The pharmacokinetics change occurring in geriatric patients is a decline in:

In old age, liver metabolism of drugs and renal excretion both are decreased but the best option is always decreased renal clearance when we have to choose one best option. GFR decreases with age- one of the reasons for the decreased clearance of drugs. Clearance of drugs that are primarily excreted unchanged (aminoglycosides, digoxin, phenobarbitone) is reduced parallel to a decrease in creatinine clearance (CLcr). A loading dose of such a drug is not altered (unless edema is present), but maintenance doses should be reduced or dose interval prolonged propoionately. Ref; KD Tripathi pharmacology 7th edition (page no; 68)