URINARY EXCRETION OF BUPRENORPHINE
Sigma minus plots. If it can assumed that buprenorphine is solely
eliminated from the central compartment, the urinary excretion rate of
intact drug can be defined as
dU/dt = ku Xc Eq. 19
where is the urinary excretion rate constant, and Xc is the amount
of drug in the central compartment at time t. Integrating equation 19
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between 0 to U (time; 0 to t) results in
I U -E U = P"e~ 1711 + A"e-at + B"e Eq. 20
oo
vhere
= P k V / ir
Eq.
21
u c
= A k V / a
Eq.
22
u c
= B k V / 6
u c
Eq.
23
The values of P, A and B are same as in Eqs. 5,6 and 7, respectively if
constant renal clearance is presumed. Thus a plot of the logarithm of
the amount of unchanged drug remaining to be excreted versus time (sigma
minus plot) gives a straight line with a terminal slope equal to
- g/2.303, i.e., the same terminal slope obtained from a semilogarithmic
plot of plasma concentration (Cp) versus time.
Representative examples of the sigma minus plots for the urinary
excretion of buprenorphine are given in Fig. 21. For dog A (Study #1,
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