The pharmaceutical industry has revenues in the hundreds of billions of dollars a year globally. With such a large industry counterfeiting and copyright infringement are serious issues, and hydrogen isotope fingerprinting has become a useful tool in verifying the authenticity of various drugs. As described in the preceding sections, the utility of D/H ratios highest when combined with measurements of other isotope ratios as well. In an early study on the stable isotope compositions of tropicamide, hydrocortisone, quinine and tryptophan, carbon, nitrogen, oxygen and hydrogen stable isotopes were analyzed by EA-IRMS and clear distinctions were able to be made between manufacturers and even batches of the drugs based on their isotope signatures. In this study it was determined that the hydrogen and oxygen isotope ratios were the two best fingerprints for distinguishing between different drug sources. A follow-up study analyzing naproxen from various lots and manufacturers also showed similar ability to distinguish between sources of the drugs. The use of these isotope signatures could not only be used to distinguish between different manufacturers, but also between different synthetic pathways for the same compound. These studies relied on the natural variations that occurred in the synthesis of these drugs, but other studies have used starting ingredients that are intentionally labelled D and 13C, and showed that these labels could be traced into the final pharmaceutical product. D/H ratios can also be determined for specific sites in a drug by 2H NMR, and has been used to distinguish between different synthetic methods for ibuprofen and naproxen in one study, and prozac and fluoxetine in another. These studies show that bulk D/H ratio information for EA-IRMS, and site-specific D/H ratios from 2H NMR have great utility for pharmaceutical drug authenticity testing.
