B. Meibohm et al., Mechanism-based PK/PD model for the lymphocytopenia induced by endogenous and exogenous corticosteroids, INT J CL PH, 37(8), 1999, pp. 367-376
Citations number
29
Categorie Soggetti
Pharmacology & Toxicology
Journal title
INTERNATIONAL JOURNAL OF CLINICAL PHARMACOLOGY AND THERAPEUTICS
Objective: Lymphocytopenia is a sensitive surrogate marker for the immunolo
gical effects of corticosteroids. This pharmacokinetic/pharmacodynamic (PK/
PD) study investigated whether the circadian variation of blood lymphocytes
observed after placebo is secondary to the circadian rhythm of endogenous
cortisol, and developed based on this relationship an improved PK/PD model
for a more sensitive description of the effect of low-dose corticosteroid t
herapy on blood lymphocytes considering the net activity of the exogenous c
orticosteroid budesonide and endogenous cortisol. Methods: In an open, para
llel study design, 3 mg oral budesonide or placebo were given at 8.00 a.m.,
4.00 p.m. and midnight to two groups of 12 volunteers. Lymphocyte counts a
nd serum concentrations of budesonide and cortisol were monitored for 24 ho
urs. A mechanism-based PK/PD model which considered the non-linear protein
binding of cortisol and the budesonide-induced cortisol suppression was emp
loyed to relate changes in blood lymphocytes to free cortisol levels after
placebo and to the net activity of free budesonide and free endogenous cort
isol after active treatment. Results: The circadian rhythm of blood lymphoc
ytes observed after placebo could inversely be related to the circadian rhy
thm of serum cortisol. After budesonide administration, lymphocyte counts c
ould accurately be linked to the net activity of budesonide and endogenous
cortisol. The resulting EC50 Values for the effect of budesonide on cortiso
l, budesonide on lymphocytes and cortisol on lymphocytes were 0.063 +/- 0.0
34, 0.22 +/- 0.13 and 26.3 +/- 15.0 ng/ml (placebo group 15.4 +/- 3.4 ng/ml
), respectively Conclusions: The presented mechanism-based PK/PD model sugg
ests that blood lymphocytes are under physiological control of cortisol. It
further indicates that endogenous and exogenous corticosteroids and their
pharmacological interaction need to be considered for modeling the effects
of low doses of exogenous corticosteroids on the immune system.