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At least 19 recordsLinked to original sources
PubMed1979

The effect of crystal size on the bioavailability of benoxaprofen: studies utilizing deuterium labeled drug.

A study of the effect of crystal size on the bioavailability of benoxaprofen, 2-[4-chlorophenyl]-alpha-methyl-5-benzoxazoleacetic acid, in man is reported. The technique utilized comparison of either the plasma concentrations or urine levels, resulting from administration of deuterium labeled (2H7) drug in solution coadministered with a test capsule formulation. Drug concentrations were determined by gas chromatography, and the ratio of labeled to unlabeled drug was obtained by gas chromatography mass spectrometry. Measurements following coadministration of labeled and unlabeled drug in solution established the absence of an isotope effect due to the presence of deuterium. The dry formulations consisted of either a 3.17--100 micron fraction (mean = 18.5 microns) or a 32--1000 micron fraction (mean = 610 microns) formulated with starch powder. The results in three subjects indicate an almost complete availability (0.95--0.98) of the small crystals as measured by comparison of either area under the plasma level curves or urine excretion (0.94--0.97) of labeled versus unlabeled drug measured to 168 hours. The larger crystals exhibited a lower availability as shown by plasma levels (0.41--0.46) or urine recovery (0.39--0.43). A higher dose of the large crystal formulation resulted in decreased relative availability with a fourfold dose dropping availability to 0.22 in a single subject.

Adult↗
PubMed1978

Drug labelling.

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Drug Labeling↗
PubMed1978

Drug labelling.

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Adult↗
PubMed1979

The effect of label affinity on the sensitivity and specificity of a hapten radioimmunoassay: a comparison of three [125I]diphenylhydantoin radioligands with the 14C-labelled drug.

The effect on the sensitivity and specificity of a radioimmunoassay for diphenylhydantoin (DPH)has been investigated using three 125I-labelled tyrosine ester derivatives of DPH having different bridge lengths between the tyrosine moiety and the DPH moiety and 14C-labelled DPH. The results demonstrate that for a hapten which does not completely fill the antibody-binding sites, greatest sensitivity is achieved when the bridge of the iodine label is most dissimilar to that present in the original immunogen, when the hapten and label affinities are nearly equivalent. Greatest specificity is achieved with the label which most resembles the original immunogen. These results illustrate the difficulty of designing satisfactory labels for assays of both high specificity and sensitivity since minimal changes in label structure may produce greatly amplified changes in the subsequent affinity of the label for the antiserum.

Affinity Labels↗
PubMed1978

Comparison of three radioligands, selenium-75, lodine-125, and tritium, in the radioimmunoassay of methotrexate.

Radioimmunoassays for methotrexate are described, involving use of a rabbit antiserum to a conjugate of the drug and bovine serum albumin and the drug labeled with tritium, selenium-75, or iodine-125. Of the two gamma emitters, the 75Se-labeled drug was prepared by the Radiochemical Centre, Amersham, England and the 125I-labeled drug in the laboratory, by the Chloramine T iodination technique. The stability of labels with both methods allows use of the faster, cheaper, and simpler gamma-counting techniques, with results available after 3 h. All three methods have acceptable sensitivity, accuracy, precision, and reproducibility, and are specific for methotrexate, with no significant interference from naturally occurring folates or leucovorin. The assays in which the gamma emitters are used have significant practical advantages over the beta emitter and are much better suited to automation and clinical application. The main advantage of 75Se=labeled methotrexate is its longer half-life, 121 days, as compared with 60 days for 125I.

Humans↗
PubMed1977

A simple method for the determination of affinity and binding site concentration in receptor binding studies.

In ligand binding studies, it is often difficult to apply kinetic analyses because of an uncertainty in experimental data obtained at high ligand concentrations. Under such circumstances, Kd value (an index of the affinity) and the binding site concentration may be estimated more accurately from the binding of a fixed concentration of labelled ligand observed in the presence of various concentrations of the non-labelled ligand, if the fraction of both labelled and non-labelled ligand bound is small. When there is no cooperative effect of the ligand binding, the Kd value may be calculated by subtracting the concentration of the labelled drug from the concentration of the non-labelled drug to cause a 50% reduction of the saturable binding of the labelled drug. From above values, the binding site concentration may be calculated. The proposed method is capable of examining the cooperativity of the ligand binding, the labelled drug concentration and the specific radioactivity of the labelled drug and does not require large amounts of the labelled drug.

Adenosine Triphosphatases↗