A patient who received streptokinase for myocardial infarction two years ago now presents with another ST elevation myocardial infarction. Streptokinase is avoided this time primarily because:
- A It causes severe hypotension requiring adrenaline support
- B Antistreptococcal antibodies from prior exposure neutralize it and raise anaphylaxis risk ✓
- C It has developed resistance through upregulation of plasminogen activator inhibitor 1
- D Its half-life shortens to under 5 minutes on repeat dosing
Correct answer: B. Antistreptococcal antibodies from prior exposure neutralize it and raise anaphylaxis risk
Explanation
Streptokinase is a bacterial protein derived from group C beta-haemolytic streptococci and is highly antigenic. Prior exposure or recent streptococcal infection generates neutralizing antibodies that reduce efficacy and increase allergic and anaphylactic reactions, so it is generally not reused after 5 days to 12 months of first administration. Alteplase or tenecteplase are non-antigenic alternatives. Hypotension occurs but is not the reason for avoidance.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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Written and medically reviewed by the StethoPrep medical team.