The thiol (-SH) functional group is found in a number of drug compounds and confers a unique combination of useful properties. Thiol-containing drugs can reduce radicals and other toxic electrophiles, restore cellular thiol pools, and form stable complexes with heavy metals such as lead, arsenic, and copper. Thus, thiols can treat a variety of conditions by serving as radical scavengers, GSH prodrugs, or metal chelators. Many of the compounds discussed here have been in use for decades, yet continued exploration of their properties has yielded new understanding in recent years, which can be used to optimize their clinical application and provide insights into the development of new treatments. The purpose of this narrative review is to highlight the biochemistry of currently used thiol drugs within the context of developments reported in the last five years. More specifically, this review focuses on thiol drugs that represent the standard of care for their associated conditions, including N-acetylcysteine, 2,3-meso-dimercaptosuccinic acid, British anti-Lewisite, D-penicillamine, amifostine, and others. Reports of novel dosing regimens, delivery strategies, and clinical applications for these compounds were examined with an eye toward emerging approaches to address a wide range of medical conditions in the future.

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Tiopronin, formally 2-mercaptopropionylglycine (MPG), is currently prescribed to treat cystinuria and rheumatoid arthritis, and its antioxidant properties have led to its investigation as a treatment for cataracts, a condition in which oxidative stress is strongly implicated. To study its accumulation in the eye, a reliable, isocratic HPLC method was developed for the determination of MPG and its primary metabolite 2-mercaptopropionic acid (MPA) in plasma and relevant ocular tissues. This method utilizes pre-column derivatization and fluorescence detection. The 3.5 min separation enables high-throughput analysis, and validation experiments demonstrated that this method is suitable for evaluating ocular accumulation of MPG and MPA at concentrations as low as 66 and 33 nm, respectively. Excellent linearity was achieved over the working concentration range with R > 0.997. Extraction recovery was reproducible within each matrix and exceeded 97%. Accuracy was within 13.3% relative error, and intra- and inter-day precisions were within 6% CV and 7% CV, respectively. Sample stability was demonstrated under various storage conditions, and the use of an internal standard conferred exceptional ruggedness. This method has been successfully applied for the determination of MPG and MPA in plasma, cornea, lens and retina following intraperitoneal administration of the drug in Wistar rats.