You are on page 1of 34

Drug Therapy Across The Lifespan Year1,Semester 2


2. 3.


At the end of the lecture, the student should be able to: List ways in which drug absorption, distribution, metabolism and excretion are altered by age and the consequent effects of drug action. Describe pediatric dosage considerations Describe the pharmacological properties that influence drug transfer both across the placenta and into the breast milk Describe factors that determine the teratogenic potential of drugs once they enter the embryonic/foetal circulation.

Learning outcomes
Describe altered physiology and polypharmacy in the

elderly. Identify common herbal and traditional medicines. List potential interactions between herbal and conventional medicene.

Key terms

Pediatric dosage, Carrier mediated transport, teratogens, Mutagens, `carcinogens, Transdermal drug administration, Non compliance, `passive diffusion, Herbal medicines, conventional medicines.

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.

Absorption and drug action

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. 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. susceptible to skin absorption because plastic acts as an occlusive dressing that increases hydration of the skin. nappy rash)

Topical administration of drugs in infants is effective

Infants wearing plastic coated diapers are also more

Inflammation also increases the drug absorption (e.g.

Absorption and Drug Action

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. Example, 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.

Absorption and Drug Action

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.

Absorption and Drug Action

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. E.g.-gastric pH,gastric emptying time, motility of GI tract, enzymatic activity, blood flow of the mucous lining of the stomach and intestines, permeability and maturation of the mucosal membrane and the concurrent disease processes.(discuss in pairs)

Distribution and drug action

Distribution refers to the ways in which drugs are transported by the circulating fluids to the site of action (receptors) Medicines are transported either dissolved in the circulating water (in blood) of the body or bound to the plasma proteins within the blood. Body water composition changes with age. The total body water content for a preterm is 83% and for an adult is 60%.Infants have larger Volume of Distribution for

water soluble drugs and may require higher doses in milligram per kilogram than the elderly.

Distribution and Drug Action

Body weight of a preterm consists of very little fat, a full term newborn also have little fat whereas an adult has a lot of fat compared to the infants and children so the drugs which are fat soluble should be given in smaller amounts to infants since there is less fat to bind to the drugs. The highly fat soluble drugs require longer onset of action, may accumulate in fat tissues, prolonging their action and increasing potential for toxicity.

Distribution and drug action

1. 2. 3.

Drugs that are insoluble are transported in the circulation by being bound to plasma proteins (albumin and globulin) Protein binding is reduced in preterm infants because of: Decreased plasma protein concentration Lower binding capacity of protein Decreased affinity of proteins for drug binding

Drugs which have lower protein binding in neonate

than in adults are phenobarbitol,phenytoin,theophilline,propanalol, lignocaine,penicillin and chloramphenicol

Distribution and drug action

Drugs used in treating neonates may compete for

binding sites. Some drugs can displace bilirubin from the protein binding sites and allow the bilirubin to pass into the brain causing Kernicterus( is the degeneration of brain nerve cells caused by binding of bilirubin to the cells).

Metabolism in drug action

Metabolism is the process by which body inactivates

medicines. It is controlled by factors such as genes,diet,age,and maturity of enzyme systems in liver. All enzyme systems are present at birth but they mature at different rates. The weight of the liver, the number of functioning hepatic cells, and hepatic blood flow decrease with age. This results in slow metabolism of drugs in elderly.

Metabolism and drug action

This can also be caused by presence of liver disease or renal failure Drugs that are extensively metabolized by the liver (e.g. morphine, lignocaine, propanalol) can have prolong duration of action if the hepatic blood flow is reduced. Dosages and timing of these medications must be adjusted to prevent drug accumulation and toxicity. Drug metabolism can be affected at all ages by genetics,smoking,diet,gender,and other medicines. (Discuss in pairs)

Excretion and drug action

Is the process by which metabolites of the drugs and the active

drug itself are excreted from the body.

(Fill in the Blanks) The primary routes are through________ and ___________.

The other routes are_________,___________,_________ and ________.

Renal function reaches to an adult level at 1 year of age As body matures, important physiologic changes take

place in the kidneys, including decreased renal blood flow caused by arthrosclerosis and reduced cardiac output, a loss of glomeruli,and decreased tubular function.

Usually elderly show a deterioration in the renal

clearance of drugs. The action of the drugs may be prolonged in this case and may accumulate to toxic levels if no adjustment of dosages is considered

Pediatric Dosage Consideration

In children, organ systems are not matured yet.e.g. kidneys, liver, and the circulatory system.

Muscle mass in children is lower but the body water percentage is higher.
These factors affect absorption, distribution,

metabolism and excretion of drugs. The physiological differences between adults and children suggest that pharmacokinetic behavior of some drugs vary according to the age. A dose administered to an adult is never equivalent to the pediatrics.

Pediatric Dosage Considerations

Age and body weight is very important in calculating the

pediatric dosage.

Pediatric Dosage Considerations

Dosage adjustments are very important to consider in

pediatrics to prevent toxicities. Therfore,it is equally important to obtain accurate height and weight measurements on a regular basis.

It is also important to accurately measure and

administer medications to pediatric patients. Oral and parenteral medications available in powder form should be diluted properly according to the manufacturers directions to allow accurate measurements of solution being administered

During pregnancy any chemical or drug substances consumed and absorbed may reach the fetus by way of the maternal circulation and cross the placenta or

be transferred to the baby and newborn via breast milk. Drugs cross the placenta and induce adverse fetal effects. This depends on the pharmacological properties of the drugs e.g. the type of drug, the drug concentration and fetal age. Transfer of drugs across the placenta depends on the physicochemical properties of the drug, protein binding and lipid solubility.

Transfer of drugs primarily involves simple diffusion. In pregnancy, low molecular weight drugs which are

lipophilic,ionized and non-protein bounded are able to cross the placenta, while drugs of high molecular weight cross very poorly.

All forms of drugs in maternal circulation can be easily

transferred to the colostrums and breast milk. Drugs are handled by different pathways in the infant and the fetus, so the impact of maternal medications on the infant is probably less as the drug is diluted in the maternal circulation and the amount of milk taken by the infant is often small.

If neonates hepatic and renal systems are immatured

then metabolism and excretion of drugs taken would be affected.

Drug concentrations in the maternal circulation depends

on the relationship of several factors: - dosing and route of administration - drugs distribution - its protein binding - maternal metabolism and excretion

Drug factors that enhance drug excretion into the milk

are higher degree of ionization, low molecular weight of the drugs, greater fat solubility and higher concentration of drugs. Transfer of drugs into milk occurs by both passive diffusion and carrier mediated transport.

Teratogenic Potential of Drugs

1st trimester, when the embryo is developing is most

vulnerable to the teratogenic effects of various drugs and chemicals. Drugs can exert a beneficial effect in the fetus, cause adverse effects or act as teratogens,mutagens or carcinogens. 3-12 weeks of pregnancy is when the extremities(arms,legs, and toes), central nervous system (CNS) ,muscle and organs are developing most rapidlyteratogens can cause birth defects characterized by the absence or malformation of arms and legs.

Use of cocainehas resulted in spontaneous abortion,

fetal hypoxia, premature delivery, and congenital abnormalities ( skull defect, cardiac abnormality), cerebral infarction or stroke.

Altered physiology and polypharmacy in elderly

Polypharmacy- refers to use of multiple medications by a patient. The elderly use more drugs because illness is more common in older persons.e.g. Cardiovascular Diseases,Arthritis,Gastrointestinal Disorders, and Bladder Dysfunction. Altered drug effects are common in elderly patients but can often be avoided. We should be aware of age related changes in drug absorption,distribution,metabolismand elimination. Doctors may need to adjust drug dose, frequency, or the choice of drug altogether as they consider the physiologic changes of aging.

Group Activity
1. Identify common herbal and traditional medicine

(brain storm) Debate: 2. We believe that herbal medicine is better than conventional medicine /disagree (1 from each group)

Common herbal medicines

Aloe Vera-member of the lily family. Juice of the leaves

used for skin applications, burns, used in many shampoos and conditioners. Garlic-member of the onion family. Consuming large amounts of garlic prevent heart disease. Ginger-used as an antiemetic in nausea associated with travel or pregnancy.

Porth, C.M. (2004). Essentials of

Path physiology: Concepts of Altered States. Philadelphia; Lippincott Williams & Wilkins.