Pharmacology and Antimicrobials Flashcards
Describe how the absorption of drugs are affected in children in oral, IM and transdermal administration
- oral - gastric emptying is prolonged and acidity is very low. Adult function occurs at 6-8 months. Absorption of acid-labile drugs is increased
- IM - delayed due to low blood flow during first few days of life. More rapid in infants than neonates and adults.
- transdermal - stratum corneum is very thin and blood flow to skin in infants is greater hence topical medications can be more rapid and complete. Risk of toxicity
Describe the differences in the distribution of medication in paediatric patients
- protein binding - transportation is affected by the binding to albumin and other plasma proteins. In infants serum albumin is low
- Blood brain barrier - not fully developed giving easy access to the central nervous system. CNS toxicity is a possibility
- Endogenous compounds compete with drugs for binding sites. In infants there are less binding sites so reduced dosage is needed
Describe how the metabolism of drugs is affected in paediatric patients
Hepatic metabolising ability is low so the Px is sensitive to drugs which rely on hepatic metabolism. Liver maturation occurs at one year of age
Describe how excretion of medications differs in paediatric patients
Kidney function is reduced at birth so drugs eliminated through this pathway must be given in reduced doses or at longer intervals. Adults levels are reached by one year of age
How is dosage calculated in paediatric patients?
Usually calculated by weight but body surface area is thought to be more accurate
How are pharmacokinetics affected in elderly patients?
ADME is decreased in the elderly (greater than 65 years of age)
What are the physiological changes in the elderly?
Less body water and muscle mass with more fat. Hepatic metabolism and excretion decreases while the baroreceptor reflex decreases in receptiveness and sensitivity.
Describe the physiological changes associated with disease states in the elderly and it’s effect on pharmacokinetics
As age increases, so does cardiac related problems. Reduced cardiac output will reduce ADME. Kidney and liver disease affect elimination and metabolism of drug. Increased neurological condition can lead to decreased compliance
How is absorption affected in the elderly?
Not significantly affected. Increase of gastric pH and slowing of gastric motility can adversely affect drug levels
How is distribution affect in the elderly?
Because of the decrease in water content, there is a decrease in distribution and an increase in concentration of water soluble drugs. Because of a decrease in lean body mass, and an increase in body fat, there is an increase in the volume of distribution causing prolonged action of fat-soluble drugs. A decrease in circulating serum proteins increases the concentration of unbound forms of the drug.
How is metabolism affected in the elderly?
It is significantly lower, particularly oxidation, reduction and dealkylation. Drug-drug interaction increases
How is elimination affected in the elderly?
Decrease in bodily functions, decrease in kidney mass, nephron size and number and renal blood flow leads to less tubular secretion and GFR. Active drug metabolites may not be effectively eliminated and accumulate causing prolonged action and adverse effects
What is polypharmacy?
Polypharmacy is the use of several drugs, common in elderly patients. It increases the risk of adverse reactions through drug-drug interaction and drug-disease interaction
How does medication affect pregnancy?
Medication should not be taken throughout pregnancy and lactation as it less predictable and potentially harmful. Almost all medications cross the placenta and reach the foetus. Drugs remain active and unchanged and metabolise slowly in the foetal liver. They can be distributed to the foetal brain and is excreted slower due to immature kidneys. It may cause spontaneous abortions, intrauterine growth retardation, prematurity, still birth, obstetric complications as well as neonatal and life long side effects.
Describe the formation of a foetus and the affect of medication
Within the first trimester (1-12 weeks) major organ system being formed, second trimester (4-6 months) the cerebellum and urogenital system are still forming and medication may affect ongoing growth and development. Third trimester (6-9 months) specific affects can occur and in near term/during labour adverse effects on labour or on neonate after deliver.y Tetrogenicity occurs during the first trimester
