CLINICAL PHARMACOLOGY
Mechanism Of Action
Eltrombopag is an orally bioavailable, small-molecule TPO-receptor agonist that interacts with the transmembrane domain of the human TPO-receptor and initiates signaling cascades that induce proliferation and differentiation from bone marrow progenitor cells.
Pharmacodynamics
In clinical trials, treatment with PROMACTA resulted in dose-dependent increases in platelet counts following repeated (daily) dosing. The increase in platelet counts reached a maximum approximately two weeks after the initiation of dosing, and returned to baseline within approximately two weeks after the last dose of PROMACTA.
Cardiac Electrophysiology
At doses up to 150 mg (the maximum recommended dose) daily for 5 days, PROMACTA did not prolong the QT/QTc interval to any relevant extent.
Pharmacokinetics
Eltrombopag demonstrated a dose-proportional increase in exposure between doses of 50 to 150 mg/day in healthy adult subjects. Eltrombopag AUC was approximately 1.7 fold higher in patients with chronic ITP and approximately 2.8-fold higher in patients with HCV compared to healthy subjects. Steady-state was achieved after approximately 1 week of once daily treatment, with geometric mean accumulation ratio of 1.56 (90% confidence interval 1.20, 1.63) at 75 mg/day. Eltrombopag AUC was approximately 3.2 fold higher in patients with definitive immunosuppressive therapy-naïve severe aplastic anemia compared to healthy subjects suggesting higher relative exposure compared to healthy subjects or patients with ITP and similar exposure compared to patients with chronic hepatitis C. Eltrombopag for oral suspension delivered 22% higher plasma AUC0-INF than the tablet formulation.
Absorption
Eltrombopag is absorbed with a peak concentration occurring 2 to 6 hours after oral administration. Oral absorption of drug-related material following administration of a single 75-mg solution dose was estimated to be at least 52%.
Effect of Food
A standard high-fat breakfast (876 calories, 52 g fat, 71 g carbohydrate, 34 g protein, and 427 mg calcium) significantly decreased plasma eltrombopag AUC0-INF by approximately 59% and Cmax by 65% and delayed Tmax by 1 hour. The calcium content of this meal may have also contributed to this decrease in exposure.
The effect of administration of a single 25-mg dose of eltrombopag for oral suspension with a high-calcium, moderate-fat, moderate calorie meal on AUC0-INF and Cmax in healthy adult subjects is presented in Table 14.
Table 14. Effect on Plasma Eltrombopag Pharmacokinetic Parameters After Administration of a Single 25-mg Dose of Eltrombopag for Oral Suspension with a High Calcium Meala in Healthy Adult Subjects
Timing of eltrombopag for oral suspension dose |
Mean (90% CI) reduction in plasma eltrombopag AUC0-INF |
Mean (90% CI) reduction in plasma eltrombopag Cmax |
With a high-calcium, moderate-fat, moderate-calorie meal |
75% ( 71%, 88%) |
79% (76%, 82%) |
2 hours after the high-calcium, moderate-fat, moderate-calorie meal |
47% (40%, 53%) |
48% (40%, 54%) |
2 hours before the high-calcium, moderate-fat, moderate-calorie meal |
20% (9%, 29%) |
14% (2%, 25%) |
a 372 calories, 9 g fat, and 448 mg calcium |
Distribution
The concentration of eltrombopag in blood cells is approximately 50% to 79% of plasma concentrations based on a radiolabel study. In vitro studies suggest that eltrombopag is highly bound to human plasma proteins (greater than 99%). Eltrombopag is a substrate of BCRP, but is not a substrate for P-glycoprotein (P-gp) or OATP1B1.
Elimination
The plasma elimination half-life of eltrombopag is approximately 21 to 32 hours in healthy subjects and 26 to 35 hours in patients with ITP.
Metabolism
Absorbed eltrombopag is extensively metabolized, predominantly through pathways including cleavage, oxidation, and conjugation with glucuronic acid, glutathione, or cysteine. In vitro studies suggest that CYP1A2 and CYP2C8 are responsible for the oxidative metabolism of eltrombopag. UGT1A1 and UGT1A3 are responsible for the glucuronidation of eltrombopag.
Excretion
The predominant route of eltrombopag excretion is via feces (59%), and 31% of the dose is found in the urine. Unchanged eltrombopag in feces accounts for approximately 20% of the dose; unchanged eltrombopag is not detectable in urine.
Specific Populations
Ethnicity
Eltrombopag concentrations in Asian (i.e., Japanese, Chinese, Taiwanese, Korean) patients with ITP or chronic hepatitis C, were 50% to 55% higher compared with non-Asian subjects [see DOSAGE AND ADMINISTRATION].
Eltrombopag exposure in healthy African-American subjects was approximately 40% higher than that observed in Caucasian subjects in one clinical pharmacology trial and similar in three other clinical pharmacology trials. The effect of African-American ethnicity on exposure and related safety and efficacy of eltrombopag has not been established.
Hepatic Impairment
Following a single dose of PROMACTA (50 mg), plasma eltrombopag AUC0-INF was 41% higher in patients with mild hepatic impairment (Child-Pugh Class A) compared with subjects with normal hepatic function. Plasma eltrombopag AUC0-INF was approximately 2-fold higher in patients with moderate (Child-Pugh Class B) and severe hepatic impairment (Child-Pugh Class C) compared with subjects with normal hepatic function. The half-life of eltrombopag was prolonged 2-fold in these patients. This clinical trial did not evaluate protein-binding effects.
Chronic Liver Disease
Following repeat doses of eltrombopag in patients with thrombocytopenia and with chronic liver disease, mild hepatic impairment resulted in an 87% to 110% higher plasma eltrombopag AUC(0-τ) and moderate hepatic impairment resulted in approximately 141% to 240% higher plasma eltrombopag AUC(0-τ) values compared with patients with normal hepatic function. The half-life of eltrombopag was prolonged 3-fold in patients with mild hepatic impairment and 4-fold in patients with moderate hepatic impairment. This clinical trial did not evaluate protein-binding effects.
Chronic Hepatitis C
Patients with chronic hepatitis C treated with PROMACTA had higher plasma AUC(0-τ) values as compared with healthy subjects, and AUC(0-τ) increased with increasing Child-Pugh score. Patients with chronic hepatitis C and mild hepatic impairment had approximately 100% to 144% higher plasma AUC(0-τ) compared with healthy subjects. This clinical trial did not evaluate protein-binding effects.
Renal Impairment
Following a single dose of PROMACTA (50 mg), the average total plasma eltrombopag AUC0-INF was 32% to 36% lower in subjects with mild (estimated creatinine clearance (CLCr) by Cockcroft - Gault equation: 50 to 80 mL/min), to moderate (CLCr of 30 to 49 mL/min) renal impairment and 60% lower in subjects with severe (CLCr less than 30 mL/min) renal impairment compared with healthy subjects. The effect of renal impairment on unbound (active) eltrombopag exposure has not been assessed.
Pediatric Patients
The pharmacokinetics of eltrombopag have been evaluated in 168 pediatric patients 1 year and older with ITP dosed once daily in two trials. Plasma eltrombopag apparent clearance following oral administration (CL/F) increased with increasing body weight. Asian pediatric patients with ITP had approximately 43% higher plasma eltrombopag AUC(0-τ) values as compared with non-Asian patients.
Plasma eltrombopag AUC(0-τ) and Cmax in pediatric patients aged 12 to 17 years was similar to that observed in adults. The pharmacokinetic parameters of eltrombopag in pediatric patients with ITP are shown in Table 15.
Table 15. Geometric Mean (95% CI) Steady-state Plasma Eltrombopag Pharmacokinetic Parametersa in Patients with ITP (Normalized to a Once-daily 50-mg Dose)
Age |
Cmax b
(mcg/mL) |
AUC(0-τ)b
(mcg·hr/mL) |
Adults (n = 108) |
7.03 (6.44, 7.68) |
101 (91.4, 113) |
12 to 17 years (n = 62) |
6.80 (6.17, 7.50) |
103 (91.1, 116) |
6 to 11 years (n = 68) |
10.3 (9.42, 11.2) |
153 (137, 170) |
1 to 5 years (n = 38) |
11.6 (10.4, 12.9) |
162 (139, 187) |
a PK parameters presented as geometric mean (95% CI)
b Based on population PK post-hoc estimates |
Drug Interaction Studies
Clinical Studies
Effect of Drugs on Eltrombopag
Effect of Polyvalent Cation-containing Antacids on Eltrombopag:
The coadministration of a single dose of PROMACTA (75 mg) with a polyvalent cation-containing antacid (1,524 mg aluminum hydroxide, 1,425 mg magnesium carbonate, and sodium alginate) decreased plasma eltrombopag AUC0-INF and Cmax by approximately 70%. The contribution of sodium alginate to this interaction is not known.
Effect of HIV Protease Inhibitors on Eltrombopag:
The coadministration of repeat-dose lopinavir 400 mg/ritonavir 100 mg (twice daily) with a single dose of PROMACTA (100 mg) decreased plasma eltrombopag AUC0-INF by 17%.
Effect of HCV Protease Inhibitors on Eltrombopag:
The coadministration of repeat-dose telaprevir (750 mg every 8 hours) or boceprevir (800 mg every 8 hours) with a single dose of PROMACTA (200 mg) to healthy adult subjects in a clinical trial did not alter plasma eltrombopag AUC0-INF or Cmax to a significant extent.
Effect of Cyclosporine on Eltrombopag:
The coadministration of a single dose of PROMACTA (50 mg) with a single dose of an OATP and BCRP inhibitor cyclosporine (200 mg or 600 mg) decreased plasma eltrombopag AUC0-INF by 18% to 24% and Cmax by 25% to 39%.
Effect of Pegylated Interferon alfa-2a + Ribavirin and Pegylated Interferon alfa-2b + Ribavirin on Eltrombopag:
The presence of pegylated interferon alfa + ribavirin therapy did not significantly affect the clearance of eltrombopag.
Effect of Eltrombopag on Other Drugs
Effect of Eltrombopag on Cytochrome P450 Enzymes Substrates:
The coadministration of multiple doses of PROMACTA (75 mg once daily for 7 days) did not result in the inhibition or induction of the metabolism of a combination of probe substrates for CYP1A2 (caffeine), CYP2C19 (omeprazole), CYP2C9 (flurbiprofen), or CYP3A4 (midazolam) in humans.
Effect of Eltrombopag on Rosuvastatin:
The coadministration of multiple doses of PROMACTA (75 mg once daily for 5 days) with a single dose of rosuvastatin (OATP1B1 and BCRP substrate; 10 mg) increased plasma rosuvastatin AUC0-INF by 55% and Cmax by 103%.
Effect of Eltrombopag on HCV Protease Inhibitors:
The coadministration of repeat-dose telaprevir (750 mg every 8 hours) or boceprevir (800 mg every 8
hours) with a single dose of PROMACTA (200 mg) to healthy adult subjects in a clinical trial did not
alter plasma telaprevir or boceprevir AUC0-INF or Cmax to a significant extent.
In Vitro Studies
Eltrombopag Effect on Metabolic Enzymes
Eltrombopag has demonstrated the potential to inhibit CYP2C8, CYP2C9, UGT1A1, UGT1A3,
UGT1A4, UGT1A6, UGT1A9, UGT2B7, and UGT2B15.
Eltrombopag Effect on Transporters
Eltrombopag has demonstrated the potential to inhibit OATP1B1 and BCRP.
Animal Pharmacology And/Or Toxicology
Treatment-related cataracts were detected in rodents in a dose- and time-dependent manner. At greater than or equal to 6 times the human clinical exposure based on AUC in patients with ITP at 75 mg/day and 3 times the human clinical exposure based on AUC in patients with chronic hepatitis C at 100 mg/day, cataracts were observed in mice after 6 weeks and in rats after 28 weeks of dosing. At greater than or equal to 4 times the human clinical exposure based on AUC in patients with ITP at 75 mg/day and 2 times the human clinical exposure based on AUC in patients with chronic hepatitis C at 100 mg/day, cataracts were observed in mice after 13 weeks and in rats after 39 weeks of dosing [see WARNINGS AND PRECAUTIONS].
Renal tubular toxicity was observed in studies up to 14 days in duration in mice and rats at exposures that were generally associated with morbidity and mortality. Tubular toxicity was also observed in a 2-year oral carcinogenicity study in mice at doses of 25, 75, and 150 mg/kg/day. The exposure at the lowest dose was 1.2 times the human clinical exposure based on AUC in patients with ITP at 75 mg/day and 0.6 times the human clinical exposure based on AUC in patients with chronic hepatitis C at 100 mg/day. No similar effects were observed in mice after 13 weeks at exposures greater than those associated with renal changes in the 2-year study, suggesting that this effect is both dose- and time-dependent.
Clinical Studies
Chronic ITP
Adults
The efficacy and safety of PROMACTA in adult patients with chronic ITP were evaluated in three randomized, double-blind, placebo-controlled trials and in an open-label extension trial.
In Study TRA100773B and Study TRA100773A (referred to as Study 773B and Study 773A, respectively [NCT00102739]), patients who had completed at least one prior ITP therapy and who had a platelet count less than 30 x 109/L were randomized to receive either PROMACTA or placebo daily for up to 6 weeks, followed by 6 weeks off therapy. During the trials, PROMACTA or placebo was discontinued if the platelet count exceeded 200 x 109/L.
The median age of the patients was 50 years and 60% were female. Approximately 70% of the patients had received at least 2 prior ITP therapies (predominantly corticosteroids, immunoglobulins, rituximab, cytotoxic therapies, danazol, and azathioprine) and 40% of the patients had undergone splenectomy. The median baseline platelet counts (approximately 18 x 109/L) were similar among all treatment groups.
Study 773B randomized 114 patients (2:1) to PROMACTA 50 mg or placebo. Study 773A randomized 117 patients (1:1:1:1) among placebo or 1 of 3 dose regimens of PROMACTA, 30 mg, 50 mg, or 75 mg each administered daily.
The efficacy of PROMACTA in this trial was evaluated by response rate, defined as a shift from a baseline platelet count of less than 30 x 109/L to greater than or equal to 50 x 109/L at any time during the treatment period (Table 16).
Table 16. Studies 773B and 773A: Platelet Count Response (≥ 50 x 109/L) Rates in Adults with Chronic Immune Thrombocytopenia
Study |
PROMACTA
50 mg Daily |
Placebo |
773B |
43/73 (59%)a |
6/37 (16%) |
773A |
19/27 (70%)a |
3/27 (11%) |
a p-value < 0.001 for PROMACTA versus placebo |
The platelet count response to PROMACTA was similar among patients who had or had not undergone splenectomy. In general, increases in platelet counts were detected 1 week following initiation of PROMACTA and the maximum response was observed after 2 weeks of therapy. In the placebo and 50-mg–dose groups of PROMACTA, the trial drug was discontinued due to an increase in platelet counts to greater than 200 x 109/L in 3% and 27% of the patients, respectively. The median duration of treatment with the 50-mg dose of PROMACTA was 43 days in Study 773B and 42 days in Study 773A.
Of 7 patients who underwent hemostatic challenges, additional ITP medications were required in 3 of 3 placebo group patients and 0 of 4 patients treated with PROMACTA. Surgical procedures accounted for most of the hemostatic challenges. Hemorrhage requiring transfusion occurred in one placebo group patient and no patients treated with PROMACTA.
In the RAISE study (NCT00370331), 197 patients were randomized (2:1) to receive either PROMACTA 50 mg once daily (n = 135) or placebo (n = 62) for 6 months, during which time the dose of PROMACTA could be adjusted based on individual platelet counts. Patients were allowed to taper or discontinue concomitant ITP medications after being treated with PROMACTA for 6 weeks. Patients were permitted to receive rescue treatments at any time during the trial as clinically indicated.
The median ages of the patients treated with PROMACTA and placebo were 47 years and 52.5 years, respectively. Approximately half of the patients treated with PROMACTA and placebo (47% and 50%, respectively) were receiving concomitant ITP medication (predominantly corticosteroids) at randomization and had baseline platelet counts less than or equal to 15 x 109/L (50% and 48%, respectively). A similar percentage of patients treated with PROMACTA and placebo (37% and 34%, respectively) had a prior splenectomy.
The efficacy of PROMACTA in this trial was evaluated by the odds of achieving a platelet count greater than or equal to 50 x 109/L and less than or equal to 400 x 109/L for patients receiving PROMACTA relative to placebo and was based on patient response profiles throughout the 6-month treatment period. In 134 patients who completed 26 weeks of treatment, a sustained platelet response (platelet count greater than or equal to 50 x 109/L and less than or equal to 400 x 109/L for 6 out of the last 8 weeks of the 26-week treatment period in the absence of rescue medication at any time) was achieved by 60% of patients treated with PROMACTA, compared with 10% of patients treated with placebo (splenectomized patients: PROMACTA 51%, placebo 8%; non-splenectomized patients: PROMACTA 66%, placebo 11%). The proportion of responders in the group of patients treated with PROMACTA was between 37% and 56% compared with 7% and 19% in the placebo treatment group for all on-therapy visits. Patients treated with PROMACTA were significantly more likely to achieve a platelet count between 50 x 109/L and 400 x 109/L during the entire 6-month treatment period compared with those patients treated with placebo.
Outcomes of treatment are presented in Table 17 for all patients enrolled in the trial.
Table 17. RAISE: Outcomes of Treatment in Adults with Chronic Immune Thrombocytopenia
Outcome |
PROMACTA
N = 135 |
Placebo
N = 62 |
Mean number of weeks with platelet counts ≥ 50 x 109/L |
11.3 |
2.4 |
Requiring rescue therapy, n (%) |
24 (18) |
25 (40) |
Among 94 patients receiving other ITP therapy at baseline, 37 (59%) of 63 patients treated with PROMACTA and 10 (32%) of 31 patients in the placebo group discontinued concomitant therapy at some time during the trial.
In the EXTEND study (NCT00351468), patients who completed any prior clinical trial with PROMACTA were enrolled in an open-label, single-arm trial in which attempts were made to decrease the dose or eliminate the need for any concomitant ITP medications. PROMACTA was administered to 302 patients in EXTEND; 218 patients completed 1 year, 180 patients completed 2 years, 107 patients completed 3 years, 75 patients completed 4 years, 34 patients completed 5 years, and 18 patients completed 6 years of therapy. The median baseline platelet count was 19 x 109/L prior to administration of PROMACTA. Median platelet counts at 1, 2, 3, 4, 5, 6, and 7 years on study were 85 x 109/L, 85 x 109/L, 105 x 109/L, 64 x 109/L, 75 x 109/L, 119 x 109/L, and 76 x 109/L, respectively.
Pediatric Patients
The efficacy and safety of PROMACTA in pediatric patients 1 year and older with chronic ITP were evaluated in two double-blind, placebo-controlled trials. The trials differed in time since ITP diagnosis: at least 6 months versus at least 12 months. During the trials, doses could be increased every 2 weeks to a maximum of 75 mg once daily. The dose of PROMACTA was reduced if the platelet count exceeded 200 x 109/L and interrupted and reduced if it exceeded 400 x 109/L.
In the PETIT2 study (NCT01520909), patients refractory or relapsed to at least one prior ITP therapy with a platelet count less than 30 x 109/L (n = 92) were stratified by age and randomized (2:1) to PROMACTA (n = 63) or placebo (n = 29). The starting dose for patients aged 6 to 17 years was 50 mg once daily for those at least 27 kg and 37.5 mg once daily for those less than 27 kg, administered as oral tablets. A reduced dose of 25 mg once daily was used for East Asian patients aged 6 to 17 years regardless of weight. The starting dose for patients aged 1 to 5 years was 1.2 mg/kg once daily (0.8 mg/kg once daily for East Asian patients) administered as oral suspension.
The 13-week, randomized, double-blind period was followed by a 24-week, open-label period where patients from both arms were eligible to receive PROMACTA.
The median age of the patients was 9 years and 48% were female. Approximately 62% of patients had a baseline platelet count less than or equal to 15 x 109/L, a characteristic that was similar between treatment arms. The percentage of patients with at least 2 prior ITP therapies (predominantly corticosteroids and immunoglobulins) was 73% in the group treated with PROMACTA and 90% in the group treated with placebo. Four patients in the group treated with PROMACTA had undergone splenectomy.
The efficacy of PROMACTA in this trial was evaluated by the proportion of subjects on PROMACTA achieving platelet counts ≥ 50 x 109/L (in the absence of rescue therapy) for at least 6 out of 8 weeks between Weeks 5 to 12 of the randomized, double-blind period (Table 18).
Table 18. PETIT2: Platelet Count Response (≥ 50 x 109/L without Rescue) for 6 out of 8 Weeks (between Weeks 5 to 12) Overall and by Age Cohort in Pediatric Patients 1 Year and Older with Chronic Immune Thrombocytopenia
Age Cohort |
PROMACTA |
Placebo |
Overall |
26/63 (41%)a |
1/29 (3%) |
12 to 17 years |
10/24 (42%) |
1/10 (10%) |
6 to 11 years |
11/25 (44%) |
0/13 (0%) |
1 to 5 years |
5/14 (36%) |
0/6 (0%) |
a p-value = < 0.001 for PROMACTA versus placebo |
More pediatric patients treated with PROMACTA (75%) compared with placebo (21%) had at least one platelet count greater than or equal to 50 x 109/L during the first 12 weeks of randomized treatment in absence of rescue therapy. Fewer pediatric patients treated with PROMACTA required rescue treatment during the randomized, double-blind period compared with placebo-treated patients (19% [12/63] versus 24% [7/29]). In the patients who achieved a platelet response (≥ 50 x 109/L without rescue) for 6 out of 8 weeks (between weeks 5 to 12), 62% (16/26) had an initial response in the first 2 weeks after starting PROMACTA.
Patients were permitted to reduce or discontinue baseline ITP therapy only during the open-label phase of the trial. Among 15 patients receiving other ITP therapy at baseline, 53% (8/15) reduced (n = 1) or discontinued (n = 7) concomitant therapy, mainly corticosteroids, without needing rescue therapy.
In the PETIT study (NCT00908037), patients refractory or relapsed to at least one prior ITP therapy with a platelet count less than 30 x 109/L (n = 67) were stratified by age and randomized (2:1) to PROMACTA (n = 45) or placebo (n = 22). The starting dose for patients aged 12 to 17 years was 37.5 mg once daily regardless of weight or race. The starting dose for patients aged 6 to 11 years was 50 mg once daily for those greater than or equal to 27 kg and 25 mg once daily for those less than 27 kg, administered as oral tablets. Reduced doses of 25 mg (for those greater than or equal to 27 kg) and 12.5 mg (for those less than 27 kg), each once daily, were used for East Asian patients in this age range. The starting dose for patients aged 1 to 5 years was 1.5 mg/kg once daily (0.8 mg/kg once daily for East Asian patients) administered as oral suspension.
The 7-week, randomized, double-blind period was followed by an open-label period of up to 24 weeks where patients from both arms were eligible to receive PROMACTA.
The median age of the patients was 10 years and 60% were female. Approximately 51% of patients had a baseline platelet count less than or equal to 15 x 109/L. The percentage of patients with at least 2 prior ITP therapies (predominantly corticosteroids and immunoglobulins) was 84% in the group treated with PROMACTA and 86% in the group treated with placebo. Five patients in the group treated with PROMACTA had undergone splenectomy.
The efficacy of PROMACTA in this trial was evaluated by the proportion of patients achieving platelet counts greater than or equal to 50 x 109/L (in absence of rescue therapy) at least once between Weeks 1 and 6 of the randomized, double-blind period (Table 19). Platelet response to PROMACTA was consistent across the age cohorts.
Table 19. PETIT: Platelet Count Response (≥ 50 x 109/L without Rescue) Rates in Pediatric Patients 1 Year and Older with Chronic Immune Thrombocytopenia
|
PROMACTA |
Placebo |
Overall |
28/45 (62%)a |
7/22 (32%) |
12 to 17 years |
10/16 (62%) |
0/8 (0%) |
6 to 11 years |
12/19 (63%) |
3/9 (33%) |
1 to 5 years |
6/10 (60%) |
4/5 (80%) |
a p-value = 0.011 for PROMACTA versus placebo |
Fewer pediatric patients treated with PROMACTA required rescue treatment during the randomized, double-blind period compared with placebo-treated patients (13% [6/45] versus 50% [11/22]).
Patients were permitted to reduce or discontinue baseline ITP therapy only during the open-label phase of the trial. Among 13 patients receiving other ITP therapy at baseline, 46% (6/13) reduced (n = 3) or discontinued (n = 3) concomitant therapy, mainly corticosteroids, without needing rescue therapy.
Chronic Hepatitis C-Associated Thrombocytopenia
The efficacy and safety of PROMACTA for the treatment of thrombocytopenia in adult patients with chronic hepatitis C were evaluated in two randomized, double-blind, placebo-controlled trials. The ENABLE1 study (NCT00516321) utilized peginterferon alfa-2a (PEGASYS®) plus ribavirin for antiviral treatment and the ENABLE2 study (NCT00529568) utilized peginterferon alfa-2b (PEGINTRON®) plus ribavirin. In both trials, patients with a platelet count of less than 75 x 109/L were enrolled and stratified by platelet count, screening HCV RNA, and HCV genotype. Patients were excluded if they had evidence of decompensated liver disease with Child-Pugh score greater than 6 (class B and C), history of ascites, or hepatic encephalopathy. The median age of the patients in both trials was 52 years, 63% were male, and 74% were Caucasian. Sixty-nine percent of patients had HCV genotypes 1, 4, 6, with the remainder genotypes 2 and 3. Approximately 30% of patients had been previously treated with interferon and ribavirin. The majority of patients (90%) had bridging fibrosis and cirrhosis, as indicated by noninvasive testing. A similar proportion (95%) of patients in both treatment groups had Child-Pugh Class A (score 5 to 6) at baseline. A similar proportion of patients (2%) in both treatment groups had baseline international normalized ratio (INR) greater than 1.7. Median baseline platelet counts (approximately 60 x 109/L) were similar in both treatment groups. The trials consisted of 2 phases – a preantiviral treatment phase and an antiviral treatment phase. In the pre-antiviral treatment phase, patients received open-label PROMACTA to increase the platelet count to a threshold of greater than or equal to 90 x 109/L for ENABLE1 and greater than or equal to 100 x 109/L for ENABLE2. PROMACTA was administered at an initial dose of 25 mg once daily for 2 weeks and increased in 25-mg increments over 2- to 3-week periods to achieve the optimal platelet count to initiate antiviral therapy. The maximal time patients could receive open-label PROMACTA was 9 weeks. If threshold platelet counts were achieved, patients were randomized (2:1) to the same dose of PROMACTA at the end of the pre-treatment phase or to placebo. PROMACTA was administered in combination with pegylated interferon and ribavirin per their respective prescribing information for up to 48 weeks.
The efficacy of PROMACTA for both trials was evaluated by sustained virologic response (SVR) defined as the percentage of patients with undetectable HCV-RNA at 24 weeks after completion of antiviral treatment. The median time to achieve the target platelet count greater than or equal to 90 x 109/L was approximately 2 weeks. Ninety-five percent of patients were able to initiate antiviral therapy.
In both trials, a significantly greater proportion of patients treated with PROMACTA achieved SVR (see Table 20). The improvement in the proportion of patients who achieved SVR was consistent across subgroups based on baseline platelet count (less than 50 x 109/L versus greater than or equal to 50 x 109/L). In patients with high baseline viral loads (greater than or equal to 800,000), the SVR rate was 18% (82/452) for PROMACTA versus 8% (20/239) for placebo.
Table 20. ENABLE1 and ENABLE2: Sustained Virologic Response (SVR) in Adults with Chronic Hepatitis C
Pre-antiviral Treatment Phase |
ENABLE1a |
ENABLE2b |
N = 715 |
N = 805 |
% Patients who achieved target platelet counts and initiated antiviral therapyc |
95% |
94% |
Antiviral Treatment Phase |
PROMACTA
N = 450
% |
Placebo
N = 232
% |
PROMACTA
N = 506
% |
Placebo
N = 253
% |
Overall SVRd |
23 |
14 |
19 |
13 |
HCV Genotype 2,3 |
35 |
24 |
34 |
25 |
HCV Genotype 1,4,6 |
18 |
10 |
13 |
7 |
a PROMACTA given in combination with peginterferon alfa-2a (180 mcg once weekly for 48 weeks for genotypes 1/4/6; 24 weeks
for genotype 2 or 3) plus ribavirin (800 to 1,200 mg daily in 2 divided doses orally)
b PROMACTA given in combination with peginterferon alfa-2b (1.5 mcg/kg once weekly for 48 weeks for genotypes 1/4/6;
24 weeks for genotype 2 or 3) plus ribavirin (800 to 1,400 mg daily in 2 divided doses orally)
c Target platelet count was ≥ 90 x 109/L for ENABLE1 and ≥ 100 x 109/L for ENABLE2
d p-value < 0.05 for PROMACTA versus placebo |
The majority of patients treated with PROMACTA (76%) maintained a platelet count greater than or equal to 50 x 109/L compared with 19% for placebo. A greater proportion of patients on PROMACTA did not require any antiviral dose reduction as compared with placebo (45% versus 27%).
Severe Aplastic Anemia
First-Line Treatment Of Severe Aplastic Anemia
PROMACTA in combination with horse antithymocyte globulin (h-ATG) and cyclosporine was investigated in a single-arm, single-center, open-label sequential cohort trial (Study ETB115AUS01T, referred to as Study US01T [NCT01623167]) in patients with severe aplastic anemia who had not received prior immunosuppressive therapy (IST) with any ATG, alemtuzumab, or high dose cyclophosphamide. A total of 153 patients received PROMACTA in Study US01T in three sequential cohorts and an extension of the third cohort. The multiple cohorts received the same PROMACTA starting dose but differed by treatment start day and duration. The starting dose of PROMACTA for patients 12 years and older was 150 mg once daily (a reduced dose of 75 mg was administered for East and Southeast Asians), 75 mg once daily for pediatric patients aged 6 to 11 years (a reduced dose of 37.5 mg was administered for East and Southeast Asians), and 2.5 mg/kg once daily for pediatric patients aged 2 to 5 years (a reduced dose of 1.25 mg/kg was administered for East and Southeast Asians).
- Cohort 1 (n=30): PROMACTA on Day 14 to Month 6 (D14-M6) plus h-ATG and cyclosporine
- Cohort 2 (n=31): PROMACTA on Day 14 to Month 3 (D14-M3) plus h-ATG and cyclosporine
- Cohort 3 + Extension cohort [PROMACTA D1-M6 cohort] (n=92): PROMACTA on Day 1 to Month 6
(D1-M6) plus h-ATG and cyclosporine (with all patients eligible to receive low dose of cyclosporine
(maintenance dose) if they achieved a hematologic response at 6 months)
PROMACTA dose reductions were conducted for elevated platelet counts and hepatic impairment. Table 21 includes the dosages of h-ATG and cyclosporine administered in combination with PROMACTA in Study US01T.
Data from the Cohort 3 + Extension cohort support the efficacy of PROMACTA for the first-line treatment of patients with severe aplastic anemia (Table 22). The results presented in this section represent the findings from the Cohort 3 and Extension cohort (n=92).
Table 21. Dosages of Immunosuppressive Therapy Administered with PROMACTA in Study US01T
Agent |
Dose Administered in the Pivotal Trial |
Horse antithymocyte globulin (h-ATG) |
40 mg/kg/day, based on actual body weight, administered intravenously on Days 1 to 4 of the 6-month treatment period |
Cyclosporinea
(therapeutic dose for 6 months, from Day 1 to Month 6, adjusted to obtain a target therapeutic trough level between 200 mcg/L and 400 mcg/L) |
Patients 12 years and older (total daily dose of 6 mg/kg/day)
3 mg/kg, based on actual body weight, orally every 12 hours for 6 months, starting on Day 1 Patients > 20 years of age with a body mass index > 35 or patients 12 to 20 years of age with a body mass index > 95th percentile:
3 mg/kg, based on adjusted body weightb, orally every 12 hours for 6 months, starting on Day 1 Patients 2 to 11 years of age (total daily dose of 12 mg/kg/day)
6 mg/kg, based on actual body weight, orally every 12 hours for 6 months, starting on Day 1 Patients 2 to 11 years of age with a body mass index > 95th percentile:
6 mg/kg, based on adjusted body weightb, orally every 12 hours for 6 months, starting on Day 1 |
Cyclosporine (maintenance dose, from Month 6 to Month 24) |
For patients who achieve a hematologic response at 6 months
2 mg/kg/day administered orally at a fixed dose for an additional 18 months |
a Dose of cyclosporine may need was adjusted to achieve the above recommended target trough levels; refer to the appropriate
cyclosporine prescribing information
b Calculated as the midpoint between the ideal body weight and actual body weight |
In the PROMACTA D1-M6 cohort, the median age was 28 years (range 5 to 82 years) with 16% and 28% of patients ≥ 65 years of age and < 17 years of age, respectively. Forty-six percent of patients were male and the majority of patients were White (62%). Patients weighing 12 kg or less or patients with ALT or AST > 5x upper limit of normal were excluded from the trial.
The efficacy of PROMACTA in combination with h-ATG and cyclosporine was established on the basis of complete hematological response at 6 months. A complete response was defined as hematological parameters meeting all 3 of the following values on 2 consecutive serial blood count measurements at least one week apart: absolute neutrophil count (ANC) > 1,000/mcL, platelet count > 100 x 109/L and hemoglobin > 10 g/dL. A partial response was defined as blood counts no longer meeting the standard criteria for severe pancytopenia in severe aplastic anemia equivalent to 2 of the following values on 2 consecutive serial blood count measurements at least one week apart: ANC > 500/mcL, platelet count > 20 x 109/L, or reticulocyte count >60,000/mcL. Overall response rate is defined as the number of partial responses plus complete responses.
Table 22. Study US01T: Hematologic Response in First-Line Treatment of Patients with Severe Aplastic Anemia
|
PROMACTA D1-M6 + h-ATG + cyclosporine
N = 92 |
Month 6, na |
87 |
Overall response, n (%) [95% CI] |
69 (79) [69, 87] |
Complete response, n (%) [95% CI] |
38 (44) [33, 55] |
Median duration of overall response, nb |
70 |
Months (95% CI) |
24.3 (21.4, NE) |
Median duration of complete response, nb |
46 |
Months (95% CI) |
24.3 (23.0, NE) |
a The number of patients who reached the 6-month assessment or withdrew earlier is the denominator for percentage calculation
b Number of responders at any time
NE = not estimable |
The overall and complete hematological response rates at Year 1 (N=78) are 56.4% and 38.5% and at Year 2 (N=62) are 38.7% and 30.6%, respectively.
Pediatric Patients
Thirty-four patients 2 to 16 years of age were enrolled in Study US01T. In the D1-M6 cohort, 7 and 17 out of 25 pediatric patients achieved a complete and overall response, respectively, at 6 months.
Refractory Severe Aplastic Anemia
PROMACTA was studied in a single-arm, single-center, open-label trial (Study ETB115AUS28T, referred to as Study US28T [NCT00922883]) in 43 patients with severe aplastic anemia who had an insufficient response to at least one prior immunosuppressive therapy and who had a platelet count less than or equal to 30 x 109/L. PROMACTA was administered at an initial dose of 50 mg once daily for 2 weeks and increased over 2-week periods up to a maximum dose of 150 mg once daily. The efficacy of PROMACTA in the study was evaluated by the hematologic response assessed after 12 weeks of treatment. Hematologic response was defined as meeting 1 or more of the following criteria: 1) platelet count increases to 20 x 109/L above baseline, or stable platelet counts with transfusion independence for a minimum of 8 weeks; 2) hemoglobin increase by greater than 1.5 g/dL, or a reduction in greater than or equal to 4 units of RBC transfusions for 8 consecutive weeks; 3) ANC increase of 100% or an ANC increase greater than 0.5 x 109/L. PROMACTA was discontinued after 16 weeks if no hematologic response was observed. Patients who responded continued therapy in an extension phase of the trial.
The treated population had median age of 45 years (range: 17 to 77 years) and 56% were male. At baseline, the median platelet count was 20 x 109/L, hemoglobin was 8.4 g/dL, ANC was 0.58 x 109/L, and absolute reticulocyte count was 24.3 x 109/L. Eighty-six percent of patients were RBC transfusion dependent and 91% were platelet transfusion dependent. The majority of patients (84%) received at least 2 prior immunosuppressive therapies. Three patients had cytogenetic abnormalities at baseline.
Table 23 presents the efficacy results.
Table 23. Study US28T: Hematologic Response in Patients with Refractory Severe Aplastic Anemia
Outcome |
PROMACTA
N = 43 |
Response ratea, n (%) |
17 (40) |
95% CI (%) |
(25, 56) |
Median of duration of response in months (95% CI) |
NRb (3.0, NRb) |
a Includes single- and multi-lineage
b NR = Not reached due to few events (relapsed) |
In the 17 responders, the platelet transfusion-free period ranged from 8 to 1,096 days with a median of 200 days, and the RBC transfusion-free period ranged from 15 to 1,082 days with a median of 208 days.
In the extension phase, 8 patients achieved a multi-lineage response; 4 of these patients subsequently tapered off treatment with PROMACTA and maintained the response (median follow up: 8.1 months, range: 7.2 to 10.6 months).