La toxicologie chez les personnes âgées

Maude St-Onge
M.D., Ph. D., FRCPC, Directrice médicale du Centre antipoison du Québec, Clinicienne chercheuse, Université Laval, CHU de Québec
Pierre-André Dubé
B. Pharm., Pharm. D., M. Sc., C. Clin. Tox., Pharmacien-toxicologue, Institut national de santé publique du Québec

Introduction

La toxicologie ne fait aucune discrimination concernant le statut socioéconomique, la religion, la race, le sexe ou l’âge. Elle touche la population mondiale à des degrés divers. Malgré tout, certaines particularités distinguent des sous-groupes de la population. Dans ce contexte, le Comité éditorial du Bulletin d’information toxicologique a décidé de traiter d’une thématique particulière, reliée à un sous-groupe de la population générale, par numéro pour l’année 2016. Toutes les chroniques de ce bulletin porteront donc sur la toxicologie chez les personnes âgées. Le présent éditorial, quant à lui, a pour objectif de présenter, sous la forme d’un interview avec une spécialiste, cette thématique particulière. Afin que soient bien reflétés ici les propos de la spécialiste, ils n’ont pas été traduits.

Entrevue avec la Dre Joanne Ho

La Dre Joanne Ho est médecin spécialiste en médecine interne, en gériatrie et en pharmacologie clinique, et s’intéresse particulièrement à la recherche sur les effets indésirables des médicaments chez la personne âgée. Diplômée en médecine à l’Université de la Colombie-Britannique, elle a complété ses trois spécialités à l’Université de Toronto. La Dre Ho a également obtenu une maîtrise en sciences à l’Institute of Health Policy, Management and Evaluation (Université de Toronto) tout en participant au programme de cliniciens-chercheurs Eliot Phillipson du département de médecine de l’Université de Toronto. Cette médecin a récemment terminé un fellowship en recherche au Li Ka Shing Knowledge Institute grâce à son implication au sein de la division de gériatrie de l’Université de Toronto et agit comme examinatrice au Collège royal des médecins et chirurgiens du Canada en pharmacologie clinique et toxicologie.

Quels sont les types d’interactions médicamenteuses et les types de surdoses les plus fréquents chez les personnes âgées?

Poisonings affect hundreds of thousands of older adults in North America every year and are associated with increased morbidity, functional decline, mortality and cost(1-7). Multimorbidity, polypharmacy and age-associated pharmacodynamics and pharmacokinetic changes predispose older individuals to drug toxicity(8-10).

Intentional overdoses by older individuals are associated with increased hospitalization, functional decline and mortality(7,11). Similar to the general population, drug overdoses in older individuals frequently involve ethanol, opioids, benzodiazepines and common non-prescription analgesics, acetaminophen and acetylsalicylic acid(2,7). Intentional poisonings in the older adult, however, are less likely to involve recreational drugs but more likely to involve lithium and tricyclic antidepressants, and medications used in the management of diabetes, and cardiovascular, Parkinson’s and rheumatic diseases(2,7).

The majority of poisonings in the elderly population are unintentional. These adverse drug events are due to errors in prescribing, administration or monitoring(1). A descriptive study using adverse event data from the National Electronic Injury Surveillance System-Cooperative Adverse Drug Event Surveillance project found four medications classes responsible for two thirds of adverse drug events requiring a hospital visit(1). These included warfarin, insulin, oral antiplatelet agents and oral hypoglycemic agents(1). With increased awareness of digoxin toxicity and therapeutic alternatives for atrial fibrillation or heart failure, there has been a decline in this drug’s use and adverse events. Nevertheless, clinicians should consider digoxin toxicity in any older patient taking this medication presenting with gastrointestinal symptoms, cognitive impairment or delirium, and cardiac arrhythmias(12).

Comment prévenir ces événements?

Frequent and rigorous medication reviews can prevent adverse drug events(9,13). These should be performed at each visit or at least prior to the introduction of any medication. Although medication reviews can be conducted by physicians, nurses or pharmacists, a Cochrane review of fall prevention strategies found that those done by primary care physicians were most effective(14). The Beers Criteria and Stopp/Start are helpful tools to identify and deprescribe potentially inappropriate medications(13,15-17).

In general, clinicians should be cognizant of the risks of falls or cognitive impairment associated with opioids, sedative hypnotics and medications with anticholinergic properties. Pharmacokinetic changes with aging which include altered body composition and drug volumes of distribution, and decreased hepatic phase one drug metabolism and renal drug clearance which may result in increased serum medication concentrations and drug toxicity(8,9).

The prevention of late-life suicide among elderly individuals also deserves attention. Clinicians should be vigilant for suicide ideation among those with psychiatric illness, specifically affective disorders(11,18). A population-based case-control study of suicides revealed that older adults who committed suicide were more likely to have comorbidities, specifically pain and depression(11). Older adults who committed suicide were at least 3 times more likely to have had 3 or more medical comorbidities, and 3 to 9 times more likely to have suffered severe pain(11). A case series of 44 suicide attempts by older individuals found medical comorbidity, social isolation and family conflict to be additional risk factors(19). Although the prevalence of depression among community dwelling older patients is reportedly lower than that of the general population, this may be due to underreporting(20,21). In addition, older patients with depression may present atypically with a predominance of somatic symptoms(22). Clinicians should also consider the variable prevalence of suicidal ideation and that suicide is less likely to be preceded by a warning in this population(18,23,24). While suicidal ideation was reported less frequently by those aged 60 years and older at prevalence rates of 6-7%, it increased to 16% among the oldest old, defined as those 80 years and older(23). Although there are fewer suicide attempts in the older population, the lethality associated with each attempt is far greater due to medical burden of illness(18). Therefore, screening and appropriate management for depression is necessary to prevent intentional overdoses in this vulnerable population(22). Furthermore, Ontario older adults who committed suicide frequently accessed medical care with almost half having been seen by a physician in the preceding week(11). Work in late-life suicide by Conwell and colleagues suggests multiple approaches to prevent suicide such as the identification and treatment of depression with pharmacological and nonpharmacological therapies, addressing social isolation with family and additional support services, and limiting access to large quantities of common non-prescription medications used in suicide, such as salicylates and acetaminophen(18).

Quels médicaments devraient être évités et de quelle façon?

The elderly population is at increased risk of medication-induced cognitive impairment and falls due to age-associated pharmacokinetic and pharmacodynamics changes, and comorbidities, particularly dementia. Clinicians can use the Beers Criteria and Stopp/Start tool during medication reviews to prevent medication-induced cognitive impairment or falls(16,17).

Medications that cause cognitive impairment or delirium, an acute decline in cognition and attention, also increase the risk of falls(25,26). Older patients are more sensitive to the neurologic effects of ethanol, opioids, sedative hypnotics, sedating antihistamines and medications with anticholinergic properties(9,17). As a result, these medications can contribute to cognitive impairment, including delirium, and increase the risk of falls(27,28). Antiseizure medications can predispose individuals to adverse events particularly at supratherapeutic levels therefore older individuals on these medications should undergo therapeutic drug monitoring particularly after initiating additional medications.

Orthostatic hypotension, defined as a drop in systolic or diastolic blood pressures of at least 20 mmHg or 10 mmHg respectively within 3 minutes of standing, is common among older individuals and increases the risk of falls(29). Medications that exacerbate orthostatic hypotension include diuretics, antihypertensives and medications with anticholinergic properties(30). The current guidelines for blood pressure management in the older frail patient are a general target blood pressure of ≤ 150/90 mm Hg, and of ≤ 140/90 mm Hg if there is concomitant diabetes or renal disease(31).

Medications that cause peripheral neuropathy, such as phenytoin and nitrofurantoin, or extrapyramidal symptoms, such as antipsychotics, prochlorperazine, metoclopramide and high dose domperidone, will also increase the risk of falls(17). If necessary, clinicians should initiate these medications at the lowest possible dose and titrate slowly while monitoring for adverse effects.

Pour toute correspondance

Pierre-André Dubé
Institut national de santé publique du Québec
945, avenue Wolfe, 4e étage, Québec (Québec)  G1V 5B3
Téléphone : 418 650-5115, poste 4647
Télécopieur : 418 654-2148
Courriel : t[email protected]

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St-Onge M, Dubé PA. La toxicologie chez les personnes âgée. Bulletin d’information toxicologique 2016;32(1):1-5. [En ligne] https://www.inspq.qc.ca/toxicologie-clinique/la-toxicologie-chez-les-pe…

Numéro complet (BIT)

Bulletin d'information toxicologique, Volume 32, Numéro 1, mars 2016