- On 2 May 2002 at 17:20:38, Rostam Namdari (chista90.-a-.yahoo.com) sent the message

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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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