This is a hard question to answer. Generally dasatinib is well tolerated. In the first few weeks, some patients may have headaches or vague abdominal discomfort but this usually resolves. Long term, as is well known, you need to watch out for the pleural effusions or very very rarely the pulmonary arterial hypertension that has been associated with the use. Obviously no two patients are the same and there may be some issues that one patient may have that are not common. As you point out, you need to distinguish between a dasatinib side effect and something else. Rather than reduce the dose, I would be tempted to hold drug for a week or so and see if the symptoms improve. It should not take much longer than this to determine where you stand and then you can decide about rechallenging and whether at full dose or a slightly reduced dose initially, planning to increase the dose in the near future.
Despite how good TKI therapy, some patients just cannot cope with the diagnosis and thought of perhaps lifelong therapy. Given that in the case of both imatinib and dasatinib, there were GI side effects here, I would consider gastroscopy to rule out some upper GI pathology. Also keep in mind, not uncommonly, our patients are or get depressed and that may require intervention.

I was hoping for some advice about a patient of mine with CML. He was diagnosed about 10 months ago in chronic phase and was commenced on imatinib. He didn’t tolerate this very well, mainly having symptoms of nausea so we switched him to dasatinib. He is feeling better than he did when he was on imatinib but is still not feeling great. He has very non-specific symptoms of lethargy, hip aches, nausea and indigestion, his mood is also a bit low which I am sure is not helping but I was wondering what your experience was of patients on dasatinib and how well it is tolerated? Is it likely all these symptoms are drug-related?
He is having a very good response to treatment, his most recent BCR/ABL was down to 0.383 down from 234.000 at diagnosis, but I do not think we should be reducing the dose of dasatinib at this stage which was his suggestion.

Any advice gratefully received.
Regards
Emma-Jane