Pharmacobezoars, bezoars comprised of medications, are unusual entities. Medications reported to cause bezoars include aluminum hydroxide gel, enteric-coated aspirin, sucralfate, guar gum, cholestyramine, enteral feeding formulas, psyllium preparations, nifedipine XL, and meprobamate. They most often occur, as do bezoars of any type, in a background of altered motility or anatomy of the gastrointestinal tract. Bowel hypoactivity, dehydration, and concomitant use of anticholinergics and narcotis appear to contribute to the propensity for bezoar formation by aluminum hydroxide gel and Isocal. The hygroscopic properties of psyllium and guar gum appear to contribute to their propensity to form bezoars. Insolubility of the carrying vehicle of enteric-coated aspirin and nifedipine is the setting in which these medications form bezoars. In contrast to nonmedication bezoars, pharmacobezoars may produce additional symptoms, those related to the release of their active ingredients. In patients with suspected gastrointestinal tract emptying problems, whether esophageal, gastric, small bowel, or colonic, the astute clinician should consider pharmacobezoar in the differential diagnosis.

Reactive transport modeling of multi-element, compound-specific isotope analysis (CSIA) data has great potential to quantify sequential microbial reductive dechlorination (SRD) and alternative pathways such as oxidation, in support of remediation of chlorinated solvents in groundwater. As a key step towards this goal, a model was developed that simulates simultaneous carbon, chlorine, and hydrogen isotope fractionation during SRD of trichloroethene, via cis-1,2-dichloroethene (and trans-DCE as minor pathway), and vinyl chloride to ethene, following Monod kinetics. A simple correction term for individual isotope/isotopologue rates avoided multi-element isotopologue modeling. The model was successfully validated with data from a mixed culture Dehalococcoides microcosm. Simulation of Cl-CSIA required incorporation of secondary kinetic isotope effects (SKIEs). Assuming a limited degree of intramolecular heterogeneity of δCl in TCE decreased the magnitudes of SKIEs required at the non-reacting Cl positions, without compromising the goodness of model fit, whereas a good fit of a model involving intramolecular CCl bond competition required an unlikely degree of intramolecular heterogeneity. Simulation of H-CSIA required SKIEs in H atoms originally present in the reacting compounds, especially for TCE, together with imprints of strongly depleted δH during protonation in the products. Scenario modeling illustrates the potential of H-CSIA for source apportionment.

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