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The Study of Drug Metabolism Using Radiotracers
Published in Graham Lappin, Simon Temple, Radiotracers in Drug Development, 2006
In human studies, a slightly different approach is taken to CO2 collection. Unless very specialized systems are available, it is not possible to collect and trap CO2 from humans over prolonged periods.18 Instead, the volunteer blows into an exact amount of sodium hydroxide solution containing an indicator such as phenolphthalein (or sometimes hyamine hydroxide with thymolphthalein as an indicator). The volunteer blows into the vial for only a short period, until the indicator changes color, showing that the sodium hydroxide is saturated. Every 2 mol of sodium hydroxide will trap 1 mol of carbon dioxide (2NaOH + CO2 → Na2CO3 + H2O); thus, by knowing how many moles of sodium hydroxide there are in the solution, the number of moles of trapped carbon dioxide can be calculated.
The Treatment of Advanced Prostatic Cancer with Drugs and Hormones
Published in Nicholas Bruchovsky, James H. Goldie, Drug and Hormone Resistance in Neoplasia, 2019
Acid phosphatase has been used in the assessment of prostate cancer for over 40 years.7 It has been remarkably successful considering the widespread presence of acid phosphatase in epithelial tissues.72 Modifications to make the test more selective for prostate origin have been of doubtful value.73 The currently preferred substrate is thymolphthalein monophosphate which generates its own chromogen and is convenient for autoanalyzer use.74 Reproducible results require considerable attention to detail, particularly rapid acidification of the sample.75, 76 Despite this, there seem to be considerable diurnal72 and also irregular77 variations. Tartrate labile “prostatic” enzyme is released from platelets during clotting and is the major component in normal serum, so that plasma samples may be preferable. Tartrate resistant enzyme sources include hemolyzed red cells and osteoclasts.78, 79 The acid phosphatase content per unit weight of cancer averages some ten-fold lower than normal prostatic tissue, varies widely,80 and is probably inversely correlated with degree of differentiation. About a quarter of patients with advanced disease do not have elevated serum acid phosphatase.81 A particular worry is the tendency for the acid phosphatase to tumor burden ratio to fall with time, and this may partly reflect the tendency of acid phosphatase secreting lines to be hormone sensitive82 and therefore selectively eliminated, but may also be a feature of the natural history of the disease.83
Metabolism, pharmacokinetics and excretion of [14C]dimethyl fumarate in healthy volunteers: an example of xenobiotic biotransformation following endogenous metabolic pathways
Published in Xenobiotica, 2023
Lin Xu, Chi-Chi Peng, Kate Dawson, Scott Stecher, James Woodworth, Chandra Prakash
Expired air was collected pre-dose and at 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 12, 24, 48, 72, 96 h post-dose. The procedure for 14CO2 collection and measurement was modified from the chemical 14CO2 breath test method (Bircher and Preisig 1981) to improve accuracy. Each subject was directed to breathe through a straw into a collection solution consisting of hyamine (1 M) mixed with ethanol and tinted with 1% thymolphthalein until the CO2 collection was saturated at 2 mmol. Each collected solution was mixed with 10–15 mL of scintillation fluid for radioactivity determination.