- What is the difference between the PC20 and the PD20 for a substance?
The PC20 is the concentration of the agonist in the inhaled aerosol leading to a fall in FEV1 of 20%.
The PD20 is the administered dose of a substance in the inhaled aerosol which causes the FEV1 to fall by 20%. Weighing the nebulizer before and after nebulization allows measurement of the amount of solution nebulized. Using the known concentration of the substance in the solution, the dose (amount) of agonist administered can be computed.