Mitapivat

Absorption

The absolute bioavailability of mitapivat after a single dose is approximately 73%. Mitapivat exposure increases dose-proportionally. Following twice-daily oral administration of mitapivat at the dose of 5 mg, 20 mg, and 50 mg, the mean (CV%) Cmax at steady state were 101.2 (17%) ng/mL, 389.9 (18%) ng/mL, and 935.2 (18%) ng/mL, respectively. The mean (CV%) AUC were 450.4 (28%) ng x h/mL, 1623.8 (28%) ng x h/mL, and 3591.4 (28%) ng x h/mL, respectively. The 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.
In healthy subjects, a high-fat meal did not affect the drug exposure 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.

Toxicity

There is no information available regarding the LD50 and overdose profile of mitapivat.

Background

Mitapivat is a novel, first-in-class pyruvate kinase activator. It works to increase the activity of erythrocyte pyruvate kinase, a key enzyme involved in the survival of red blood cells. Defects in the pyruvate kinase enzyme in various red blood cells disorders lead to the lack of energy production for red blood cells, leading to lifelong premature destruction of red blood cells or chronic hemolytic anemia.
On February 17, 2022, the FDA approved mitapivat as the first disease-modifying treatment for hemolytic anemia in adults with pyruvate kinase (PK) deficiency, a rare, inherited disorder leading to lifelong hemolytic anemia. Mitapivat has also been investigated in other hereditary red blood cell disorders associated with hemolytic anemia, such as sickle cell disease and alpha- and beta-thalassemia.

Indications

Mitapivat is indicated for the treatment of hemolytic anemia in adults with pyruvate kinase (PK) deficiency.

Pharmacokinetics

Mitapivat is a pyruvate kinase activator that works to increase the activity of erythrocyte pyruvate kinase, an enzyme responsible for energy production for and survival of red blood cells. It is effective in upregulating the activity of both wild-type and mutant forms of erythrocyte pyruvate kinase.
Interestingly, mitapivat is a mild-to-moderate inhibitor of the aromatase enzyme (CYP19A1), which is an enzyme involved in biosynthesis of estrogens from androgen precursors. Inhibition of aromatase is associated with bone density loss, as estrogen mediates suppressive, antiresorptive effects on osteoclasts and generally favours bone formation over resorption. Thus, low estrogen levels can increase bone turnover and osteoclast activity, resulting in net bone loss and decreased bone quality. Inhibition of aromatase by mitapivat may have some clinical implications, as patients with pyruvate kinase deficiency have considerably high rate of osteopenia and osteoporosis. The long-term effect of mitapivant on bond mineral density requires further investigation. One study suggests that this off-target effect may have negligible clinical effects on adults, but may potentially have some clinical implications in developing children.

Metabolism

According to in vitro studies, mitapivat is primarily metabolized by CYP3A4. It is also a substrate of CYP1A2, CYP2C8, and CYP2C9. Following a single oral dose administration of 120 mg of radiolabeled mitapivat in healthy subjects, unchanged mitapivat was the major circulating component in plasma.