I'm a nursing student in my maternal child rotation. In one of my lectures, we learned that Brethine is to be avoided in pt.s with preterm labor AND asthma. I don't understand the rationale for this. Brethine is given to pregnant women with asthma for acute attacks, and it is used to stop contractions in preterm labor. I don't understand why it is avoided in patients with both: asthma and in preterm labor? Can someone explain the rationale for this to me?