Age is an important variable in the drug therapy due to the

1.normal physiologicial changes of aging that can alter pharmacokinetics and pharmacodynamics.

It is assumed that there is usually is a gradual decline in renal function in most individuals.

Serum creatinine is usually used to assess the level of renal function: Serum Creatinine Renal function formulas

Depending on the degree of decrease in renal function, dosage of a drug may need to be adjusted or a different drug given, e,g, one excreted by another route such as via the liver.

2. Presence of multiple chronic conditions and/or multiple medications.

3. Changes affecting the ability to adhere to a drug regimen such as difficulty with vision for reading instructions and labels on medications, decline in hearing ability affectinghearing instruction, difficulty in administering medications because of memory problems, psychomotor difficulties, or econominc problems( eg. inabiltiy to pay for medications prescribed and/or difficulty in filling a prescription due to lack of mobility or access to transportation to a pharmacy).