Duane B. Lakings

Determination of pioglitazone in dog serum using solid-phase extraction and high-performance liquid chromatography with ultraviolet (229 nm) detection

An analytical method is described for the determination of the free base of pioglitazone hydrochloride (U72, 107A, AD-4833) in dog serum. The method used solid-phase extraction of pioglitazone from serum followed by high-performance liquid chromatographic analysis on an octadecylsilane column with an eluent of acetonitrile-water (41:59, v/v) containing 1.2 ml/l acetic acid (pH 6.0 +/- 0.05). The column effluent was monitored at 229 nm. The analytical procedure has a linear range of 25 ng/ml to 20 micrograms/ml, a minimum quantifiable level of 25 ng/ml, absolute recovery of greater than 90% (n = 15), and precision of less than or equal to 8.8% (n = 45). The method was used in a preliminary dose proportionality study in the dog.

Thromboxane Synthase Activity and Platelet Function After Furegrelate Administration in Man

Furegrelate sodium (U‐63,557A), a pyridine‐derivative thromboxane synthase inhibitor, was administered orally in single doses of 200 to 1600 mg to normal male subjects. Furegrelate produced a dose‐related inhibition of thromboxane synthesis for 8–12 hours when measured either ex vivo from platelet‐rich plasma (PRP) or in vivo from urine. In general, the extent of thromboxane synthesis inhibition was greater in PRP than in urine. Furegrelate significantly inhibited platelet aggregation, but the effect was variable and measurements of thromboxane synthase did not predict the impact on platelet aggregation. Bleeding times and coagulation parameters were not altered significantly. Furegrelate was well absorbed orally with Tmax = 1 hr and t½ = 3.5 to 5 hrs. There was no marked metabolism; elimination was primarily by renal excretion of parent compound. Thus, furegrelate is an effective inhibitor of thromboxane synthase in man with a relatively long biologic and circulating half‐life.

Multiple dose trial of the thromboxane synthase inhibitor furegrelate in normal subjects.

SummaryFuregrelate sodium, a pyridinyl derivative thromboxane synthase inhibitor, was evaluated for its effects on thromboxane synthesis in normal volunteers after multiple dose administration. Twenty-four subjects were randomized to 200, 400, 800 or 1600 mg furegrelate or placebo treatment BID for 4 1/2 days.Furegrelate (800 or 1600 mg) significantly inhibited thromboxane synthesis throughout the dosing interval as assessed by thromboxane B2 generation from platelet-rich plasma challenged with arachidonic acid or from serum. Platelet aggregation was inhibited, but the effect was variable and a clear dose response relationship was not apparent. Bleeding times were also variable but tended to increase at the higher doses. There was no clinically significant change in any coagulation parameters or in any safety laboratory evaluations. Peak serum concentrations occurred approximately 1 h after dosing; t1/2ke was approximately 2 h. There was no significant change in furegrelates effects or pharmacokinetics over time (ie. Day 1 vs Day 5).

Development of a sensitive activity assay for high-volume evaluation of human renin inhibitory peptides in rat serum : results with U-71,038

A sensitive activity assay for high volume evaluation of human renin inhibitory peptides (RIPs) in rat sera (range 2–80 ng/ml) was developed based on the low affinity of RIPs to rat renin and their high affinity to human renin. The utility of this activity assay was tested by measuring concentrations of a human RIP, U-71,038 (BOC-Pro-Phe-N-MeHis-Leu Ψ [CHOHCH2]Val-Ile-Amp), in rat sera, determined by the activity assay, by a sensitive radioimmunoassay (RIA), and by tracking tritiated drug. Rats were given radiolabeled drug as an intravenous bolus, and blood samples were collected at various times after dosing. The serum level of U-71,038 equivalents was determined by the three techniques. Whole blood was also counted for total radioactivity to evaluate the potential for U-71,038 incorporation into red blood cells. Results from the three serum assays indicate good agreement between the calculated U-71,038 equivalents for the 30 min and 1 hr collection times. The 2 and 4 hr collection times show excellent agreement for the activity assay and RIA; [3H]-U-71,038 determinations gave substantially higher values. Serum levels for U-71,038 determined 30 min after dosing averaged less than 300 ng equivalents/ml suggesting that less than 1% of the administered dose was in the systemic circulation at that time. Thus, U-71,038 was rapidly cleared. At the 4 hr collection time, the level of U-71,038 equivalents, as determined by activity assay and RIA, was ten times the in vitro IC50 for the renin inhibitory activity of U-71,038. Analysis of whole blood levels of 3[H]-U-71,038 indicated little or no incorporation of drug related material into red blood cells. In addition to predicting pharmacological response, the activity assay can be used to quantify human RIPs in rat serum when biotransformation is absent.

A primate bioassay for the determination of renin inhibitory peptides in serum.

The study of renin inhibitory peptides (RIPs) in rodents and primates requires the establishment of a simple, high volume method for determining the concentration of RIPs in serum after intravenous or oral dosing. The human renin inhibition assay useful for rodents is not directly applicable to primates due to inherent production of angiotensin I from the primate serum angiotensinogen and added recombinant human renin. Therefore, a novel approach to analyze the serum concentrations of RIPs in primates is described based on in vitro studies with monkey serum. The procedure involves the inactivation of monkey angiotensinogen and monkey renin by thermal denaturation prior to analysis. Application of this assay was demonstrated by analyzing serum samples from an in vivo study in monkeys using ditekiren (U-71,038), a renin inhibitory peptide, and by validation of the assay and results using a tritium-based radioimmunoassay (RIA) for ditekiren. The minimum detectable limit of ditekiren for both the RIA and the bioassay for primates was 10ng/ml serum. The reported bioassay should be of value for monitoring serum levels of thermostable RIPs from pharmacokinetic, bioavailability, and pharmacodynamic studies in primates as well as in humans.

Pharmacokinetics of Furegrelate After Oral Administration to Normal Humans

Furegrelate sodium is a thromboxane synthetase inhibitor with potential for the treatment of various diseases including hypertension, thrombosis, and renal disorders. The absorption and disposition of the parent drug in normal male volunteers have been studied after single- and multiple-dose oral administration. The results from the single-dose study indicate that furegrelate is rapidly absorbed, with a Tmax of 1.0–1.7 hr, has an apparent terminal disposition rate constant of 0.12–0.17 hr−1, and is eliminated primarily by the kidney, with 62–78% of the dose excreted as parent drug. After multiple-dose oral administration for 4.5 days using a b.i.d. dosing regimen, no apparent change in the absorption, disposition, and elimination kinetics is detected and only a slight potential for drug accumulation is observed.

High-performance liquid chromatographic method for the determination of eclanamine and its N-desmethyl and N,N-didesmethyl metabolites in urine.

A high-performance liquid chromatographic method has been defined for the determination of eclanamine (free base of eclanamine maleate) and two of its metabolites, N-desmethyleclanamine and N,N-didesmethyleclanamine in urine. The method employs 10-ml urine samples, has a linear range from 5 to 500 ng/ml for the three compounds, and has a detection limit of 0.5 ng/ml for each compound. Sample preparation uses a cyanopropylsilane extraction column with washes of water, acetonitrile-water (30:70, v/v), and acetonitrile, and elution with 2% trifluoroacetic acid in acetonitrile. The eluate is evaporated to dryness, the residue dissolved in 1.0 ml acetonitrile-water (10:90, v/v) and 100 microliter are injected onto a Supelcosil LC-CN column. Eclanamine and its metabolites are eluted with an acetonitrile-water (35:65, v/v) eluent containing 0.01 M triethylamine and adjusted to pH 7.0 with phosphoric acid. The method has been validated by preparing and analyzing a series of fortified urines (range 2-500 ng/ml for each compound) on four separate days. Good linearity, precision, reproducibility, and specificity were obtained. Certification of the analytical method was accomplished by analyzing urine specimens collected from one volunteer administered a single oral dose of 45 mg eclanamine maleate. The data suggest that the metabolites of eclanamine have long elimination half-lives with levels still quantifiable in the 72-96 h collection interval.