Dose conversion of opioid

 

It is recommended that all opiates should be converted into the equivalent morphine dose prior to conducting any dose conversion. Below is a table showing conversion of oral morphine to other opiates and vice versa

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

For example: to convert subcutaneous morphine (i.e 15mg)  to oral morphine requires multiplying by a factor of 2, this suggests a dose of 30mg of oral morphine to be administered.

 

Fentanyl patches:

• Conversion from oral morphine (mg) to fentanyl patch (mcg/hour) ; divide morphine dose by a factor of  3 if the morphine dose is less than 250mg daily.

• If the dose of morphine is higher than 250mg then divide by a factor of 3.6 to derive fentanyl  (mcg/hour)

To calculate morphine dose from fentanyl patch :

• Multiply by 3 (fentanyl) if the fentanyl patch is below 75mcg/hour

• Mutiply by 3.6 if the fentanyl patch is 75mcg/hour or more

 

 

Buprenorphine patches;

• Patients on weak opiates such as codeine, co-codamol and dihydrocodeine should start on 5mcg/hour (Butrans) for 7 days. In moderate to high doses of weak opiates, consider prescribing 10mcg/hour every 7 days, with dose titrated every 3 days.

• Once titration dose reaches 20mcg/hour, patients should be switched to transtec 35mcg/hour applied every 4 days.

• Patients who are taking stronger opiates i.e morphine may use the conversion ratio in the table (dividing by 2.3) to derive the buprenorphine patch strength (mcg/hour).

However, patients on less than 120mg of morphine should normally be started on Transtec 35mcg/hour applied every 4 days. If dose of morphine is over 120mg then patients should start on transtec  52.5mcg/hour patch (applied every 4 days).