How does extreme heat affect medicines and those taking them?

(This July 25 story has been corrected to fix the temperature conversion in paragraph 15)

By Nancy Lapid

(Reuters) - The world just experienced the hottest day on record and prolonged heat waves have become more common due to climate change, conditions that can alter medications and their effects on patients taking them.

Here is what you need to know about medicines in hot weather:   

HOW DOES HEAT ALTER THE EFFECTS AND QUALITY OF MEDICINES?

Medications for common conditions can increase patients' sensitivity to heat by impairing the body's response to high temperatures, including the ability to sweat and the rate of blood flow. 

Heat waves also increase the risk of deterioration for nearly all medications, whether capsules, sprays, tablets, syrups, or some other form, if they are not kept within a certain temperature range.

The heat-related effects of medications can vary based on individual health status, dosage and environmental conditions.

Patients should consult their physicians about potentially adjusting doses or scheduling in hot weather, and they should keep cool by staying hydrated, carrying fans, and seeking shade or air conditioning, experts say. 

WHAT MEDICATIONS INCREASE SENSITIVITY TO HEAT?

 - Blood pressure and heart failure medications: Angiotensin converting enzyme (ACE) inhibitors suppress thirst, making it harder to know when to drink more water and increasing the risk of dehydration. Calcium channel blockers can cause mineral imbalances, making it harder for the body to regulate its temperature, while beta blockers can make it harder to sweat and keep the body cool. Diuretics, or water pills, can also cause dehydration and mineral imbalances. 

- Allergy medications: Some over-the-counter antihistamines reduce sweating and can impair temperature regulation.

- Psychiatric medications: Certain antipsychotic medications limit patients' ability to sweat. Some antidepressants have the opposite effect, increasing sweating and repressing thirst. Stimulants such as amphetamines and other drugs used to treat attention deficit hyperactivity disorder may interact with the central nervous system to raise body temperature.

- Thyroid medications: Thyroid hormone pills also can raise body temperature, impair temperature regulation and cause excessive sweating.

WHAT IS A SAFE TEMPERATURE RANGE FOR STORING MEDICATIONS?

Extreme heat (and extreme cold) can significantly alter the effectiveness of prescription and over-the-counter drugs.

Some medications can tolerate temperatures up to 86 degrees Fahrenheit (30 Celsius), but in general they should be stored at 59-77 F (15-25 C) in a cool, dry place, away from sunlight. Temperature storage guidelines for specific drugs can be found on manufacturers' websites.

It's hard to predict the extent to which a medication will degrade in extreme temperatures because each drug is different, said Amy Bachyrycz, a pharmacy faculty member at the University of New Mexico in Albuquerque.

In general, medicines should not be left in hot cars or for hours in hot mail boxes if they are mail-ordered medications.

A spokesperson for CVS Health's Caremark pharmacy benefits unit said the company's electronic shipping system takes weather data into account to determine appropriate packaging materials for each shipment.     

An Amazon.com Pharmacy spokesperson said the company employs strict storage and delivery safety measures to protect medications from extreme temperatures throughout the shipping process.

(Reporting by Nancy Lapid; Editing by Bill Berkrot)