There is a qualifier when talking about potency and equivalency- the '50x' or '10x' etc stronger statements are talking about the amount of drug (weight) to gain analgesia (pain relief) compared to another opioid, by weight.
Also, these charts are made regarding a
SINGLE DOSE equivalency. Meaning, in an average opioid naive person with no other opioids in their system, x-mg of Opioid 1 is equal to y-mg of Opioid 2.
There are differences between charts, some charts use oral doses or IV, IM, SC, etc doses, some use extended release or instant release versions of the drugs, etc.
Orally, 10mg Morphine is generally the standard by which other drugs are judged.
If you understand all of the naunces of the chart(s) your're looking at (whether they are talking about XR drugs, oral or other routes of administration, about particular patient groups like the elderly, etc), you also then need to consider that the doses for analgesia or equal analgesia have nothing to do with 'how it feels' or how much of x-opioid do I need to take to equal y-mg of opioid z?
Example:
Dose Conversion—Step 1
The first step in conversion to methadone therapy is to determine the daily oral morphine equivalent dose of the current opioids. The latter may include long-acting medications as well as short-acting medications used for breakthrough pain. The daily dosage of each opioid is multiplied by the ratio of equianalgesic doses, using morphine in the numerator and the current opioid in the denominator (Table 2).18 These are summed, and the result is the daily oral morphine equivalent dose. If the current route of administration is not oral, the additional step of converting this route to the oral-equivalent dose is required. These conversion ratios usually are found in the package inserts of the associated products or on the manufacturers’ Web sites. Figure 1 shows a sample calculation of the daily oral morphine equivalent dose from oxycodone (Oxycontin) and hydromorphone (Dilaudid).
http://www.aafp.org/afp/2005/0401/p1353.html
Fentanyl is very potent by weight, and is available in highly concentrated, potent forms by prescription (dura and duro gesic patches, Actiq pops).
Given its characteristics, and the high doses that are available, it has gained a nasty reputation for opioid overdoses and deaths. Similar to Methadone in that regard.
By weight, Fentanyl is dozens of times more potent than Morphine, depending on the route of administration it could be more times or less times as potent (every drug has a different bio-availability based on the route of administration).
Oral is not a preferred route of administration for Fentanyl. It is far more effective buccally (as the Actiq is meant to be taken) or transdermally (as Duro and Dura gesic patches are meant to be used). Similar to Buprenorphine- swallowing it will not produce anywhere near the effects had the same dose been taken sublingually. Fentanyl will be more efficient and kick in faster if used buccally father than by swallowing it.
In either case, 0.12mg Fentanyl is a high dose.
Fentanyl is approximately 100 times more potent than morphine,[6] with 100 micrograms of Fentanyl approximately equivalent to 10 mg of morphine and 75 mg of pethidine (meperidine) in analgesic activity
http://en.wikipedia.org/wiki/Fentora
Bio-availibility:
92% (transdermal)
50% (buccal)
33% (ingestion)
Eating half an Actiq: reckless.
