Desmopressin for treatment of thrombocytopenia or platelet dysfunction
Keywords: Desmopressin
Aspirin
Clinical trial
Transfusion
Platelets
Systematic review
Anti-platelet drugs
Meta-analysis

The objective of the work presented in this thesis was to explore the role of potential alternatives to platelet transfusions and specifically to investigate whether desmopressin could be used for treatment of thrombocytopenia or platelet dysfunction. Patients with thrombocytopenia or platelet dysfunction are often treated with platelet transfusions to treat or prevent bleeding. However the evidence for the efficacy of platelet transfusion is limited and there is some evidence of harm. I have focused on thrombocytopenic patients with haematological malignancies or critically ill patients, who are amongst the groups most commonly treated with platelet transfusions.
The aims of this research were to determine:
1. If levels of Von Willebrand factor (VWF) or other measures of haemostasis are predictive of bleeding in severe thrombocytopenia;
2. Whether VWF compensates for thrombocytopenia in vitro;
3. The evidence for the efficacy of desmopressin in all patients undergoing surgery or invasive procedures;
4. The evidence for desmopressin for platelet dysfunction or thrombocytopenia;
5. If it is feasible to use desmopressin to treat critically ill thrombocytopenic patients in a clinical trial.
To identify derangements of haemostasis that may signify candidates for alternatives to platelet transfusions, I analysed blood samples from an observational trial of fifty patients with haematological malignancies and profound thrombocytopenia due to intensive chemotherapy. I used a panel of tests to investigate measures of primary haemostasis, thrombin generation, cross-linked fibrin formation and fibrinolysis. Using multivariable logistic regression, I found no consistent correlation between any measures of haemostasis and the risk of clinically significant bleeding. VWF antigen levels were the best predictor of clinically significant bleeding on the same day (odds ratio 0.31, 95% confidence interval 0.10 to 0.98, p=0.047) but were not predictive of severe bleeding over the 24 hours after the test (odds ratio 0.48, 95% confidence interval 0.10 to 2.34, p=0.36).
In a separate set of experiments, I evaluated thrombus formation under flow in thrombocytopenia. This technique was sensitive to the platelet count . Addition of exogenous VWF to thrombocytopenic blood resulted in improvement in thrombus formation, suggesting that agents that affect or influence VWF pathways might have a role.
Desmopressin can be used to increase VWF levels, so leading on from my laboratory experiments; I used systematic reviews and meta-analyses to assess whether desmopressin could be used in unselected patients to reduce bleeding peri-operatively. I identified 62 randomised controlled trials. Overall there was no evidence of benefit for administering desmopressin to unselected patients. However further analysis of eleven randomised controlled trials that focused on patients with platelet dysfunction found that desmopressin resulted in transfusion of fewer units of red cells (equivalent to a 25% reduction compared to control), less blood loss (equivalent to a 23% reduction compared to control) and a lower risk of requiring a re-operation due to bleeding (Peto odds ratio 0.39, 95% confidence interval 0.18 to 0.84). There was no evidence for an increase in thrombotic events. There was no randomised controlled trial evidence for perioperative desmopressin for patients with thrombocytopenia. These specific research gaps were addressed by designing new clinical trials.
I have commenced a randomised controlled feasibility trial of desmopressin versus placebo for critically ill patients with thrombocytopenia undergoing invasive procedures. This trial is ongoing and is the first randomised trial evaluating peri-procedural desmopressin in thrombocytopenia.
The programme of work arising from this research has the potential to benefit a large number of patients by preventing bleeding and reducing exposure to allogeneic blood components such as platelets. The results presented in this thesis are exploratory but are an important step on a path towards larger trials using desmopressin as an alternative, or adjunct to platelet transfusion.