Monday, February 19, 2007

Patients' understanding of risk; Hydromorphone a morphine metabolite; More confusion on assisted death (or not); Opioid conversions review

Thanks to all of you who said Hi at AAHPM and came to the happy hour. It was a good few days, although I'm ecstatic to be home with my boy. In the interim many articles have been piling up and here they are... (JCO has published a spate of interesting articles in the last 2 weeks and I'll try to get to them by the end of the week.)

Annals of Internal Medicine has a study examining the effects of an educational intervention to patients to help them understand medical risk. Patients were given a booklet/primer explaining medical risk. Basically they found it was helpful and higher socioeconomic status patients did better than lower socioeconomic status patients. Unfortunately you can't actually access the primer online and so you tell if it would be helpful for a palliative care population (one assumes it'll be made commercially available at some point). It's an interesting idea and certainly understanding risk is important for decision making for, say, chemotherapy for advanced cancer.

Medscape is reporting that hydromorphone is a minor metabolite of morphine and can be positive in urine drug tests for people taking morphine only (not hydromorphone). The story is from a presentation from the recent AAPM meeting and cannot be otherwise vetted. (Medscape articles are available for free if you sign-up).

BMJ has a news story about a woman in the UK seeking permission from a court to get enough morphine to relieve her pain which, apparently, will kill her. She's a 30 year old woman with end stage Eisenmenger's syndrome (ineligible for heart-lung transplant) and chronic pain. It's unclear from the article, because it's probably unclear to many involved, whether the woman is asking for terminal sedation (with morphine as the primary agent god help us), or for some sort of assisted death like euthanasia. Or, is she asking for simple pain relief and it just happens that she, apparently, only responds to morphine but unfortunately the amount she would need would, in the estimation of her physician, kill her (sound unlikely? I agree). This last scenario seems to be being invoked by the patient herself although what seems to be being talked about is a terminal sedation scenario. Anyway it's another example of coverage of end of life issues that abut hastened death that is confusing.

Annals of Pharmacotherapy has published a review looking at opioid conversions (both PO to IV and between different agents). It's one of the better pieces I've read on the subject and I'd highly recommend it for the teaching file. It is relatively concise, discusses the difficulties of defining rigid conversion ratios, and argues for different ratios depending on which direction you're going ( e.g. morphine to hydromorphone using 3.7:1 vs. hydromorphone to morphine of 1:5). One caveat stems from this paragraph about fentanyl and morphine:

A potential error that is especially dangerous with fentanyl can occur when a conservative ratio for conversion in one direction is reversed, resulting in a liberal conversion in the opposite direction. For example, converting 100 μg of fentanyl to 1 mg of morphine, using a conservative ratio of 100:1, is substantially different from converting 1 mg of morphine to 100 μg of fentanyl.

By my math 100mcg of fentanyl = 0.1mg of fentanyl & by using a 100:1 ratio that would be 10mg of morphine. 1mg of morphine divided by 100 is 0.01mg = 10mcg fentanyl. So
A) I'm not really sure what their point is, and
B) The fact that they made this error in an article about opioid conversions is disquieting. If I'm wrong here, feel free to comment and publicly humiliate me.

Back to their point though--being conservative with these ratios, especially with those we know the least about, is of course prudent, provided the patient has access to sufficient ad lib meds or attentive dose titration, but I'm not sure specifically what their point is here about fentanyl.

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