Specimen collection:
(1) Saliva flow may be stimulated by chewing on a semi-solid material or by spraying citric acid onto the tongue.
(2) Subjects may be asked to spit into glass vials, or parotid outflow can be captured using a variety of methods.
Estimated Plasma Level
estimated plasma drug level in µg/mL =
= (saliva drug level in µg/mL) / (ratio of saliva-to-plasma concentration)
Equation for Acidic Drugs
ratio of the saliva-to-plasma concentration =
= (1 + 10^((pH of saliva) - pKa)) / (1 + 10^((pH of plasma) - pKa)) * (fraction of unbound drug in plasma) / (fraction of unbound drug in saliva)
Equation for Basic Drugs
ratio of the saliva-to-plasma concentration =
= (1 + 10^(pKa - (pH of saliva))) / (1 + 10^(pKa - (pH of plasma))) * (fraction of unbound drug in plasma) / (fraction of unbound drug in saliva)
Limitations:
• Not all drugs are suitable for monitoring by use of salivary drug levels. This includes digoxin and theophylline.
