Expert: Dr Alan Galbraith - 6/18/2006

Question
I am a cancer patient, living in the U.S. I have been prescribed Morphine to control diarreah which in my case will be long term.  My problem and question:  The pharmacy that fills my medication carries 2 different morphine tablets, listed as:
a.) Morphine 30 mg SR TAB and
b.) Morphine 30 mg ER TAB

Although the pharmacist swears there is no difference, I have noted over a 3 year period that when given the "SR TAB" that I am able to maintain control over my bowels but when given the "ER TAB" that it does nothing to constipate me thus giving me no control and very often causing humilating experiences.  Is there a difference between the "SR TAB" and the "ER TAB"?
Has the "ER" tablet been treated somehow to prevent the constipation normally associated with morphine? I apologize for the lengthy question.

Steve C.

Answer
Dear Steve

Your pharmacist is wrong, even though theoretically there should be no difference in practice there often is, SR means slow release and ER means extended release. A slight knowledge of the English language sugests that there should be no difference. However, a very common problem amonst drugs manufactured by different processes causes differences in the way that they are broken down in the gut and the resultant absorption. The ER tablet has not been treated in any way to prevent constipation. Morphine usually always `causes constipation but when it is absorbed it does not last long in the bloodstream, so slower absorption causes more sustained action in the body. You may find in someone else with similar problems to you is better on the ER tablets as it not be just the formulation but also differences in the bowels which causes differences in action. I would tell your pharmacist that you only want the SR tablets. You could also tell her/him to read up on basic pharmaceutics, drug dissolution, the effect of different excipients etc but this would be cheeky. Just ask for the prescription to be made out for the SR tablets and if the USA is like Australia the pharmacist must comply unless the doctor or patient agrees to being dispensed a different form.

I wish you well
Regards

Dr Alan Galbraith