Hi Tom, There are charts out there called equianelgesic conversion charts that some docs use as a reference. However the charts are just ballpark guides. You may end up in the parking lot or in the obstructed veiw seats.
Some factor in a cross tolerance percentage or allow a doc to do this, meaning because it's a new med, hopefull you will respond better so less can be used, a med can always be adjusted but I understand your concern going from a relatively low dose of Morphine to the strngest patch. Although the 100ugh patch is the largets they make I have met folks that wear 4-9 at a time plus use other long acting meds. It simply takes what it takes.
Tee best chart on the net I had seen doesn't seem to be available right now but there is other infor out there. Some docs may use the PDR some may use palm pilots with programs for conversion and some may use their experience or the Brietbart method.
If this is a PM doc that made the conversion, I wouldn't be too concerned. If it's your GP doing this it would have me a little concerned because it is a med GP's don't noramlly use, not that the dose is outragous when you factor in and look at everything.
However we all respond differently to different meds. Fentanyl wasn't effctive for me, so I could use lots of 100ugh patches and achieve sedation before I got pain relief that I could still function with.
I did do some checking and it's really not that out of line based on the PDR and other guidelines. If you factor in your BT med use, add another 45 mgs of morphine based on 30mg of oxy used daily. I'm using a pretty standard 1:1.5 conversion from oxy to morphine. This brings your daily morphine dose up to 135 mgs a day.
You also have to consider that when you take 20 mgs of oxycodone in a single dose at night this significantly increases your serum level and effect of opiates. Proportionally that's a huge dose of BT meds when it increases your serum level 6 fold rather than 20-30% that most docs use for BT. If you can manage the respirtory supression of taking the additional 20 mgs of oxy for 4 hours at night, you can safely manage it throughout the entire day.
If you were to take 20 mgs of oxy every 4 hours that would be an additional 120 mgs of oxy per day or 180 mgs of morphine. If you converted all the oxy we already know you can tolerate, to Avinza and add it t the 90 you already take, This would bring your dose to 270 mgs of Avinza a day and sustain roughly what you feel after taking your BT meds at night. You have that same level during those 4 hours and it hasn't hurt you yet, so why would it hurt you if you had that same level constantly. The only unknown is the cross tolerance variable. I may take very little Fentntyl compared to morphine or Fent may not be effective and youmay have t take twice what some cahart says, it's all just part of the fun of trying new drugs.
That totally changes the picture, You know what you can tolerate in avainza plus BT meds, This means your tolerance is much higher than what 90 mgs of Avinza actually sustains in your sytem if you can safely take 20 mgs of oxy on top of the Avinza. Wait and see how things go before using any more BT meds just to be safe.
The Brietbart method suggests Converting every 2 mgs of oral morphine per day to 1ug of Fentanyl, THis means the combined 270 mgs of morphine per day you know you can already tolerate, equates to 135 ugh of fentanyl or a dose between 125ugh-150ugh.
Patches take about 17 hours to reach peak effect, Ideally you should have someone there when this happens, your spouse, a friend, family member, anyone, should you find you have difficulty breathing or experience other side effects.
Based on your abilty to tolerate the oxy on top of the avinza, most likely you will feel closer to how you feel after taking the 20mgs of oxy at night all the time. IF this is a dose to simply allow you to sleep, you may have to cut back to prevent the meds from causing more impirment then your condition. IF the meds just make you sleep all day, that's not productive and most docs, and family member won't go for it, and you would get tired of sleeping your life away after a ferw months too. The goal is to shoot for improved function, not total pain relief. If your unable to work, even the higest doses of opiates may not allow that. I hav a ump and when you compare pump strengthto oral strength myd dose would probably sound astounding. BUt at best it allows me to function around the house, It takes 8 hours to knock out 2 hours of houswork, But I get it done in little pieces resting when my legs start to shake.
Another reason I say it doesn't sound outragous aside from charts is that the dose your on now isn't working. When the dose isn't working, you can handle a much greater increase than you would make compared to when you're simply fine tuning a dose for max effect with minmal side effects. You can safely double most doses of medication other than methadone that continues to build up for 5 days. It honestly sounds like they are trying to give you much better relief throughout the entire day, and the only thing preventing them from increasing the dose is if your still not getting relief are the side effects.
If it' makes you too drowsy, or causes Urinary retention or any other unpleaseant side effect. But just because 100ugh is the largest patch it definitely doesn't mean that's the highest dose anyone should ever use. Even in clinical trials they tested hundreds of micrograms per hour.
Here is some info on converting to fentanyl, including the PDR method.
[url]http://www.eperc.mcw.***/FastFactPDF/Concept%20002.pdf[/url]
Convert the oral morphine dose to Duragesic-there are two methods:
A. Standard Table: look up fentanyl transdermal in the PDR, find the morphine conversion table, it says that 135-
224 mg of morphine = 50 mcg patch. Note: this range of morphine is very broad which may result in significant
under dosing.
B. Alternate Formula: In 2000, Brietbart et al published an alternative method, based on the results of a multi-center
trial by Donner et al, that relied on a fixed dose conversion ratio to calculate the fentanyl transdermal dose.
Brietbart recommended the ratio of:
2 mg oral morphine = 1 ug of fentanyl transdermal—rounded to the nearest patch size. In the case example above,
216 mg of oral morphine is approximately equianalgesic to 100 ug fentanyl transdermal.
Note: using this formula, 25 ug fentanyl transdermal is roughly equivalent to 50 mg oral morphine/24 hours. This
dose may be excessive when used in an opioid naïve patient and/or the elderly.
Key Considerations
1. All equianalgesic ratios/formulas are approximations; clinical judgment is needed when making dose or drug conversions.
2. The risk of sedation/respiratory depression with fentanyl transdermal is probably increased in the elderly or patients with
renal impairment due to its long half-life, thus, choose the lower end of the dosing spectrum.
3. When in doubt, go low and slow, using prn breakthrough doses generously while finding the optimal dose.
I hope things work out and this brings you more relief but anytime you start a new med, docs should be prepared to see you more often, If your still miserable after 2 or 3 cycles, let him know. If it's simply too sedating in the day time, you need to let them know about that too.
Take care, Dave
I haven't slept in a bed for 10 years. I have a recliner.
