Comparison of the "zero crossing" method in derivative spectroscopy and ultrafiltration for the determination of free and bound fractions of mitoxantrone.

In vitro mitoxantrone binding to human serum, human serum albumin (HSA, 600 microM) and alpha-1-acid glycoprotein (AAG, 15 microM) was investigated by ultrafiltration and the first-derivative spectrophotometry based on the "zero crossing" method. The binding of mitoxantrone to isolated proteins was studied at eight concentrations whose range depended on the protein used. The results showed that mitoxantrone binding to human plasma and HSA involved a saturable binding. The AAG binding involved a saturable binding followed by a non saturable process. Within the concentration range studied, the percent and binding parameters which characterize the drug-protein interaction were comparable in both methods.

Pharmacokinetic study of fentiazac and its main metabolite hydroxyfentiazac in the elderly.

The pharmacokinetics of fentiazac (F, CAS 18046-21-4) and hydroxyfentiazac (OH-F) were estimated in 12 elderly (> 76 years). After an oral single dose of 200 mg F, the plasma and urine profiles were determined using high-performance liquid chromatography with a fluorescence detection. When compared to results obtained in young adults, the maximum plasma concentrations (5.4 +/- 1.9 mg/l) and-the time to reach them were identical. The terminal half-life (7.0 +/- 9.1 h) was longer, due to a slight increase of the apparent volume of distribution and a decrease of the elimination clearance. The findings suggest that the dosage regimen of this drug should be decreased in the elderly. Moreover, the variability of the pharmacokinetics being larger, individual adaptation of the daily dose should be performed.

First-derivative spectroscopic determination of binding characteristics of rifampicin to human albumin and serum.

A first-derivative spectroscopic method for the simultaneous determination of bound and unbound drug in human serum and serum albumin solution was developed. As an example, the binding characteristics of rifampicin were studied. In serum albumin solution, the rifampicin bound and unbound fractions were determined at 473.5 and 475.8 nm, respectively. For human serum, the unbound fraction was determined at 479.4 nm. The results obtained by the first-derivative spectroscopic method were in agreement with those obtained by equilibrium dialysis. The proposed method is very simple and accurate when applied to measurements of drug:protein binding. Moreover, it allows a direct measurement of the bound and unbound forms without any physical separation.

Protein binding of methotrexate to human albumin and serum. A first derivative spectroscopic analysis.

Usual methods allowing the measurement of the free concentration of a drug in serum, i.e. equilibrium dialysis, ultrafiltration and ultracentrifugation, are generally based on a physical separation of the bound and free fractions. During this, variations or errors may occur which are probably at the origin of the variability of the previously published results for methotrexate (CAS 59-05-2). In order to verify these results as well as to experience a technique recently applied to rifampicine the first derivative spectroscopic analysis was used to estimate the bound and free fractions of methotrexate in human serum and serum albumin (HSA). Free drug concentrations were measured at 377 nm and the bound form at 372.5 nm. In human serum, bound methotrexate was 54.1% on average for total concentrations ranging from 10(-5) mol/l to 10(-3) mol/l, without any saturation. With HSA, a saturation occurred. Scatchard analysis showed one family of binding sites characterized by 2 binding sites and an affinity constant of 3200 mol/l, in mean, values close to that previously calculated using equilibrium dialysis.

Pharmacokinetics of two spiroarsoranes administered intravenously or orally to rabbits.

The pharmacokinetics of two spiroarsorane molecules (1,2) were investigated after both intravenous bolus and an oral administration in rabbits. After iv administration of a 15-mg/kg dose, for the two substances, the plasma concentration-time curves were well described by an open two-compartmental model. The half-lives of the first phase were 0.47 +/- 0.12 and 0.27 +/- 0.02 h for 1 and 2, respectively. The half-lives of the terminal phase were of the same order of magnitude for the two substances: 4.38 +/- 0.24 and 6.03 +/- 1.14 h, respectively. Total plasma clearances were 2.47 +/- 0.44 and 0.81 +/- 0.04 L/h, respectively, and the steady-state volume of distribution of 2 (14.99 +/- 2.57 L) was larger than that of 1 (4.27 +/- 0.28 L). After oral administration, spiroarsorane 2 was not absorbed. The availability of the suspension of 1 was 18%. The rate of the absorption phase of 1 showed a saturation process, probably due to the solubility of the molecule. When increasing oral doses of 1 (15, 30, and 60 mg/kg) were administered, the plasma concentrations did not increase to the same extent.

High performance liquid chromatographic method for routine monitoring of amiodarone and desethylamiodarone plasma levels.

The authors describe a normal phase liquid-chromatographic assay suitable for therapeutic monitoring of amiodarone and desethylamiodarone in human plasma. The compounds were extracted at pH 3.8 into methyl tert-butyl ether containing [2-ethyl-3-3.5-dibromo-4-dipropylaminoproxybenzoyl)benzothiophe ne] as internal standard. The separation was obtained by using a mobile phase of methanol-methyl tert butyl ether-sulfuric acid (60-40-0.015; v/v/v). The absorbance of the compounds was monitored at 254 nm with a sensitivity limit of 0.05 mg/l for amiodarone and 0.02 mg/l for desethylamiodarone. The mean overall recovery from plasma samples was greater than 90 p. cent for both compounds. This method was applied to therapeutic and pharmacokinetic studies.

Pharmacokinetics of veralipride after chronic administration in humans.

A pharmacokinetic study of veralipride (N-[(1-allyl-2-pyrroli dinyl)methyl]-5-sulfamoyl-o-veratramide) was performed in healthy volunteers during a chronic administration. The pharmacokinetic model based on the hypothesis of a double site for drug absorption, previously used after a single-dose oral administration, was developed to fit the data obtained after chronic administration. The empirical model used allows correct depiction of the behavior of the drug in the body, especially secondary peaks. According to the results, veralipride pharmacokinetics did not show any change upon chronic administration.