Pharmacology of pain


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this is an important topic in palliative care. a form of care each of us may need when we suffer terminal illness and severe trauma at one point in our life time.

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Pharmacology of pain

  1. 1. Pharmacology of pain Dr. Turyahikayo jack Palliative care unit
  2. 2. Clinical Terms For The SensoryDisturbances Associated With Pain• ANALGESIA: absence of pain in response to stimulation which would normally be painful.• ACUTE PAIN: usually due to a definable acute injury or illness.• BREAKTHROUGH PAIN: a transitory exacerbation of pain that occurs on background of otherwise stable and controlled pain.• CHRONIC PAIN: results from a chronic pathological process. Pocket guide for Pain management in Africa
  3. 3. Clinical Terms For The SensoryDisturbances Associated With Pain• INCIDENT PAIN: pain that occurs in certain circumstances e.g. during movement• NEURALGIA: pain in the distribution of a nerve• NEUROPATHY: a disturbance of function of pathological change in a nerve• NEUROPATHIC PAIN: pain which is transmitted by a damaged nervous system; partially opioid sensitive• NOCICEPTOR: a receptor preferentially sensitive to a noxious stimulus
  4. 4. Clinical Terms For The Sensory Disturbances Associated With Pain• Dysesthesia – An unpleasant abnormal sensation, whether spontaneous or evoked.• Allodynia – Pain due to a stimulus which does not normally provoke pain, such as pain caused by light touch to the skin• Hyperalgesia – An increased response to a stimulus which is normally painful• Hyperesthesia - Increased sensitivity to stimulation, excluding the special senses. Hyperesthesia includes both allodynia and hyperalgesia, but the more specific terms should be used wherever they are applicable.
  5. 5. Aims of chronic pain mgt• Prompt relief of pain• Prevention of pain recurrence
  6. 6. • Optimal pain management includes drug therapy with the analgesic drugs in addition to non-pharmacological methods and addressing non-physical pain.• Types of analgesics• Non-opioids• Opioids• Adjuvants
  7. 7. Principles of analgesia Correct use of By the ladder analgesics should be based on the following principles; By the clock-By the mouth
  8. 8. cotd-By the individual-Use of adjuvants
  9. 9. By the clock SIDE EFFECTS: Drowsiness Morphine dose By the clock Too High PRN PAIN
  10. 10. • Expert committee by the cancer and palliative care unit of WHO proposed a structured approach to drug selection for cancer pain known as the ‘WHO analgesic ladder’• Controls pain in 70- 90%
  11. 11. • The choice of analgesic depends on;• Type of pain i.e nociceptive vs neuropathic pain.• Severity of pain use step 1 for mild pain , step 3 for severe pain. If you start on lower step and pain doesn’t improve go up the ladder• Co morbidities• Reassess pain always to find out if you can go up or down the ladder.• Treat underlying cause (eg, radiation for a neoplasm, antibiotics, antifungal for opportunistic infections)
  12. 12. Pharmacology of pain
  13. 13. Nociception Cortex Thalamus Spinal Cord Receptor09/13/12
  14. 14. • Paracetamol (step 1 Increased risk of analgesic) hepatotoxicity in;Centrally acting non- • old age opioid,it inhibits cyclo- • Poor nut.status oxygenase in brain • Fasting and reduces • Chronic alcohol use production of prostanoids. • Conc. Use of enzyme inducing drugsMax dose /day= 4g/day
  15. 15. • Paracetamol (step 1 Increased risk of analgesic) hepatotoxicity in;Centrally acting non- • old age opioid,it inhibits cyclo- • Poor nut.status oxygenase in brain • Fasting and reduces • Chronic alcohol use production of prostanoids. • Conc. Use of enzyme inducing drugsMax dose /day= 4g/day
  16. 16. NSAIDSExamples of NSAIDS• Ibuprofen 400mg 8 hrly max 2.4 g/d• Diclofenac 25-50mg 8hourly max 150mg/d• Indications :As a group, NSAIDs are of benefit for pain due to inflammation and bone pain. They also lower fever.Side effects;• ankle oedema, renal failure, can injure the gastric mucosa and cause platelet dysfunction• Avoid in above conditions, liver disease and bleeding. Use with Caution in elderly. Avoid aspirin use in asthmatics
  17. 17. OpioidsExamples; codeine, tramadol,morphine ,fentanylMorphine pharmacology• If Taken orally, absorbed upper small bowel, under goes first pass metabolism in liver and metabolized into M3G and M6G.Half life 2-3 hrs, duration of analgesia 4-6 hrs.• Excreted through the kidneys• Agonist at opioid receptors (μ,κ,δ)found in the brain and spinal cord. Analgesia is mainly mediated through theμ receptors.• Opioid receptors are found pre and post synaptically with the former dominating and when opioids bind on the former they inhibit the release of neuro transmitters.
  18. 18. Plasm IVaCo SC/IMncentration po / pr 0 Half life time
  19. 19. Morphine continuedSide effects Toxicity and over dose• Constipation- • Signs of morphine toxicity• Nausea and vomiting and over dose include; • Drowsiness that does not• Drowsiness- may occur in the first few days, if it improve does not improve after • Confusion about 3 days cut down on • Hallucinations dose of morphine. • Myoclonus (sudden• Itching- less common jerking of the limbs) • Respiratory depression (slow breathing rate) • Pin point pupils
  20. 20. Myths about oral morphine• Respiratory depression;• This is not common if morphine doses are titrated against pain as pain is a physiological antagonist to respiratory depression.
  21. 21. Tolerance “If I take it now, what will I take when I really need it?”• The need for increasing doses of morphine is usually related to disease progression.• Reassure the patients there is adequate scope to treat more severe pain if it occurs. There is no maximum dose of morphine.
  22. 22. Addiction – Differentiate addiction from physical dependence which is a normal physiological response to chronic opioid use – Psychological dependence-Compulsive use-Loss of control over drugs-Loss of interest in pleasurable activities
  23. 23. …addiction• Consider – substance use (true addiction) – pseudo-addiction (under treatment of pain) – behavioral / family / psychological disorder
  24. 24. cotd• Morphine hastens death;• morphine can be used for many months and years and is compatible with a normal life style. It can only lead to death by causing respiratory depression if given not correctly and not orally.
  25. 25. Pain not very responsive to opioids• 1.Neuropathic pain• 2. Bone pain
  26. 26. Adjuvant analgesia• These are drugs which were not designed as analgesics but help in some types of pain along side standard analgesics. They include;• Antidepressants• Anticonvulsants• Corticosteroids• Antispasmodics/smooth muscle relaxants• Skeletal Muscle relaxants• bisphosphonates
  27. 27. corticosteroids• Dexamethasone commonly used• Indications; bone pain, neuropathic pain from infiltration or compression of neuronal structures, raised ICP, athralgia, pain due to obstruction of a hollow viscus.• Mechanism of action; ↓peritumoral oedema ,may reduced concentrations of PGs and LKs• Metabolized by cyt system. Can increase metabolism of cbz. Phenytoin increases levels of dexamethasone
  28. 28. antidepressants• Amitriptilline, imipramine (start with12.5-25 mg nocte)• Indication: neuropathic pain• Mode of action: facilitate one or both of the 2 descending spinal inhibitory pathways by blocking presynaptic re-uptake of serotonin or noradrenaline• Sideffects; dry mouth, drowsiness,constipation,cardiac toxicity, othostatic hypotension.• Use with caution in elderly and cardiac disease
  29. 29. anticonvulsants• Indication: neuropathic pain• CBZ 100-200mg bd• Phenytoin 300mg od• CBZ induces liver enzymes that are responsible for its metabolism• Phenytoin is a hepatic enzyme inducer• Mechanism of action; suppress paroxysmal discharges and their spread from site of origin, and reduce neuronal hyper excitability.• Side effects: sedation, dizziness,unsteadiness
  30. 30. Smooth muscle relaxants• Hyoscine butylbromide commonly used• Indication; colicky pain• Mode of action: in the gut reduces the propulsive and non-propulsive gut motility and decrease intraluminal secretions.• Side effects: anticholinergic effects
  31. 31. Skeletal muscle relaxants• Indication; muscle spasms• Drug ; baclofen• Mode of action: agonist at the gamma aminobutyric acid receptor• Sideeffects: sedation,drowsiness,nausea,hypotonia.• diazepam
  32. 32. Bisphosphonates• Indication: bone pain not responding to NSAIDs or radiotherapy• Drug; pamidromate sodium• Mode of action: reduce osteoclastic activity in bone.
  33. 33. The message …• between the painful part and the patient’s experience of pain lies the nervous system• the nervous system is a learning system• pain is more than a nerve activation
  34. 34. • Thank you for listening