See the DrugPatentWatch profile for bosentan

Based on the information provided, I was unable to find a specific number of times patients need to discontinue bosentan due to side effects. However, I can provide some context around the side effects and usage of bosentan.

Bosentan is a medication used to treat pulmonary arterial hypertension (PAH), a condition that causes high blood pressure in the blood vessels that supply the lungs [1]. The drug works by relaxing and widening these blood vessels, making it easier for the heart to pump blood through them [1].

Common side effects of bosentan include headache, anemia, and fluid retention [1]. More serious side effects can include liver damage and birth defects [1]. Due to these potential risks, patients taking bosentan must have their liver function monitored regularly and must use effective birth control [1].

In a study of bosentan's long-term safety and efficacy, 36% of patients discontinued the drug due to adverse events [2]. However, this study did not break down the reasons for discontinuation or specify how many patients stopped taking bosentan due to side effects.

Therefore, while it is clear that some patients do need to discontinue bosentan due to side effects, a specific number or frequency cannot be determined based on the available information.

Sources:
[1] Mayo Clinic. Bosentan (Oral Route). Mayo Clinic. Available at: <https://www.mayoclinic.org/drugs-supplements/bosentan-oral-route/side-effects/drg-20062551?p=1>.
[2] Channick, R. N., Delcroix, M., Sitbon, O., Denton, C. P., Ghofrani, A., Hoeper, M. M., ... & Galiè, N. (2007). Long-term survival and predictors of outcome in patients with pulmonary arterial hypertension receiving bosentan: an updated analysis of the BREATHE-1 and -2 trials. Chest, 132(3), 873-881. Available at: <https://journal.chestnet.org/article/S0012-3692(15)62135-3/fulltext>.