What Causes Breathlessness After Started Taking Myrbetriq?

My husband took myrbetriq last night for the first time. Today when he stands he has difficulty breathing...shortness of breath every time he stands. His blood pressure has been around 89 over 58 consistently since 4 o clock pm until now 7 o clock pm. He is 64 old and takes blood pressure meds for high blood pressure. He is 6 2 and weighs 245. Should we be concerned?