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P H Siedlik

Publications and source records attributed to P H Siedlik.

8 recordsLinked to original sources
PubMed2000

Impact of population pharmacokinetic-pharmacodynamic analyses on the drug development process: experience at Parke-Davis.

BACKGROUND: Continued scepticism about the benefits of population pharmacokinetics and/or population pharmacodynamics, here referred to collectively as the population approach, hampers its widespread application in drug development. At the same time the sources of this scepticism have not been clearly defined. In an attempt to capture and clearly define these concerns and to help communicate the value of the population approach in drug development at Parke-Davis we conducted a survey of customers within the company. The results of this survey are presented here. METHODS: All drug development programmes conducted over the past 10 years that included a population approach in data analysis and interpretation were identified. A brief description of the population analysis was prepared together with a brief description of how the resulting information was used in each drug development programme. These synopses were forwarded to relevant members of each drug development team together with a survey designed to solicit opinions as to the relevance and impact of these analyses. RESULTS: The most frequent use of information derived from population-based analysis was in labelling. In all cases of drugs making to New Drug Application (NDA) submission the analyses resulted in information that was included in approved or proposed labelling. In almost half of the cases summarised here (5 of 12), population-based analysis was perceived to have resulted in information that influenced the direction of individual development programmes. In many of these cases the information was serendipitous. It is also noted that most of these analyses were not the result of clearly defined objectives and prospective analysis plans. CONCLUSIONS: Use of the population approach, even when applied retrospectively, may have value in complementing or supporting interpretation of other data collected during the course of a trial. Atypical systemic exposure is quickly and easily assessed for correlation with adverse events or exceptional efficacy in retrospective or ad hoc evaluation. Although we know of no direct evidence, it is possible that such use of population pharmacokinetic data has facilitated NDA review and approval by providing insight into the role of atypical systemic drug exposure in otherwise spurious events.

Data Collection↗
PubMed1999

Erythromycin coadministration increases plasma atorvastatin concentrations.

The effect of erythromycin on the pharmacokinetics of atorvastatin, an inhibitor of HMG-CoA reductase, was investigated in 12 healthy volunteers. Each subject received a single 10 mg dose of atorvastatin on two separate occasions, separated by 2 weeks. Erythromycin (500 mg qid) was given from 7 days before through 4 days after the second atorvastatin dose. Atorvastatin concentrations were determined by an enzyme inhibition assay, which measured both atorvastatin and active metabolites. When erythromycin was coadministered with atorvastatin, mean Cmax and AUC(0-infinity) increased by 37.7% and 32.5%, respectively. Mean terminal half-life was similar following each atorvastatin dose. Possible mechanisms for this interaction include erythromycin inhibition of first-pass conversion of atorvastatin to inactive metabolites and erythromycin inhibition of P-glycoprotein-mediated intestinal or biliary secretion.

Adolescent↗
PubMed1994

The temporal effect of food on tacrine bioavailability.

A four-way cross-over study was performed to assess the temporal effect of food on the rate and extent of tacrine (Cognex, THA) absorption after drug administration to healthy, older volunteers. Each volunteer received four single 40-mg THA doses at 1-week intervals. Doses were administered after an 8-hour overnight fast, 1 hour before a standard breakfast, 15 minutes after beginning a standard breakfast, and 2 hours after completion of a standard breakfast. Gastrointestinal side effects were most frequently reported after drug administration to fasted subjects. Mean Cmax and AUC(0-infinity) values after THA administration during breakfast (9.9 ng/mL and 70.2 ng.hr/mL) and 2 hours after breakfast (11.6 ng/mL and 74.2 ng.hour-1.mL-1) were significantly lower than values determined after administration of THA to fasting subjects (15.8 ng/mL, and 91.8 ng.hour-1.mL-1). Little effect was evident when THA was administered 1 hour before breakfast.

Aged↗
PubMed1994

Simultaneous determination of tacrine and 1-hydroxy-, 2-hydroxy-, and 4-hydroxytacrine in human plasma by high-performance liquid chromatography with fluorescence detection.

An analytical method was developed for the simultaneous reversed-phase (cyano) high-performance liquid chromatographic determination with fluorescence detection of tacrine and 1-hydroxy-, 2-hydroxy-, and 4-hydroxytacrine in human plasma. Alkalinized human plasma samples were extracted with a mixture of chloroform/l-propanol (90:10, v/v). Extraction recoveries generally ranged from 68% to 83% for all four compounds and did not appear to be concentration dependent over the range examined. Calibration curves were constructed over the following ranges: 0.5-30.0 ng/mL for tacrine (THA) and 4-hydroxytacrine (4-OH-THA), 1.0-30.0 ng/mL for 2-hydroxytacrine (2-OH-THA), and 0.925-46.2 ng/mL for 1-hydroxytacrine (1-OH-THA). The intra- and interassay precision (RSD) for the quality control specimens analyzed during validation were < or = 11.8% and < or = 9.28%, respectively. The intra- and interassay accuracy (RE) for the quality control specimens analyzed during validation ranged from 14.1% to -7.5% and 12.1% to -3.33%, respectively, for all four compounds. The limit of quantitation was estimated as the level of the lowest concentration in the calibration curve for each compound based on acceptable interassay precision and accuracy statistics generated at this concentration. The sensitivity of the method was adequate for the determination of THA, 1-OH-THA, 2-OH-THA, and 4-OH-THA following oral administration of Cognex (40 mg single dose) to normal volunteers.

Cholinesterase Inhibitors↗
PubMed1984

Mechanism of the stimulation of prostaglandin H synthase and prostacyclin synthase by the antithrombotic and antimetastatic agent, nafazatrom.

Nafazatrom, an antithrombotic and antimetastatic agent containing a pyrazolone functionality, is a reducing substrate for the peroxidase activity of prostaglandin H (PGH) synthase. Nafazatrom inhibits the hydroperoxide-dependent oxidation of phenylbutazone, stimulates the reduction of 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid, and is oxidized by microsomal or purified enzyme preparations from ram seminal vesicles. Consonant with the effects of other peroxidase-reducing substrates, nafazatrom stimulates the oxygenation of arachidonic acid to prostaglandin endoperoxides by the cyclooxygenase component of PGH synthase. In addition, nafazatrom causes an elevation in the levels of 6-keto-prostaglandin F1 alpha, the non-enzymatic hydrolysis product of prostacyclin (PGI2) biosynthesized from arachidonic acid by ram seminal vesicle microsomes. Elevation of PGI2 biosynthetic capacity by nafazatrom occurs under conditions in which prostaglandin endoperoxide biosynthesis is maximal, suggesting that nafazatrom has a stimulatory effect on the conversion of prostaglandin endoperoxides to PGI2. Nafazatrom has no effect on the ability of ram seminal vesicle microsomes to convert PGH2 to PGI2 but protects microsomal PGI2 synthase from inactivation by 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid. Nafazatrom stimulates PGI2 biosynthesis in ram seminal vesicle microsomes by acting as a substrate for the peroxidase-catalyzed reduction of hydroperoxy fatty acids that are irreversible inactivators of PGI2 synthase. Several other compounds, including dipyridamole and triiodothyronine, exert similar effects. This may contribute to the reported ability of nafazatrom and related compounds to elevate the levels of bioassayable PGI2 in vivo and to the antithrombotic and antimetastatic activities of nafazatrom.

Animals↗
PubMed1982

Oxidation of phenidone and BW755C by prostaglandin endoperoxide synthetase.

1-Phenyl-3-pyrazolidone (phenidone) and 3-amino-1-(m-(trifluoromethyl)-phenyl)-2-pyrazoline (BW755C) are oxidized by the hydroperoxidase component of prostaglandin endoperoxide synthetase and by horseradish peroxidase. The initial oxidation products are radical cations which exhibit visible absorption maxima at 514, 490, and 472 nm (phenidone) and 535, 500, and 488 nm (BW755C). The radical cation of phenidone can be detected by electron paramagnetic resonance spectroscopy as a complex multiline signal centered at g = 2.0039. In addition to being oxidized by peroxidases both compounds are cofactors for the reduction of 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid to 15-hydroxy-5,8,11,13-eicosatetraenoic acid by the hydroperoxidase activity of purified and hematin-reconstituted prostaglandin endoperoxide synthetase. As a consequence of their oxidation by prostaglandin endoperoxide synthetase, phenidone and BW755C inhibit the hydroperoxide-dependent oxidation of phenylbutazone, luminol, diphenylisobenzofuran, epinephrine, and guaiacol by ram seminal vesicle microsomes. The inhibition of phenylbutazone oxidation is competitive and exhibits Ki values of 16 microM (BW755C) and 45 microM (phenidone). BW755C and phenidone stimulate prostaglandin biosynthesis by purified and reconstituted prostaglandin endoperoxide synthetase at concentrations up to 100 microM but inhibit at higher concentrations (I50 values approximately 210 microM and 1180 microM, respectively). The ability of phenidone and BW755C to act as peroxidase reducing cofactors or radical scavengers may contribute to their observed biochemical and pharmacological effects.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗