Dm. Wood et al., VARIABILITY IN THE PLASMA-PROTEIN BINDING OF VELNACRINE (1-HYDROXY TACRINE HYDROCHLORIDE) - A POTENTIAL AGENT FOR ALZHEIMERS-DISEASE, European Journal of Clinical Pharmacology, 50(1-2), 1996, pp. 115-119
Objectives: To quantify the protein binding of velnacrine in healthy i
ndividuals and investigate potential sources of variability. Setting:
Medical School Unit, Southmead Hospital, Bristol. Subjects: Plasma sam
ples were obtained from the following groups: a) 11 healthy volunteers
aged 18 to 30 years; b) 10 healthy volunteers aged 73 to 87 years; c)
10 patients aged 65 to 85 years hospitalised for a variety of acute i
llnesses. Methods: Aliquots of plasma from the above subjects were inc
ubated with various concentrations of velnacrine, in the presence and
absence of tacrine hydrochloride. Standard solutions of human serum al
bumin and alpha(1) acid glycoprotein were incubated with velnacrine. T
he degree of protein binding was determined using the Amicon centrifre
e micropartition system. Results: 1) Over the range of concentrations
from 10 to 320 ng . ml(-1), there was a decrease in protein binding fr
om 59.1 to 46.7%. 2) At 40 ng . ml(-1) the plasma protein binding of v
elnacrine was 54.8% in the group a subjects, 51.9% in the group b subj
ects and 53.0% in the group c subjects (NS). 3) The mean total plasma
protein concentration was significantly lower in the samples from elde
rly subjects. The mean albumin and alpha(1) acid glycoprotein concentr
ations were lower and higher respectively in patients with acute disea
se. 4) Velnacrine was shown to bind to both albumin and alpha(1)-acid
glycoprotein, but together they did not account for total binding. 5)
The binding of velnacrine was significantly decreased from 59.3 to 43.
9% in the presence of a therapeutic concentration (25 ng . ml(-1)) of
THA. There was no evidence that velnacrine displaced THA. Conclusion:
Protein binding can be discounted as a major source of variation in th
e relationship between drug concentration and effect.