This has been a difficult summer for Aylssa McDermott. The Maplewood 12-year-old, who wears an insulin pump for diabetes, has landed in the emergency room three times after softball tournaments in which hot, humid air combined with her body heat to destroy her medication.

"This never happened before this summer," said her mother, Callie McDermott. "Now we've started carrying a backup reservoir of insulin to have ready for when the insulin in the pump deactivates."

The McDermotts' situation isn't unique. Excessive heat and humidity can make your medicine less effective, and worse, the heat can adversely affect how your body reacts to the medicine.

A day or two of hot weather typically isn't a problem, said Mike Haag, pharmacy practice manager at HealthPartners. But stretches of days in which temperatures exceed 85 can be cause for concern. "Prolonged periods of excessive heat can start to break down medications," he said.

The National Weather Service reports that in late June and early July, the Twin Cities had 21 consecutive days in which the temperature reached at least 85.

Within that streak, there were eight consecutive days in which we reached at least 90 and five in a row in which the temperature was 95 or more. And the heat wave is hardly over; temperatures through this week are expected to be in the 90s or upper 80s.

"This could be a real problem for people who live in homes with no air conditioning," said Ann Brigino, a pharmacist at Hennepin County Medical Center. Most medicines are intended to be kept at room temperature, "but what we're getting now far exceeds room temperature. Heat like this starts to raise questions about whether the medication is still working."

Medicines that have lost their effectiveness because of the heat usually don't look any different, making it difficult to tell if anything is wrong with them.

"That's the tricky part," said Dr. Sara Johnson, a family physician at Fairview Uptown Clinic. "There's no way to tell that they're not working until you take them and they don't work. And that can be a dangerous if it's an emergency situation. I'm thinking of an EpiPen that a child who is allergic to nuts or bee stings might take with them to camp."

'Each medication is different'

While there have been tests on individual drugs in controlled conditions, there's been no all-encompassing study that shows how a range of drugs react to heat over time. "Each medication is different," Brigino said.

If you suspect that your medicine has been compromised by the heat, check with your pharmacy. "Many insurance plans will pay for replacements," Haag said. Some drug manufacturers also have replacement procedures.

Even if the heat doesn't affect your medication, it can affect your body's reaction to it, sometimes to dire ends. Many medicines act as diuretics, which can exacerbate the dehydration caused by the heat. Blood pressure and seizure medications are particularly prone to this problem, but you also want to be keep an eye on antihistamines, treatments for Parkinson's disease and neurologic or psychiatric medication.

"You need to drink a lot of water if you're taking these medications," Brigino said.

The experts recommend that you start drinking water before you feel the need to. If you wait until you get thirsty to reach for water, your body already is stressed.

At the Mayo Clinic emergency room in Rochester, Dr. Torrey Laack sees a lot of patients facing heat problems that have been brought on by their medicines.

"There's a huge list of medications that impact the body's ability to deal with heat," he said. "They predispose people to heat-related medical problems. People taking those medications need to be aware of that."

Cardiac medications lead the list, he said. "They impair the body's ability to regulate its core temperature by dissipating heat," he said. "They also can throw off the electrolyte balance. When you add in that as Minnesotans, sometimes we have trouble getting acclimated to heat waves, it throws off the way the body is running."

Some medicines are designed to be kept in a refrigerator. But others are not, and trying to beat the heat by storing those meds next to the cream cheese isn't the answer, Brigino said.

"For medications that are not intended to be refrigerated, the cold would have the same effect on them as the heat," she said.

Diabetics face multiple challenges. High heat and humidity can affect the reliability of monitors and test strips, and excessive exposure to sun can affect the body's glucose levels. And then, of course, there's the heat's effect on insulin. There are insulin pens that people can carry with them that are supposed to remain viable for 30 days.

"During heat waves, many diabetics carry their insulin with them in insulated lunch bags," Haag said. "Whatever you do, never keep any medications in your car's glove box or trunk. Temperatures there are much higher."

Heart medications also are susceptible to the weather, Haag said. "Especially something like nitroglycerin tablets that are intended to be dissolved under the tongue. They are extremely vulnerable to humidity."

Johnson added that there's nothing harmful about taking medications that have lost some of their effectiveness. They just won't work as well as they would at maximum strength.

Jeff Strickler • 612-673-7392