Quantitation of drug levels and platelet receptor blockade caused by a thromboxane antagonist.

SQ 28,668 is a structural analog of thromboxane A2. It inhibits the effects of thromboxane in vitro. Fifty-six healthy male subjects were given either placebo or three equal daily doses of SQ 28,668 ranging from 25 to 1200 mg. Plasma drug concentrations increased in a dose-dependent manner. The shape of the plasma drug concentration-time curve was consistent with enterohepatic recirculation. The effects of SQ 28,668 on ex vivo platelet aggregation suggested that SQ 28,668 is a specific competitive antagonist of thromboxane A2 with a platelet receptor dissociation constant (estimated by Schild analysis) of about 19 nmol/L. Approximately 94% occupation of thromboxane receptors by SQ 28,668 was required to produce a small but measurable increase of the template bleeding time. Dose-ranging studies of antithrombotic drugs are difficult and expensive. For this reason, a method was developed that allows estimation of the dose of a thromboxane receptor antagonist that would be expected to be therapeutically equivalent to a given dose of aspirin.

Pharmacokinetics of captopril in elderly healthy male volunteers.

The pharmacokinetics of captopril were studied in 12 healthy male volunteers aged 65 to 76 years, who each received a single 100-mg oral dose. Blood and urine samples were collected over a 24-hour period, and assayed for unchanged captopril (CAP), S-methylcaptopril (Me-CAP, plasma concentrations from 2 subjects only), and total captopril levels (TOT, a mixture of CAP and its dimer and mixed disulfides with endogenous thiol-containing compounds such as glutathione and cysteine). Mean values for the maximum concentration (Cmax) were 803 and 66.3 ng/mL for CAP and Me-CAP, respectively. Mean time to maximum concentration (tmax) was determined as 1.0, 1.4, and 1.0 for CAP, TOT, and Me-CAP, respectively. Mean areas under the plasma concentration-time curve (AUC) were 1,394 hr-ng/mL (CAP, 0-8 hr) and 17,316 hr-ng/mL (TOT, 0-24 hr). The mean estimated half-life (t 1/2) for CAP was 1.4 hr, and its renal clearance was 187 mL/hr/kg. Mean urinary excretion over 24 hr was 20.8 and 53.1 for CAP and TOT, respectively. Cmax, and AUC for CAP were 9% less and 13% greater, respectively, than in a historical control group of 18-35-year-old men, treated in the same clinic, by the same personnel, using the same analytic procedures, whereas the 24-hour urinary excretion was 25% lower and eight-hour renal clearance 36% lower in the older population. Since the values for Cmax, AUC, and t 1/2 were similar in the two populations, it does not appear that the pharmacokinetics of CAP are altered markedly with age alone.

Determination of serum nadolol levels by GLC--selected ion monitoring mass spectrometry: comparison with a spectrofluorometric method.

A method to determine the serum concentration of the beta-adrenergic receptor blocking agent, nadolol, by GLC--selected ion monitoring mass spectrometry of the tri(trimethysilyl) ether derivative is described. A basic solution of serum was extracted, known amounts of internal standard were added to the extract, and the extract was back-extracted into acidic media and lyophilized. The resulting solids were reacted with N-trimethylsilylimidazole. Coded serum samples of 12 subjects, given nadolol alone or in combination with a second drug, were analyzed. The ions at m/e 86 and 100 were monitored to establish the relative concentration ratio of nadolol and the internal reference N-methylnadolol. No interferences from blood components or other administered drugs were observed. A detection level of 6.95 ng/ml of serum was found.

Hydrolysis and subsequent cyclization of etazolate hydrochloride and related compounds in aqueous solutions: application of PMR and mass spectrometry in accelerated stability studies.

The hydrolysis of etazolate hydrochloride, an inhibitor of cyclic nucleotide 3',5'-monophosphate phosphodiesterase that degrades cyclic adenosine 3',5'-monophosphate (cyclic AMP) to adenosine 5'-monophosphate, and related compounds was studied by PMR and mass spectrometry. The compounds underwent reversible acid-catalyzed hydrolysis in aqueous solutions at 60 degrees, followed by cyclization to a major and a minor product formed by independent pathways. Under the experimental conditions, the minor product was stable. The formation rate of the major product, 6-ethyl-1,6-dihydrodipyrazolo [3,4-b:3',4'-d] pyridin-3(2H)-one, was considerably greater than that of the minor component, 3-ethoxy-6-ethyl-1,6-dihydrodipyrazolo [3,4-b:3',4'-d] pyridine. For the 6-methyl analog of etazolate, the rate of methyl deuteration was considerably slower than the rate of cyclization.

Determination of captopril in human blood and urine by GLC-selected ion monitoring mass spectrometry after oral coadministration with its isotopomer.

A modified electron-impact GLC-selected ion monitoring mass spectrometric method for captopril is described. Positive chemical ionization GLC-selected ion monitoring and direct chemical ionization confirms the specificity of this procedure for captopril and establishes the chemical ionization techniques as potential analytical methods. This procedure has been adapted to the simultaneous measurement of captopril and its isotopomer. The results of a pilot oral bioavailability study of four subjects receiving either 100 mg of captopril as a direct compression tablet or a solution concomitantly with a 100-mg solution of isotopomer is discussed.

Determination of orally coadministered nadolol and its deuterated analogue in human serum and urine by gas chromatography with selected-ion monitoring mass spectrometry.

A cartridge serum and urine extraction procedure of the beta-adrenergic antagonist, nadolol, employing a cross-linked styrene-divinyl benzene macroreticular resin is described. Samples were analyzed as the silylated derivative by gas chromatography-mass spectrometry (GC-MS) using selected-ion monitoring. When nadolol was orally coadministered with its deuterated analogue, relative bioavailability could be demonstrated with six or fewer subjects. Employing a base-deactivated GC phase, the limit of detection is 1 ng and 0.5 ng/mL of serum for nadolol and the deuterated analogue, respectively. For levels of less than 10 ng/mL, the respective coefficients of variation are 4 and 2%. For concentrations of greater than 10 ng/mL, the CV is 1% for nadolol and nadolol-d9.

Pharmacokinetics of pravastatin in elderly versus young men and women.

OBJECTIVE: To assess the effect of age on the pharmacokinetics of pravastatin in men and women. A secondary objective was to evaluate the effect of oral contraceptive steroids on the pharmacokinetics of pravastatin in young women. DESIGN: Open, single-dose study. SETTING: Clinical Pharmacology Unit of Princeton Medical Center for study in men and Hill Top Pharmatest, Cincinnati, for study in women. PARTICIPANTS: Normal, healthy male (aged 19-75 y) and female (aged 18-78 y) volunteers. INTERVENTIONS: Subjects received a single 20-mg dose of pravastatin after an overnight fast. MAIN OUTCOME MEASURES: The maximum plasma pravastatin concentration (Cmax), time required for that concentration to develop (Tmax), and the elimination half-life (beta t1/2). Serum concentrations of pravastatin and its major metabolite, the 3-alpha isomer, SQ 31,906, were determined at 12 intervals from 0.33 to 48 hours after the dose. Urine was collected cumulatively during the same period to determine urinary excretion of pravastatin and SQ 31,906. Both measures were used to determine pharmacokinetic parameters. RESULTS: The pharmacokinetic profiles of pravastatin and SQ 31,906 in young and elderly subjects of men and women differed little. Although the mean area under the concentration time curve of pravastatin was higher in the elderly and significantly higher in the elderly women, Cmax and beta t1/2 values were similar in the young and the elderly volunteers. Concomitant administration of oral contraceptives in young women did not affect the pharmacokinetics of pravastatin or SQ 31,906. CONCLUSIONS: The pharmacokinetics of pravastatin do not necessitate dosage adjustments in elderly men or women. No differences were detected between the disposition of the parent drug or its metabolite in men and women.

Effect of antifungal agents on lipid biosynthesis and membrane integrity in Candida albicans.

Eight antifungal agents were examined for effects on lipid biosynthesis and membrane integrity in Candida albicans. Lipids were labeled in vivo or in vitro with [14C]acetate and analyzed by thin-layer and gas chromatography. Membrane integrity was measured by a recently developed [14C]aminoisobutyric acid radiolabel release assay. The imidazole antifungal agents miconazole, econazole, clotrimazole, and ketoconazole, at concentrations inhibiting ergosterol biosynthesis (0.1 microM), decreased the ratio of unsaturated to saturated fatty acids in vivo but not in vitro. Similarly, naftifine, tolnaftate, and the azasterol A25822B, at concentrations inhibiting ergosterol biosynthesis (10, 100, and 1 microM, respectively), decreased the ratio of unsaturated to saturated fatty acids in vivo only. This suggests that the effect on fatty acids observed with ergosterol biosynthesis inhibitors may be secondary to the effect on ergosterol. With imidazoles, oleic acid antagonized inhibition of cell growth but not inhibition of ergosterol. This suggests that, with the C-14 demethylase inhibitors, decreased unsaturated fatty acids, rather than decreased ergosterol, are responsible for growth inhibition. Cerulenin, previously reported to be a potent inhibitor of both fatty acid and ergosterol biosynthesis, was found in the present study to inhibit the former (at 5 microM) but not the latter (up to 100 microM). Of the antifungal agents tested, econazole and miconazole (at 100 microM) produced complete release of [14C]aminoisobutyric acid, which is consistent with membrane damage.

Determination of pravastatin sodium and its major metabolites in human serum/plasma by capillary gas chromatography/negative ion chemical ionization mass spectrometry.

A capillary gas chromatography/negative ion chemical ionization mass spectrometry method has been developed to measure pravastatin sodium, an anti-hypercholesterolemic agent, and two of its major metabolites in human serum. Injected on a capillary column, derivatized pravastatin sodium and the two, metabolites were detected at levels of 0.5 pg microliters-1 injected with a signal-to-noise ratio of 3 to 1. The limit of detection was 0.3 ng ml-1 serum of each compound with 95% confidence using a weighted linear regression analysis. Prior to analysis, samples were purified on 200 mg C18 solid-phase extraction columns and derivatized with pentafluorobenzyl bromide and N,O-bis-(trimethylsilyl)-trifluoroacetamide. An excess of pentafluorobenzyl bromide was removed by reaction with propionic acid.