Drugs That Stop Bleeding: Tranexamic Acid and Desmopressin
In the Cardiovascular section you met the clot-busters — alteplase and its cousins that dissolve a thrombus to reopen a blocked artery. Here we meet their mirror image: the clot-savers. When a patient is bleeding to death, we do the exact opposite — we protect the clot and rebuild the missing clotting proteins. Two cheap, elegant drugs — tranexamic acid and desmopressin — carry most of this work, and knowing them well can save a life in a trauma bay or a dental chair.
A motorcyclist arrives in the trauma bay, pale and bleeding, blood pressure sliding. Amid the crossmatching and the fluids, a nurse hangs a small, cheap infusion that will not be found on any high-tech shelf: tranexamic acid. It is given within the first hours — and in large trials, given early, it measurably lowers the chance he bleeds to death. Down the corridor, on the ward, a seven-year-old boy with mild haemophilia needs a tooth pulled. Instead of transfusing clotting factor, the dentist gives one dose of desmopressin an hour before; the boy's own stores of clotting protein surge, the socket clots, and he goes home. Two very different bleeds, two drugs that tip the balance back toward the clot.
First, the balance: making clots vs breaking them
Haemostasis is a tug-of-war. The body constantly builds fibrin clots to seal small injuries and constantly dissolves them once healing is underway. The dissolving side is the fibrinolytic system: an enzyme called plasmin chews through fibrin and takes the clot apart. Plasmin is made from an inactive precursor, plasminogen, which must first bind to the fibrin mesh to be activated. In the Cardiovascular section we deliberately turned this system UP with thrombolytics like alteplase, to melt a coronary clot. Here we want the opposite — to turn the dissolving system DOWN so a clot we badly need can hold.
Antifibrinolytics: stabilising the clot
Tranexamic acid and aminocaproic acid are lysine analogues. Plasminogen has lysine-binding sites that it uses to dock onto fibrin; these drugs sit in those sites and physically block the docking. If plasminogen cannot bind fibrin, it cannot be converted to active plasmin at the clot, and the fibrin mesh is not dissolved. The clot is stabilised. This is precisely the reverse of what alteplase does — one drug family promotes plasmin at the clot, the other forbids it.
The landmark CRASH-2 trial randomised over 20,000 trauma patients with significant bleeding to tranexamic acid or placebo. It reduced death due to bleeding — and the benefit depended sharply on timing: given within about 3 hours of injury it helped, but given later it did not, and may even harm. That is the origin of the trauma rule: give tranexamic acid EARLY or not at all.
The WOMAN trial randomised about 20,000 women with postpartum haemorrhage to tranexamic acid or placebo and found it reduced death due to bleeding, again best when given early. Together, CRASH-2 and WOMAN made tranexamic acid a cheap, WHO-listed, life-saving drug for two of the most common fatal bleeds worldwide.
The uses extend well beyond emergencies. Tranexamic acid controls surgical and dental bleeding — it is especially valued in haemophilia, where a mouthwash or short course lets a patient undergo a tooth extraction with far less oozing. It reduces heavy menstrual bleeding taken during the period, controls recurrent nosebleeds (epistaxis), and helps other mucosal bleeding. It is one of the most useful, underused drugs a clinician can reach for.
Because these drugs prevent clots from dissolving, the danger is a clot in the wrong place. Avoid them in active thromboembolism (a current DVT, PE, or clotting stroke), be cautious in DIC (disseminated intravascular coagulation, where widespread clotting is already the problem), and be wary in bleeding from the upper urinary tract — a stabilised clot can lodge in the ureter and cause obstruction and painful clot colic.
- Antifibrinolytics = tranexamic acid and aminocaproic acid (lysine analogues).
- They block plasminogen from binding fibrin, so plasmin can't dissolve the clot → clot stabilised.
- This is the exact opposite of thrombolytics (alteplase), which promote clot breakdown.
- Strong evidence: trauma (CRASH-2), postpartum haemorrhage (WOMAN) — give EARLY.
- Also for surgical/dental bleeding (esp. haemophilia), heavy periods, epistaxis, mucosal bleeds.
- Caution: active thromboembolism, DIC, and upper-urinary-tract bleeding (clot obstruction).
Desmopressin (DDAVP): borrowing the body's own factor
Desmopressin does not act on the clot — it restocks the shelves. Desmopressin (1-deamino-8-D-arginine vasopressin, DDAVP) is a synthetic analogue of vasopressin (antidiuretic hormone). Given for bleeding, it acts on endothelial cells to trigger the release of stored von Willebrand factor (vWF) and factor VIII into the blood. Von Willebrand factor is the glue that lets platelets stick to an injured vessel wall, and it also chaperones factor VIII; factor VIII is a key clotting-cascade protein. So a single dose of desmopressin transiently raises BOTH — improving platelet plugging and clotting at once.
In mild haemophilia A (a factor VIII deficiency) and type 1 von Willebrand disease (a partial vWF deficiency), the patient still has some stores to release — so desmopressin can raise their levels enough to cover a minor procedure like a dental extraction, avoiding a plasma-derived factor transfusion. It is also used for the platelet dysfunction of uraemia (kidney failure), where it improves clotting despite normal factor levels. (Desmopressin has an entirely separate life in the Endocrine section for diabetes insipidus, and in nocturnal enuresis — same drug, different job.)
Two traps make desmopressin different from just "giving factor." First, tachyphylaxis: because it releases PRE-STORED vWF and factor VIII, the endothelial stores deplete after one or two doses, and repeated dosing loses effect until the cells restock. Second, it is an antidiuretic hormone analogue — it makes the kidneys retain water, so it can cause hyponatraemia (low sodium) and fluid overload, especially with repeated doses or free-water intake. Restrict fluids and watch the sodium.
- Desmopressin (DDAVP) is a vasopressin (ADH) analogue that releases stored vWF and factor VIII.
- It transiently boosts platelet adhesion and clotting — no transfusion needed for minor bleeds.
- Uses: mild haemophilia A, type 1 von Willebrand disease, uraemic platelet dysfunction.
- Tachyphylaxis: stores deplete after repeated doses, so effect fades.
- It's an ADH analogue → risk of hyponatraemia and fluid retention; restrict fluids.
- Giving tranexamic acid in active thrombosis (DVT/PE/clotting stroke) or without considering DIC — you'd be stabilising the very clots that are the problem.
- Giving tranexamic acid late in trauma and expecting benefit — CRASH-2 showed early (≤3 h) or not at all.
- Forgetting desmopressin causes hyponatraemia — repeated doses plus free water can drop the sodium dangerously.
- Relying on repeated desmopressin doses and being surprised it stops working — that is tachyphylaxis from depleted stores.
- Confusing antifibrinolytics with anticoagulants. They have OPPOSITE goals: antifibrinolytics protect clots, anticoagulants prevent them.
How does tranexamic acid help stop bleeding?
- Antifibrinolytics (tranexamic acid, aminocaproic acid) block plasminogen from binding fibrin → the clot is stabilised — the mirror image of thrombolytics like alteplase.
- Tranexamic acid saves lives in trauma (CRASH-2) and postpartum haemorrhage (WOMAN) when given EARLY; also for surgical/dental (haemophilia), heavy periods, epistaxis.
- Avoid antifibrinolytics in active thromboembolism, DIC, and upper-urinary-tract bleeding.
- Desmopressin (DDAVP) releases stored vWF and factor VIII for mild haemophilia A, type 1 vWD, and uraemic platelet dysfunction — watch for tachyphylaxis and hyponatraemia.
- Rang HP, Dale MM, et al. Rang & Dale's Pharmacology — Haemostasis: antifibrinolytic and haemostatic agents; desmopressin.
- Katzung BG. Basic & Clinical Pharmacology — Drugs used in disorders of coagulation: antifibrinolytic agents and desmopressin.
- CRASH-2 trial collaborators. Effects of tranexamic acid on death and vascular occlusion in trauma patients (CRASH-2). Lancet, 2010.
- WOMAN trial collaborators. Effect of early tranexamic acid administration on mortality in postpartum haemorrhage (WOMAN). Lancet, 2017.
- Brunton LL, et al. Goodman & Gilman's The Pharmacological Basis of Therapeutics — Antifibrinolytic drugs and desmopressin.
