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dotsUtah Chemists Devise Fast Way to Test the
Shelf Life of New Drugs

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Embargoed by the American Chemical Society for release at 8 p.m. MDT (7 p.m. PDT) Weds. April 4, 2001. Long will present the study during a 7-10 p.m. PDT Weds. April 4 poster session in the San Diego Convention Center’s Sails Pavilion.

April 4, 2001
University of Utah chemists have devised a quick way for pharmaceutical companies to estimate the shelf lives of new medicines.

“This is going to help drug companies decide which formulations of new medicines are most stable and have the longest shelf life,” said Chuck Wight, a professor of chemistry.

Chemist Greg T. Long, a postdoctoral research associate at the University of Utah, was scheduled to outline the new method April 4 during the American Chemical Society’s national meeting in San Diego. He conducted the study with Wight; Sergey Vyazovkin, a research associate professor; and Nicoleigh Gamble, a former Utah undergraduate now in medical school elsewhere.

The proof-of-concept study tested the technique on pure acetylsalicylic acid, the active ingredient in aspirin. Like other organic substances, aspirin decomposes with time. Heat accelerates the drug’s breakdown.

Long and Wight said drug companies normally test the shelf life of a new medication by letting it sit for many months at 30 degrees Celsius (86 degrees Fahrenheit) – somewhat above room temperature – and seeing how long it takes for 5 percent of the medication to break down.
“Right now, it is a very time-intensive and expensive process to do these determinations,” Long said. “It can be a two-year experiment to determine decomposition.”

Such tests have showed 5 percent of aspirin decomposes in about two years. The Utah method – which involves heating aspirin at a variety of temperatures or heating rates while its decay is measured – came up with a shelf-life estimate of 2.4 years.

Unlike conventional tests of a drug’s stability, “we can get an estimate of shelf life on the order of days,” Long said.

Long said using such high heats to speed decomposition of a drug “is clearly much different than what happens in your medicine cabinet,” but produces estimates of room-temperature shelf life that agree reasonably well with measurements based on letting the drug slowly decay at near-room temperatures for months.

Wight said if a drug company was developing a new medicine that had five possible chemical formulations of equal or similar effectiveness, the test could quickly determine which formulations were most stable and thus would have longer shelf lives. Then the more conventional shelf-life measurements could be done on those formulations.

“Our idea is not to replace conventional room-temperature determinations of shelf life, but to help screen out less stable drugs first,” Long said.

The Utah chemists have started discussing the new test method with drug company representatives, but “so far there’s only been a mild amount of interest because there are a lot of mathematics and analysis that go into the method,” Wight said. “This paper is a proof-of-concept which we hope to use in the future to get more people interested.”

Wight said chemists have known for a long time that a drug’s shelf life can be estimated by using heat to accelerate its decomposition. But the method of extrapolating such experiments has, in the past, given poor estimates of a medication’s shelf life at room temperature, he added.

“What we did is find a way of taking eight experiments [each involving heating a drug at different temperatures and rates] and analyzing them simultaneously to get a better prediction of shelf life,” Wight said.

By watching a drug decompose, the chemists determine “kinetic equations” that can be used to calculate the medicine’s shelf life at room temperature.

Long and colleagues used two methods in their study. Both techniques involved placing a tiny sample of pure aspirin in a quarter-inch-wide pan that is then put inside an instrument that includes a small furnace to heat the sample.

One instrument, a differential scanning calorimeter, measures the release or absorption of heat produced by chemical decomposition of the medication as it is heated, for example, from 25 to 600 degrees Celsius (77 to 1,112 degrees Fahrenheit). The other instrument uses what is called “thermogravimetric analysis,” which measures how the medication decreases in mass as it breaks down.

The latter method proved simpler for making measurements used to estimate shelf life, Long said. But both methods showed aspirin decomposes in two steps.

Media Contacts:
Greg Long, chemist office (801) 581-6285, home (801) 581-9767,
Chuck Wight, chemist – office (801) 581-8796, home (801) 474-2220,
(NOTE: During April 1-5, Long and Wight may be reached at the Holiday Inn on the Bay in San Diego, (619) 232-3861 and ask for Wight’s room)
Lee Siegel, University Science Writer office (801) 581-8993, cell (801) 244-5399,
American Chemical Society meeting press room, San Diego Convention Center (619) 645-6941



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