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Rifabutin is structurally similar to rifampin, but there are important pharmacokinetic differences between the two drugs. Rifabutin is more lipid soluble than is rifampin, resulting in more-extensive tissue uptake, a larger volume of... more
Rifabutin is structurally similar to rifampin, but there are important pharmacokinetic differences between the two drugs. Rifabutin is more lipid soluble than is rifampin, resulting in more-extensive tissue uptake, a larger volume of distribution, lower maximum plasma concentrations, lower trough concentrations, a longer terminal half-life, and higher tissue-to-plasma drug concentration ratios. The oral bioavailability of rifabutin is low. Like rifampin, rifabutin induces its own metabolism during multiple dosing. Rifabutin is extensively metabolized. The two major metabolites of rifabutin contribute to its antimicrobial activity. Rifabutin induces hepatic metabolism but is not as potent an inducer as is rifampin. Rifabutin does not affect the pharmacokinetics of antiretroviral drugs that are excreted in the urine. Although rifabutin decreases plasma concentrations of zidovudine, this finding does not appear to be clinically relevant. When administered during rifabutin prophylaxis, fluconazole decreases the incidence of Mycobacterium avium complex bacteremia. The coadministration of clarithromycin and rifabutin results in increased plasma concentrations of rifabutin and decreased plasma concentrations of clarithromycin ; however, the plasma concentration of clarithromycin's active metabolite is increased.
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The disposition profile of 6-mercaptopurine (6MP) was studied from plasma and cerebrospinal fluid (CSF) in the rhesus monkey following a single iv bolus dose (4 mg/kg). A new, sensitive, and specific high performance liquid chromatography... more
The disposition profile of 6-mercaptopurine (6MP) was studied from plasma and cerebrospinal fluid (CSF) in the rhesus monkey following a single iv bolus dose (4 mg/kg). A new, sensitive, and specific high performance liquid chromatography procedure has been employed for drug quantitation in biological fluids. An equation consisting of three exponential terms was simultaneously fitted to the 6MP plasma and CSF concentration vs. time data using the SAAM 27 digital computer program. 6MP in plasma and CSF had a mean half-life (t1/2, lambda z) of 2.9 hr and an apparent volume of distribution (Vd, lambda z) of 3.00 liter/kg. Estimates of total body clearance average 0.731 +/- 0.412 liter/hr/kg and ranged between 0.446 and .1204 liter/hr/kg. In the postdistributive phase, the decline of 6MP concentration from the CSF paralleled plasma. The t1/2, lambda z obtained by fitting Ccsf vs. t data separately was not significantly different (p greater than 0.2) than the one obtained above in a simultaneous fitting of the data. Therefore, it appears that the unbound 6MP concentration in plasma may be the driving force in the diffusion of the drug into CSF. Comparison of experimental CSF/plasma ratio of 6MP with the theoretical values obtained using the pH-partition hypothesis is also discussed.
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Research Interests: Endocrinology, Behavior, Medicine, Humans, Prolactin, and 15 moreInternal Medicine, Nicotine, Female, Male, Psychoneuroendocrinology, Aged, Middle Aged, Adult, Adrenocorticotropic Hormone, Alzheimer Disease, Radioimmunoassay, Psychiatric Status Rating Scales, Psychology and Cognitive Sciences, hydrocortisone, and Medical and Health Sciences
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A high-performance liquid chromatographic assay was developed that separates and quantitates benzocaine and its primary degradation product, p-aminobenzoic acid. This method is rapid, sensitive, and specific. Preliminary stability data... more
A high-performance liquid chromatographic assay was developed that separates and quantitates benzocaine and its primary degradation product, p-aminobenzoic acid. This method is rapid, sensitive, and specific. Preliminary stability data obtained with this method demonstrate its utility for this purpose.
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The cardioactive drug quinidine has a narrow therapeutic index; consequently, determination of serum quinidine concentrations can be important. We describe a relatively rapid and specific assay for quinidine in serum by high-performance... more
The cardioactive drug quinidine has a narrow therapeutic index; consequently, determination of serum quinidine concentrations can be important. We describe a relatively rapid and specific assay for quinidine in serum by high-performance liquid chromatography. It is suitable for use in patient monitoring or pharmacodynamic studies. Alkalinized serum is extracted with benzene, which is evaporated under nitrogen and reconstituted with methanol; an aliquot is chromatographed. Quinidine is separated from its metabolites and dihydroquinidine (a contaminant in quinidine raw materials). The retention time for quinidine is 4 min 10 s, for dihydroquinidine it is 5.5 min. Results for patients' sera by this assay method and the double-extraction method of Cramer and Isaksson [Scand. J. Clin. Lab. Invest. 15, 553 (1963] correlate well (r = .975).
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The antipurine 6-mercaptopurine (6-MP) is effective in the induction and maintenance of remission in patients with acute lymphocytic leukemia. This report presents a compartmental model that describes the kinetics of 6-MP in the plasma... more
The antipurine 6-mercaptopurine (6-MP) is effective in the induction and maintenance of remission in patients with acute lymphocytic leukemia. This report presents a compartmental model that describes the kinetics of 6-MP in the plasma and cerebrospinal fluid (CSF) of the monkey. Analysis is based on simultaneously measured plasma and CSF 6-MP concentrations after intravenous and intraventricular bolus administration. Results indicate that 6-MP administered intraventricularly remains largely in the CSF. Disappearance of 6-MP from CSF is principally due to convective losses at a rate equivalent to CSF turnover. Diffusion of 6-MP across the ependymal surface accounts for only 7% of the 6-MP appearing in the plasma. Conversely the dominant route for entry of 6-MP into the CSF from the plasma is entrainment in choroidally formed CSF. Only 12% of 6-MP in the CSF after intravenous administration can be accounted for by permeation of cerebral capillaries and diffusion through brain parenchyma and across the ependymal surface into CSF. These results indicate that the choroid plexus is not a significant barrier for the transfer of molecules like 6-MP from plasma to CSF.
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Research Interests: Chemistry, Schizophrenia, Medicine, Cerebrospinal Fluid, Humans, and 13 moreBlood brain barrier, Female, Male, P-glycoprotein, Central Nervous System, Steady state, High Pressure Liquid Chromatography, Adult, Drug evaluation, Blood Proteins, Verapamil, Clinical Pharmacology and Therapeutics, and Pharmacology and pharmaceutical sciences
... Offices John Wiley & Sons, Inc., 605 Third Avenue, New York NY 10158-0012, USA Jacaranda Wiley Ltd, 33 Park Road, Milton ... Data Pharmacodynamics and drug development: perspectives in clinical pharmacology/edited... more
... Offices John Wiley & Sons, Inc., 605 Third Avenue, New York NY 10158-0012, USA Jacaranda Wiley Ltd, 33 Park Road, Milton ... Data Pharmacodynamics and drug development: perspectives in clinical pharmacology/edited by Neal R. Cutler, John J. Sramek and Prem K. Narang. ...
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Clinical Pharmacology & Therapeutics (1996) 59, 141–141; doi: 10.1038/sj.clpt.1996.64
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3'-Deamino-3'-(2-methoxy-4-morpholinyl)doxorubicin (FCE 23762, PNU 152243) is a highly lipophilic doxorubicin derivative which possesses potent in vitro and in vivo antitumor activity. Previous phase I studies had been... more
3'-Deamino-3'-(2-methoxy-4-morpholinyl)doxorubicin (FCE 23762, PNU 152243) is a highly lipophilic doxorubicin derivative which possesses potent in vitro and in vivo antitumor activity. Previous phase I studies had been conducted using a single bolus every 28 days. We conducted a phase I study of FCE 23762 on a daily x3 every 28 days schedule. Thirty patients received 68 cycles of therapy at 5 dose levels (200-600 micrograms/m2/d). Prolonged neutropenia and thrombocytopenia were the dose-limiting toxicities. Other nonhematological toxicities included nausea and vomiting, anorexia, fatigue and transient elevations of serum creatinine and hepatic transaminases. No cardiac toxicity was demonstrated. There were no partial or complete antitumor responses. The recommended phase II dose using the schedule defined in this study is 500 micrograms/m2/dx3.
Research Interests: Medicine, Humans, Toxicity, Female, Male, and 9 moreNausea, Aged, Middle Aged, Doxorubicin, Adult, Neoplasms, Anorexia, Vomiting, and neutropenia
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Clinical Pharmacology & Therapeutics (1999) 65, 161–161; doi:
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Research Interests: Pharmacology, Pharmacokinetics, Clinical Pharmacology, Adolescent, Medicine, and 15 moreHumans, Female, The, Middle Aged, Premenopausal women, Adult, Fever, Rifampicin, Luteinizing Hormone, Area Under Curve, Follicle stimulating hormone, Oral Contraceptive, neutropenia, Pharmacology and pharmaceutical sciences, and Rifampin
The effect of carbamazepine on adenosine receptors in vitro has been well documented, with findings from several groups showing that therapeutic doses of this drug are sufficient to inhibit binding to the major portion of adenosine... more
The effect of carbamazepine on adenosine receptors in vitro has been well documented, with findings from several groups showing that therapeutic doses of this drug are sufficient to inhibit binding to the major portion of adenosine receptors in brain. In this study, we describe the effects of chronic carbamazepine on central adenosine receptors from several areas of rat brain using [3H]diethylphenylxanthine [( 3H]DPX) and [3H]cyclohexyladenosine [( 3H]CHA) as ligands. Carbamazepine was administered to rats orally in the diet at doses of 2.25 g/kg of diet and 5.0 g/kg of diet for periods of 3 and 11 days, respectively. Carbamazepine-treated animals displayed higher levels of adenosine receptors in virtually all brain areas tested, most of which reached significance in the 11-day treatment group. Scatchard analysis revealed increases in the number of receptors. There was no change in peripheral and central type benzodiazepine receptors or beta-adrenergic receptors in the carbamazepine-treated animals. Therefore, carbamazepine treatment in vivo appears to upregulate adenosine receptors, suggesting that this drug may act as an adenosine antagonist.
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Cognitive enhancers are compounds that have been purported to improve memory. Several drugs from various classes have been investigated clinically in the elderly population with different types of dementia. It is important to clarify that... more
Cognitive enhancers are compounds that have been purported to improve memory. Several drugs from various classes have been investigated clinically in the elderly population with different types of dementia. It is important to clarify that the dose-response relationships with these agents in the elderly population are almost nonexistent. This difficulty associated with the clinical trials in dementia patients is primarily due to problems related to quantification of the drug effect, as neuropsychological assessments have a large degree of associated measurement error. Pharmacokinetic and dynamic studies with these drugs have been few. Therefore, rather than choosing to discuss kinetics, as expected from the contributions in this part, we have decided to address methodological issues that pertain to all agents being evaluated in the elderly with some form of dementia.
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The effects of hepatic and presystemic enzyme induction on the bioavailability (F) and disposition of antipyrine after repeated rifampicin (RFM) and rifabutin (RBT) exposure were studied in mice. ICR mice were divided to receive 4 daily... more
The effects of hepatic and presystemic enzyme induction on the bioavailability (F) and disposition of antipyrine after repeated rifampicin (RFM) and rifabutin (RBT) exposure were studied in mice. ICR mice were divided to receive 4 daily oral dosing of either the dosing vehicle or 50 mg/kg of REM or RBT. At the completion of rifamycin dosing, the pharmacokinetics of antipyrine were assessed following either a single 50 mg/kg oral dose or a 20 mg/kg intravenous dose. Blood samples were collected (n=4/timepoint) over a 6 h period. The content of P450 in the liver and small intestine (GI) was also assessed in parallel. Systemic antipyrine clearance (CL) increased from 31.8 ml/min/kg (controls) by 64% and 42% following repeated exposure to RFM and RBT, respectively. Estimate of F for antipyrine decreased from 0.97 in controls to 0.58 and 0.82 in animals treated with RFM and RBT, respectively. The content of P450 (nmol/mg protein) in the liver increased from 0.61 (control) to 1.36 following RFM and 0.82 for RBT, while no significant changes were observed for the GI tract. The i.v. dosing data confirmed the induction of antipyrine metabolism in the liver by both rifamycins yet the induction potential was approximately 1/3 lower for RBT. This difference was consistent with the changes observed in the hepatic P450 protein content, but this alone could not account for the reduction in the F for antipyrine. Therefore, predictions for changes in F of an interacting agent should not be judged solely on the basis of the metabolic status of the liver. The relative contribution of metabolic induction and presystemic drug loss to bioavailability/absorption should also be further delineated for its relevance to poly-pharmacy in patients likely to receive long-term rifamycin based treatment.
Research Interests: Metabolism, Pharmacokinetics, Enzyme Inhibitors, Comparative Study, DISTRIBUTION, and 15 moreMice, Animals, Male, Absorption, Bioavailability, Anti-Bacterial Agents, Digestive System, Distribution, Biological activity, Drug Interaction, Biological Availability, Antipyrine, Enzyme Induction, Pharmacology and pharmaceutical sciences, and Rifampin
We investigated the effects of chronic carbamazepine treatment in rats on brain somatostatin. Following 12 days of carbamazepine treatment, no changes in somatostatin levels were found in any of the brain areas examined which included:... more
We investigated the effects of chronic carbamazepine treatment in rats on brain somatostatin. Following 12 days of carbamazepine treatment, no changes in somatostatin levels were found in any of the brain areas examined which included: amygdala, hippocampus, caudate-putamen, median eminence, arcuate nucleus, nucleus accumbens, nucleus interstitialis of the stria terminalis, nucleus periventricularis, parietal cortex, and occipital cortex. Thus, carbamazepine in low doses does not affect basal levels of brain somatostatin in the rat, in contrast to the previous reports of decreased somatostatin in the cerebrospinal fluid of affectively ill patients.
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It has been suggested that didanosine (ddI) may undergo hepatic metabolism. Rifabutin is an inducer of drug metabolism. Fifteen human immunodeficiency virus-infected patients whose conditions were stabilized on twice-daily doses of ddI... more
It has been suggested that didanosine (ddI) may undergo hepatic metabolism. Rifabutin is an inducer of drug metabolism. Fifteen human immunodeficiency virus-infected patients whose conditions were stabilized on twice-daily doses of ddI participated in a Phase I, open-label, pharmacokinetic and safety drug interaction study between rifabutin and ddI. Twelve patients completed the study. All patients received their regular ddI dose (167-375 mg) on day 1. On days 2-13 they received once-daily rifabutin (600 mg, three patients; 300 mg, nine patients) with their regular twice-daily ddI regimen. On days 14-16 they received rifabutin alone. Serial blood and urine samples were collected for 12 h on day 1 and for 24 h on days 13 and 16, and safety evaluations were made throughout the study. Average day 1/day 13 ddI pharmacokinetic ratios and 95% confidence interval values for Cmax, AUC0-infinity, Cls/F, and t 1/2, lambda z were 1.17 (0.96-1.38), 1.13 (0.99-1.27), 0.91 (0.81-1.01), and 0.97 (0.79-1.15), respectively (p > 0.05 for all comparisons; paired t test). A 20% difference in AUC0-infinity could be detected with 90% power. Also, there were no significant changes in laboratory values or electrocardiograms, or in rifabutin pharmacokinetic parameters when the two agents were coadministered. Based on the safety and pharmacokinetic assessments, rifabutin did not appear to interact with ddI.
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For over 30 years, oral 6-mercaptopurine (6-MP) has been a mainstay of systemic maintenance therapy for acute lymphoblastic leukemia. De spite its efficacy as an antileukemic agent, 6-MP has not been previously administered by the... more
For over 30 years, oral 6-mercaptopurine (6-MP) has been a mainstay of systemic maintenance therapy for acute lymphoblastic leukemia. De spite its efficacy as an antileukemic agent, 6-MP has not been previously administered by the intrathecal (IT) route. In anticipation of a clinical trial of IT 6-MP, preclinical cytotoxicity and pharmacology studies were performed to define'a safe, effective dose. The
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A simple, selective, sensitive and rapid procedure is described for the quantitation of 6-mercaptopurine (6-MP) in biological fluids. A sensitivity of at least 5 ng/ml is easily achieved in plasma on a reversed-phase octadecylsilane (C18)... more
A simple, selective, sensitive and rapid procedure is described for the quantitation of 6-mercaptopurine (6-MP) in biological fluids. A sensitivity of at least 5 ng/ml is easily achieved in plasma on a reversed-phase octadecylsilane (C18) column using a high-performance liquid chromatography system following an initial protein precipitation and a clean-up step. Mean extractability of the drug from plasma following this procedure is greater than 98% and the overall coefficient of variation for the assay is below 6%. Plasma levels of 6-MP were measured in a rhesus monkey for 12 h following an intravenous administration of a single bolus dose (4 mg/kg) of 6-MP.
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Bretylium kinetics were examined in patients with varying degrees of renal impairment after a single intravenous dose of bretylium tosylate. Maximum plasma concentrations achieved at the end of the infusion, when normalized to the dose,... more
Bretylium kinetics were examined in patients with varying degrees of renal impairment after a single intravenous dose of bretylium tosylate. Maximum plasma concentrations achieved at the end of the infusion, when normalized to the dose, correlated strongly with creatinine clearance. Drug disposition from plasma was biexponential, with a short distributive phase, but drug elimination was reduced, especially in patients with creatinine clearance below 30 ml/min X 1.73 m2. There was reduction in renal and total clearance and prolongation of t 1/2, with deteriorating renal function. In one patient who was reevaluated after a year, there was 76% reduction in the total clearance, corresponding to 43% deterioration of renal function. The difference of 33% between these values is due to a reduction of nearly 36% in volume of distribution, caused by the further deterioration of the renal function. Six-hour hemodialysis procedure on two anephric patients, resulted in an apparent one- to three...
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A simple, selective and sensitive procedure is described for the quantitation of flupirtine maleate (FLU) and its active acetylated metabolite (Met. 1) in plasma and urine. Using a 0.5-ml sample, a sensitivity of 10 ng/ml is easily... more
A simple, selective and sensitive procedure is described for the quantitation of flupirtine maleate (FLU) and its active acetylated metabolite (Met. 1) in plasma and urine. Using a 0.5-ml sample, a sensitivity of 10 ng/ml is easily achieved with a reversed-phase octadecylsilane (C18) column, and a high-performance liquid chromatographic system with fluorescence detection. Quantitation from plasma involves addition of an internal standard, protein precipitation with acetonitrile and a sample concentrating step, while for urinalysis the samples are taken through a single extraction with methylene chloride. Analytical recoveries of FLU and Met. 1 from plasma averaged greater than or equal to 95%, while from urine only 60 and 50%, respectively, could be recovered. The overall, inter- and intra-day variability for both FLU and Met. 1 averaged 6, 5 and 3%, in plasma, respectively. Standard calibration plots in plasma were linear (r greater than or equal to 0.99) for FLU (range: 0.01-10.0 ...
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We examined the influence of age on vancomycin kinetics in 12 normal healthy men (six young and six elderly) after an intravenous infusion of 6 mg/kg. Serial blood and urine samples were collected for up to 2 days after dosing and were... more
We examined the influence of age on vancomycin kinetics in 12 normal healthy men (six young and six elderly) after an intravenous infusion of 6 mg/kg. Serial blood and urine samples were collected for up to 2 days after dosing and were assayed for unchanged drug by a specific radioimmunoassay. Serum concentrations of vancomycin after infusion declined in a multiphasic manner. Both serum and urinary excretion data were simultaneously fit by a three-compartment model with SAAM-27 computer programs. Estimates of mean t1/2 obtained from the terminal phase of the drug disposition profile showed the t1/2 to be longer in the elderly than in the young subjects (12.1 and 7.2 hr). Although there was no change in the initial distribution volume of the central compartment, total systemic and renal clearances were reduced in the elderly and did not correlate with renal function. The increase in the vancomycin volume of distribution at steady state was ascribed to enhanced tissue binding of drug ...
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It is important to understand both the kinetic and the dynamic implications of dosing TCAs and BZs in the elderly, for whom these drugs are frequently prescribed. The TCAs are used to treat responsive signs and symptoms including such... more
It is important to understand both the kinetic and the dynamic implications of dosing TCAs and BZs in the elderly, for whom these drugs are frequently prescribed. The TCAs are used to treat responsive signs and symptoms including such somatic complaints as chest pain, dizziness, and arthralgias, as well as the endogenous signs such as loss of appetite with associated weight loss, psychomotor retardation, loss of libido, and insomnia. The pharmacokinetic studies of TCAs such as desipramine and nortriptyline have shown few, if any, age-related changes. The dose required for responsivity is significantly reduced for both TCAs (desipramine and nortriptyline) in the elderly, which may suggest increased end-organ responsiveness. The major recommendations for treatment of depression with nortriptyline in the elderly are (1) to administer small doses in order to avoid side effects, and (2) to expect a longer response time for the antidepressant effect than in young and middle-aged depressed...
Research Interests: Anxiety Disorders, Kinetics, Aging, Adipose tissue, Humans, and 14 moreBenzodiazepines, Depressive Disorder, Aged, Middle Aged, Adult, Stomach, Psychiatric Clinics of North America, Amitriptyline, Imipramine, Glomerular Filtration Rate, desipramine, Psychology and Cognitive Sciences, Medical and Health Sciences, and Nortriptyline
Alzheimer's disease is a slowly progressive disorder involving deterioration of both intellect and personality. The neuropathological features of Alzheimer's disease include abundant neurocortical senile plaques and... more
Alzheimer's disease is a slowly progressive disorder involving deterioration of both intellect and personality. The neuropathological features of Alzheimer's disease include abundant neurocortical senile plaques and neurofibrillary tangles. Drug therapies of Alzheimer's disease have been based on empirical observations of the signs and symptoms of the disease and have included the use of hypnotics to reverse insomnia or inverse sleep rhythms; anxiolytics to relieve anxiety, tension and restlessness antipsychotics to "tranquilize" or control psychotic symptoms, such as delusions and hallucinations; stimulants to overcome withdrawn behavior or lethargy; and lastly, antidepressants to control depression. Our growing knowledge of neuropathological and neurochemical changes associated with normal aging and Alzheimer's disease has made it possible to explore and develop pharmacologically-based therapies in Alzheimer's disease. Recent research has revealed beh...
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A sensitive and specific bioanalytical method for quantitation of a novel antiemetic (ADR-851) in plasma and urine has been developed and validated. The drug and internal standard (metoclopramide) are extracted from the plasma matrix by... more
A sensitive and specific bioanalytical method for quantitation of a novel antiemetic (ADR-851) in plasma and urine has been developed and validated. The drug and internal standard (metoclopramide) are extracted from the plasma matrix by solid-phase extraction on cyanopropyl bonded-phase columns. After extraction, samples are separated by isocratic reversed-phase high-performance liquid chromatography. The parent drug, internal standard and a yet unidentified metabolite are detected by fluorescence. The method requires 1.0 ml of plasma or 0.1 ml of urine and has a lower limit of quantitation of 2 ng/ml with 10.9% relative standard deviation (R.S.D.). Method linearity has been established over a 2-800 ng/ml range when 1.0 ml of plasma is used. The intra- and inter-day imprecisions for the method are typically better than 6% and 11% R.S.D., respectively, in both plasma and urine over the entire dynamic range. The pooled estimate of bias is less than 5% and attests to the excellent accu...
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Sensitive HPLC-UV methodology has been developed and validated for quantitating rifabutin, an antimycobacterial, and its 25-desacetyl metabolite, LM-565, in human plasma and urine. The HPLC separation for both plasma and urine samples was... more
Sensitive HPLC-UV methodology has been developed and validated for quantitating rifabutin, an antimycobacterial, and its 25-desacetyl metabolite, LM-565, in human plasma and urine. The HPLC separation for both plasma and urine samples was performed on an ODS, 5-microns, reverse-phase column (25 cm x 4.6-cm ID) using a mobile phase of acetonitrile/0.05 M potassium phosphate, pH 4.2, with triethylamine, (38:61.5:0.5, v/v), at a flow rate of 1.0 ml/min. The separation eluate was monitored by absorbance at 275 nm. Plasma samples (1 ml) were spiked with an internal standard (medazepam), buffered at pH 7.4 and extracted with 80:20 (v/v) hexane:ethyl acetate, and then back extracted with acidified water (0.05 M H3PO4). Linearity was established between 5.0-800 and 2.5-400 ng/ml for rifabutin and LM-565, respectively. Intraday imprecision for rifabutin and LM-565 plasma quality controls prepared at 7.3 and 3.2 ng/ml, respectively, was less than 15% relative standard deviation (RSD). Absolut...
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It has been shown that the antiarrhythmic and toxic effects of lidocaine may be in part dependent on its two active metabolites, monoethylglycylxylidide (MEGX) and glycylxylidide (GX). Presently available gas liquid chromatographic... more
It has been shown that the antiarrhythmic and toxic effects of lidocaine may be in part dependent on its two active metabolites, monoethylglycylxylidide (MEGX) and glycylxylidide (GX). Presently available gas liquid chromatographic analytic methods require long and tedious steps or sophisticated equipment such as gas liquid chromatography-mass spectrometry. The assay method reported here with the use of high-performance liquid chromatography is rapid and allows accurate, precise determination of lidocaine, MEGX, and GX in biologic fluids. On the 3 patients studied extensively with the use of this assay, one patient had MEGX concentrations almost twice those of lidocaine. At 83% lidocaine potency, the contribution of MEGX in this patient was about 1.5 times that of lidocaine. The second patient studied on two consecutive days had a 20% increase in serum lidocaine concentration and an equivalent decrease in MEGX concentration on the second day. In the third patient lidocaine was stopp...
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Serum and saliva quinidine concentrations were measured in eight subjects with cardiac arrhythmias on various dosage regimens. There was good correlation between serum and saliva quinidine concentration after a single dose, but there was... more
Serum and saliva quinidine concentrations were measured in eight subjects with cardiac arrhythmias on various dosage regimens. There was good correlation between serum and saliva quinidine concentration after a single dose, but there was no such relationship after repeated dosing. Comparison of the area under a hysteresis loop, obtained by plotting the saliva/serum quinidine concentration ratio as a function of serum quinidine concentration over a dosing interval, indicated an exponential increase with increasing mean serum quinidine concentration. Salivary quinidine concentration predictions based on the Henderson-Hasselbalch equation did not correlate with the serum quinidine concentration under the steady-state conditions. These data suggest that quinidine concentration in saliva is not a direct reflection of its serum concentration in cardiac patients on maintenance (steady-state) therapy and hence not useful for therapeutic drug monitoring.
Research Interests: Metabolism, Kinetics, Treatment, Clinical Pharmacology, Therapeutic drug monitoring, and 13 moreHumans, Male, Steady state, Aged, Middle Aged, Cardiac Arrhythmias, Saliva, Hydrogen-Ion Concentration, Hysteresis Loop, Clinical Pharmacology and Therapeutics, Quinidine, excretion, and Pharmacology and pharmaceutical sciences
It has been suggested that didanosine (ddI) may undergo hepatic metabolism. Rifabutin is an inducer of drug metabolism. Fifteen human immunodeficiency virus-infected patients whose conditions were stabilized on twice-daily doses of ddI... more
It has been suggested that didanosine (ddI) may undergo hepatic metabolism. Rifabutin is an inducer of drug metabolism. Fifteen human immunodeficiency virus-infected patients whose conditions were stabilized on twice-daily doses of ddI participated in a Phase I, open-label, pharmacokinetic and safety drug interaction study between rifabutin and ddI. Twelve patients completed the study. All patients received their regular ddI dose (167-375 mg) on day 1. On days 2-13 they received once-daily rifabutin (600 mg, three patients; 300 mg, nine patients) with their regular twice-daily ddI regimen. On days 14-16 they received rifabutin alone. Serial blood and urine samples were collected for 12 h on day 1 and for 24 h on days 13 and 16, and safety evaluations were made throughout the study. Average day 1/day 13 ddI pharmacokinetic ratios and 95% confidence interval values for Cmax, AUC0-infinity, Cls/F, and t 1/2, lambda z were 1.17 (0.96-1.38), 1.13 (0.99-1.27), 0.91 (0.81-1.01), and 0.97 (0.79-1.15), respectively (p > 0.05 for all comparisons; paired t test). A 20% difference in AUC0-infinity could be detected with 90% power. Also, there were no significant changes in laboratory values or electrocardiograms, or in rifabutin pharmacokinetic parameters when the two agents were coadministered. Based on the safety and pharmacokinetic assessments, rifabutin did not appear to interact with ddI.
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Bretylium (Bretylol), an antiarrhythmic agent, is currently being used in the prophylaxis and treatment of patients with life-threatening ventricular fibrillation and tachycardia not responsive to conventional therapy. Because bretylium... more
Bretylium (Bretylol), an antiarrhythmic agent, is currently being used in the prophylaxis and treatment of patients with life-threatening ventricular fibrillation and tachycardia not responsive to conventional therapy. Because bretylium has a delayed onset of action that commonly causes hypotension and may increase ventricular irritability, its use in patients (especially patients with renal impairment) must be exercised with caution. Our results show that the maximum plasma concentration (Cmax) observed at the end of bretylium infusion, when normalized to the dose, increases significantly as renal function diminishes. Significant reductions in renal and total body clearance of bretylium have been observed in patients with renal insufficiency. In order to minimize the risk of potential toxicity following multiple dosing in such patients, dosage adjustments are necessary. Based on correlations developed between the total body clearance of bretylium and renal function, we present a nomogram herein that can be effectively used for adjusting the dosage of bretylium in patients with renal impairment.