Final answer:
Magnesium sulfate is a contraindication for tocolytic therapy specifically in patients with myasthenia gravis due to its potential to exacerbate muscle weakness.
Step-by-step explanation:
The contraindication for tocolytic therapy in a patient with myasthenia gravis is magnesium sulfate. Myasthenia gravis is a neuromuscular disorder characterized by weakness and fatigue of the voluntary muscles. It is caused by an error in the transmission of nerve impulses to muscles. Magnesium sulfate is known to exacerbate muscle weakness in individuals with myasthenia gravis and should be avoided as it may worsen their condition.