Eugene Ivashkiv

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 × hr/mL, respectively, P < .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. Pravastatin treatment resulted in 21% and 26% decreases in total and LDL‐cholesterol, respectively (P < .001); lovastatin reduced these parameters by 18% and 22%, respectively (P < .003). These results indicate that, although pravastatin and lovastatin have very similar chemical structures and effects on serum lipids, they differ sharply in pharmacokinetic properties.

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 < 0.001 versus baseline) and low‐density lipoprotein cholesterol by 23% to 35% (p < 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 < 0.001 versus baseline), and low‐density lipoprotein cholesterol was reduced by 47% to 56% (p < 0.001). High‐density lipoprotein cholesterol increased by 11% to 18% (p < 0.05). Pravastatin was well tolerated; no clinical adverse events directly attributable to the drug were reported.

Determination of pravastatin sodium and its isomeric metabolite in human urine by HPLC with UV detection.

An assay was required to determine the amounts of pravastatin sodium and the metabolite in human urine. A solid-phase extraction using a disposable cartridge was developed to isolate both pravastatin and metabolite from urine. Measurements by high-performance liquid chromatography with ultraviolet detection is described

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.

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.

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.

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

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.