CH 3: Lifespan Considerations

Changes in absorption for older adults

• Reduction in hydrochloric acid

• Decreased cardiac output; higher risk for atherosclerosis

• Approximately 50% reduction in blood flow to GI tract

• Muscle tone and motor activity are reduced; increased body fat

Differences in absorption for children

• Gastric pH less acidic

• Slowed gastric emptying due to irregular/slowed peristalsis

• Immature liver so no first pass metabolism

• Intramuscular absorption is faster and irregular

• Skin is thinner and more permeable

Changes in distribution for older adults

• Decreasing total body water with age

• Decrease in lean muscle mass and increased body fat

• Reduced liver function

Changes in metabolism for older adults

• Metabolism declines with advancing age

• Liver loses mass with age

• Protein (albumin) binding sites are reduced because of decreased production of proteins by the aging liver and reduced protein intake

• Decrease in total body water leads to decreased distribution of some drugs, such as antibiotics, leading to risk for toxicity because of greater concentrations of drug in the blood stream.

Changes in excretion for older adults

• Renal function declines with age – often requiring dose adjustments; due to decreased blood flow to nephrons and impaired GFR

Differences in distribution for children

• Total body water is 70-80% in full term infant

• Fat content is lower due to higher total body water

• Protein binding decreased

• Immature blood brain barrier

Differences in metabolism for children

• Levels of microsomal enzymes decreased

• CYP enzymes have lower activity

• Older children have increased metabolism and require higher doses

Differences in excretion for children

• GFR and tubular secretion and resorption are decreased due to kidney immaturity

• Perfusion (blood flow) to kidney decreased