Taking Care to Avoid Hyperthermia
Q. In a past column you said that numerous medications could increase the risk for hyperthermia during hot weather. Could you provide a detailed list?
A. Coming up, but let’s get our bearings first.
Hot weather can cause the body to overheat (hyperthermia). This sets the stage for heat exhaustion or heat stroke, covered in a prior column. These serious conditions have felled many a person during a summer in which record-scorching heat waves have blanketed large areas of the country.
The evaporation of sweat is the body’s primary way of cooling off and protecting itself from overheating.
High humidity (moisture in the air) slows the evaporation of sweat and is a risk factor for hyperthermia.
Medications that possess anticholinergic action, which impairs the body’s ability to sweat, are the chief culprits among drugs that ratchet up the risk for hyperthermia.
Agents with anticholinergic effects include antihistamines, antidepressants, antipsychotics, anti-Parkinson’s disease agents, anti-nausea/motion sickness agents, anti-diarrhea agents, antispasmodic agents, anti-asthma drugs, and antiarrhythmic heart drugs.
There’s a good chance many readers have taken one or more of these medications. If so, you may recognize the classic anticholinergic side effects: dry mouth, dry skin, blurred vision, rapid heartbeat, constipation, and urinary retention. (The last-mentioned effect further worsens urination difficulties caused by an enlarged prostate.)
Anticholinergic drugs also tend to cause confusion and impaired memory, particularly in the elderly. In fact, they directly oppose the effects of drugs prescribed to improve memory in those with Alzheimer’s disease.
The following detailed list is fairly comprehensive.
Agents with anticholinergic action (listed by generic name):
Antihistamines (chlorpheniramine, clemastine, cyproheptadine, dexchlorpheniramine, diphenhydramine, hydroxyzine); Antidepressants (amitriptyline, clomipramine, doxepin, imipramine, mirtazapine, nortriptyline, protriptyline); Antipsychotics (chlorpromazine, clozapine, fluphenazine, haloperidol, mesoridazine, olanzapine, pimozide, prochlorperazine, promethazine, risperidone, thioridazine, thiothixene, quetiapine, ziprasidone); anti-Parkinson’s disease agents (amantadine, benztropine, biperiden, trihexyphenidyl); anti-nausea/motion sickness agents (dimenhydrinate, meclizine, prochlorperazine, promethazine, scopolamine (e.g., ear patch for motion sickness), trimethobenzamide); anti-diarrhea agents (diphenoxylate/atropine); Antispasmodic agents (belladonna alkalids, clidinium, darifenacin, dicyclomine, flavoxate, hyoscyamine, oxybutynin, propantheline, solifenacin, tolterodine, trospium); anti-asthma drugs (ipratropium bromide, tiotropium); Antiarrhythmic heart drugs (disopyramide, quinidine, procainamide).
Dehydration (excessive loss of body water) also boosts the risk for hyperthermia. Drugs with the potential to cause diarrhea or nausea/vomiting can lead to dehydration due to loss of body water. These include magnesium-containing antacids, laxatives, misoprostol, and exenatide (Byetta injection for diabetes). Aspirin and other salicylates may lead to dehydration by increasing perspiration and the rate and depth of breathing.
Dehydration also may be associated with excessive blood levels of calcium.
Amphetamines, carbenicillin, dexmethylphenidate, methylphenidate, topiramate, and zonisamide increase the risk for hyperthermia in other ways.
If you need help sorting out whether any of your medications might put you at greater risk during hot weather, ask your pharmacist.
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Richard Harkness is a consultant pharmacist, natural medicines specialist, and author of eight published books. Write him at 1224 King Henry Drive, Ocean Springs, MS 39564; or rharkn@aol.com. Selected questions will be used in the column.
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