Any substance that causes disturbance to organisms by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by the organism.
An EC 3.6.3.* (acid anhydride hydrolase catalysing transmembrane movement of substances) inhibitor that interferes with the action of Na+/K+-transporting ATPase (EC 3.6.3.9).
Any member of a group of drugs that reversibly inhibit the propagation of signals along nerves. Wide variations in potency, stability, toxicity, water-solubility and duration of action determine the route used for administration, e.g. topical, intravenous, epidural or spinal block.