What are the causes and symptoms of adverse reactions to medication, also known as allergic reactions to pharmaceuticals (drugs)?

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Last updated: April 18, 2025View editorial policy

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From the Guidelines

Allergic reactions to medications should be managed promptly and aggressively, with severe reactions requiring immediate medical attention and potentially life-saving interventions like epinephrine administration, as noted in the most recent and highest quality study 1.

Key Considerations

  • Allergic reactions can range from mild rashes to life-threatening anaphylaxis, with symptoms including hives, itching, rash, swelling, wheezing, or gastrointestinal distress.
  • Common medications that frequently cause allergic reactions include antibiotics, NSAIDs, anticonvulsants, and certain chemotherapy drugs, such as platinum agents like carboplatin and cisplatin 1.
  • For mild reactions, antihistamines like diphenhydramine (Benadryl) 25-50mg every 4-6 hours may help manage symptoms temporarily, but severe reactions require immediate medical attention and may need epinephrine (via an EpiPen), corticosteroids, or other emergency interventions 1.

Management of Drug Reactions

  • For patients with a history of allergic reactions to platinum agents, consultation with an allergist or specialist with desensitization expertise is recommended before rechallenge 1.
  • Desensitization treatment should be managed by a physician with expertise and experience in platinum desensitization, and patients should be desensitized before resuming chemotherapy even if the symptoms resolved 1.
  • In cases of life-threatening reactions, such as anaphylaxis, the implicated drug should not be used again, and referral to an academic center with expertise in desensitization is preferred 1.

Prevention and Education

  • Patients should always inform all healthcare providers about their medication allergies and consider wearing a medical alert bracelet if they have severe allergies.
  • Genetic factors often influence susceptibility to medication allergies, and having one drug allergy may increase the risk of developing others.
  • Education on recognizing and managing allergic reactions, as well as the importance of prompt medical attention in severe cases, is crucial for patients and healthcare providers alike.

From the FDA Drug Label

Adrenalin® is a non-selective alpha and beta adrenergic agonist indicated for: Emergency treatment of allergic reactions (Type 1), including anaphylaxis Common adverse reactions to systemically administered epinephrine include anxiety, apprehensiveness, restlessness, tremor, weakness, dizziness, sweating, palpitations, pallor, nausea and vomiting, headache, and respiratory difficulties Arrhythmias, including fatal ventricular fibrillation, rapid rises in blood pressure producing cerebral hemorrhage, and angina have occurred

Allergic reactions to medication can be treated with epinephrine (IM) as it is indicated for emergency treatment of allergic reactions (Type 1), including anaphylaxis.

  • Key considerations:
    • Administer 0.3 to 0.5 mg (0.3 to 0.5 mL) intramuscularly or subcutaneously into anterolateral aspect of the thigh every 5 to 10 minutes as necessary for adults and children 30 kg (66 lbs) or more.
    • For children 30 kg (66 lbs) or less, administer 0.01 mg/kg (0.01 mL/kg), up to 0.3 mg (0.3 mL), intramuscularly or subcutaneously into anterolateral aspect of the thigh every 5 to 10 minutes as necessary.
    • Monitor for adverse reactions, including anxiety, apprehensiveness, restlessness, tremor, weakness, dizziness, sweating, palpitations, pallor, nausea and vomiting, headache, and respiratory difficulties.
    • Use with caution in patients with underlying heart disease, hyperthyroidism, Parkinson's disease, diabetes, and pheochromocytoma. 2 2

From the Research

Allergic Reactions to Medication

  • Allergic reactions to medication can be life-threatening and require immediate attention 3, 4
  • The most common symptoms of anaphylaxis, a severe allergic reaction, include urticaria, difficulty breathing, and mucosal swelling 3
  • Medications are one of the most common triggers of anaphylaxis, along with stinging insect venoms and foods 3

Management of Allergic Reactions

  • Epinephrine is the drug of choice for treating anaphylaxis and should be administered intramuscularly as soon as possible 5, 6, 7
  • Adjunct medications such as histamine H1 and H2 antagonists, corticosteroids, beta2 agonists, and glucagon may be considered after epinephrine administration 3
  • Patients should be monitored for a biphasic reaction, which can occur 4-12 hours after the initial reaction 3, 7

Prevention and Education

  • Patients who have experienced an allergic reaction to medication should be educated on how to avoid triggers and use an epinephrine auto-injector 3
  • Healthcare professionals should be aware of the clinical features and risk factors of allergic reactions to medication and be able to differentiate between allergic and non-allergic adverse drug reactions 4

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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