Frequently Asked Questions
Can drug allergies develop after years of safe use?
Yes. Drug allergy requires prior sensitisation — the immune system must have previously encountered the drug and developed a memory response. You can use a drug safely for years before developing a true allergic reaction. This is one reason why stopping a drug and restarting it can occasionally reveal an allergy that was not apparent initially.
Is cross-reactivity between penicillin and cephalosporins a concern?
Historical teaching suggested high cross-reactivity between penicillins and cephalosporins. Modern data shows cross-reactivity is much lower than previously thought — approximately 1–2%, primarily between specific structural side chains rather than the beta-lactam ring alone. Many patients with penicillin allergy labels can safely receive cephalosporins, but this should be assessed individually.
Can I take paracetamol if I’m allergic to NSAIDs?
Yes. Paracetamol (acetaminophen) works through a different mechanism from NSAIDs and does not cross-react with NSAID hypersensitivity in most patients. It is the preferred analgesic for NSAID-intolerant patients.
My child was given antibiotics as a baby and developed a rash. Are they allergic?
Probably not. Rashes in infants and young children during antibiotic courses are very common — most represent viral exanthems (rashes from the underlying infection) rather than drug allergy. Formal evaluation, when the child is old enough (typically 5 years or older), can clarify this and prevent lifelong avoidance of important medications.
What is drug provocation testing?
A drug provocation test (oral challenge) involves administering a small, then incrementally increasing dose of the suspected drug under medical supervision. It is the gold standard for confirming or excluding drug allergy and is used as part of the de-labelling process. It is performed in a setting equipped to manage allergic reactions.
This article is for educational purposes. It does not constitute medical advice. Dr. Keerthi Vardhan, MD (Internal Medicine), DM (Clinical Immunology & Rheumatology), Assistant Professor, NIMS Hospital, Hyderabad.