THIS project was undertaken to find if water given by mouth has a pharmacological expectorant action in the sense that it is able to augment the output of demulcent respiratory tract fluid. Respiratory tract fluid is a secretion rich in soluble and insoluble mucus which can be collected through a cannula ligated into the trachea of an animal under certain conditions.1 An agent capable of increasing the output of this fluid may be said to have pharmacological expectorant activity.2 Therapeutic expectorant activity is present if the agent has the same properties at the dosage range and conditions of therapeutic use.
Relatively few drugs reputed to be expectorants have been found to have pharmacological expectorant activity at doses near the range recommended in human therapy.2 This may be due in part to the fact that pharmacological expectorant activity has been found recently to vary with season.3
Boyd EM, Boyd CE. Expectorant Activity of Water in Acute Asthma Attacks. Am J Dis Child. 1968;116(4):397-399. doi:10.1001/archpedi.1968.02100020401008