carfentanil - 100x more potent than fentanyl, used to tranquilize elephants, extremely dangerous to humans
pholcodine - antitussive cough medication withdrawn by TGA in Australia in 2023 as increases risk of anaphylaxis during general anaesthesia by 300x for the next 12 months after dosing.
new highly potent synthetics such as nitazene (linked in 64 deaths in UK in last half of 2023)
opiates, in particular, oxycodone is the number one cause of deaths from prescription medications in Australia
mixing opiates for acute pain, or use with pregabalin or gabapentin1) requires close observation as there is a risk of fatal resp. depression, especially in those who are obese or have obstructive sleep apnoea
adverse reactions related to dose, or known side effect profiles such as nausea, itch and dysphoria, should be managed with careful attention to dose, speed of administration and pre-emptive management of expected side effects, and the use of non-opiate analgesics.
opiates are generally a poor choice for migraine headaches and most cases of low back pain
the oral route should be used if not contraindicated and patient likely to tolerate oral dose and rapid onset not required:
codeine should be avoided due to its high incidence of nausea, vomiting, constipation and its variable effectiveness
avoid mixing routes of administration of opiates
for short periods of analgesia such as for joint reductions:
fentanyl iv is the preferred opiate due to its short duration of action
for most other pain conditions warranting parenteral opiates:
morphine iv is the preferred opiate in the ED - usually in 2.5mg titrated doses for adults.
pethidine:
pethidine is no longer regarded as having a significant role in the management of ED patients, and thus, many ED's have decided to stop using it because of its tendency for substance abuse and that there are more effective options.
repeated doses of pethidine runs the risk of accumulation of its metabolite causing seizures.
indications for pethidine are very limited and usually restricted to:
maternity
oncology
palliative care
true type I hypersensitivity reactions to opiates (but anaphylaxis to opiates is actually quite rare)
certain rare conditions such as systemic mastocytosis which is associated with true anaphylaxis to NM blockers and opiates.
chronic pain patients should be considered for referral to a chronic pain service
patients requesting pethidine should be considered for referral to an addiction medicine specialist.
pharmacology
opiates act upon various opioid receptors
action via mu receptors:
generally acts to inhibit inhibitory neurons thereby resulting in disinhibition of release of dopamine from dopaminergic neurons
discovered in 2024, mu opioid receptors are also abundant on cells in the dorsal peduncular nucleus and these neurons project to a part of the brain that drives aversive feelings 2)
in this case opioids inhibit these neurons which results in inhibition of aversive feelings which leads to reward – a process called negative reinforcement.
this contributes to the pleasurable and addictive qualities of opioids
this brain region seems to be not only involved in the rewarding properties of opioids but also the aversive aspects of opioid withdrawal