Analgesics Flashcards
Pain acute/nociceptive
short-term pain, with an easily identifiable cause. A warning of present damage to tissue or disease which responds well to medication.
Pain chronic/neuropathic
pain which persists. Is constant or intermittent and has “outlived its purpose” since it no longer help the body to prevent further injury.
Pain allodynia
pain from a stimulus that does not normally cause pain
Pain parasthesis
painful feelings (e.g. pins & needles) with no apparent stimulus
Pain management - general considerations
Assessments Type of pain (nociceptive versus neuropathic) Form of pain (acute versus chronic) Severity of pain Route of administration
Objectives
Best analgesic for the individual
Lowest effective dose
Least invasive route - topical, oral, sublingual, i.v., i.m., i.p., i.t., epidural
Opioids – Mechanism of Action
Act at the level of the spinal cord and the CNS:
Decrease neurotransmitter release
Block postsynaptic receptors
Activate inhibitory pathways
Opioids – side effects
Dose-related; from nausea, vomiting, constipation, drowsiness, to respiratory depression, hypotension, sedation, dependency
opioids cautions/contradictions
Acute respiratory depression, acute alcoholism, head injury
opioids interactions
alcohol - hypotensive and sedative effects
MAOI - CNS excitation/inhibition
SSRI / TCA - sedation
carbamazepine -plasma conc. of methadone
cimetidine (ulcer healing) - inhibit opioids metabolism
SSRI
Selective serotonin reuptake inhibitor
TCA
Tricyclic antidepressants
Opioids neuropharmacology
-Mimic Our Endogenous Ligands “enkephalins”
β-Endorphin; Leu-enkephalin;
Met-enkephalin; dynorphin
-Signal Transduction
G-protein coupled receptors
-Integrated Physiology
“act as suppressors..”
-Act as Agonists at Opioid Receptors
Three types of receptors: m, k, d
Six sub-types: m, k1,2,3: d1,2
Opioid receptor - delta
CNS & Peripheral Sensory Neurons
May contribute to analgesia
opioid receptor - μ
CNS, Spinal Cord,
Peripheral Sensory Neurons, GI Tract
Responsible for most of the analgesic effects
Responsible for side effects
Most analgesic opioids are μ-receptor agonists
opioid receptor - kappa
CNS, Spinal Cord, Peripheral Sensory Neurons
Sedation & dysphoria, but few side effects
Does not contribute to dependence
Opioids Pharmacodynamics
Pure Agonists
Typified by morphine-like drugs
Have high affinity for μ-receptors; low affinity for δ & κ
Opioids Pharmacodynamics
Partial agonists & Mixed Agonist-Antagonists
e. g. nalorphine: mixed effects on μ-receptors
e. g. pentazocine & cyclazocine: (-) at μ-, but partial (+) on δ- & κ-
Opioids Pharmacodynamics
Antagonists
Block the actions of opiates
e.g. naloxone and naltrexone; treatment of heroin/morphine overdose
Morphine
Oral; i.v.; Intrathecal; subcutaneosly Acute & Chronic pain pharmacokinetic t1/2=3-4 h side effects: Sedation, Respiratory depression, Constipation, Nausea, vomiting, Itching, Tolerance, Dependence, Euphoria
Diamorphine
Oral;i.v.
Acute & chronic pain
Pharamacokinetic - More rapid than morphine; metabolised to morphine. Has a greater solubility
side effects:
Sedation, Respiratory depression, Constipation, Nausea, vomiting, Itching, Tolerance, Dependence, Euphoria