The safety and efficacy of argatroban were evaluated in a historically controlled efficacy and safety study (Study 1) and a follow-on efficacy and safety study (Study 2). These studies were comparable with regard to study design, study objectives, dosing regimens as well as study outline, conduct, and monitoring. In these studies, 568 adult patients were treated with argatroban and 193 adult patients made up the historical control group. Patients had a clinical diagnosis of heparin-induced thrombocytopenia, either without thrombosis (HIT) or with thrombosis (HITTS [heparin-induced thrombocytopenia and thrombosis syndrome]) and were males or non-pregnant females between the age of 18 and 80 years old. HIT/HITTS was defined by a fall in platelet count to less than 100,000/μL or a 50% decrease in platelets after the initiation of heparin therapy with no apparent explanation other than HIT. Patients with HITTS also had an arterial or venous thrombosis documented by appropriate imaging techniques or supported by clinical evidence such as acute myocardial infarction, stroke, pulmonary embolism, or other clinical indications of vascular occlusion. Patients who had documented histories of positive heparin-dependent antibody tests without current thrombocytopenia or heparin challenge (e.g., patients with latent disease) were also included if they required anticoagulation. 

These studies did not include patients with documented unexplained aPTT >200% of control at baseline, documented coagulation disorder or bleeding diathesis unrelated to HIT, a lumbar puncture within the past 7 days or a history of previous aneurysm, hemorrhagic stroke, or a thrombotic stroke within the past 6 months unrelated to HIT. 

The initial dose of argatroban was 2 mcg/kg/min. Two hours after the start of the argatroban infusion, an aPTT level was obtained and dose adjustments were made (up to a maximum of 10 mcg/kg/min) to achieve a steady-state aPTT value that was 1.5 to 3.0 times the baseline value, not to exceed 100 seconds. Overall the mean aPTT level for HIT and HITTS patients during the argatroban infusion increased from baseline values of 34 and 38 seconds, respectively, to 62.5 and 64.5 seconds, respectively. 

The primary efficacy analysis was based on a comparison of event rates for a composite endpoint that included death (all causes), amputation (all causes) or new thrombosis during the treatment and follow-up period (study days 0 to 37). Secondary analyses included evaluation of the event rates for the components of the composite endpoint as well as time-to-event analyses. 

In Study 1, a total of 304 patients were enrolled as follows: active HIT (n = 129), active HITTS (n =144), or latent disease (n = 31). Among the 193 historical controls, 139 (72%) had active HIT, 46 (24%) had active HITTS, and 8 (4%) had latent disease. Within each group, those with active HIT and those with latent disease were analysed together. Positive laboratory confirmation of HIT/HITTS by the heparin-induced platelet aggregation test or serotonin release assay was demonstrated in 174 of 304 (57%) argatroban-treated patients (i.e., in 80 with HIT or latent disease and 94 with HITTS) and in 149 of 193 (77%) historical controls (i.e., in 119 with HIT or latent disease and 30 with HITTS). The test results for the remainder of the patients and controls were either negative or not determined. 

There was a significant improvement in the composite outcome in patients with HIT and HITTS treated with argatroban versus those in the historical control group (see Table 9). The components of the composite endpoint are shown in Table 9. 

Time-to-event analyses showed significant improvements in the time-to-first event in patients with HIT or HITTS treated with argatroban versus those in the historical control group. The between-group differences in the proportion of patients who remained free of death, amputation, or new thrombosis were statistically significant in favor of argatroban by these analyses. 

A time-to-event analysis for the composite endpoint is shown in Figure 3 for patients with HIT and Figure 4 for patients with HITTS. 

* Censored indicates no clinical endpoint (defined as death, amputation, or new thrombosis) was observed during the follow-up period (maximum period of follow-up was 37 days).

* Censored indicates no clinical endpoint (defined as death, amputation, or new thrombosis) was observed during the follow-up period (maximum period of follow-up was 37 days).

In Study 2, a total of 264 patients were enrolled as follows: HIT (n = 125) or HITTS (n = 139). There was a significant improvement in the composite efficacy outcome for argatroban-treated patients, versus the same historical control group from Study 1, among patients having HIT (25.6% vs. 38.8%), patients having HITTS (41.0% vs. 56.5%), and patients having either HIT or HITTS (33.7% vs. 43.0%). Time-to-event analyses showed significant improvements in the time-to-first event in patients with HIT or HITTS treated with argatroban versus those in the historical control group. The between-group differences in the proportion of patients who remained free of death, amputation, or new thrombosis were statistically significant in favor of argatroban. 

Anticoagulant Effect

In Study 1, the mean (± SE) dose of argatroban administered was 2.0 ± 0.1 mcg/kg/min in the HIT arm and 1.9 ± 0.1 mcg/kg/min in the HITTS arm. Seventy-six percent of patients with HIT and 81% of patients with HITTS achieved a target aPTT at least 1.5-fold greater than the baseline aPTT at the first assessment occurring on average at 4.6 hours (HIT) and 3.9 hours (HITTS) following initiation of argatroban therapy. 

No enhancement of aPTT response was observed in subjects receiving repeated administration of argatroban. 

Platelet Count Recovery

In Study 1, 53% of patients with HIT and 58% of patients with HITTS, had a recovery of platelet count by Day 3. Platelet Count Recovery was defined as an increase in platelet count to >100,000/μL or to at least 1.5-fold greater than the baseline count (platelet count at study initiation) by Day 3 of the study.