rFVIIa Treatment and Efficacy Prediction in a Patient with Hermansky-Pudlak Syndrome Type 1 (HPS-1) Using Global Clotting Tests and Flow Cytometry.

The use of hemostatic agents for patients with platelet function related disorders causing impaired clotting is predominantly monitored via clinical parameters to date. For HPS patients, which suffer from a platelet storage pool disease, up to now mainly desmopressin and/or platelet concentrates have been administered as therapeutic agent in case of bleeding or surgery, with variable success. A more recent option is rFVIIa (NovoSeven®, N7), but there are few reports of its use in HPS patients. Before administering, it would be of therapeutical interest to know the maximum efficacy and the patient’s individual response. We investigated the hemostatic efficacy of rFVIIa in a patient with HPS-1 (63 y; 2 mutations: 972delC, T322N), who was undergoing tooth extraction. rFVIIa (90 U/kg body weight bolus) was administered 30 minutes before the procedure. Citrated blood samples were taken before, 15 minutes after rFVIIa administration and after the dental treatment was completed. Platelet rich plasma was generated by centrifugation (750g, 5 min) and the samples assayed using a fluorometric thrombin generation test (TGT), thrombelastography (RoTEG) and flow cytometry (FACS). The TGT was started adding Ca 16,7 mM and fluorogenic substrate. RoTEG was used with Ca, N7, tissue factor separately and combined. From the pre-substitution samples a reference value with rFVIIa, 80 U/ml added in vitro, and a dose-response curve from 0 to 400 U/ml were measured. N7 recovery was evaluated from pre-, post-substitution and the reference values. The TGT showed a presubstitutional residual activity of 50 % of the maximum ETP value, and 100% after substitution. TGT response to N7 was dose-dependent and entered a plateau at 90 % of the value after substitution, from 80 U/ml N7 on. The effect of subsituted rFVIIa persisted 2h after the extraction. Other TGT parameters (peak, time to peak, lag time) changed concordantly. RoTEG changes were most pronounced for Ca 12 mM alone as a trigger, which showed a transient reduction of clotting time and clot formation time after N7 substitution. FACS showed a 2.2fold CD62P increase indicating platelet activation after administration. Altogether, the TGT parameter changes corresponded best to the clinical outcome, as no bleeding events were observed during and 2h after the dental procedure. Thrombin generation may thus be useful to evaluate and predict N7 therapeutic efficacy in HPS patients. More HPS patients have to be treated to confirm these findings.