S4: Pharmacology and Older People Flashcards
Statistics on elderly patients and drugs
- Older 65s make up around 14% of the population and 45% of regular prescriptions are dispensed to the over 65s.
- Regular medication use increases with age but despite this, older people are not always represented proportionately in clinical trials.
- Prevalence rate of ADR related acute hospital admissions of 9.5% for patient over the age of 75.
- Over 80% of elderly patients admitted to hospital were taking drugs.
- Over 50% were taking between 4 and 6 medications daily.
- 15% were admitted because of side effects of drugs.
How are older people more vulnerable to drugs?
- More likely to take over the counter drugs, use a mean of about 2. Most include analgesics, vitamins, antacids and laxatives. Older people tend to take them and not disclose the fact to doctors which can interact with prescribed drugs.
- Care home patients are on an average of 8 drugs, understandably this has financial consequences.
- More likely to experience ADR which can be due to polypharmacy and frailty with age (e.g. Metabolism is slower).
- Elderly often take multiple drugs with potential interactions and they suffer more serious and prolonged consequences of any adverse effect compared not old people.
- So by understanding how drugs work in the older population we can hopefully try minimise unnecessary prescriptions, ADRs and hospital admissions.
What are the biggest drug offenders that cause side effects in elder.ly?
Digoxin, diuretics, hypotensive drugs, non steroidal anti inflammatory drugs and anti parkinsonian drugs were the biggest offenders.
Describe normal absorption of oral medication
The absorption of a drug is the movement of the drug from the site of administration into the bloodstream. The amount of drug that reaches the systemic circulation gives the blood concentration and thus reaches the site of action is partly dependent on the absorption of the drug. Various factors can influence the likelihood of a drug being absorbed, such as features of the drug itself but also aspects of the GI tract.
Describe the effect age has on absorption of oral medication
The GI tract undergoes normal changes with age and this can affect drug absorption, changes include:
- Reduced GI motility (would increase drug absorbed).
- Reduced GI blood flow (Decreases drug absorbed).
- Decreased gastric secretions resulting in an increased gastric pH (depends on drug, but generally decrease absorption as most drugs are weak acids that require being neutral in stomach to be absorbed e.g. aspirin).
- The overall effect of age on drug absorption is therefore difficult to predict on an individual basis, but it is thought that there is likely to be no significant change in oral absorption with age.
- There other extrinsic factors that can affect absorption that are more common older people, for example polypharmacy which means there is increased likelihood of drug interactions or having feeding tubes. Thus these will result in changes in concentration of the drug in the plasma.
What is drug distribution?
Drug distribution is the movement of the drug between different body compartments and therefore will affect the concentration in the plasma and at the site of action. It also affects the clearance of the drug. The measure we use for the amount a drug is distributed is the volume of distribution.
Describe how age affects drug distribution
Drug distribution changes in older adults due to changes in their body composition such as:
- A decrease in lean body mass.
- A decrease in total body water.
- An increase in body fat.
- These changes result in changes of distribution depending on the drug. A drug that is hydrophilic like alcohol in an older person will have a higher concentration for a set volume drunk as it is in less water.
- Increased body fat means that drugs that are lipophilic will distribute into fat more and stay for longer, this means that clearance will take longer and effects be prolonged.
- There is a reduced volume of distribution of water-soluble drugs and an increased volume of distribution of lipid soluble drugs.
Describe how age affects protein binding which then affects drug distribution
- Drug distribution is also affected by protein binding, only unbound (free) drug can distribute out of the plasma and have effects on tissue.
- In older people there are lower levels of plasma proteins and albumin, although this is not thought to be directly due to the ageing process, rather due to associated changes like lower nutrition.
- A reduction in plasma proteins means that there will be more free drug and thus increase the free drug concentration, this can be problematic with drugs that have a narrow therapeutic range as then the dosage becomes an overdose and ADRs may be experienced.
- An example is with phenytoin that binds strongly to albumin, if it decreases means more free phenytoin in blood and reaches toxic levels.
Describe effect of ageing on drug elimination
The elimination of a drug from the body primarily occurs via the renal excretion, this is the removal of the unaltered or metabolised drug from the body. As the body ages kidney function is seen to decline:
- we see a decreased GFR as a result of decreased blood flow.
- a decrease in kidney mass.
- reduction in the size and number of nephrons.
- Again, this decline in kidney function means that the drug is cleared from the body at a slower rate and its half-life is increased.
Various illnesses in the older population can also worsen kidney function e.g. hypertension.
- We use formula’s to estimate renal function, this is because want to ensure that we do not overdose the patient. Generally we use creatinine clearance as a marker of renal function, however with creatinine it is important we adjust for age in the equation as creatinine levels are also dependent on muscle mass. As older individuals have less muscle mass it may give us a false reading of creatinine being poor. Clearance is volume of serum from which the drug is removed per unit of time (mL/min or L/hr).
- Drug dosages can then be adjusted according to the estimated renal function.
Describe how age changes the pharmacodynamics of a drug
Generally we see that with age a lower drug dose is required to achieve the same effect, in other words older people are more sensitive to drugs.This is thought to be due to the number of receptors and the affinity of the drug to them, we see this especially in the CNS with the receptors being more sensitive to drugs.
- Also as older individuals have decreased homeostatic mechanisms and are less able to compensate to change, this can lead to the drug overshooting in its effects.For example in people taking anti-hypertensives, it can mean that when they stand up their body is unable to compensate as its homeostatic mechanisms are less effective leading to orthostatic hypotension.
- Increased sensitivity to sedation and psychomotor impairment.
- Increased intensity and duration of effects of morphine / opiates.
- Increased cardiac sensitivity to digoxin.
What is optical pharmacotherapy?
A balance between overprescribing and underprescribing. Using knowledge of pharmacokinetics, pharmacodynamics and common sense when prescribing to ensure:
- Correct drug
- Correct dose
- Targets appropriate condition
- Is appropriate for the patient (discuss with patient about the drug e.g. Side effects for individual patient may be at high risk for complication).
Avoid “a pill for every ill” and always consider non-pharmacologic therapy.
Two criteria for inappropriate medication use
- Beers criteria (came first).
2. Stop start criteria
Describe stop start criteria
As polypharmacy is a risk, we can use the STOPP/START criteria to do a medication review, this is a critical examination of a patients medication in order to try optimise their regime.
- STOPP -> Screening Tool of Older Person’s Prescriptions.
- START -> Screening Tool to Alert doctors to Right Treatment.
The aims of using the STOPP/START on patients is to:
- Improve the appropriateness of their medication.
- Prevent them suffering ADRs due to their drug regime.
- Reduce the drug costs.
How do we approach common side effects from drugs on elderly?
- Distinguish between common side effect and ADR (sometimes they interlink).
- Often non specific and symptoms could be due to drug or illness e.g. postural hypotension.
- Many different drugs can cause similar side-effects.
- Certain drug groups particularly common e.g. cardiovascular, psychotropic, anti-parkinsonian.
- Warn the patient and discuss with them the common side effects of their medication regime –> increases adherence. Discuss: pro and cons, rationale, side effects.
- Common drug side effects: confusion, cognitive impairment, hypotension
and acute renal failure.
What is polypharmacy?
Polypharmacy is defined taking more than 5 drugs regularly and it is very common in the older population. This includes over the counter medications and vitamins, sometimes patients don’t reveal they are taking these as they don’t think they are drugs. Polypharmacy can be the rational thing to do for an individual, where each medication they take is required and necessary. This is appropriate polypharmacy.
