Analgesics and anti-inflammatory Flashcards
Describe the pharmacokinetics of oxycodone
Absorption - Effective orally due to low first pass metabolism compared with other opioids. Good oral absorption. 10mg morphine = 4.5mg oxycodone
Distribution - High Vd
Duration of analgesia - 3-4 h, longer if CR formulation
Metabolism - Hepatic
Excretion - Renal
What adverse effects might you anticipate with oxycodone?
Sedation, respiratory depression, nausea/vomiting
Hypotension
Dysphoria
Biliary colic
Pruritus
Caution in renal failure
When prescribing oxycodone, what prescribing strategies may help in reducing the development of dependence?
Smaller doses at longer intervals
Limit doses
Use with other analgesics
Establish goals at start of treatment
Frequent evaluation of ongoing need
Use of modified CR formulations
What is methadone?
Methadone is a phenylheptylamine class narcotic agonist.
Can be given oral, IV, subcut, spinal and rectal.
Methadone is well absorbed from the GIT tract.
Its bioavailability far exceeds that of morphine.
It is an agonist at the mu receptors and an antagonist at the non opioid receptors including NMDA and monoaminergic reuptake receptors. These receptor properties may explain methadone’s ability to treat chronic pain and cancer patients when regular opioids have failed.
It has a long half life of 25-52hrs.
Methadone is widely used in the treatment of opioid abuse. Tolerance and physical dependence develop more slowly with methadone than with morphine. The withdrawal signs and symptoms occurring after abrupt discontinuation of methadone are milder, although more prolonged, than those of morphine. These properties makes methadone useful drug for detoxification and for maintenance of chronic relapsing heroin addict.
It has proven to be beneficial in treating chronic pain when morphine has failed. A side effect of methadone is constipation.
What is fentanyl?
Fentanyl is a phenylpiperidine class narcotic agonist
One of the most widely used synthetic opioid
Subgroup includes sufentanil, alfentanil,m remifentanil in addition to the parent coumpound, fentanyl.
Opioid receptor subtypes - 3
mu, delta and kappa - all three mediate supraspinal and spinal analgesia
mu - inhibition of respiration, slowed GI transit, modulation of hormone and neurotransmitter release; causes physical dependence, miosis, sedation and euphoria,
delta - modulation of hormone and neurotransmitter release
kappa - psychotomimetic effects, slowed GI transit, inhibit ADH release; cause miosis, sedation and dysphoria
Allopurinol
Indication
Pharmacokinetics
Side effects
Indications - Prophylaxis of gout. Reduces uric acid production by inhibiting xanthine oxidase, and lowers plasma and urinary urate concentrations. Allopurinol is metabolised to oxypurinol, which also inhibits xanthine oxidase.
PK
A - 80% oral bioavailability
D - Serum T1.2 1-2 hours
M - Metabolism by xanthine oxidase to alloxanthine, which retains the capacity to inhibit xanthine oxidase and has a long enough duration of action so that allopurinol can be given once a day.
E - Renal
Side effects include GIT intolerance, depression of bone marrow, hepatic toxicity and renal disease.
What is dextropropoxyphene?
Dextropropoxyphene is a centrally acting, synthetic opioid analgesic structurally related to methadone. Combination with paracetaomol produces extra pain relief but no anti-inflammatory actions. The potency of the drug is about two thirds that of codeine.
What is naloxone?
Naloxone is a pure antagonist. It has a very high affinity for mu receptors and a lower affinity for the other receptor binding sites.
Naloxone has a half life of 1-2 hours when given by injection and 10 hours when taking via the oral route.
Although naloxone is well absorbed via the oral route it undergoes rapid first pass metabolism.
IVI administration reverses opioid toxicity in 1-3 minutes.
There is no tolerance to the antagonistic action of these agnets, nor does withdrawal of naloxone after chronic administration precipitate an abstinence syndrome
