Heat stroke is much more severe than heat exhaustion and can be fatal. Any agent that reduces the body's ability to cool can quickly turn heat exhaustion into heat stroke. Cholinergic blocking agents and anti-cholinergic treatments limit sweating ability and as a result reduce the body's ability to cool off. Drugs like antihistamines, parkinsonism medication, atropine, neuroleptics, antispasmodics and tricyclic antidepressants all have anticholinergic properties. The effects of such cholinergic treatments upon a person who might normally tolerate increased environmental heat can be devastating and are listed below.
Pediatric Risk
Mayo Clinic staff report that when antihistamine, decongestant and anti-cholinergic combination drugs are given to children in hot weather, a dangerous increase in body temperature may result. This increase could turn into heat stroke and cause major organ failure. They say the younger the child, the higher the danger.
Geriatric Effects
The anti-cholinergic drugs available as over-the-counter cold medicine in combination with antihistamine and decongestant ingredients can lead to dry mouth and painful urination. The lack of fluid production and resultant cooling effect can be especially harmful in the elderly when compounded with hot weather and the possibility of heat stroke. Mayo Clinic staff say the elderly are especially sensitive to the effects of the medication when combined with hot weather.
Fluid Loss
Anticholinergic medications like atropine, hyoscyamine and methscopolamine reduce moisture in the chest and nose. Mayo Clinic staff say the loss of fluids there tend to increase body temperature and make the patient more susceptible to heat stroke in hot weather.
Dizziness, Faintness
Other heated environments such as saunas or hot baths can make a patient taking anticholinergic medication faint or dizzy. Mayo Clinic staff warn against any heated environment when taking anticholinergics. The loss of mental acuity, faintness, dizziness and drowsiness may impair the patient enough not to notice impending heat exhaustion and possible heat stroke onset.
Fatalities
The National Institutes of Health has reported on cases where young men taking anticholinergic drugs died on a warm summer day. At first the men became comatose and then "massive liver damage, disseminated intravascular coagulation, anaemia, thrombopenia and acute renal failure" resulted, leading to death. In the two cases cited, the patients were ingesting drugs with antidopaminergic and anticholinergic effects.
