Should adrenaline (epinephrine) be administered during the early stages of an allergic reaction to intravenous (IV) antibiotics or only after anaphylaxis occurs?

Early Administration of Adrenaline in Allergic Reactions to IV Antibiotics

Adrenaline (epinephrine) should be administered as early as possible at the first signs of an allergic reaction to IV antibiotics, without waiting for full anaphylaxis to develop, as early intervention prevents progression to life-threatening anaphylaxis and improves outcomes. 1

Rationale for Early Adrenaline Administration

The decision to administer adrenaline early in allergic reactions is supported by strong evidence:

• The Anaesthesia guidelines explicitly state that "adrenaline should be given as early as possible" in suspected anaphylactic reactions 2
• Delays in administering adrenaline have been implicated in contributing to fatalities 2
• Allergic reactions to IV antibiotics can progress rapidly to life-threatening anaphylaxis within minutes 1

Recognition of Early Allergic Signs

Early signs of allergic reactions to IV antibiotics that warrant immediate adrenaline administration include:

• Cardiovascular signs: hypotension, tachycardia (or bradycardia in ~10% of cases) 2
• Respiratory signs: bronchospasm, difficulty breathing, hypoxia 2
• Cutaneous signs: flushing, rash, urticaria, angioedema 2

It's important to note that hypotension may be the sole clinical feature in approximately 10% of patients with allergic anaphylaxis 2.

Management Algorithm for IV Antibiotic Allergic Reactions

1. Immediate Actions

• Stop administration of the suspected antibiotic immediately
• Call for help and note the time 2
• Administer adrenaline at first signs of allergic reaction:
  • Adults: 0.5 mg (0.5 mL of 1:1000 solution) IM into anterolateral thigh 2, 3
  • Children >30 kg: 0.3-0.5 mg IM 3
  • Children <30 kg: 0.01 mg/kg (up to 0.3 mg) IM 3
• Maintain airway and administer 100% oxygen 2
• Position patient appropriately (supine with elevated legs if hypotensive) 2

2. Secondary Management

• Administer IV fluids: initial crystalloid bolus of 0.5-1L for adults 2
• After adequate adrenaline and fluid resuscitation, administer:
  • Chlorphenamine 10 mg IV (adult dose) 2
  • Hydrocortisone 200 mg IV (adult dose) 2
• For persistent bronchospasm, consider inhaled bronchodilators 2
• For persistent hypotension despite adrenaline, consider alternative vasopressors 2

3. Ongoing Management

• Monitor patient in a monitored area for minimum 6 hours 2
• Obtain mast cell tryptase levels (ideally at 1-2 hours after reaction onset and again at 24 hours) 2

Common Pitfalls to Avoid

• Delayed administration of adrenaline: This is the most critical error and has been linked to fatalities 2
• Overreliance on antihistamines and corticosteroids: These are second-line treatments and should never be used alone in place of adrenaline 1
• Inadequate fluid resuscitation: Essential to combat vasodilatation 2
• Failure to remove the triggering agent: Can worsen the reaction 1
• Inappropriate route of administration: IM injection into the anterolateral thigh is preferred over subcutaneous injection for faster absorption 2

Special Considerations

• For patients with persistent Grade I allergic reactions that are difficult to manage with IM adrenaline, IV administration under close monitoring may be considered 4
• If several doses of adrenaline are required, consider starting an intravenous infusion of adrenaline (adrenaline has a short half-life) 2
• There is no absolute contraindication to epinephrine administration in anaphylaxis 2

In conclusion, the evidence strongly supports immediate administration of adrenaline at the first signs of an allergic reaction to IV antibiotics, rather than waiting for full anaphylaxis to develop. This approach saves lives by preventing progression to severe, potentially fatal anaphylaxis.