Well, there have been several different opinions and I will tell you what I do according to the literature.
IMIV to PO dose is 1:3
20mg IM Q4hrs = 120mg/day
Converted to PO 120x 3 = 360 mg/day
Given in BID dosing it = 180 mg
Decrease the dose by 25% over 24 hrs = 270mg /day
New dose is 135mg BID. The closest anwer is 120 mg BID.
I go with C.
If you reduce it by 33% over 24 hrs = 241mg/day
Now the dose is 120mg BID.
The answer is C
In our insitution we usually decrease the dose by 33% d/t the lack of cross tolerance,
So how do you figure it out?
Always Round Down When Doing Dosage Conversions
1. Calculate total 24h dose of current opioid.
2. Convert 24h dose to new 24h dose using equi-analgesic dosing table.
3. Decrease the converted equi-analgesic dose by proper percentage for the type of drug (e.g. 25-50% for most opioids, 75-90% for methadone).
4. Determine the administration interval of the new drug
Two articles that review equianalgesic calculations are useful to keep on hand for reference. They are:
1. Gordon DB, Stevenson KK, et al. Opioid equianalgesic calculations. J Pall med 1999;2(2): 209-218.
2. Gammaitoni AR, Fine P, et al. Clinical application of opioid equianalgesic
data. Clin J Pain 2003;19:286-297.
I hope this helps???