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Blood distribution of mycophenolic acid
L J Langman1, D F LeGatt, R W Yatscoff
1Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Canada.
Abstract:
RS-61443 (RS) a morpholinoethyl ester of mycophenolic acid (MPA), can be considered a prodrug, as immunosuppressive activity is expressed only after hydrolysis to MPA upon absorption. Little is known about the blood distribution of MPA; such information would have an impact on the medium used for analysis of the drug in clinical trials. This was investigated by spiking whole blood having an initial temperature of either 4 degrees or 22 degrees C with increasing amounts of MPA ranging from 100 to 10,000 micrograms/L. These drug concentrations span the range seen when immunosuppressive doses of the RS are administered. This was followed by incubation of the blood at 37 degrees C for 0-120 min prior to separation of the cells. The drug concentration was measured in the plasma and whole blood fractions by high-performance liquid chromatography. MPA was almost exclusively found in the plasma fraction and did not exhibit any temperature or concentration dependence. The free or unbound fraction of MPA over the same concentration range was determined by ultracentrifugation and demonstrated a concentration dependence ranging from 7.2 to 16.5% of total drug for a concentration range spanning 500-10,000 micrograms/L. The drug was found to be primarily associated with the non-albumin proteins in the plasma. Less than 10% of the drug was found to be bound to lipoproteins. The data suggest that from an analytical standpoint, plasma, rather than whole blood, would be the most suitable medium for analysis because of the higher concentrations of the drug found in this fraction.
Insights
Mycophenolic acid (MPA) distributes almost exclusively into plasma, not blood cells. This finding is crucial for accurate drug analysis in clinical trials, indicating plasma is the preferred sample medium.
Area of Science:
- Pharmacology
- Clinical Chemistry
- Drug Metabolism
Background:
- RS-61443 is a mycophenolic acid (MPA) prodrug.
- Understanding MPA blood distribution is vital for clinical trial analysis.
- Current knowledge on MPA distribution in blood components is limited.
Purpose of the Study:
- To investigate the distribution of MPA in whole blood and plasma.
- To determine the impact of temperature and concentration on MPA distribution.
- To identify the optimal biological matrix for MPA analysis in clinical settings.
Main Methods:
- Whole blood was spiked with MPA at various concentrations (100–10,000 µg/L).
- Blood samples were incubated at 37°C before cell separation.
- MPA concentrations in plasma and whole blood fractions were measured using HPLC; unbound fraction determined by ultracentrifugation.
Main Results:
- MPA was found almost exclusively in the plasma fraction.
- Distribution showed no dependence on initial temperature (4°C or 22°C) or concentration.
- The unbound fraction of MPA was concentration-dependent (7.2–16.5% from 500–10,000 µg/L).
- MPA primarily binds to non-albumin plasma proteins, with minimal lipoprotein association.
Conclusions:
- Plasma is the most suitable medium for MPA analysis due to higher drug concentrations.
- Accurate MPA quantification in clinical trials requires analysis in plasma.
- Understanding MPA's plasma protein binding is essential for interpreting drug levels.