J - Prescribing in the elderly - Pharmacology

Question 1

What is the difference between pharamockinetics and pharmacodynamics? Think of it as pharmacokinetics being kinetic so the drug is moving through the body from its ingestion to excretion

Answer 1

Pharamcokinetics - this is how the body acts on the drug - absorption, distribution, metabolism and excretion Pharmacodynamics - this is how the drug acts on the body Never too late to review the drugs

Question 2

There are two simple principles regarding the absorption of basic drugs What type of environment do acidic and basic drugs require for absorption?

Answer 2

Acidic drugs require an acidic environment for absorption eg pH 7.35

Question 3

Name 2 acidic and 2 basic drugs?

Answer 3

2 acidic drugs - Penicillins and apsirin 2 basic drugs - diazepam and morphine

Question 4

What happens to the gastric pH in the elderly? What does this do to the absorption of acidic drug? What happens to the size of the small bowel in the elderly?

Answer 4

The gastric pH in the elderly increases, meaning the acidity of the stomach is less decreasing the rate of absorption of the acidic drugs The small bowel also decreases in size in the elderly - decreased area for absorption

Question 5

Distribution Proteins bind to drugs to either enhance or detract their efficacy What protein binds to basic drugs? Which protein binds to acidic drugs? Basic drugs will bind to acidic proteins and acidic drugs will bind to basic roteins

Answer 5

Basic drugs bind to alpha-1 acid glycoprotein Acidic drugs bind to albumin which is alkalotic (basic)

Question 6

• Elderly patients (particularly those who are cachexic- weakness and wasting of the body due to severe chronic illnes) often have low protein that binds acidic drugs, which protein is this? and higher levels of the basic binding protein, which is this? As there is a higher pH in an elderly persons stomach, what protein binder is there also a higher concentration of?

Answer 6

Elderly patients often have low albumin levels making it more difficult for acidic drug absorption Elderly patients also have a higher stomach pH and a higher concentration of alpha-1 acid glycoprotein which binds the basic drugs

Question 7

If there is an increased fat proportion t muscle mass (this is common in the elderly), the half life of lipophilic drugs will increase Lipid binding increases the half-life of the drug and lipophilic drugs have a high Vd (eg diazepam, anaesthetics) - volume of distribution Define half life?

Answer 7

Half life is the time it takes for a drug to reduce to 50% of its active metabolite concentration

Question 8

How would you calculate the volume of distribution? ie if giving a 100mg tablet and measuring blood conc. at 0.5mg/L

Answer 8

Then as 100mg was given and the blood concentration was 0.5mg/L of the drug Then the volume of distrubtuion would be the number of litres to distribute all 100mg = 200L Therefore this drug would take 200litres to be uniformly distrubutred to produce the observed 0.5mg/L blood concentration

Question 9

In old people there is an increased fat to muscle mass meaning lipophilic drugs will have a longer half life and greater volume of distrutuion How much body water percentage is lost in the elderly and what does this mean for hydrophilic drugs?

Answer 9

Decreased body water in older people (by about 10-15%) The most important change is that the lower water concentration will lower the volume of distribution of hydrophilic drugs

Question 10

Name 2 hydrophilic drugs What happens to the hydrophilic drugs in old age and why?

Answer 10

Lithium and digoxin Due to the body water content decreasing by 10-15%, this decreases the volume of distribution of hydrophilic drugs Lower volume of distribution and lower clearance rate in the elderly cause the half life to usually remain unchanged significantly in the elderly

Question 11

Metabolism and excretion Hepatic metabolism Renal metabolism Are these metabolism increased or decreased in the elderly?

Answer 11

Both renal and hepatic metabolism is reduced in the elderly

Question 12

In general in an older patient, lower doses of drugs achieve the same effect in the elderly (eg alcohol) When is this not the case?

Answer 12

This is not the case for beta blcokers and heart rate In the elderly beta blockers are not as effective in slowing the heart rate

Question 13

How is the therapeutic window calculated? Beware of the therapeutic window when the drug therapetuic window is below what number?

Answer 13

Calculated by Maximum tolerated concentration / minimum effective concentration (MTC/MEC) Therapeutic window <2 beware of drugs INcreasing age decreases therapeutic window of the drug

Question 14

Give example of some drugs with low therapeutic window?

Answer 14

Warfarin Gentamicin Lithium Digoxin Theophylline Carbamezapine - for epilepsy

Question 15

What is polypharmacy? What is the number of medications the average care home resident is on?

Answer 15

Polyphramcy is when a ptient is on 4 or more medications The average nursing home resident is on 7 medications

Question 16

Avoid treating adverse reactions/side effects of drug with more drugs! (e.g Amlodipine oedema) • Attempt to prescribe a drug that will treat more than one existing problem (e.g CCB/BB for BP and angina) Whould a BB or CCB be given in heart failure?

Answer 16

A BB would be the choice in heart failure, calcium channel blocker can worsen heart failure

Question 17

ADVERSE DRUG REACTIONS Very common – even in the ambulatory elderly - Legal responsibility to tell the patient of the common side effects of the drug (can get sued if not informing the patient of the frequent side effects of the drugs) – and you NEED to document you have explained rationale for the drug and the common side effects What drugs in combination with statins can worsen the muscle side effects and why?

Answer 17

Macrolides inhibit the liver cytochrome p450 enzyme that breaks down statins and therefore increases the statin concentration in the body Co-prescribing statins and fibrates also causes a 40% increase in the likelihood of muscle effects

Question 18

Which drug causes an increase in the hypoglycaemic effect of sulphonylureas when prescribed at higher doses?

Answer 18

This would be an ACE inhibtor

Question 19

The new oral LMWHs have interactions with other drugs and are being used more commonly – always think about the coexisting problems a patient may have Which two types of juice should be avoided in those who are on warfarin?

Answer 19

Grapefruit juice and cranberry juice should not be taken with warfarin as they inhibit a key enzyme required to metabolise warfarin which can cause high warfarin levels

Question 20

• Patient with PD (parkinsons disease) have a much higher increased risk of drug induced confusion What receptors do beta blockers work on that can worsen asthma?

Answer 20

Non-selective BBlockers work on B1 (heart) and B2 (lungs) They work on beta-2-adrenergic receptors which are present in the lungs and can therefore cause bronchoconstriction

Question 21

WHat are the four drugs most commonly associated with adverse reactions in the elderly?

Answer 21

Warfarin Digoxin Insulin Benzodiazepines

Question 22

Summary • Start low go slow with older patients • Often require much lower doses for most medications – beta blockers being the common exception • Quality of life versus living longer/prolonging death • Anticipate or even assume side effects – eg presibing a strong opioid – prescribe a laxative with it • Review medications regularly What is the yellow card scheme?

Answer 22

This is a legal requirement where you fill in a card documenting if you believe a patient’s side effect to be a previously unkown side effect of a certain drug