Path pharmacology Flashcards
State and explain the method of medication prescription
Recognise – individual and cultural influences – impact on community – benefits andreview of management
Assess – site, severity and cause – classification
Treat – non-pharmacological – pharmacological – WHO ladder for cancer pain – WHO reverse ladder for severe acute pain – anti neuropathies – appropriate use of opioids
State the three classifications of pain
- Acute or chronic/ persistent
- Nociceptive (specific stimulus of pain) or neuropathic (no specific stimulus identified, damage to nerve or nervous system)
- Cancer or non-cancer
What do analgesic agents do to reduce pain?
-Altering perception of pain in central nervous system
- inhibiting local production of pain mediators
- interrupt neural impulses in spinal cord
Need awareness of how analgesic regimes work
What is bupicacaine?
Longer term local anaesthetic
- Post operative pain relief to reduce reliance on
Slow onset of action – 30 minutes so used alongside opioids during operation (eg. Diamorphine and/or fentanyl.)
What is a reversal agent?
any drug used to reverse the effects of anaesthetics, narcotics or potentially toxic agents
What is a local anaesthetic?
-cause reversible sensory block to nerve conduction providing analgesia to patient (can cause motor block)
- sodium channels of nerve membrane a receptor for local anaesthetic molecule
- If excessive amounts in systemic circulation – symptoms and signs of toxicity may appear (must be monitored)
- Clearance almost entirely due to liver metabolism
What is fentanyl?
-Synthetic opioid with my-agonist pharmacological effects
- Clinical potency of 50-100 times that of morphine
- primarily used in analgesia and sedation for adults with moderate to severe pain
- rapid onset of action and duration of action is short
- highly lipid soluble
- redistributed to other tissues and released into blood – up to 80% bound to plasma proteins
- metabolised by liver and excreted mainly in urine
- large inactive metabolites
- reversed by naloxone – opioid antagonist
What is naloxone?
Reversal agent for all opioids
What is morphine?
-Relief of severe acute pain in adults
Oral opioid
-As effective as more invasive routes if equianalgesic doses administered
- First line choice when treating severe acute pain
- little evidence in why they are useful in management of long term pain
- should always receive lowest dose providing effective pain control
- opioid analgesic – act on receptors in CNS
- competitive agonist in my receptors mediating other action of respiratory depression, euphoria, inhibition of gut motility and physical dependence
- rapid onset of action – peak analgesic effect within 20 minutes
- same metabolism and excretion as oral doses
Why is morphine very widely used?
- Concentration 2mg/ml is schedule 5 drug meaning not controlled drug – does not require 2 person check so very easy to be dispensed
- other conc. Schedule 2 controlled drug with tighter restrictions (IV then step down oral)
What is PCA?
Patient control analgesia
patient control of pain relief – relevant when patient has been on opioid previously (not opioid naïve)
Explain the absorption of morphine
-Extensive first pass metabolism in liver
– result in systemic bioavailability 25-33%
-10mg morphine equates to 3 mg IV
- Important to consider in slinical when stepping down from parenteral routes
Explain the metabolism of morphine
-Mainly liver
- conjugation to morphine 3 and 6 glucuronides
- Particular in M6G (morphine-6-Glucuronide)
- half life of morphine 2 hours but M6G longer
How is morphine excreted?
Urine
- Reduced renal function delayed clearance allow drug and metabolites to continue to exert effect
Monitoring essential
What are the contraindications of morphine?
-Sensitivity to morphine
- respiratory depression
- renal disease
- reduced sedation, drug interactions, enzyme inducers e.g. rifampicin (decreasing effect), enzyme inhibitors e.g. cimetidine (increasing effect), CNS depressant
What are the side effects of morphine?
• Nausea, constipation, respiratory depression, opioid induced ventilatory impairment
- Withdrawal - symptoms may occur if an opioid is stopped or reduced abruptly
Explain how addition is related to morphine
Consider if the patient is displaying any warning signs that may make opioid weaning difficulty.
• Depression/anxiety etc.
• Careful monitoring and may need weaning prior to discharge. Can still be given in a controlled clinical environment.
This is especially important due to rise in prescription of opioids
Explain what a weak opioid is
eg. codeine
-Exerting effect on my-receptor
- metabolised by liver isoenzyme CYP2D6 into active metabolite morphine – 10% caucasian pop deficient in this enzyme result in adequate analgesic effect – poor metabolisers
- some patients metabolise codeine rapidly and high risk of developing adverse effects of opioid toxicity (ultra rapid metabolisers)
- not used on children below 12 years old
Give an example of a reliable a preferable weak opioid
- dihydrocodeine more reliable and preferable
What is an ultra rapid metabolisers?
some patients metabolise codeine rapidly and high risk of developing adverse effects of opioid toxici
Whats the classification of paracetamol?
mild analgesia and antipyretic
Explain the action of paracetamol
- no clear mechanism of action
- few adverse effects that NSAIDs and used when latter are contraindications ( renal impairment, asthma or peptic ulcers)
- care in administration with renal or hepatic impairment
- liver damage possible taking 10g or more in adults – injection of 5g lead to liver damage if patient has other risk factors
- if patients have continuous pain – 4 times a day paracetamol is available – must not be exceeded due to rare adverse effects
What is deprescribing?
Process of withdrawing an inappropriate medication – supervised by healthcare professional with the goal of managing polypharmacy and improving outcomes – recognised as part of good clinical care
