A patient is brought in with acute ischaemic stroke. tPA (alteplase) is considered. Which property of alteplase compared to streptokinase makes it preferred in acute stroke?

• A Alteplase has a longer half-life, allowing a single bolus dose with no infusion required
• B Alteplase is fibrin-selective: it preferentially activates plasminogen bound to fibrin clot rather than circulating plasminogen, reducing systemic lytic state and haemorrhage risk ✓
• C Alteplase does not cross the blood-brain barrier, preventing cerebral haemorrhage
• D Alteplase is non-antigenic (unlike streptokinase) and can be used within 4.5 hours only in non-allergic patients

Explanation

Alteplase (tPA) is a serine protease that has preferential affinity for plasminogen bound to fibrin clots (fibrin-selectivity). In a clot, fibrin acts as a cofactor that dramatically enhances tPA-mediated plasminogen activation. This selectivity results in local clot lysis with less activation of circulating plasminogen to plasmin, reducing the systemic lytic state and theoretically lowering bleeding risk compared to non-fibrin-selective agents like streptokinase. Streptokinase is also antigenic (prior streptococcal infection causes antibodies, reducing efficacy). Alteplase's short half-life (~5 minutes) requires IV infusion, not single bolus. Non-antigenicity (option D) is an additional advantage but not the primary reason for preference in stroke.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.