Drug Response With Advancing Age

Aging, Effects on Drug Metabolism and Drug Response – Many drugs have different therapeutic effects as well as potential adverse drug reactions, depending on a person’s age.

The very young and the very old often have limited liver function, which affects the ways in which the liver metabolizes drugs, resulting in lower thresholds for toxicity and unpredictable therapeutic effects. In the infant and young child, the liver has not yet fully developed and lacks the structural capacity to metabolize certain substances.

The elderly may lose liver function due to cirrhosis, fatty deposits accumulating within the liver (steatohepatitis), or the normal loss of cells that occurs with aging. Reduced kidney function may further affect drug response by slowing clearance of the drug from the body and thus maintaining higher than expected concentrations of the drug in the blood circulation.

Drugs in Children

Two significant issues surround medication therapy in children. The first is the continually changing metabolic capability and status of the child’s body as organ systems grow and mature. The liver remains relatively unsophisticated in its function until a child reaches age 10 or 12 years. Not only does this limit the liver’s ability to metabolize drugs such as antibiotics and analgesics (pain relievers), the most common kinds of drugs children may need, but also it makes the liver vulnerable to damage from substances that enter the blood circulation.

Incompletely metabolized drugs increase the risk for damage to other developing organ systems as well, notably the central nervous system. These factors become of therapeutic concern when treating serious childhood diseases for which medications are the primary course of treatment, such as seizure disorders, congenital heart disease, and cancer.

The second issue in regard to medication therapy in children is that many drugs do not undergo testing or evaluation for their effectiveness or safety in pediatric use because children make up a very small percentage of the drug’s intended patient population or because the potential risks of involving children in clinical research studies are too high. The consequence is that doctors rely on best practices standards and off-label use of drugs in prescribing medications, which are safe and effective in adults but untested in children, to treat health conditions in children.

Drugs in the Elderly

The body undergoes significant metabolic and functional changes by the seventh and eighth decades of life, a blend of the normal processes of aging and the cumulative effect of health conditions. The liver and kidneys become less efficient, which affects the amount of a drug that enters the blood circulation and how long the drug remains in the body. Health conditions such as atherosclerosis (fatty deposits in the walls of the arteries) may alter the flow of blood through the body. Changes in nervous system function may alter the release of neurotransmitters. These kinds of changes in the body influence how, and how well, drugs work.

Often the very reasons elderly people need to take therapeutic drugs (such as to treat cardiovascular disease [cvd], diabetes, kidney disease) have significant effects on the ways in which the body can handle the drugs and how those drugs affect the body. As well, older people are more likely to have complex or multiple health conditions and take multiple medications, increasing the risk for adverse drug reactiondrug interaction, and overdose.


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