Chapter 16

Routes of Excretion

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Salivary Excretion

Saliva volume is typically one to two liters per day with flow rates ranging from 0.5 ml/min to more than 10 times that in the presence or thought of food. Saliva pH commonly ranges between 7.4 and 6.2 although lower values are possible. Saliva also contains a number of enzymes including amylase, ptylin, lipase, and esterases.

Salivary excretion is not really a method of drug excretion as the drug will usually be swallowed and reabsorbed, thus a form of 'salivary recycling'. Drug excretion into saliva appears to be dependent on pH partition and protein binding. In many cases salivary concentration represents the free drug concentration in plasma. This mechanism appears attractive in terms of drug monitoring, that is determining drug concentration to assist in drug dosage adjustment. For some drugs, the saliva/free plasma ratio is fairly constant. Therefore drug concentrations in saliva could be a good indication of drug concentration in plasma. For some drugs localized side effects maybe due to salivary excretion of the drug. Pharmacokinetic studies in special populations may be more feasible using saliva concentrations.


References

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