Parkinson’s medications may impair body’s ability to keep cool: Study

Drugs may pose potential harm to patients, lead to heat-related illness

Patricia Inácio, PhD avatar

by Patricia Inácio, PhD |

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Medications commonly used in the treatment of Parkinson’s disease may affect the body’s ability to control its core temperature, part of the body’s so-called automatic functions, which include sweating, a review study found.

Such agents — which include anticholinergic medications and cholinesterase inhibitors, dopamine replacement therapies, and dopamine agonists — may impair the body’s ability to keep cool, which can pose a potential threat to people with Parkinson’s, according to researchers.

“Physicians are often unaware of the potential harms certain drugs may cause by compromising the body’s thermoregulatory control mechanisms,” Melvin Leow, PhD, a clinical associate professor at the Yong Loo Lin School of Medicine at the National University of Singapore, and one of the study’s authors, said in a university press release.

“This is an especially important area to delve into as those with chronic diseases and older adults are susceptible to adverse health outcomes in the heat, due to their reduced thermoregulatory capacity,” Leow added, noting climate change also may have an impact on patients.

The review, “Effects of medications on heat loss capacity in chronic disease patients: health implications amidst global warming,” was published in the journal Pharmacological Reviews.

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Use of Parkinson’s medications may increase patients’ risk of heat-related illness

Parkinson’s is caused by the death and dysfunction of cells in the brain responsible for making the signaling molecule dopamine. This loss or drop in dopamine levels results in the accumulation of acetylcholine, a chemical messenger nerve cells use to signal muscles to contract, leading to the disease’s typical motor symptoms. An imbalance in dopamine and acetylcholine is believed to drive Parkinson’s progression.

Anticholinergic medications and cholinesterase inhibitors are a class of therapies often used to control overall Parkinson’s disease symptoms. Anticholinergic medications are designed to block the action of acetylcholine, while cholinesterase inhibitors prevent an enzyme, called acetylcholinesterase, from breaking down acetylcholine.

However, while these medicines can be helpful for controlling symptoms, researchers at the National University of Singapore now highlight that they can impact other body systems, namely the ability to control body temperature.

This means that these medications can increase the risk among patients of developing illnesses related to heat and high temperatures.

“Clinicians need to consider that the use of medications which alter the levels of ACh [acetylcholine] may confer an increased risk of developing heat-related illnesses in patients.

In their review, the team described the case of a patient treated with the anticholinergic Artane (trihexyphenidyl) and Thorazine (chlorpromazine) who developed heat stroke and heat exhaustion.

The use of anticholinergics also has been linked to an increased rate of rise in core body temperature under heat stress in young healthy adults.

According to the researchers, “clinicians need to consider that the use of medications which alter the levels of ACh [acetylcholine] may confer an increased risk of developing heat-related illnesses in patients.”

Indeed, the team added that “future research should consider dose-response studies on Ach [acetylcholine ]-modulating medications to identify the ‘dose threshold’ at which thermoregulatory responses will be altered (and how it will be altered).”

Dopamine replacement therapies, such as levodopa, and dopamine agonists, which work by mimicking dopamine in the brain, are now the mainstay of Parkinson’s treatment.

However, these agents may significantly influence the body’s capacity to regulate temperature. In one case report, levodopa helped to stabilize the body temperature of a Parkinson’s patient experiencing spontaneous periodic hypothermia, a condition marked by a drop in body temperature below 35°C (95°F). According to researchers, this highlights “the central control of thermoregulation by” dopamine.

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Researchers cite concerns about impact of rising global temperatures

Additionally, according to researchers, reports have linked the rapid withdrawal of levodopa or dopamine agonists to a rare condition, called parkinsonism hyperpyrexia syndrome, in which body temperatures rises as high as 40°C (104°F).

These findings highlight the importance to “note the potential thermoregulatory dangers of patients adjusting their dosage or withdrawing from DPA [dopamine] replacement agents or dopaminergic medications,” the researchers wrote.

One issue with many common Parkinson’s medications — and those for other related disorders — are that the drugs “can make it harder for the human body to handle hot weather by
reducing its ability to sweat or increase blood flow to the skin,” the university release stated.

Adding climate change to this mix amplifies the impact that can have, the researchers noted.

“Rising global temperatures caused by climate change pose a significant health concern for clinical patients reliant on long-term medications and healthcare,” said Jericho Wee, a PhD candidate at the National University of Singapore and the study’s first author.

“Increasingly, we will continue to see more elderly patients, many who have multiple health conditions and are taking different types of medication concurrently to manage their chronic diseases, compounding the risk of heat-related illness and dehydration,” Wee said, adding, “Understanding how each medication impacts thermoregulation, in the face of warmer environments, is the crucial first step to predicting the possible health outcomes when multiple medications are taken concurrently.”