Heatwaves can impact chronic conditions and medications

This week has been a timely reminder extreme heat can have a serious impact on people’s health.

Heatwaves and hot weather have killed more people in Australia than any other disaster.

Extreme heat can be dangerous for anyone, however it is particularly dangerous for those:

• over the age of 75
• babies and young children
• overweight or obese
• pregnant or breastfeeding
• poor mobility
• who are homeless
• socially isolated, living alone
• working in a hot environment
• have a chronic illness (such as diabetes, heart disease, high blood pressure, cancer, mental illness)
• have an acute illness (an infection with fever or gastroenteritis)
• taking certain medications

Heat stroke is a life-threatening emergency.

It occurs when the body temperature rises about 40.5 degrees.

Immediate first aid is critical to lowering the body temperature as soon as possible.

The effect of heat on chronic conditions

Most heat-related morbidity and mortality is due to the exacerbation of chronic conditions.

Conditions which most commonly contribute to death during a heatwave include:

• cardiac events
• asthma or other respiratory illness
• kidney disease
• diabetes
• nervous system diseases
• cancer

Dehydration and subsequent medication toxicity may exacerbate:

• altered mental state
• kidney stones
• cardiovascular impairment
• falls

Heat and medication

Some medications can increase the risk of heat-related illness. Some can also be less effective when exposed to high temperatures.

The following medications can be impacted by heat. (This list should be used as a guide only)

Interference with sweating, caused by:

• anticholinergics, for example tricyclic antidepressants and benztropine
• beta blockers
• antihistamines
• phenothiazines
• vasoconstrictors

Interference with thermoregulation, caused by:

• antipsychotics or neuroleptics, for example risperidone, clozapine, olanzapine
• serotoninergic agonists
• stimulants, for example amphetamine, cocaine
• thyroxin

Decreased thirst, caused by:

• butyrophenone, for example haloperidol and droperidol
• angiotensin-converting enzyme (ACE) inhibitors

Dehydration or electrolyte imbalance, caused by:

• diuretics, especially loop diuretics
• any drug causing diarrhoea or vomiting, for example colchicines, antibiotics, codeine
• alcohol

Reduced renal function, caused by:

• NSAIDS
• sulphonamides
• indinavir
• cyclosporine

Aggravation of heat illness by worsening hypotension, caused by:

• vasodilators, for example nitrates (GTN) and calcium channel blockers
• anti-hypertensives

Levels of drug affected by dehydration (possible toxicity for drugs with a narrow therapeutic index), caused by:

• digoxin
• lithium
• warfarin
• antiepileptics
• biguanides, for example metformin
• statins
• altered state of alertness, caused by any drugs which alter the state of alertness, for example alcohol, benzodiazepine and narcotics

Resources to help you prepare for heatwaves

At-risk community members can prepare for heatwaves and heatstroke using the resources below:

Heatstroke – Health Resource Directory

Preparing for a heatwave – Health Resource Directory

Healthcare providers can find more information at:

Beat the heat (nsw.gov.au)

Brief overview of heat-related illnesses 

Illness	Cause	Symptoms
Heat rash	Inflammation of sweat glands	Erythematous papular rash, pruritus, secondary infection
Heat cramps	Muscle relaxation is affected by loss of salt in sweat	Muscle spasms in the abdomen, arms or legs
Heat exhaustion	Dehydration leading to poor blood flow affecting the brain and heart	Flushed or pale complexion, sweating, tachycardia, muscle cramps, weakness, dizziness, headache, nausea, vomiting, syncope
Heat stroke	Core temperature rise leading to widespread organ injury	Same symptoms as for heat exhaustion, plus hyperthermia, shock, arrhythmia, dry skin with no sweating (skin may be damp from earlier sweat), altered mental state, ataxic gait, convulsions, unconsciousness, death
Exertional heat stroke	Core temperature rise precipitated by intense or prolonged exercise in hot weather	As for heat stroke, plus rhabdomyolysis and renal failure