RIPTION
SYNRIBO contains the active ingredient omacetaxine mepesuccinate, a cephalotaxine ester. It is a protein synthesis inhibitor. Omacetaxine mepesuccinate is prepared by a semi-synthetic process from cephalotaxine, an extract from the leaves of Cephalotaxus sp. The chemical name of omacetaxine mepesuccinate is cephalotaxine, 4-methyl (2R)-hydroxyl-2-(4-hydroxyl-4-methylpentyl) butanedioate (ester).
Omacetaxine has the following chemical structure:
The molecular formula is C29H39NO9 with a molecular weight of 545.6 g/mol. SYNRIBO for injection is a sterile, preservative-free, white to off-white, lyophilized powder in a single-use vial. Each vial contains 3.5 mg omacetaxine mepesuccinate and mannitol.
SYNRIBO is intended for subcutaneous administration after reconstitution with 1.0 mL of 0.9% Sodium Chloride Injection, USP. The pH of the reconstituted solution is between 5.5 and 7.0.
12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action
The mechanism of action of omacetaxine mepesuccinate has not been fully elucidated but includes inhibition of protein synthesis and is independent of direct Bcr-Abl binding. Omacetaxine mepesuccinate binds to the A-site cleft in the peptidyl-transferase center of the large ribosomal subunit from a strain of archaeabacteria. In vitro, omacetaxine mepesuccinate reduced protein levels of the Bcr-Abl oncoprotein and Mcl-1, an anti-apoptotic Bcl-2 family member. Omacetaxine mepesuccinate showed activity in mouse models of wild-type and T315I mutated Bcr-Abl CML.
12.3 Pharmacokinetics
The dose proportionality of omacetaxine mepesuccinate is unknown. A 90% increase in systemic exposure to omacetaxine mepesuccinate was observed between the first dose and steady state.
Absorption
The absolute bioavailability of omacetaxine mepesuccinate has not been determined. Omacetaxine mepesuccinate is absorbed following subcutaneous administration, and maximum concentrations are achieved after approximately 30 minutes.
Distribution
The steady-state (mean ± SD) volume of distribution of omacetaxine mepesuccinate is approximately 141 ± 93.4 L following subcutaneous administration of 1.25 mg/m2 twice daily for 11 days. The plasma protein binding of omacetaxine mepesuccinate is less than or equal to 50%.
Metabolism
Omacetaxine mepesuccinate is primarily hydrolyzed to 4′-DMHHT via plasma esterases with little hepatic microsomal oxidative and/or esterase-mediated metabolism in vitro.
Elimination
The major elimination route of omacetaxine mepesuccinate is unknown. The mean percentage of omacetaxine mepesuccinate excreted unchanged in the urine is less than 15%. The mean half-life of omacetaxine mepesuccinate following subcutaneous administration is approximately 6 hours.
Drug Interactions
Cytochrome P450 Enzymes (CYPs): Omacetaxine mepesuccinate is not a substrate of CYP450 enzymes in vitro. Omacetaxine mepesuccinate and 4′-DMHHT do not inhibit major CYPs in vitro at concentrations that can be expected clinically. The potential for omacetaxine mepesuccinate or 4′-DMHHT to induce CYP450 enzymes has not been determined.
Transporter Systems: Omacetaxine mepesuccinate is a P-glycoprotein (P-gp) substrate in vitro. Omacetaxine mepesuccinate and 4′-DMHHT do not inhibit P-gp mediated eff
