PharmPK Discussion - Affinity constant

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On 14 Mar 1996 at 11:00:39, "N. Van Brandt" (vanbrandt.-at-.fatc.ucl.ac.be) sent the message



I have completed a study about unbound fraction of midazolam and sufentanil
in ICU.

I have studied 50 patients divided in 5 groups (control, cardiac, hepatic,
renal and pateint under ECMO).
For all patients I have a minimum of 20 oberservations of free fraction and
protein concentration.

I have determined free fraction by equilibrium dialysis for both drugs,
I have also determined albumin and AAG in serum.

May I calculate nKA by the formula fu = 1/ (1+nKa.Pt) ? Will nKa (or K')
parameter
reflect the affinity of drugs for proteins because if Ka increase and the
number of
binding sites decrease. Finallly, nKa won't change.

Because I think that with the parameter I have, I cannot determine n and Ka
separetly.

Any help ?
----------------
Nicolas VAN BRANDT (tel: 32.2.764.11.11 bip:7353)
Pharmacist
Lab. of Pharmacokinetics (Prof R.K. Verbeeck)
UNIVERSITY OF LOUVAIN
Av. E. MOUNIER, 73-55
1200 Brussels, Belgium, EUROPE
Belgium,
Europe.
vanbrandt.-a-.fatc.ucl.ac.be

from: "N. Van Brandt"

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