Fred P. Abramson

Methadone plasma protein binding: Alterations in cancer and displacement from α1‐acid glycoprotein

Because of their elevated concentrations of plasma α1‐acid glycoprotein (AAG), cancer patients had a lower free fraction of methadone in plasma than did members of a control group. This difference was not great (‐20%), but there was a fourfold variation in free fraction among a group of 13 patients (0.064 to 0.23). The bound/free methadone concentration ratio correlated linearly with plasma AAG. The binding of methadone to AAG was characterized by two classes of binding sites, the more avid having an association constant of 4 × 105M−1 and an N of 0.38. Methadone could be displaced from AAG binding sites by a number of drugs: propranolol, chlorpromazine, prochlorperazine, thioridazine, and imipramine. The concentrations required for significant displacement (27 μM), as well as the relatively low Ka for methadone, suggest that the free fraction of methadone will not be significantly affected by elevated methadone concentrations or through displacement by other drugs that also bind to AAG.

Effects of cancer and its treatments on plasma concentration of alpha1‐acid glycoprotein and propranolol binding

The plasma concentrations of α1 acid glycoprotein (AAG) and albumin, and the plasma protein binding of propranolol were measured in a group of cancer patients and a group of normal subjects. In cancer patients the AAG concentrations were twice that in controls (142 and 78 mg/dl, P < 0.005), the albumin concentrations were lower (3.11 and 4.37 gm/dl, P < 0.001), and the free fraction of propranolol was lower (0.127 and 0.190, P < 0.005). Propranolol binding correlated strongly with AAG concentrations. These data imply that untreated or unsuccessfully treated cancer patients will have reduced free fractions for any drug for which AAG is an important binding protein. Successfully treated patients may have longitudinal changes towards normal. No consistent effect of the treatments themselves on AAG was observed after radiation therapy in five patients or after intravenous adriamycin in six patients.

Bioavailability, Distribution and Pharmacokinetics of Diethylstilbestrol Produced from Stilphostrol

The kinetic behavior of diethylstilbestrol (DES) produced from stilphostrol has been studied in man, dog and rat. A sensitive and selective assay for DES in plasma and tissues has been developed with the use of gas chromatographic separation and mass spectrometric detection. In patients with prostate cancer, the plasma concentrations of DES produced by 1,000-mg. infusions of stilphostrol are 1,500 times the DES concentrations produced by conventional oral DES doses. The pharmacokinetics of DES show 2 separate phases; 1 with a t1/2 of approximately 1 hour, another with a t1/2 of approximately a day. In rats, stilphostrol does not selectively liberate DES in the prostate compared to dosing with DES itself. In dogs, a 50-mg. tablet of stilphostrol was bioequivalent to 40 mg. of DES taken orally. Some of these data support the idea that the high DES concentrations produced by stilphostrol infusions underlie in its ability to produce objective responses in patients refractory to conventional oral DES therapy.

Element- and isotope-specific detection for high-performance liquid chromatography using chemical reaction interface mass spectrometry

We have developed a combination of high-performance liquid chromatography (HPLC) and the chemical reaction interface mass spectrometry (CRIMS) method by using a Vestec Universal Interface (UI). This interface provides the extremely high degree of solvent removal that the CRIMS process requires. In doing so, we have produced an HPLC detector with the ability to carry out the element- and isotope-selective analyses with detection that is inherently: linear, structure-independent, sensitive, selective, comprehensive and flexible. The characteristics of the instrumentation and its performance are described.

Development of an isotope-selective high-performance liquid chromatography detector using chemical-reaction-interface mass spectrometry: application to deuterated cortisol metabolites in urine.

An isotope-selective detector for HPLC based on the particle-beam-interface and the chemical-reaction-interface mass spectrometer (CRIMS) principle is described. This paper focuses on the selective detection of deuterium-labeled analytes. The CRIMS product HD is detected as has been previously described for GC-CRIMS. The analytical performance was not affected by analyte structure or solvent composition. Deuterium detection was linear from 20 ng to 490 ng using 2H3-labeled cortisol. Based on this method, the fractional abundance of three labeled metabolites of cortisol were determined in the urine of a patient infused with tracer amounts of deuterated cortisol.

Selective detection of sulfur-containing compounds by gas chromatography/chemical reaction interface mass spectrometry

Addition of a reactant gas to a low pressure microwave-induced plasma creates a reaction interface in which complex molecules are converted into small polyatomic neutral species. For a given reactant gas the array of these small molecules reflect s the elemental composition of the original analyte. In this study HCI has been found highly effective as a reactant gas for selective detection of sulfur-eontaining compounds using capillary gas chromatography/ chernical reaction interface mass spectrometry. Detection limits as low as 30 pg of a sulfur-containing compound and a dynamic range of two orders of magnitude were achieved.

Urea Kinetic Modeling at High Urea Clearances: Implications for Clinical Practice

The original description of urea kinetic modeling in hemodialysis was based on a single pool of fluid equal to total body water. This assumption is valid only if the rate of transport between compartments is sufficiently rapid compared with the rate of urea removed by hemodialysis. We have reexamined the issue of urea compartmentation using 10 patients with initial BUN values ranging from 28 to 101 mg/dL who were studied while on high flux hemodiafiltration. Sampling was carried out at times as short as 1 minute after the beginning of the treatment. In 4 patients, samples were also drawn after the dialysis ended. The measured BUN values were used to fit a two-compartment, variable-volume kinetic model. The mean urea diffusive clearance of the dialyzer during the treatment was 503 mL/minute, and the bidirectional urea clearance between compartments was 1,282 mL/minute. The percentage of total body water in the rapidly exchangeable compartment was 35.4%. Comparison with a one-compartment, variable-volume model showed a statistically better fit for all patients with the more complex model. In the 4 patients studied in the postdialysis period, the rebound in BUN ranged from 22% to 24%. These studies show that, at high urea clearances, the urea distribution space and, therefore, dialysis modeling requires two compartments. These results explain the majority of the rebound in urea concentration observed 30 to 60 minutes following the discontinuation of the dialysis treatment and point out an improved strategy for monitoring the efficiency of the treatment delivered to the patient.

Relationships between propranolol plasma protein binding, glycoprotein concentration, and enzyme induction following phenobarbital administration in the dog☆

Les donnees obtenues ne sont pas suffisamment precises pour repondre definitivement a la question posee initialement: linduction de la production de glycoproteine α 1 -acide est-elle differente de linduction du metabolisme des medicaments? Il a ete montre quil nexiste pas de differences importantes dans le parametre principal gouvernant la sensibilite de chacun des phenomenes envers le phenobarbital

Direct determination of human urinary cortisol metabolites by HPLC/CRIMS.

Feasibility of using high performance liquid chromatographic input to the chemical reaction interface mass spectrometry system was assessed by measuring the profile of hydrolyzed urinary metabolites of [9,12,12-2H3] cortisol in six human subjects with no preparation other than hydrolysis and solid phase extraction. Relative amounts of tetrahydrocortisol, tetrahydrocortisone, and cortolones (as the sum of alpha- and beta-) were 0.417 +/- 0.047, 0.523 +/- 0.036 and 0.059 +/- 0.019, respectively. The constant reproducibility of the measurements coupled with a profile consistent with that observed by other workers shows that the technique represents an important tool in the determination of metabolites of endogenous molecules.

Detection of carbon-14 eluting from a capillary gas chromatograph using chemical reaction interface—mass spectrometry

We have applied a chemical reaction interface-mass spectrometric (CRIMS) technique to the detection of 14C-labeled phenytoin and its metabolites in urine following separation by capillary gas chromatography. The presence of 14C was followed by monitoring 14CH4 which is produced by the chemical reaction interface from carbon when hydrogen is used as the reactant gas. Chromatograms showing 14C are obtained by measuring 14CH4 at m/z 18.034 with a resolution of 1800. The chemical reaction interface permits symmetrical, narrow chromatographic peaks to be obtained. Detection limits of 6.3 Bq/ml (1.26 Bq on-column which is equivalent to detection of 187 pg) of a diethylated 14C-labeled metabolite was detected at a signal-to-noise ratio of 3. The analysis was determined to be linear and similar detection limits were obtained following analysis of phenytoin-spiked urine or a phenytoin solution. Radiocarbon detection is not completely selective because nitrogen-containing compounds present at greater than 250 ng on-column are detected as NH4+. However, such interferences are infrequently of analytical importance because the capacity limits of CRIMS are 500-1000 ng. Furthermore, these interferences are readily discovered in a NH3 chromatogram which is the precursor of NH4+. After a 3.3-MBq dose, the major metabolites of phenytoin were detected by CRIMS.