Summary Drugs Therapy across the Lifespan

Absorption and Drug Action • The function of the gastrointestinal tract is different in very young and the elderly. • Infants and the very elderly tend to be the most sensitive to the effects of the drugs. • Common problem is the slowed peristalsis and the gastric emptying time. • Activity and concentrations of digestive secretions are lower in newborns. • Infants and elderly require special considerations for medication administration. An example can be: absorption of medicines given intramuscularly may be affected by the differences in muscle mass, blood flow to the muscles, and muscle inactivity of patients who are bedridden. Topical administration of drugs in infants is effective though the outer layer of the skin (stratum corneum) is not fully developed. The reason being that the skin at this stage would be fully hydrated and thus the water soluble drugs are absorbed more easily. Infants wearing plastic coated diapers are also more susceptible to skin absorption because plastic acts as an occlusive dressing that increases hydration of the skin. Inflammation also increases the drug absorption (e.g. napkin rash) Transdermal administration in elderly is always unpredictable. Dermal thickness usually decreases with aging which may enhance absorption but there can be some factors which diminish absorption. (drying of skin, wrinkles, and a decrease in hair follicles). With aging there will be decreased cardiac output and diminished tissue perfusion. This may affect transdermal drug absorption. Drug administration through oral route may be difficult for the infants and elderly to swallow. The medication needs to be crushed and mixed with water. Taste becomes a factor when administering liquid medications because liquid medications comes in contact with the taste buds. However, time-release tablets, enteric-coated tablets and sublingual tablets should not be crushed because of the effect of the absorption rate and potential for the toxicity. Oral routes considerations • Infants and elderly often have less teeth to chew the medications. • Elderly patients usually have reduced salivary flow and this makes chewing and swallowing more difficult. Gastrointestinal absorption of medicines is often influenced by a variety of factors: 1.Gastric pH 2.Gastric emptying time 3.Motility of GIT 4- Enzymatic activity 5- Blood flow of the mucous lining of the stomach and intestines 6- Permeability and maturation of the mucosal membrane 7- The concurrent disease processes. Distribution and drug action • Distribution refers to the ways in which drugs are transported by the circulating fluids to the site of action (receptors)