Complex sentence: Clonazepam has been found to be effective in the acute control of non-convulsive status epilepticus; however, the benefits tended to be transient in many of the patients, and the addition of phenytoin for lasting control was required in these patients.
Split into simpler sentences: Clonazepam has been found to be effective in the acute control of nonconvulsive status epilepticus. However, the benefits tended to be transient in many of the patients, and the addition of phenytoin for lasting control was required in these patients.