Clinical Pharmacology for Pyrukynd
Mechanism Of Action
Mitapivat is a pyruvate kinase activator that acts by allosterically binding to the pyruvate kinase tetramer and increasing pyruvate kinase (PK) activity. The red blood cell (RBC) form of pyruvate kinase (PK-R) is mutated in PK deficiency, which leads to reduced adenosine triphosphate (ATP), shortened RBC lifespan, and chronic hemolysis.
Pharmacodynamics
Mitapivat decreases 2,3 diphosphoglycerate (2,3-DPG) and increases ATP in healthy volunteers.
Cardiac Electrophysiology
At a dose 6 times the maximum recommended dose, mitapivat did not prolong the QT interval to any clinically relevant extent.
Pharmacokinetics
Mitapivat exposure increased in an approximately dose proportional manner over the clinically relevant dose range of 5 mg to 50 mg twice daily.
The population pharmacokinetic model simulated Cmax, Ctrough, AUC0-12 and accumulation ratio of mitapivat at recommended dosages are listed in the table below.
Table 5: Steady State Mitapivat Exposure at Recommended Dosagesa
| Mitapivat Dosage |
Cmax
(ng/mL) |
Ctrough
(ng/mL) |
AUC0-12
(ng*h/mL) |
Accumulation Ratio |
| 5 mg twice daily |
101.2 (17%) |
10.1 (74%) |
450.4 (28%) |
1.2 |
| 20 mg twice daily |
389.9 (18%) |
32.3 (77%) |
1623.8 (28%) |
1.1 |
| 50 mg twice daily |
935.2 (18%) |
62.1 (80%) |
3591.4 (28%) |
1.0 |
a Pharmacokinetic parameters are presented as geometric mean (CV%). The simulations were performed until 100 days after first dose. The interval of the last 12 hours was selected for steady state PK parameters calculation.
Residual error was not included during simulation. |
Absorption
Median tmax values at steady state were 0.5 to 1.0 hour post-dose across the dose range of 5 mg to 50 mg twice daily.
The absolute bioavailability after a single dose was approximately 73%.
Effect Of Food
Following administration of a single dose of PYRUKYND in healthy subjects, a high-fat meal (approximately 900 to 1,000 total calories, with 500 to 600 calories from fat, 250 calories from carbohydrate, and 150 calories from protein) did not change the exposure (AUCinf) of mitapivat, but reduced the rate of mitapivat absorption, with a 42% reduction in Cmax and a delay in tmax of 2.3 hours when compared to dosing under fasted conditions.
Distribution
Mitapivat is highly protein bound (97.7%) in plasma with low RBC distribution (RBC-to-plasma ratio of 0.37). The mean volume of distribution at steady state (Vss) was 42.5 L.
Elimination
The mean effective half-life (t1/2) of mitapivat ranged from 3 to 5 hours following multiple dose administrations of 5 mg twice daily to 20 mg twice daily in patients with PK deficiency.
Population pharmacokinetics derived median CL/F at steady state was 11.5, 12.7, and 14.4 L/h for the 5 mg twice daily, 20 mg twice daily, and 50 mg twice daily regimens, respectively.
Metabolism
In vitro studies showed that mitapivat is primarily metabolized by CYP3A4. Following a single oral dose of 120 mg of radiolabeled mitapivat to healthy subjects, unchanged mitapivat was the major circulating component.
Excretion
After a single oral administration of radiolabeled mitapivat to healthy subjects, the total recovery of administered radioactive dose was 89.2%, with 49.6% in the urine (2.6% unchanged) and 39.6% in the feces (<1% unchanged).
Specific Populations
No clinically meaningful effects on the pharmacokinetics of mitapivat were observed based on age, sex, race, or body weight.
Pediatric Population
The pharmacokinetics of mitapivat in children and adolescents (<18 years old) have not been studied.
Hepatic Impairment
Mitapivat undergoes extensive hepatic metabolism. Moderate and severe hepatic impairment is expected to increase the systemic exposure of mitapivat. The pharmacokinetics of mitapivat in patients with hepatic impairment have not been studied.
Renal Impairment
The effects of renal impairment on mitapivat pharmacokinetics were assessed with population pharmacokinetic analyses. Steady state AUC of mitapivat in patients with eGFR 60 to <90 mL/min/1.73 m2 was not significantly different compared to patients with eGFR ≥90 mL/min/1.73 m2.
There are limited data available in patients with eGFR 30 to <60 mL/min/1.73 m2 and no data available in patients with eGFR <30 mL/min/1.73 m2.
Drug Interaction Studies
Clinical Studies And Model-Based Approaches
Effect of Strong CYP3A Inhibitors on PYRUKYND
Itraconazole (a strong CYP3A inhibitor) increased mitapivat AUCinf and Cmax by 4.9-fold and 1.7- fold, respectively, following a single PYRUKYND dose of 20 mg. Itraconazole increased mitapivat AUC0-12 and Cmax by 3.6-fold and 2.2-fold, respectively, following PYRUKYND 50 mg twice daily. Ketoconazole (a strong CYP3A inhibitor) increased mitapivat AUC0-12 and Cmax by approximately 3.9- fold and 2.4-fold, respectively, following PYRUKYND doses of 5, 20 or 50 mg twice daily.
Effect of Moderate CYP3A Inhibitors on PYRUKYND
Fluconazole (a moderate CYP3A inhibitor) increased mitapivat AUC0-12 and Cmax by approximately 2.6-fold and 1.6-fold, respectively, following PYRUKYND doses of 5, 20 or 50 mg twice daily.
Effect of Strong CYP3A Inducers on PYRUKYND
Rifampin (a strong CYP3A inducer) decreased mitapivat AUCinf and Cmax by 91% and 77%, respectively, following a single PYRUKYND dose of 50 mg. Rifampin decreased mitapivat AUC0-12 and Cmax by approximately 95% and 85%, respectively, following PYRUKYND doses of 5, 20 or 50 mg twice daily.
Effect of Moderate CYP3A Inducers on PYRUKYND
Efavirenz (a moderate CYP3A4 inducer) decreased mitapivat AUC0-12 and Cmax by approximately 60% and 30%, respectively, following PYRUKYND doses of 5 or 20 mg twice daily. Efavirenz decreased mitapivat AUC0-12 and Cmax by 55% and 24%, respectively, following PYRUKYND doses of 50 mg twice daily.
Effect of PYRUKYND on CYP3A substrates
Midazolam (a CYP3A substrate) AUCinf and Cmax decreased by 21% and 19%, respectively, following co-administration of midazolam with PYRUKYND 5 mg twice daily. Midazolam AUCinf and Cmax decreased by 43% and 39%, respectively, following co-administration with PYRUKYND 20 mg twice daily, and 57% and 52%, respectively, with PYRUKYND 50 mg twice daily.
Effect of PYRUKYND on P-gp Substrates
Co-administration of PYRUKYND with drugs that are substrates of P-gp may result in a clinically relevant increase in plasma concentrations of these substrates.
In Vitro Studies
CYP450 and UGT Enzymes
Mitapivat induces CYP2B6, CYP2C8, CYP2C9, CYP2C19, and UGT1A1.
Drug Transporter Systems
Mitapivat is a substrate and an inhibitor of P-gp.
Clinical Studies
Patients With PK Deficiency
Patients Not Regularly Transfused
The efficacy of PYRUKYND was evaluated in ACTIVATE, a multinational, randomized, doubleblind, placebo-controlled clinical study (NCT03548220) of 80 adults with PK deficiency who were not regularly transfused, defined as having had no more than 4 transfusions in the 52- week period prior to treatment and no transfusions in the 3-month period prior to treatment.
Patients were included if they had documented presence of at least 2 variant alleles in the pyruvate kinase liver and red blood cell (PKLR) gene, of which at least 1 was a missense variant, and Hb less than or equal to 10 g/dL. Patients who were homozygous for the c.1436G>A (p.R479H) variant or had 2 non-missense variants (without the presence of another missense variant) in the PKLR gene were excluded because these patients did not achieve Hb response (change from baseline in Hb ≥1.5 g/dL at >50% assessments) in the dose-ranging study.
Randomization was stratified by average screening Hb (<8.5 vs ≥8.5 g/dL) and PKLR gene variant category (missense/missense vs. missense/non-missense).
Among the 80 patients with PK deficiency, 40 patients were randomized to PYRUKYND. Following a period of dose titration up to 50 mg twice daily, patients continued a fixed dose of PYRUKYND for 12 weeks. Eighty-eight percent of patients were maintained on 50 mg twice daily.
The median duration of treatment with PYRUKYND was 24.1 weeks (range 23.6 to 27.4 weeks). Overall, 30 (75%) patients were exposed to PYRUKYND for >24 weeks and <28 weeks. Among the 80 randomized patients, the median age was 33 years (range 18 to 78) and 40% were male; race was reported in 88% of patients: 75% were White, 10% Asian, 1.3% Native Hawaiian/Other Pacific Islander and 1.3% were other races. The median baseline hemoglobin was 8.5 g/dL (range: 6.4 to 10.2 g/dL). There were 55 patients (69%) with the missense/missense PKLR gene variant category, and 25 patients (31%) with the missense/non-missense PKLR gene variant category. There were 58 patients (73%) who had a history of splenectomy. Complications and comorbidities associated with PK deficiency included iron overload with a median baseline ferritin of 479 ng/mL (range: 21 to 5890 ng/mL), chelation therapy use in the year before the first dose of study treatment in 15 patients (19%), decreased bone mineral density in 64 patients (80%) who had a baseline femoral neck T-score or lumbar spine T-score <-1.0, and history of cholecystectomy in 58 patients (73%).
Efficacy was based upon Hb response, defined as a ≥1.5 g/dL increase in Hb from baseline sustained at 2 or more scheduled assessments (Weeks 16, 20, and 24) during the fixed dose period without transfusions. The efficacy results, including changes in markers of hemolysis are shown in Table 6.
Table 6: Efficacy Results in Patients with PK Deficiency Who Were Not Regularly Transfused (ACTIVATE)
| Endpoint |
PYRUKYND
N=40 |
Placebo
N=40 |
Difference1, 2
p-value |
| Hb Response, n (%) |
16 (40%) |
0 |
39 (24, 55)
<0.0001 |
| Hemoglobin (g/dL) |
| Baseline Mean (SD) |
8.6 (1.0) |
8.5 (0.8) |
|
| LS Mean Change (95% CI) |
1.7
(1.3, 2.1) |
-0.1
(-0.6, 0.3) |
1.8 (1.2, 2.4)
<0.0001 |
| Indirect bilirubin (mg/dL) |
| Baseline Mean (SD) |
4.8 (3.6) |
5.2 (3.6) |
|
| LS Mean Change (95% CI) |
-1.2
(-1.7, -0.7) |
0.3 (-0.2, 0.8) |
-1.5 (-2.2, -0.9)
<0.0001 |
| Reticulocyte (fraction of 1) |
| Baseline Mean (SD) |
0.37 (0.24) |
0.40 (0.22) |
|
| LS Mean Change (95% CI) |
-0.10
(-0.13, -0.07) |
0
(-0.02, 0.03) |
-0.10 (-0.14, -0.06)
<0.0001 |
| LDH (U/L) |
| Baseline Mean (SD) |
348 (276) |
260 (140) |
|
| LS Mean Change (95% CI) |
-92
(-124, -60) |
-21 (-53, 11) |
-71 (-116, -26)
0.003 |
| Haptoglobin (mg/dL) |
| Baseline Mean (SD) |
8.2 (10.7) |
8.3 (13.8) |
|
| LS Mean Change (95% CI) |
16.9
(8.8, 25.1) |
1.2
(-7.0, 9.4) |
15.8 (4.3, 27.3)
0.008 |
CI: confidence interval, Hb: hemoglobin, LDH: lactate dehydrogenase, LS Mean Change: least square mean change from baseline, SD: standard deviation
1 All results are statistically significant.
2 For Hb response, the difference is adjusted for randomization stratification factors, which included average screening Hb (<8.5, ≥8.5 g/dL) and PKLR gene variant category (missense/missense, missense/non-missense). The two-sided p-value is based on the Mantel-Haenszel stratum weighted method adjusting for the randomization stratification factors.
For the endpoints of average change from baseline at Weeks 16, 20, and 24 for hemoglobin, indirect bilirubin, reticulocytes, LDH, and haptoglobin, the two-sided p-value is based on the mixed-effect model repeat measurement (MMRM) method, which included change from baseline as the dependent variable, baseline as a covariate, and treatment arm, visit, treatmentby- visit interaction, and the randomization stratification factors as fixed factors and subject as the random effect. All scheduled visits were included in the model. |
In ACTIVATE, the LS Mean change from baseline with PYRUKYND compared to placebo was -0.4 (standard error [SE] 0.1) for jaundice (scale: 0-4), -1.1 (SE 0.4) for tiredness (scale: 0-10), and -0.3 (SE 0.3) for shortness of breath (scale: 0-10), assessed with the daily Pyruvate Kinase Deficiency Diary (PKDD) where lower scores represent less sign/symptom severity.
In ACTIVATE, the majority of PYRUKYND-treated patients experienced an increase in Hb, while the majority of patients in the placebo arm experienced a decrease in Hb as measured by average change from baseline at weeks 16, 20, and 24 (Figure 1).
Figure 1: Average Change at Weeks 16, 20, and 24 from Baseline in Hemoglobin (Hb) by Patient - All Randomized Patients (ACTIVATE)a
 |
| a Approximately 99% of all randomized patients completed 24 weeks of treatment. |
Figure 2: LS Mean Change from Baseline in Hemoglobin Over Time - All Randomized Patients (ACTIVATE)
 |
| CI: confidence interval, Hb: hemoglobin, LS: least square |
Fifteen of the 16 patients with a Hb response in ACTIVATE continued in a long-term extension study and were evaluable for maintenance of response. Thirteen maintained increases in Hb concentration from baseline above the response threshold of ≥1.5 g/dL at the last available Hb assessment without requiring any transfusions. The median duration of response for the 16 patients with Hb response was 6.9 months (range: 3.3, 18.4+).
Patients Who Were Regularly Transfused
The efficacy of PYRUKYND in patients with PK deficiency who were regularly transfused was evaluated in ACTIVATE-T, a multinational single-arm clinical trial (NCT03559699) of 27 adults with PK deficiency who had a minimum of 6 transfusion episodes in the 52-week period prior to informed consent. Patients were included if they had documented presence of at least 2 variant alleles in the PKLR gene, of which at least 1 was a missense variant. Patients who were homozygous for the c.1436G>A (p.R479H) variant or had 2 non-missense variants (without the presence of another missense variant) in the PKLR gene were excluded. Following a period of dose titration up to 50 mg twice daily, patients continued on a fixed dose of PYRUKYND for 24 weeks.
The median duration of treatment with PYRUKYND was 40.3 weeks (range 16.3 to 46.3 weeks). Overall, 20 (74%) patients were exposed to PYRUKYND for >40 weeks and <47 weeks. The median age was 36 years (range 18 to 68) and 26% were male; race was reported in 85% of patients: 74% were White and 11% Asian. The median baseline hemoglobin was 9.1 g/dL (range: 7.4 to 10.9 g/dL). Patients had a median of 9 transfusion episodes (range: 6 to 17 episodes) in the 52 weeks before the first dose of study treatment and a median of 7 red blood cell units transfused (range: 3 to 20 units) standardized to 24 weeks. There were 20 patients (74%) with the missense/missense PKLR gene variant category, and 7 patients (26%) with the missense/non-missense PKLR gene variant category. There were 21 patients (78%) who had a history of splenectomy. Patients had evidence of complications and comorbidities associated with PK deficiency including iron overload (median baseline ferritin was 1324 ug/L; range: 163 to 5357 ng/mL), chelation therapy use in the year before the first dose of study treatment in 24 patients (89%), decreased bone mineral density in 20 patients (74%) who had a baseline femoral neck T-score or lumbar spine T-score <-1.0, and history of cholecystectomy in 23 patients (85%).
Efficacy was based on transfusion reduction response and was defined as ≥33% reduction in the number of red blood cell (RBC) units transfused during the fixed dose period compared with the patient’s historical transfusion burden.
Efficacy results for patients with PK deficiency who were regularly transfused are presented in Table 7.
Table 7: Efficacy Results in Patients with PK Deficiency Who Were Regularly Transfused (ACTIVATE-T)
| Endpoints |
PYRUKYND
N=27 |
| Patients with Transfusion Reduction Response |
| n (%) |
9 (33) |
| 95% CI |
(17, 54) |
| Patients who were Transfusion Free |
| n (%) |
6 (22) |
| 95% CI |
(9, 42) |
| CI: confidence interval, RBC: red blood cell CI is based on Clopper-Pearson method. |
All 6 (22%) patients who were transfusion free in ACTIVATE-T remained transfusion free in a longterm extension study. The median duration of response for the 6 patients was 17 months (range: 11.5+, 21.8+).