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Drugs more dangerous in heat

"Hot as hell" is a phrase we have heard a lot this summer. And with good reason. Temperatures have soared in much of the country. And it's not over yet.

Anyone without air conditioning has really been suffering. So has anyone who has to work or participate in sports outside. Heatstroke is a very real danger, and it can be life-threatening.

That's why military personnel, firefighters, telephone linemen and athletes all are warned to recognize the early signs of dehydration and overheating, which include dizziness, nausea, confusion, headache and changes in speech or behavior.

There is another group that is often forgotten, however, and it includes tens of millions of Americans. Older people and those who take certain medications are especially vulnerable to both heat exhaustion and heatstroke.

Part of the problem is sweat, or more precisely, the lack of perspiration. As moisture evaporates from your skin, it helps cool down the body. Slow or stop the sweating process and you are quickly headed for overheating. Blood flow to the skin also is crucial for cooling the body.

To better understand this process, it helps to imagine your car on a hot day. The way your automobile cools its engine is through airflow. Hot water from your motor passes through coils in the radiator. As you drive, air passes through the coils and cools down the liquid that then recirculates through the engine. Disconnect the radiator and the engine overheats.

When people can't circulate blood to the skin adequately or sweat efficiently, the core temperature of the body may rise and put people at risk. A wide variety of medications interfere with the body's natural cooling process.

Drugs that decrease sweating are far more common than most people realize. Antidepressants that interfere with a chemical called acetylcholine are especially problematic. This anticholinergic effect slows sweating substantially. Medications include amitriptyline, desipramine and doxepin.

Pills for overactive bladder such as Detrol, Ditropan and Toviaz also have this kind of effect. Many antihistamines have anticholinergic activity. Diphenhydramine is of particular concern because it is found in OTC products like Benadryl as well as PM pain relievers like Advil PM and Tylenol PM.

Decongestants that contain pseudoephedrine are another problem. You frequently find this ingredient as the "D" (for decongestant) in allergy medication such as Allegra-D, Claritin-D and Zyrtec-D. The vasoconstrictor action of pseudoephedrine may reduce blood flow to the skin, making it a little harder for your body's radiator to dissipate heat.

Antipsychotic drugs are being prescribed for conditions other than schizophrenia. Medications such as Abilify and Zyprexa are increasingly used to treat depression, bipolar disease, dementia and personality disorders. Such drugs also may make it harder for the body to cool down when temperatures climb.

We have barely touched the surface when it comes to all the medicines that make people vulnerable to high heat. When temperatures hover around triple digits, it is crucial for those on medications to check with a pharmacist to make sure that their pills aren't putting them at risk for heatstroke.