Objective: To update readers on research being conducted with the aldose reductase inhibitor (ARI) tolrestat in treating complications of diabetes mellitus. The article briefly describes early investigations with other ARIs and reviews the more recent studies of tolrestat. In addition, the article gives readers a simplified overview of the biochemical background pertinent to the use of these agents.
Data sources: A MEDLINE search was performed to identify articles relating to the clinical use of, and research involving, the following ARIs: sorbinil, alrestatin, ponalrestat, and tolrestat. In addition, pharmaceutical manufacturers were contacted in an attempt to obtain data relating to ongoing investigations.
Study selection: Review articles and clinical trials of sorbinil, alrestatin, and ponalrestat were included. Articles dealing with clinical trials of tolrestat were selected from the MEDLINE search. As there were only a few trials, all studies identified were included. No additional written data were available from the manufacturers.
Data synthesis: ARIs, which when first introduced were proclaimed to be major advances in treating diabetic complications, have never produced the expected results. Problems with efficacy and toxicity relegated most of this class of agents to historical interest. One compound, tolrestat, has continued to be tested and has potential clinical application. To date, the extent of benefit that has been realized in tolrestat-treated patients is small to moderate. Improvements have occurred in paresthesia and neuropathy, but unfortunately, not in pain symptoms. Adverse effects have been minor and are primarily confined to elevations of hepatic alanine aminotransferase. Additional clinical trials are being conducted with this agent.
Conclusion: Tolrestat is the only one of the original ARIs still undergoing clinical trials. Results so far have been encouraging, but by no means definitive, for improvement in some aspects of diabetic neuropathy. Information from ongoing investigations is necessary before the true usefulness of tolrestat therapy can be determined.