N-of-1 Trial for Statin-Related Myalgia: Consider Conducting These Studies in Your Practice

The March 4th edition of the Annals of Internal Medicine contains an article by Joy and colleagues in which they conducted an N-of-1 trial in patients who had previously not tolerated statins. This is important because patients often complain that they cannot tolerate statins despite needing them.  I have wondered how much of this was a self-fulfilling prophecy because they hear a lot about this from friends and various media outlets. A N-of-1 trial is a great way to determine if the statin-related symptoms are real or imagined.

First, lets discuss N-of-1 trials. What is a N-of-1 trial? It’s a RCT of active treatment vs. placebo in an individual patient. The patient serves as his or her own control thus perfectly controlling for a variety of biases. When is a N-of-1 trail most useful? This design is not useful for self-limited illnesses, acute or rapidly evolving illnesses, surgical procedures or prevention of irreversible outcomes (like stroke or MI). It’s most useful for conditions that are chronic and for with therapy is prolonged. It’s best if the effect you are looking for occurs fairly quickly and goes away quickly when treatment is stopped. These trials are a good way to determine the optimal dose of a medication  for a patient. They are also good to determine if an adverse effect is truly due to a medication. Finally, they are good way to test a treatment’s effect when the clinician feels it will be useless but the patient insists on taking it. How is a N-of-1 trial conducted? Get informed consent from the patient and make sure they understand that a placebo will be part of the study. Next the patient randomly undergoes pairs of treatment periods in which one period of each pair applies to the active treatment and one to placebo. A pharmacist will need to be involved to compound the placebo and to develop the randomization scheme (so as to keep clinician and patient blinded). Pairs of treatment periods are replicated a minimum of 3 periods. There needs to be a washout period between moving from active to placebo and vice versa. The length of the treatment period needs to be long enough for the outcome of interest to occur. Use the rule of 3s here (if an event occurs on average once every x days, then observe 3x days to be 95% confident of observing at least 1 event). What outcome should be measured? Most commonly these types of trials will be conducted to determine the effect of an intervention on quality of life type measures (eg pain, fatigue, etc).  Ask the patient what is the most troubling symptom or problem they have experienced and measure that as your outcome. Have the patient keep a diary or ask them to rate their symptoms on some meaningful scale at certain follow-up intervals. Do this while on active and placebo treatments. You will have to determine how much of a difference is clinically meaningful.  How do I interpret N-of-1 trial data? This can be a little difficult for non-statistically oriented clinicians. You could do the eyeball test and just see if there are important trends in the data. More rigorously you could calculate the differences in means scores of the placebo and active treatment periods. These would then be compared using a t test (freely available on the internet).

Back to Joy and colleagues N-of-1 trial on statins. They enrolled patients with prior statin-related myalgias. Participants were randomly assigned to get the same statin and dose that they previously didn’t tolerate or placebo. They remained on “treatment” for 3 week periods with 3 week washout periods in between. Patients weekly rated their symptoms on visual analogue scales for myalgias and specific symptoms (0-100, with 0 being no symptoms and 100 being the worst symptoms). It was felt a difference of 13 was clinically significant. What did they find? There were no statistically or clinically significant differences between statins and placebo in the myalgia score (4.37) nor on the symptom specific score (3.89). The neat thing the authors did was to determine if patients resumed taking statins after reviewing the results of their N-of-1 trial and 5 of the 8 patients resumed statins (one didn’t because a statin was no longer indicated).

So are statin related myalgias mostly in our patients’ heads? Maybe. This study is by no means definitive because it only enrolled 8 patients but it at least suggests a methodology you can use to truly test if a patient’s symptoms are statin related or not. This is important to consider because the most recent lipid treatment guidelines focus on using statins only and not substituting other agents like ezetimibe or cholestyramine. So give this methodology a try. You and your patients will likely be amazed at what you find.

One thought on “N-of-1 Trial for Statin-Related Myalgia: Consider Conducting These Studies in Your Practice

  1. You really make it seem so easy with your presentation but I find this matter to be actually
    something that I think I would never understand.
    It seems too complex and extremely broad for me. I’m looking forward for your next post, I’ll try to get the hang of it!

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