A 1,5 y.o. child fell seriously ill: chill, body temperature rise up to 40,1°C, then rapid dropping to 36, 2°C, skin is covered with voluminous hemorrhagic rash and purple cyanotic spots. Extremities are cold, face features are sharpened. Diagnosis: meningococcosis, fulminant form, infection-toxic shock. What antibiotic must be used at the pre-admission stage?