Analgesia Flashcards
Codeine
Indications - mild to moderate pain, diarrhoea, cough suppression
MoA - weak opioid - metabolised to morphine in the liver, active metabolites act via µ opioid receptor
S/Es - constipation, abdominal pain, N/V, anorexia
CIs - Caution in hepatic and renal impairment and the elderly - avoid or reduce dose.
Other - salt formulation e.g. codeine phosphate or sulphate. Can use in combination with paracetamol e.g. co-codamol 30/500 or 8/500.
1/10 potency of morphine therefore 30mg of codeine is 3mg of morphine
Tramadol
Indications - mild, moderate to severe pain, fibromyalgia
MoA - opioid, metabolised to morphine in the liver and excreted in the kidneys. Also acts at other receptors; 5HT, DA, muscarinic and nicotinic receptors.
S/E - most common side effects - nausea, headache, vertigo, dizziness, constipation, constipation and somnolence
CI - reduced dose in hepatic and renal impairment. Met by CYP2D6 which some people can be deficient.
Other - 1/10 potency of morphine therefore 400mg tramadol over 24hrs is 40mg of morphine.
Morphine
Indications - severe acute and chronic pain, ACS protocol (pain and vasodilation), dyspnoea and cough in palliative care, acute diarrhoea
MoA - strong opioid agonist, mechanism of use in SoB unknown - theories: decreased perception of breathlessness, related to resp depression
S/E - constipation, nausea and vomiting (lasts three days post change in meds), dry mouth, biliary spasm. Larger doses can cause muscle rigidity, hypotension and resp depression.
CI - acute resp depression, paralytic ileus, delayed gastric emptying, acute abdomen, HF secondary to chronic lung disease, phaeochromocytoma, renal failure (use oxycodone or alfentanil)
Other - reduce dose in elderly patients, start with 5-10mg every four hours. PRN dose is 1/6 of total dose in 24hours.
Oxycodone
Indications - moderate to severe pain in cancer patients, post-op pain, severe pain
MoA - opioid agonist
S/E - common side effects euphoria, constipation, fatigue, dizziness, N/V/D/abdo pain, anxiety, itching and sweating.
CI - severe renal failure (eGFR<10), moderate to severe hepatic impairment
Other - 2x as potent as morphine so decrease dose
Fentanyl
Indications - severe chronic pain, breakthrough pain, operative pain
MoA - opioid agonist, rapid onset and short durartion of action
S/E - as other opioids - most common = diarrhoea, constipation, nausea, dry mouth, somnolence, confusion, weakness and sweating. Less sedation, cognitive impairment and constipation than morphine.
CI - acute resp depression, paralytic ileus and head injury/raised intracranial pressure
Other - use as patch (avoid exposure to heat and monitor for fever, change every 72hrs), lozenges, nasal spray and tablets.
Other analogues available for example alfentanil and remifentanil. Also used during surgery. Alfentanil can be given subcut so used in palliative medicine when morphine not appropriate (renal failure - excretes inactive metabolites).
Much more potent than morphine. Look up patch conversion - fentanyl 100-150x potent as oral morphine. Alfentanil 15x potent as subcut morphine, 10x potent subcut diapmorphine.
Buprenorphine
Indications - chronic pain (BuTrans patch), opioid dependence
MoA - mixed opioid agonist and antagonist effects, long duration of action
S/E - as other opioids e.g. N/V, drosiness, can induce mild withdrawal symptoms if dependent on opioids
CI - as other opioids, caution in renal and hepatic impairment. May interact with drugs using CYP3A4 e.g. macrolides
Can get 72-96 hours patch or 7day patch
Methadone
Diamorphine
Ketamine
Methadone - opioid, used in severe pain, cough in terminal disease and opioid dependence treatment. Caution if heart conduction abnormalities or FHx of sudden death. S/E additionally include QT prolongation and Torsades de pointes, endocrine dysfunc e.g. dysmenorrhoea, hyperPL.
Diamorphine - heroin. Used in acute and chronic pain, ACS, acute pul oedema. May cause less nausea and hypotension than morphine. Less potent than morphine. Can give higher doses in smaller volumes.
Ketamine - NMDA antagonist, little published evidence about analgesic efficacy. S/E sedation, hallucinations, HTN and nausea. Should only be used by chronic pain/palliative care.
Paracetamol
Indications - mild to moderate pain, pyrexia
MoA - unknown. Main mechanism proposed is COX inhibition, particularly COX-2. No anti-inflammatory properties.
S/E - rare. Malaise, skin reactions incl SJS and TEN, blood disorders incl thrombocytopenia. Hepatotoxic in overdose - N/V, sweating and pain.
CI - caution in alcohol dependence, hepatocellular insuff, chronic malnutrition. Decrease dose in renal impairment.
In combination with codeine. Max dose 1g QDS (4g daily)
NSAIDs
Indications - mild to moderate pain, inflammation in rheumatic disease and musculoskeletal disorders. Specific NSAIDs good at certain conditions for example diclofenac PR in renal colic.
MoA - COX inhibitors, decreases production of prostaglandins. Vary in selectivity for different COX.
S/E - GI disturbances incl discomfort, nausea and diarrhoea, GI bleeding and ulceration. Can worsen asthma and provoke renal failure. Other S/E incl hypersensitivity reactions, headache and dizziness.
CI - severe heart failure, active GI ulceration and bleeding. Diclofenac and COX-2 selective inhibitors are CI in IHD, cerebrovasc disease and PAD. Caution/reduced dose in the elderly.
Consume with food or milk.
Examples - ibuprofen, diclofenac, indomethacin, mefenamic acid
Neuropathic Pain
1st line = TCA or anticonvulsant
Amitriptylline = inhibit transmission of pain impulses through activation of inhibitory pathways. Lower doses than in depression. Start 10mg at night. Can take few days to work.
Other TCAs - ddesipramine and imipramine
Pregabalin - start 25-75 mg BD, max 300mg BD
Gabapentin - start 100mg TDS, max 600mg TDS
2nd line = both, expert advice
Painful diabetic neuropathy - duloxetine 20-60mg/day (SNRI), amitriptylline if dulox CI
