Pharmacokinetics and pharmacodynamics of pravastatin alone and with cholestyramine in hypercholesterolemia.

The pharmacokinetics, pharmacodynamics, and safety of pravastatin, a new selective 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, were evaluated during monotherapy and with subsequent concomitant cholestyramine therapy in 33 patients with primary hypercholesterolemia in this randomized study. After 4 weeks, pravastatin monotherapy (5 mg, 10 mg, and 20 mg twice daily) significantly decreased total cholesterol by 17% to 24% (p less than 0.001 versus baseline) and low-density lipoprotein cholesterol by 23% to 35% (p less than 0.001). High-density lipoprotein cholesterol increased by 8% to 9%, and triglycerides decreased by 6% to 9%. The area under the serum concentration-time curve and maximum serum concentration of pravastatin showed dose-proportionality; time to maximum serum concentration and serum elimination half-life were independent of dose. When added to pravastatin therapy, cholestyramine enhanced the lipid-lowering effects of pravastatin. After 4 weeks of combination therapy, total cholesterol was reduced by 32% to 38% (p less than 0.001 versus baseline), and low-density lipoprotein cholesterol was reduced by 47% to 56% (p less than 0.001). High-density lipoprotein cholesterol increased by 11% to 18% (p less than 0.05). Pravastatin was well tolerated; no clinical adverse events directly attributable to the drug were reported.

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.

Comparative pharmacokinetics and pharmacodynamics of pravastatin and lovastatin.

The oral bioavailability of two HMG-CoA reductase inhibitors, pravastatin and lovastatin, was investigated in this randomized, two-way crossover study. Twenty healthy men were randomly assigned to treatment with a 40-mg dose of pravastatin or lovastatin once daily for 1 week; steady state kinetics were assessed after the last dose. After 1 week of washout, each subject received the alternate treatment. Serum specimens were assayed by gas chromatography/mass spectrometry (GC/MS) for intact pravastatin or lovastatin acid and by bioassay for active inhibitor concentration and, after hydrolysis of lactones, for total inhibitor concentration. The systemic bioavailabilities of total (active plus potentially active) inhibitors for the two drugs were different, with the mean AUC value for lovastatin being 50% higher than that of pravastatin (mean +/- SEM AUC0-24 values of 285 +/- 25 and 189 +/- 13 ng-equiv x hr/mL, respectively, P less than .0001). Pravastatin, which is administered as the monosodium salt, is present in the systemic circulation as the open acid; lovastatin, which is administered as the lactone, is present as both open-acid active metabolites (62%) and closed-ring lactone metabolites (38%), which are potentially active. Based on mean AUC values, pravastatin accounted for 75% of the active inhibitors from a pravastatin dose. Lovastatin acid accounted for just 25% of the active inhibitors from a lovastatin dose, with the remainder due to other active metabolites. Significant decreases from baseline in total and low-density lipoprotein (LDL) cholesterol were observed during the first treatment leg for both pravastatin and lovastatin.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluorometric determination of nadolol in human serum and urine.

To determine nadolol, a new beta-adrenergic blocking agent, in serum and urine, the drug is extracted into n-butyl acetate or ether from alkaline potassium chloride saturated samples. After back-extraction into 0.1 N HCl, the drug is oxidized with periodic acid; the resulting aldehyde is coupled with o-phenylenediamine to produce a fluorescent compound. The method can measure as little as 0.01 microgram of nadolol/sample.

Colorimetric determination of peptide antibiotics: in-process assay of cyclic octapeptidic antibiotics in fermentation broths.

A spectrophotometric method is presented for monitoring the biosynthesis of a new complex of cyclic octapeptidic antibiotics in fermentation broths. The method is based on the extraction of antibiotic from alkaline broth with butanol. An ion-pair, formed between the octapeptides and bromthymol blue, is extracted into chloroform from a solution buffered to pH 7.5. The absorbance of the colored solution is measured at 420 nm. Results are in good agreement with those obtained by microbiological assay. The method is also applicable to other peptidic antibiotics such as polymyxin B and gramicidin.

Spectrofluorometric determination of captopril plus captopril disulfide metabolites in plasma.

Captopril disulfides and the drug covalently bound to proteins were reduced with tri-n-butylphosphine. After sample purification on an XAD-2 column, captopril was treated with 1-(7-dimethylamino)-4-methyl-2-oxo-2H -1-benzopyran-3-yl)-1H-pyrrole-2,5-dione to form a fluorescent derivative. After acidification, the fluorescent derivative was extracted into toluene and purified on a C18 cartridge. The fluorescence of the dimethyl-formamide eluate was measured at an excitation wavelength of 380 nm and a fluorescence wavelength of 440 nm.

Determination of total captopril in human plasma by gas chromatography-mass spectrometry with selected-ion monitoring after reduction of disulfides.

Captopril is liberated from covalently protein-bound disulfides and other disulfide metabolites in human plasma by reduction with tri-n-butyl-phosphine. The captopril is then treated with N-ethylmaleimide, purified on XAD-2 resin, eluted with ethyl acetate, and methylated prior to its determination by gas chromatography-mass spectrometry with selected-ion monitoring. The limit of detection is 20 ng/mL of plasma.

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.

Identification and determination of the S-methyl metabolite of captopril in human plasma by selected-ion monitoring gas chromatography-mass spectrometry.

The S-methyl metabolite of captopril was identified and determined in human plasma by positive chemical ionization selected-ion monitoring gas chromatography-mass spectrometry. After oral administration of 100 mg of captopril to healthy subjects, the maximum plasma level was 60-114 ng/mL. These data for the S-methyl metabolite of captopril were correlated to total and unchanged captopril levels. Captopril--identification and determination of the S-methyl metabolite in human plasma, gas chromatography-selected-ion monitoring mass spectrometry Gas chromatography-selected-ion monitoring mass spectrometry--determination of the S-methyl metabolite of captopril in human plasma after oral administration.

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.

Spectrophotometric methods for monitoring the microbial transformation of steroids. I. Determination of 9-alpha-fluorohydrocortisone and 9-alpha-fluoro-16-alpha-hydroxyhydrocortisone in fermentation broths.

A method has been devised for the determination of 9alpha-fluorohydrocortisone and 9alpha-fluoro-16alpha-hydroxyhydrocortisone in fermentation broths. The method involves extraction of the two steroids from the broth with ethyl acetate, separation through the formation of the water-soluble borate complex of the vicinally hydroxylated steroid, and estimation of each steroid spectrophotometrically.

Simultaneous determination of the prodrug zofenopril and its active drug in plasma by capillary gas chromatography-mass-selective detection.

After oral administration of zofenopril, the active sulfhydryl angiotensin-converting enzyme inhibitor is released. Zofenopril is currently under clinical investigation as an antihypertensive. Blood samples are reacted with N-ethylmaleimide, immediately after collection, processed into plasma and stored frozen for subsequent analysis. After addition of two internal reference standards, one each for the prodrug and the active compound, the plasma samples are purified by a combination of liquid-liquid and solid-phase extractions. The dried methylated extracts are reconstituted with tetramethylbenzene and chromatographed by automated splitless injection on a fused-silica capillary column, connected to a mass-selective detector. The analytes and the internal reference standards are chromatographically resolved and a common fragment ion is monitored for the analytes. A limit of quantitation of approximately 1 ng/ml of plasma is achieved.

Simultaneous determination of captopril and S-benzoyl captopril in human blood by capillary gas chromatography-mass selective detection.

Using a new table-top electron-impact mass selective detector, interfaced with a narrow bore, fused silica capillary gas chromatograph, a method has been developed for the simultaneous determination of captopril and S-benzoyl captopril. With a capillary column the two components could be chromatographically resolved, thus permitting the use of electron-impact ionization for quantitative measurements.

Determination of SQ 27,519, the active phosphinic acid-carboxylic acid of the prodrug SQ 28,555, in human serum by capillary gas chromatography with nitrogen-phosphorus detection after a two-step derivatization.

A method for the determination of SQ 27,519 (II), the active phosphinic acid-carboxylic acid of the prodrug SQ 28,555 (I), in human serum is presented. Compounds I and II are simultaneously extracted from acidified serum into ethyl acetate, and II is back-extracted into aqueous sodium bicarbonate. Compound I, in ethyl acetate, can be subsequently hydrolyzed and measured as II. The two acidic groups of II are selectively esterified, first by methylation of the carboxylic acid with methanolic hydrochloric acid and then by formation of the hexafluoroisopropyl ester of the phosphinic acid. The resulting product is measured by splitless-injection capillary gas chromatography with nitrogen-phosphorus detection. Linear standard curves were obtained for II with a detection limit of less than 10 ng/ml of serum. The method was successfully applied to the analysis of serum samples obtained from normal individuals after administration of I. In an ascending-dose study involving several human subjects the serum levels of II ranged from less than 10 to 7000 ng/ml of serum.

Body fluid analysis of a phosphonic acid angiotensin-converting enzyme inhibitor using high-performance liquid chromatography and post-column derivatization with o-phthalaldehyde.

A method is described for the extraction of a phosphonic acid angiotensin-converting enzyme inhibitor from either urine or plasma, and subsequent quantitation using high-performance liquid chromatographic (HPLC) analysis and post-column o-phthalaldehyde reagent derivatization. The compound cannot be quantitatively extracted from the body fluids, but use of a fluorinated internal standard allowed for the computation of accurate results. With the use of an internal standard, excellent precision, linearity, and recovery were obtained for analyte response in both urine and plasma. In urine a working range of 0.2-10 micrograms/ml was found, with a limit of detection of 0.1 micrograms/ml. For plasma the working range was found to be 2-500 ng/ml, and the limit of detection was established as 1 ng/ml. Due to the non-polar character of the analyte at low pH values, it was possible to use novel extraction (solid-phase C8 column) and HPLC [poly(styrenedivinyl benzene) HPLC column] conditions to separate and quantitate the compound from plasma and urine.

Determination of lovastatin acid in serum by gas chromatography/mass spectrometry.

The acid form of lovastatin, an HMG-CoA reductase inhibitor, was analyzed by gas chromatography/negative-ion chemical ionization mass spectrometry after derivatization with pentafluorobenzyl bromide and bis-(trimethylsilyl)trifluoroacetamide (BSTFA). Mass spectrometry of this derivative produced a dominant [M-181]- ion under chemical ionization conditions using ammonia as the reagent gas. The limit of detection was approximately 2 pg injected on column.