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Biomedical subjects

P E Grebow

Publications and source records attributed to P E Grebow.

14 recordsLinked to original sources
PubMed1999

A double-blind, placebo-controlled, ascending-dose evaluation of the pharmacokinetics and tolerability of modafinil tablets in healthy male volunteers.

A randomized, double-blind, placebo-controlled, ascending-dose study was conducted to evaluate the pharmacokinetic and safety profiles of increasing modafinil doses (200 mg, 400 mg, 600 mg, 800 mg) administered orally over a 7-day period in normal healthy male volunteers. Eight subjects (six modafinil; two placebo) were randomized to each of the four dose groups. Modafinil or a placebo was administered once daily for 7 days. Serial blood samples were obtained following administration of the day 1 and day 7 doses for characterization of pharmacokinetics, and trough samples were obtained prior to dosing on days 2 through 6 to assess the time to reach the steady state. Pharmacokinetic parameters were calculated using noncompartmental methods. Modafinil steady state was reached after three daily doses. Modafinil pharmacokinetics were dose and time independent over the range of 200 mg to 800 mg. Steady-state pharmacokinetics of modafinil were characterized by a rapid oral absorption rate, a low plasma clearance of approximately 50 mL/min, a volume of distribution of approximately 0.8 L/kg, and a long half-life of approximately 15 hr. Modafinil was primarily eliminated by metabolism. Modafinil acid was the major urinary metabolite. Stereospecific pharmacokinetics of modafinil were demonstrated. The d-modafinil enantiomer was eliminated at a threefold faster rate than 1-modafinil. Modafinil 200 mg, 400 mg, and 600 mg doses were generally well tolerated. The modafinil 800 mg dose panel was discontinued after 3 days of treatment due to the observation of increased blood pressure and pulse rate. The safety data from this study suggest that the maximum tolerable single daily oral modafinil dose, without titration, may be 600 mg.

Adolescent↗
PubMed1998

Single-dose pharmacokinetics of modafinil and methylphenidate given alone or in combination in healthy male volunteers.

Modafinil is a novel wake-promoting agent being developed for treatment of excessive daytime sleepiness associated with narcolepsy. An open, 3 x 3 Latin square, randomized, cross-over study was performed in healthy males to compare the pharmacokinetics of single-dose oral modafinil (200 mg) and methylphenidate (40 mg) administered alone or in combination. Blood samples were obtained for analysis of d- and l-threo-methylphenidate and modafinil and its acid and sulfone metabolites. Pharmacokinetic parameters were determined by noncompartmental methods, but could not be evaluated for modafinil sulfone due to plasma levels that were close to the assay quantitation limit. Although sporadic differences in plasma concentrations were observed between treatments, coadministration of modafinil and methylphenidate did not significantly alter the plasma concentrations of modafinil, modafinil acid, modafinil sulfone, or methylphenidate enantiomers compared with administration of these agents alone. Half-life (t1/2), maximum concentration (Cmax), area under the concentration-time curve (AUC0-infinity), total clearance (Cl/F), and apparent volume of distribution (Vd/F) for modafinil and t1/2, Cmax, and AUC0-infinity for modafinil acid were not affected by concomitant administration of methylphenidate. Small but statistically significant increases in time to Cmax (tmax) were observed for modafinil and modafinil acid after methylphenidate coadministration compared with modafinil alone. Modafinil coadministration did not significantly alter the pharmacokinetics of d- or l-threo-methylphenidate, except for a small decrease in Vd/F of l-threo-methylphenidate. Concomitant methylphenidate may cause a delay in the oral absorption of modafinil, but this delay might not be relevant clinically. Coadministration did not alter the extent of oral absorption and disposition of either agent. Therefore, a pharmacokinetic interaction between modafinil and methylphenidate would be unlikely.

Adolescent↗
PubMed1993

Insulin-like growth factor-I: potential for treatment of motor neuronal disorders.

Motor neuronal disorders, such as the loss of spinal cord motor neurons in amyotrophic lateral sclerosis or the degeneration of spinal cord motor neuron axons in certain peripheral neuropathies, present a unique opportunity for therapeutic intervention with neurotrophic proteins. Normally, such proteins do not cross the blood-brain barrier, but spinal cord motor neuron axons and nerve terminals lie outside the barrier and thus may be targeted by systemic administration of protein growth factors. Insulin-like growth factor-I (IGF-I) receptors are present in the spinal cord, and, like members of the neurotrophin receptor family, IGF-I receptors mediate signal transduction via a tyrosine kinase domain. IGF-I was found to prevent the loss of choline acetyltransferase activity in embryonic spinal cord cultures, as well as to reduce the programmed cell death of motor neurons in vivo during normal development or following axotomy or spinal transection. Consistent with earlier reports that IGF-I enhances motor neuronal sprouting in vivo, subcutaneous administration of IGF-I increases muscle endplate size in rats. Subcutaneous injections of IGF-I also accelerate functional recovery following sciatic nerve crush in mice, as well as attenuate the peripheral motor neuropathy induced by chronic administration of the cancer chemotherapeutic agent vincristine in mice. Doses of IGF-I that accelerate recovery from sciatic nerve crush in mice result in elevated serum levels of IGF-I which are similar to those obtained following subcutaneous injections of formulated recombinant human IGF-I (Myotrophin) in normal human subjects. Based on these findings, together with evidence of safety in animals and man, clinical trials of recombinant human IGF-I have been initiated in patients with amyotrophic lateral sclerosis and are planned to begin soon in patients with chemotherapy-induced peripheral neuropathies.

Amino Acid Sequence↗
PubMed1988

Determination of a new inotropic agent in human plasma by high-performance liquid chromatography.

A new orally active inotropic agent, 6-[3,4-dihydro-3-methyl-(2H)-2-oxoquinozolinyl)]-4,5-dihydro-3- (2H)-pyridazinone (I), is currently under investigation. In support of clinical studies, a HPLC assay for the analysis of compound I in human plasma has been developed. The method involved a solid-phase extraction using C18 cartridge columns washed with methanol-water (20:80) and eluted with acetonitrile-water (70:30). The eluate was then extracted with dichloromethane. A reversed-phase alkylphenyl-bonded column was used as the analytical column. The mobile phase was a mixture of methanol, acetonitrile, 2-propanol and phosphate buffer (pH 4.6). A wavelength of 311 nm was used for detection. The limit of detection of the assay was 2 ng/ml, and the limit of quantitation was 5 ng/ml. A linear calibration range of 5 ng/ml to 1200 ng/ml was obtained with a correlation coefficient less than 0.99. The precision and accuracy were evaluated by analyzing samples of three different concentrations (n = 5), 40, 200 and 800 ng/ml in plasma. The coefficients of variation and the differences from nominal values were less than 10%. The average recovery for 5, 50 and 100 ng/ml of analyte in plasma was about 90%. This assay has been applied to clinical studies with satisfactory performance and to plasma of different species in preclinical studies.

Cardiotonic Agents↗
PubMed1983

Lack of effect of bilateral nephrectomy on the pharmacokinetics of 14C-indapamide (REV 2555) and its metabolites in the dog.

Renal impairment can affect the disposition of metabolites, as well as unchanged drug, especially when there is significant renal clearance of metabolites. The pharmacokinetics of indapamide, a highly metabolized drug, and total indapamide equivalents (as an indicator of metabolites plus unchanged drug) were determined in the anephric dog. An intravenous dose of 14C-indapamide was administered to dogs first after a sham-operation, and then following bilateral nephrectomy. The disposition of total indapamide equivalents, calculated from total radioactivity, was not substantially different after nephrectomy as compared to after sham-operation, with an increase after nephrectomy in the area under the blood level curve (+26.2%), and decreases in the elimination rate constant (-6.9%), volume of distribution (-12.7%) and total blood clearance (-21.9%). The only statistically significant change was the decrease in the volume of distribution. The elimination kinetics of unchanged drug were also qualitatively similar in both cases. After nephrectomy, a decrease was seen in the elimination rate constant (-10.9%) and the volume of distribution (-16.3%) while slight increases in the total blood clearance (+1.9%) and the area under the blood level curve (+4.8%) were noted. These findings could have important implications for advantageous use of indapamide in treatment of hypertensive patients with renal failure since these data suggest that metabolites as well as unchanged drug could still be effectively eliminated by an alternate, non-renal route, thus minimizing accumulation of these compounds.

Animals↗
PubMed1982

Pharmacokinetics and bioavailability of indapamide--a new antihypertensive drug.

Two formulations of indapamide tablets (2.5 mg) were given as a 5.0 mg dose and the subsequent blood levels were compared to those obtained after administration of a 5.0 mg solution. The study was conducted as a randomized three-way crossover design using healthy male volunteers. The drug was well tolerated by all the subjects involved. The area under the blood concentration versus time curve, extrapolated to infinity was essentially the same for all three formulations (4.2, 4.7, and 4.4 microgram-h/ml). Statistical comparison of the blood levels from the two tablets showed that one tablet had a significantly shorter time of maximum blood concentration (2.3 vs 3.5). Cmax(333ng/ml) and tmax (0.7h) values for the solution were significantly higher than either tablet. The average half-life (beta-phase) for all three formulations was 15 h, while the average systemic clearance was 20 ml/min. Indapamide has a low clearance rate and there was no evidence that the drug undergoes a first-pass effect.

Adolescent↗
PubMed1981

Semiautomated assay for indapamide in biological fluids.

A sensitive fluorescence procedure for the determination of indapamide in plasma and whole blood was developed. The procedure requires preextraction of the biological sample followed by continuous-flow analysis. The assay is sensitive to indapamide levels of 25 ng/ml in plasma and blood. A linear response from 25 to 200 ng/ml is observed. The procedure also can be used to measure urinary levels of indapamide. The assay has been used to obtain whole blood and plasma level curves from subjects receiving 2.5 mg of indapamide.

Autoanalysis↗
PubMed1981

Pharmacokinetics of indapamide in dogs.

Four beagle dogs received both an oral and intravenous dose (1 mg/kg) of indapamide in a crossover design. The blood levels and urinary excretion of intact indapamide were measured, and the pharmacokinetic parameters of the drug were defined. The results indicate that indapamide is completely bioavailable after an oral dose and does not undergo first-pass metabolism. Excretion of unchanged drug from the kidney accounted for only a small percentage of the drug's clearance. While the dog is very similar to the human in its handling of indapamide, the dogs clears indapamide approximately twice as fast as humans.

Administration, Oral↗
PubMed1980

Automated analysis of indapamide in drug-rodent food mixtures.

Indapamide, an antihypertensive agent, is an aryl sulfonamide that inhibits carbonic anhydrase in vitro but not in vivo. An assay was developed for indapamide in drug-rodent food mixtures that utilizes this inhibitory effect. Indapamide was extracted from the mixtures with methanol, and an aqueous dilution of the extract was sampled by a continuous-flow system. In the system, the drug was extracted with butanol and then back-extracted into alkali. This solution was neutralized, buffered, and mixed with bovine erythrocyte carbonic anhydrase. The substrate, p-nitrophenyl acetate, was added, the solution was incubated, and the amount of p-nitrophenol formed was measured. The assay was sensitive to 20 micrograms of indapamide/g of food, and 20 unknown samples could be analyzed per hour on the continuous-flow system. It is possible that the method could be extended to the analysis of other toxicological test substances that inhibit carbonic anhydrase in vitro.

Animal Feed↗
PubMed1978

Fluorometric assay for urinary indapamide.

A sensitive fluorescence method for the determination of indapamide was developed. Reaction of indapamide with sodium hydroxide at 100 degrees yielded a fluorescent product, and addition of formaldehyde to the fluorescent product increased its fluorescence intensity by a factor of three. The assay is sensitive to levels of indapamide of 0.025 microgram/ml in an aqueous solution, and a linear response between 0.025 and 2.0 microgram/ml was observed. The procedure was adapted to the analysis of intact indapamide in urine. Concentrations of indapamide of 0.05 microgram/ml can be detected in dogs given 20 mg of the drug.

Animals↗