Based on morphine milligram equivalents (MME), order the following opioids from the least potent to the most potent: 

A. Oxycontin 

B. Dilaudid 

C. Codeine  

D. Duragesic 

E. Norco 

Answer with Rationale: 

The correct answer from least to most potent is CEABD. 

If you were not expecting this as a question type, I recommend you review the 5 different types of questions possible on the NAPLEX. This one is termed "ordered-response". The different question types with examples can be found here: https://nabp.pharmacy/wp-content/uploads/2020/07/NAPLEX-Sample-Questions.pdf. 

Opioid analgesics remain a common medication to alleviate acute and chronic pain. Opioids, specifically the full agonists, work primarily through the mu receptor leading to suppression of the pain response in the CNS. Opioids have different potencies due to a variety of factors such as affinity to mu receptor and its pharmacokinetics. The higher the dose required in mg, the less the potency and vice versa. That is why a drug like fentanyl since listed in mcg is extremely potent and reserved for non-opioid naive patients. It is important to note that a higher potency agent does not mean it is more effective, it just takes less of a dose to produce the same effect. 

Due to the variability in potency between opioids and risk of overdose and death with dose conversions, the CDC has created a Morphine Milligram Equivalents (MME) chart using morphine 1mg as a base to determine morphine milligram equivalents. Below are some samples from this resource with some trade names added but the full resource can be found here: https://www.cdc.gov/drugoverdose/pdf/calculating_total_daily_dose-a.pdf. You determine the total daily amount of opioid, convert each to MMEs, and add them together. This is not recommended solely to determine dosages required for converting from one opioid to another. Considerations for incomplete cross-tolerance and pharmacokinetic differences should also be assessed before making a final dose estimation. In the above question, Norco contains hydrocodone and acetaminophen so you would use the hydrocodone conversion factor to assess potency.