For high extraction drugs this could alter the overall elimination of the drug. The liver is the major organ involved in metabolism and as shown in the table, liver blood flow and liver mass tend to decrease with age. Protein binding also is reduced, especially to albumin, as mentioned in the previous section. The third determinant of drug metabolism, intrinsic clearance is quite variable and dependent on the metabolic pathway. Acetylation appears to be unchanged with age, isoniazid clearance is not altered.
Examples are lidocaine, phenytoin, propranolol, theophylline.
Serum creatinine is also decreased with age because of the reduced muscle mass. However, the formulas presented earlier in the section on renal disease can be used to calculate creatinine clearance as a function of age and thus make dosage regimen adjustments. An illustration of the type of change in pharmacokinetics with age is shown in the following table. 0.6 Dosing recommendations The effects of age on drug disposition depend on the particular compound in question and the characteristics of the population being studied. Some of the changes ascribed to the elderly may be due to immobility of the patient or an underlying disease or diseases.