A method for administering a drug to a patient comprises coupling a valve system to the patient's airway. The valve system is configured to prevent or impede respiratory gases from flowing into the lungs for at least some time such that the intrathoracic pressure is less than atmospheric pressure. A drug is introduced into the patient, and the intrathoracic pressure is lowered using the valve system to cause blood to flow into the thorax and thereby increasing vital organ perfusion to enhance the circulation of the drug.