitalization, emergency treatment, or intensive care required? 1
• Mucosal involvement: Were mouth, eyes, or genitourinary tract affected? 1
• Systemic symptoms: Was there fever, lymphadenopathy, or organ involvement? 1

Previous Exposures and Reactions

• Prior exposure: Had the patient taken this drug before? 1
• Previous reactions: Has the patient had reactions to the same or similar drugs? 1, 2
• Cross-reactivity concerns: Has the patient reacted to drugs in related classes? 3
  • For example, penicillin reactions and potential cephalosporin cross-reactivity

Management of the Reaction

• Treatment received: What treatments were given for the reaction? 1
• Response to dechallenge: Did symptoms improve after stopping the drug? 4
• Rechallenge information: Was the drug restarted? If so, what happened? 1
• Alternative explanations: Could other factors (infection, underlying disease) explain symptoms? 1

Risk Assessment Questions

• History of atopy: Does the patient have asthma, eczema, allergic rhinitis, or food allergies? 2
• Multiple drug allergies: Does the patient report allergies to multiple medications? 3
• Family history: Do relatives have drug allergies, particularly to similar medications? 2

Specific Reaction Pattern Questions

For Immediate Reactions (within hours)

• Timing: How quickly did symptoms appear after taking the drug? 1
• Anaphylaxis features: Was there difficulty breathing, throat tightness, hypotension? 5
• Skin manifestations: Were there hives, angioedema, flushing? 6

For Delayed Reactions (days to weeks)

• Rash characteristics: What did the rash look like? Was there blistering or skin detachment? 1
• SCAR warning signs: Were there painful skin, mucosal lesions, skin detachment, or systemic symptoms? 1
• Organ involvement: Were there abnormalities in liver function, kidney function, or blood counts? 1

Documentation and Follow-up Planning

• Previous documentation: Do you have medical records of the reaction? 2
• Current medications: What medications are you currently taking without problems? 2
• Alternative medications: What safe alternatives have been used since the reaction? 1

Critical Pitfalls to Avoid

• Failing to distinguish between drug intolerance and true hypersensitivity - many reported "allergies" are actually predictable side effects 4
• Not obtaining a complete medication list including over-the-counter drugs, supplements, and intermittently used medications 1
• Overlooking the timeline between drug initiation and symptom onset, which is crucial for determining causality 1
• Missing signs of severe reactions that require immediate specialist referral (mucosal involvement, skin detachment, organ dysfunction) 1

Special Considerations

• For patients with Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), routine drug hypersensitivity testing is not recommended, but specialist advice should be sought when the culprit drug is uncertain 1
• Patients with severe reactions should be given written information about drugs to avoid and encouraged to wear a MedicAlert bracelet 1, 2
• All drug allergies should be prominently documented in the patient's medical records and communicated to all healthcare providers 1, 2

Remember that a thorough clinical history remains the cornerstone of drug hypersensitivity evaluation, with additional testing guided by the specific reaction pattern and suspected medications.