I am currently doing a pain management and palliative care rotation and I have been learning so much! Hence I thought I would share some important points on opioids with you all.
Morphine
A pure opioid that is also the standard for comparison to other opioid medications. It comes in many different formulations such as extended release (Ms Contin), immediate release, solutions, injectable and more. It is metabolized in the liver to form 2 active metabolites morphine-6-glucuronide (M6G) and morphine-3-glucuronide (M3G). It is believed that M6G has analgesic effects while M3G does not, but it does however have neuro-excitatory effects that could be toxic with accumulation in renal insufficiency.
Fentanyl
Is a synthetic opioid that is available in a patch formulation and also injectable form. It is beneficial in those who may not be able to take anything by mouth and who tend to experience itching from other opioids. It is also beneficial in those who have renal impairment since it has no active metabolites.
Methadone
This is a very effective and relatively inexpensive opioid commonly used in palliative care settings. It has a very long half-life and because of this, when switching to it from another opioid the equianalgesic dose should be reduced. It does pose a risk of QT-prolongation which should be kept in mind when looking at a patient profile.
Codeine
Always remember that codeine by itself does not produce an analgesic effect, only its metabolite does which is morphine. Codeine metabolizes to morphine through a CYP2D6 enzyme, however this enzyme is polymorphic and if someone is an ultra-rapid metabolizer of CYP2D6, codeine could be very dangerous for them. On the contrary if someone is a poor metabolizer codeine will not help control their pain.
Tramadol and Tapentadol
These two opioids have mixed mechanism of actions, not only are they partial agonists at opioid receptors they also help increase amounts of serotonin and norepinephrine to help control pain. One must remember that because they increase serotonin amounts you should monitor for signs of serotonin syndrome. Also tramadol can potentially lower the seizure threshold and cause seizures in certain patients.
Oxycodone and Hydrocodone
Both of these opioids are metabolized primarily by CYP3A4 enzymes in the liver to from active metabolites which are also used as opioids. For instance, oxycodone can form oxymorphone and hydrocodone can form hydromorphone. Also because these are metabolized by CYP enzymes one must be weary of drug interactions with CYP inhibitors and inducers.
Oxymorphone and hydromorphone
These two opioids are a result of the metabolism of oxycodone and hydrocodone. They are perfect in avoiding drug interactions and those who have renal impairment.
Always remember when it comes to opioids there is a risk of addiction and people on opioids must remember to be careful with taking alcohol and benzodiazepines (such as Xanax) because of the risk of slowed down breathing.
Opioids are great for pain but remember they are not the only medications for pain they generally should be utilized for more moderate to severe pain that is uncontrolled with NSAIDS and acetaminophen.
–Ms Rx Geek
Kgrant