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Dear colleagues and Liposomal experts
As far as I know, not all the plasma
concentration-time curves with mono-exponential decay
can be described by one compartment model. For example
in case of liposomal drug, the mono-exponential decay
curve for total drug (encapsulated + released)
concentration-time observed following iv
administration of liposomal formulation does not
follow the assumptions of one compartmental model, as
there is no instantaneous or very rapid distribution
of liposome to the tissues (liposomes are designed to
slowly cleared from the blood). In other words, the
equilibrium has not been reached between blood and the
tissues therefore, mono-exponential loss of drug from
the plasma dose not indicate kinetic homogeneity with
respect the drug leaving the body. It is solely
reflective of total drug elimination from the plasma.
Therefore, comparing elimination t1/2 of free drug
(t1/2b, assuming bi-phasic decay for free drug which
is usually true) to that of liposomal formulation
which often measured as total (encapsulated +
released) drug is not relevant. A more relevant
comparison would be the comparison between t1/2a of
free drug to t1/2 of mono-exponential decay of
liposomal drug (since this is mainly representative of
distribution phase (mainly encapsulated drug
distribution) rather than elimination from the body.
Your thoughts and comments would be appreciated.
Rostam
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)