Medicines and hot weather: Reducing the risk of dehydration and heat-related illness

The use of medicines associated with increasing the risk of dehydration or heat-related illness is common in veterans and war widows. Five or more medicines associated with increasing the risk of heat-related illness were dispensed to:

• one in five veterans and war widows with diabetes, dementia, cardiovascular or respiratory disease,
• one in three with chronic renal failure and
• almost half with a psychiatric illness.¹

Having a psychiatric illness and taking psychotropic medicines or having a cardiovascular or respiratory illness is associated with a significant increase in risk of death during hot weather.²

Consuming heavy amounts of alcohol is associated with a significant risk of heat-related death, due in part to its diuretic effects, but also to reduced alertness, judgement and perception of heat and thirst.³

Hot days are common in Australia, and are often associated with significant morbidity and mortality, especially in the elderly.^4-6 The principal causes of death include dehydration, hyperthermia, heat exhaustion, heat stroke, complications of delirium and exacerbation of a preexisting illness.^{6, 7} Heat-related deaths most often occur in vulnerable elderly people living at home alone who lack social support and are unable to call for assistance.^{2, 8}

Most heat-related illness and deaths are preventable.⁹ Initiation of individualised preventive measures before summer is key to preventing heat-related illness and death.¹⁰

This therapeutic brief identifies older patients most at risk of heat-related illness this summer and suggests strategies to reduce that risk. Older patients most at risk include those:

1. taking certain medicines
2. prone to dehydration
3. having other associated risk factors.

1. Is your patient taking medicines that may increase the risk of dehydration or heat-related illness this summer?

Many commonly prescribed medicines can increase the risk of heat-relatedillness in a number of ways:

1. Dehydration and electrolyte imbalance.^{9, 11}
2. Impaired sweating.^{10, 11}
3. Reduced thirst sensation.¹¹
4. Hypotension and reduced cardiac output, which may also increase the risk of fainting and falls.^{10, 11}
5. Sedation and cognitive impairment which may reduce alertness, judgement and perception of heat and thirst.^9-11
6. Drug toxicity associated with reduced renal clearance of medicines in dehydrated patients.^9-11
7. Altered central thermoregulation.¹⁰ (Commonly used medicines associated with increasing the risk of heat-related illness)

Alterations in the body’s thermoregulatory responses due to the effect of medicines may go unnoticed during winter and only become apparent in the heat of summer. Review all of your patients’ medicines, including those purchased over the counter and monitor closely.¹²

Use caution when initiating new medicines as they may act together, or with existing medicines, to further impede normal heat responses.¹³ The risk of hospitalisation for heat-related illness in veterans is significantly increased following initiation of an angiotensin converting enzyme (ACE) inhibitor or an angiotensin II receptor blocker (ARB) in combination with a diuretic or following initiation of an antidepressant.¹

2. Is your older patient prone to dehydration?

Dehydration is common in older people and can occur quickly.¹⁹ This is partly because of physiological changes that are part of the ageing process, and include:

• impaired renal function
• decreased total body water
• a reduced thirst sensation.²⁰

These changes affect the water/sodium balance and the ability to maintain homeostasis.¹⁹ Older people also have:

• a reduced ability to sweat
• decreased plasma volume
• reduced cardiac output
• decreased blood flow to the skin and extremities
• generally lower fitness, increased body fat and reduced lean body mass.²¹

In the presence of comorbidities and use of multiple medicines, the risk of dehydration and heat-related illness is increased significantly, especially during hot weather.¹⁹

Other contributing factors may include a reluctance to drink fluids because of concerns about bladder control problems, advice from the doctor about fluid restrictions,¹⁷ or a lack of understanding of the importance of proper hydration or²⁰ of perceived vulnerability to the effects of hot weather.²²

Some electrolyte disturbances and elevated glucose levels can increase urine output to predispose the patient to dehydration.^{19, 23} Older people may not feel thirsty even when they are dehydrated.¹⁸

Dehydration can have serious consequences including confusion, falls, respiratory or urinary tract infections, constipation and delayed wound healing.²⁰ It can lead to acute changes in renal function which may increase the risk of toxicity from other medicines that are renally excreted (eg. dabigatran, rivaroxaban, apixaban, digoxin, gliptins, oxycodone, morphine and lithium).²³ Identifying older patients at risk of dehydration is essential as diagnosis of mild dehydration can often be difficult.¹⁹

If an older person complains of substantially reduced urine output and thirst, it is highly likely they are severely dehydrated.¹⁹

3. Does your patient have other associated risk factors?

The people most likely to suffer heat‑related illness during periods of hot weather often have clusters of risk factors (see Table 1).^{2, 24}

Many older people consider they are able to cope during hot weather and don’t perceive they may be prone to the effects of heat, even if they have a pre‑existing chronic condition, live alone or take prescribed medicines.^{17, 22} In Australia approximately one in five people aged 60–79 years of age and one in three people aged 80 years of age and over, live alone.²⁵

Rapid onset of extreme hot weather early in the season or travelling to other temperature zones that are considerably hotter and more humid increases the risk of heat-related illness in older people.¹⁷

Worsening of a pre-existing illness is the most common reason older people die during hot weather.^{16, 18}

Table 1: Risk factors for heat-related illness ^{2, 10, 24, 26}

Taking certain medicines

See Commonly used medicines associated with increasing the risk of heat-related illness

Poor general health and comorbidities

Cardiovascular disease Mental illness including dementia and confusion Respiratory disease Diabetes mellitus Obesity Hypertension or renal disease Substance misuse Excessive alcohol intake Neurological diseases, such as Parkinson’s disease Acute illness

Limited function, frailty and physical disabilities

Reduced mobility Confined to bed or housebound High dependency level Poor self-care or unable to care for themselves At risk of falls

Socioeconomic factors

Living alone Low socioeconomic status with limited financial resources Poor quality housing or homelessness Lack of use of or access to air‑conditioning at home Living in dense inner urban areas especially on the top floor Social isolation

Lifestyle factors

Playing outdoor sports or exercising outdoors Lack of access to health care Unnecessary outdoor excursions Working outdoors

Recommendations for patients at risk of heat-related illness

Review your patient’s medicines and make a hot weather plan

• During hot weather, it is even more important to apply the general principles of prescribing the lowest effective dose for the shortest possible time.²³
• People prescribed a psychotropic medicine are at a particularly high risk because of the combined effect of their illness on behaviour and the medicines they take.² It is especially important in these patients for you to review the dose and to talk about the risks of heat-related illness and protective measures they can take.
• If practical, consider delaying initiation or increasing the dose of a psychotropic medicine until the hot weather is over.
• If your patient is prescribed a diuretic, consider reducing the dose during hot weather. If appropriate, consider providing an individualised plan for your patient to adjust their diuretic medicine themselves on hot days.
• If your patient is on fluid restrictions, consider relaxing them during periods of hot weather, if appropriate.
• Give careful consideration when initiating combinations of medicines, such as a diuretic and ACE inhibitor or ARB during hot weather, as together they may increase the risk of hypovolaemia and dehydration.²³ Consider initiating the diuretic at a lower dose.²³
• Consider a medicines review (HMR or RMMR) by an accredited pharmacist. Ask the pharmacist to provide counselling about how to stay well and store medicines safely during hot weather.

Ensure your patient has a good understanding of how to stay well during hot weather, encourage them to:

• Drink small amounts of their preferred fluids, often²⁰ (sports or energy drinks do not appear to provide any added benefits and are an unnecessary extra cost).²¹
• Avoid consuming large amounts of plain water in a short period of time, especially if a low salt diet is being followed.^{10, 29}
• Drink fluids even when not feeling thirsty.¹⁰
• Eat cold foods that have a high fluid content.²⁰
• Observe and report any decrease in urine output to you or their pharmacist.
• Be aware of the early signs of dehydration/heat stress
  • report any symptoms that worry them to you or their pharmacist.
• Stay cool by:
  • using the air-conditioner at home (using an air-conditioner at home or having access to air-conditioned areas, such as shopping centres, is associated with a lower risk of death during hot weather).²
  • staying indoors out of the heat during the hottest part of the day, and taking extra showers if able.¹⁰
  • wearing lightweight, loose fitting clothes.¹⁰
  • keeping the home as cool as possible.¹⁰
• Maintain frequent contact with family, friends or carers.¹⁰

Organise or provide contact details for support services for your patient living alone and isolated:

• DVA Veterans’ Home and Community Care program: available to veterans and war widows/widowers living independently at home who may need help with personal or respite care, social support or domestic assistance. For further information go to: www.dva.gov.au/health-and-wellbeing/home-and-care/veterans-home-care-vhc
• Australian Red Cross Telecross program: a free Australia‑wide service that assists people who live alone and are at risk of illness or accident, by telephoning them daily to check on their wellbeing and safety. For further information go to: www.redcross.org.au/telecross or telephone: 1300 885 698

• Telecross REDI is a free South Australian service available to vulnerable and isolated people in the community who may need support during hot weather. For further information go to: www.redcross.org.au/telecross-redi.aspx
• State heatwave plans are a good resource for people wishing to seek further information (use a search engine to find each state’s heatwave plan).

Commonly used medicines associated with increasing the risk of heat-related illness.^{9-11, 23}

Antidepressants Tricyclic antidepressants (TCAs) For example amitriptyline These medicines have strong anticholinergic effects Selective Serotonin Re-uptake Inhibitors (SSRIs) For example sertraline, citalopram and escitalopram Serotonin and Noradrenaline Re-uptake Inhibitors (SNRIs) For example venlafaxine, duloxetine and desvenlafaxine Possible Effects Altered central thermoregulation associated with antidepressants that have anticholinergic effects Impaired sweating – increased with SNRIs and SSRIs, decreased with TCAs Sedation and cognitive impairment: reduced alertness, judgement and perception of hot weather Hypotension and reduced cardiac output associated with TCAs: may increase risk of fainting and falls SSRIs commonly associated with hyponatraemia include sertraline, fluoxetine, paroxetine and citalopram.27, 28 Venlafaxine may also contribute to hyponatraemia.27, 28

Anti-convulsants For example pregabalin, gabapentin and sodium valproate Possible Effects Sedation and cognitive impairment: reduced alertness, judgement and perception of hot weather Ataxia, impaired balance, dizziness and blurred vision, especially on initiation/increase in dose: increased risk of fainting and falls.

Antipsychotics (typical and atypical) For example risperidone, olanzapine, quetiapine and haloperidol Possible Effects Impaired sweating Altered central thermoregulation Hypotension & reduced cardiac output: may increase risk of fainting & falls Sedation and cognitive impairment: reduced alertness, judgement and perception of hot weather

Medicines with anticholinergic effects For individual medicines see Module 39: The anticholinergic burden at: www.veteransmates.net.au/TB_anticholinergic Possible Effects Altered central thermoregulation Sedation and cognitive impairment Impaired sweating Hypotension and reduced cardiac output: may increase risk of fainting and falls Dizziness

Diuretics, ACE inhibitors, ARBs and other medicines for hypertension Possible Effects Hypovolaemia Postural hypotension: increased risk of fainting or falls Reduced thirst sensation Renal impairment – increases risk of hyperkalaemia Dehydration (diuretics and ACE inhibitors reduce the effects of sodium retention), causing: reduced visceral blood flow to the liver and kidneys reduced clearance of medicines and toxins electrolyte imbalances, including hyponatremia (commonly associated with indapamide, hydrochlorothiazide and frusemide)27, 28

Benzodiazepines and opioids Possible Effects Sedation and cognitive impairment: reduced alertness, judgement and perception of hot weather Increased risk of falls

Other medicines Novel oral anticoagulants (including dabigatran, rivaroxaban & apixaban), oxycodone, morphine, gliptins & metformin, lithium & digoxin Possible Effects In dehydrated patients, drug toxicity may result from reduced renal clearance of medicines

References

1. DVA Health Claims Database, University of South Australia, QUMPRC. [Accessed August 2014].
2. Bouchama A. et. al. Prognostic factors in heat wave-related deaths. Arch Intern Med. 2007;167(20):2170-2176.
3. Kilbourne E. et al. Risk factors for heatstroke. JAMA 1982;247(24):3332-36.
4. Nitschke M. et. al. Impact of two recent extreme heat episodes on morbidity and mortality in Adelaide, South Australia: a case-series analysis. Environmental health 2011;10:42
   http://www.ehjournal.net/content/10/1/42
5. Steffen W, Hughes L & Perkins S. Heatwaves: Hotter, Longer, More Often. Climate Council of Australia Limited. 2014. Available at: http://www.climatecouncil.org.au/uploads/9901f6614a2cac7b2b888f55b4dff9cc.pdf [Accessed July 2014].
6. Aström D, Forsberg B & Rocklöv J. Heat wave impact on morbidity and mortality in the elderly population: a review of recent studies. Maturitas. 2011;69:99-105.
7. Fouillet A. et. al. Excess mortality related to the August 2003 heat wave in France. International Archives of Occupational and Environmental Health. 2006;80:16-24.
8. Basu R & Ostro B. A multicounty analysis identifying the populations vulnerable to mortality associated with high ambient temperature in California. American Journal of Epidemiology. 2008;168(6):632-637.
9. Hajat S, O'Connor M & Kosatsky T. Health effects of hot weather: from awareness of risk factors to effective health protection. Lancet. 2010;375:856-863.
10. World Health Organisation, Regional office for Europe. Public Health Advice on preventing health effects of heat - new and updated information for differenct audiences. World Health Organisation, 2011. Available at: http://www.euro.who.int/__data/assets/pdf_file/0007/147265/Heat_information_sheet.pdf [Accessed July 2014].
11. Rowett D. Medicines and Heatwaves. RGH Pharmacy E-Bulletin. 2013;49(1). Available at: http://www.auspharmlist.net.au/ebulletin.php [Accessed August 2014].
12. Cheshire W & Fealey R. Drug-induced hyperhidrosis and hypohidrosis. Drug Safety. 2008;31(2):109-126.
13. O'Connor M & Kosatsky T. Systematic review: How efficacious and how practical are personal health protection measures recommended to reduce morbidity and mortality during heat episodes? For The Consortium on Regional Climatology and Adaptation to Climate Change and The National Collaborating Centre for Environmental Health 2008. Available at: http://www.ouranos.ca/media/publication/125_Rapport_Kosatsky_anglais_sante_2008.pdf [Accessed August 2014].
14. Williams S. et. al. Heat and health in Adelaide, South Australia: assessment of heat thresholds and temperature relationships. Science of the Total Environment. 2012;414:126-133.
15. Nicholls N. et. al. A simple heat alert system for Melbourne, Australia. International Journal of Biometeorology. 2008;52:375-384.
16. Basu R. High ambient temperature and mortality: a review of epidemiologic studies from 2001 to 2008. Environmental Health. 2009;8:40 Available at: http://www.ehjournal.net/content/8/1/40 [Accessed August 2014].
17. Hansen A. et. al. Perceptions of heat-susceptibility in older persons: barriers to adaptation. International Journal of Environmental Research and Public Health. 2011;8:4714-4728.
18. Ibrahim J. et. al. Minimising harm from heatwaves: a survey of awareness, knowledge, and practices of health professionals and care providers in Victoria, Australia. International Journal of Public Health. 2012;57:297-304.
19. Schols J. et. al. Preventing and treating dehydration in the elderly during periods of illness and warm weather. The Journal of Nutrition, Health & Aging. 2009;13(2):150-157.
20. Australian Medicines Handbook Aged Care Companion. Fourth Edition. Adelaide: Australian Medicines Handbook Pty Ltd. 2014.
21. Health Canada. (2011). Extreme Heat Events Guidelines: Technical Guide for Health Care Workers. Water, Air and Climate Change Bureau, Healthy Environment and Consumer Safety Branch, Health Canada. Ottawa, Ontario, 149. Available at: http://www.hc-sc.gc.ca/ewh-semt/alt_formats/pdf/pubs/climat/workers-guide-travailleurs/extreme-heat-chaleur-accablante-eng.pdf [Accessed August 2014].
22. Abrahamson V. et. al. Perceptions of heatwave risks to health: interview-based study of older people in London and Norwich, UK. Journal of Public Health. 2008;31(1):119-126.
23. Australian Medicines Handbook, Adelaide: Australian Medicines Handbook Pty Ltd. 2014.
24. Kenny G. et. al. Heat stress in older individuals and patients with common chronic diseases. CMAJ. 2010;182(10):1053-1060.
25. Australian Bureau of Statistics. Age Matters, June 2011. Canberra, Australia. Available at: http://www.abs.gov.au/ausstats/abs@.nsf/mf/4914.0.55.001 [Accessed August 2014].
26. Wilson L, Black D & Veitch C. Heatwaves and the elderly: the role of the GP in reducing morbidity. Australian Family Physician. 2011;40(6):637-640.
27. Fourlanos S & Greenberg P. Managing drug-induced hyponatraemia in adults. Australian Prescriber. 2003;26(5):114-117.
28. eTG Complete. Melbourne: Therapeutic Guidelines Limited. 2014 March. Available at: http://online.tg.org.au/ip/desktop/index.htm [Accessed August 2014].
29. Grandjean A. World Health Organisation (WHO) guidelines for Drinking-Water Quality. 2004. Water Requirements, Impinging Factors, and Recommended Intakes. Available at: http://www.who.int/water_sanitation_health/dwq/en/nutwaterrequir.pdf [Accessed August 2014].

Return to top