Daniel S. Sitar, BScPharm, PhD, FCP Professor Emeritus University of Manitoba Editor: Journal of Clinical Pharmacology

Transcription

1 March 8, 2011 Daniel S. Sitar, BScPharm, PhD, FCP Professor Emeritus University of Manitoba Editor: Journal of Clinical Pharmacology

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4 DEFINITIONS Pain: The unpleasant sensory and emotional experience associated with a noxious event, including, tissue damage or inflammation Nociception: The process of encoding and sensing tissue injury and inflammation Significant developmental/maturational changes Analgesia: Relief of the perception of pain Accompanying sedation unintended

5 ANATOMY/PHYSIOLOGY Pain Initiation: Pain fiber stimulation in response to tissue injury Bradykinin, serotonin, substance P, prostaglandins, histamine Pain Propagation: Transmission of signal from nerve endings to spinal cord A-δ and C-fibers Pain Integration: Modulation (amplification/inhibition) of pain signal In spinal cord and cortex

6 THE GOLD STANDARD OF PAIN ASSESSMENT IS SELF REPORT - BUT HARDLY FEASIBLE IN COGNITIVELY IMPAIRED PERSONS

7 INADEQUATE PAIN MANAGEMENT PHYSICAL MANIFESTATIONS Best studied in preterm infants Sleep disturbances Feeding difficulties Intraventricular hemorrhage Chronic pain syndromes Altered pain thresholds/hyperalgesia

8 ASSESSMENT OF PAIN Can caregivers or relatives rate pain in nursing home residents? Proxy report of caregivers and relatives on presence and intensity of pain is unreliable, especially for cognitively impaired persons. J Clin Nurs 2009;18(17):

9 PAIN MANAGEMENT STRATEGIES

10 DRUG MANAGEMENT OF PAIN World Health Organization Three-Step Analgesic Ladder

11 Figure 1: Percentage of Seniors Who Reported Having 1 or More of 11 Chronic Conditions, for Canada and by Province (Age Sex Standardized) 76% Canada Y.T. N.W.T. Nun. 79% P.E.I. 85% * N.L. 75% 82%* B.C. Alta. 76% 70% Sask. Man. 75% Ont. 74% Que. N.B. 81% N.S. 81% Canadian Survey of Experiences With Primary Health Care, 2008, Statistics Canada; Canadian Institute for Health Information. from Jan 2011 CIHI Report

12 SENIOR CITIZENS STATISTICS Manitobans with one or more chronic conditions: 70 % (76 % for Canada) For all of Canada: Chronic pain prevalence 17 % Arthritis 1.2 million Canadians (second most common chronic condition) 3+ Chronic conditions 24 % 1-2 chronic conditions 50 % Canadian Survey of Experiences With Primary Health Care, 2008, Statistics Canada; Canadian Institute for Health Information from Jan 2011 CIHI Report

13 J Am Geriatr Soc 1988;36: NUMBER OF DRUGS

14 Nonopioid Choices for Analgesia Opioid Co-analgesics

15 OTC ANALGESICS - CANADA Acetylsalicylic acid (ASA) Acetaminophen (Paracetamol UK) Ibuprofen Naproxen Combination products with codeine phosphate up to 8 mg/tablet - Not recommended

16 Biopharm Drug Disposit 1986;7:21-5

17 Acetaminophen is not an NSAID

18 PHARMACOLOGY OF ACETAMINOPHEN Rapidly and completely absorbed Peak plasma concentrations in 30 to 60 minutes Half-life of 2 hours in adults

19 PHARMACOKINETICS OF ACETAMINOPHEN - I.V. Fit young Fit elders Frail elders Mean age 25 years Liver volume 1124 ml Half life 123 min Clearance 4.7 ml/min/kg

20 RATIONAL NONOPIOID ANALGESIC COMBINATIONS ASA + Acetaminophen ASA + Caffeine Acetaminophen + Caffeine ASA + Acetaminophen + Caffeine

21 Don t mix NSAIDs DRUG USE PRINCIPLE Increased cardiovascular risk Illogical therapeutic approach due to same mechanism of action

22 PROBLEMS WITH NONOPIOID DRUGS FOR PAIN MANAGEMENT Cardiovascular NSAIDS Bleeding NSAIDS Hypertension NSAIDS Hepatotoxicity mostly with acetaminophen Kidney toxicity both NSAIDs and acetaminophen Brain toxicity mostly with NSAIDs

23 CODEINE FOR ANALGESIA

24 CYP2D6 AND ETHNICITY Population % Poor Metabolizers Caucasian 5-10 Canadian Native Indian 1.1 Inuit 3.3 Chinese 1 African 0-20 Int J Clin Pharmacol Ther 2000;38:61

25 DRUG SUBSTRATES FOR CYP2D6 Cardiovascular Propafenone Flecainide Mexiletine Metoprolol Propranolol Timolol CNS active Amitriptyline Nortriptyline Imipramine Desipramine Fluoxetine Paroxetine Codeine Haloperidol Pediatrics 1999;104:640

26 ANTIDEPRESSANTS AND POLYPHARMACY Setting Patients Only drug And 1+ other drugs Primary care Psychiatric clinic And 3+ other drugs % 72% 34% % 71% 30% VAMC % 93% 68% J Pract Psychiatry Behav Hlth 1998:37-40

27 ISSUES WITH OPIOID ANALGESICS Respiratory Depression Constipation Bladder Evacuation Difficulties

28 ADVERSE PERSON EVENTS AFTER CODEINE Consistent with literature on lack of analgesic effect of codeine in persons lacking CYP2D6 Same incidence of adverse events regardless of analgesic efficacy (sedation, dizziness etc. but not nausea) Beware: large placebo response in effectiveness of analgesics

29 ANALGESICS EFFICACY

30 TYLENOL WITH CODEINE ORDERS One tablet T3 equals 2 tablets of plain acetaminophen Tylenol #1 has an ineffective dose of codeine Analgesic range should be allowed: e.g. 2 tablets Tylenol #2 or #3 QID as a regular dose March 9, 2011

31 TYLENOL ORDERS Tylenol #3 1-2 tabs OH4 prn March 9, 2011

32 CONCLUSIONS Acute and chronic pain are very prevalent and an important issue for person satisfaction Simple analgesics are among the most frequently used medications Clinicians need to carefully monitor analgesic use (and abuse) and optimize regimens using pharmacologic principles