A 26-year-old pregnant woman was hospitalized into the intensive care unit at 36 weeks of her pregnancy with complaints of an intense headache in the frontal region: Physical examination detected the following: blood pressure-170/90 mm Hg, pulse 85 /min., respiratory rate-15 /min., body temperature-36.9° C, edema of the limbs, fetal heart rate-159 /min. During the examination, the woman developed an attack of generalized tonic-clonic seizures. What drug must be administered first in this case?