Monitoring Drug Dosage for the Elderly - Drug Reactions and Considerations

Introduction

Optimal drug dosage is a factor to be considered, especially in elderly people. It includes selecting the best medication to be prescribed, determining the appropriate dose, schedule, and possible side effects, educating the patients or caretakers, and the general health of the patient. Prescribing drugs to the elderly population is quite challenging as most of the premarketing drug trials may not include older adults, and many drugs need to be used with caution due to the age-related changes in patients concerning drug absorption and metabolism.

What Are Some of the Changes Associated With Aging?

Aging in most individuals is associated with impaired vision, hearing, hand-eye coordination, difficulty swallowing, etc. chronic medical conditions, use of various medications, and adverse reactions that may be associated due to drug interactions.

Some main causes of disability include:

1. Back and neck pain.

2. Lung diseases.

3. Depressive disorders.

4. Dementia.

5. Bone and joint disorders.

6. Metabolic disorders such as diabetes, hypertension, etc.

These diseases not only cause significant changes in the body but also affect the quality of life.

Biological aging and a decline in bodily functions are due to changes in biological mechanisms caused by alterations in gene expressions, mitochondrial and nuclear DNA changes, increased oxidative stress, and lipid peroxidation. These alter the absorption, distribution, metabolism, and excretion of drugs and lead to decreased bioavailability (ingested dose that reaches the circulation) of the drug. Studies also indicate that older people encounter problems such as missing the dose, altering the dose or schedule, and facing difficulties in reading and understanding the instructions, which may result in complications.

How Does the Human Body React to Drugs in Older Age?

Biologic aging affects the pharmacokinetics of the drugs to a significant extent depending on the individual's age and comorbidities. Normal physiological changes in the liver due to aging cause a decreased cytochrome P450 enzyme activity, which may affect hepatic clearance.

• An increased proportion of body fat causes an increased distribution of fat-soluble drugs, leading to prolonged effects even after discontinuing the drug.

• Decreased body mass and total body water cause a slow or reduced distribution of water-soluble drugs.

• Low food intake or malnutrition increases the free drug concentration, which may lead to drug toxicity.

• Renal diseases or impaired renal function due to aging can cause decreased drug removal, leading to its accumulation in the blood plasma. Polypharmacy or chronic use of five or more drugs, is also known to be associated with the risk or severity of adverse reactions. Non-steroidal anti-inflammatory drugs or over-the-counter drugs on chronic use can produce adverse effects on the gastrointestinal tract, liver, and kidneys.

How Do the Changes Affect Drug Absorption?

The movement of the drug from the site of administration into systemic circulation through the small intestine, skin, muscles, subcutaneous layer, rectum, etc., is termed drug absorption. Alterations in protein binding and fat content affect the absorption of drugs and play an important role in the bioavailability of the drug.

Absorption of drugs is affected by decreased gastric acid and motility, reduced bowel area, and first-pass metabolism (metabolism of the drug before it reaches the circulation), leading to impaired drug dissolution and absorption.

The absorption of the drug through subcutaneous or intramuscular routes is reduced due to decreased blood perfusion and reduced muscle mass. Changes in the chest wall compliance and alveolar surface area decrease the drug absorption through the inhalation route.

How Should Aging Be Considered in Prescribing Drugs?

1. Therapeutic drug monitoring (TDM) is a strategy that helps in guiding the dose regimen based on plasma drug concentrations. Despite some limitations, it helps confirm drug toxicity, diagnose adverse reactions, and verify the patient’s compliance with the drug regimen.

2. Monitoring the drug used by the patient involves documentation of the indicated drug, maintaining a list of drugs used, improvements in therapeutic goals, monitoring for any adverse reactions, and periodic reviewing of the drugs as per requirement.

3. It is essential to periodically evaluate the medicine regimen, as it helps identify any changes or discontinuation of medicines if not required further. It also helps to substitute the existing medicines with better and safer alternatives.

4. Drug monitoring considers any change in the physiological status of the individual, such as alterations in the liver and kidney functions that might require a change in the drugs. Before adding any new drug to the current regimen, it is important to rule out any adverse drug reactions that might happen.

5. Adverse drug reactions can occur in any patient; however, in elderly adults, it can lead to the following:

   • Increase in sedation.

   • Falls.

   • Bleeding.

   • Hallucinations.

   • Confusion.

6. These measures are very important, especially in elderly patients, to focus on appropriate dosages and avoid possible drug interactions.

7. For minor conditions, non-pharmacological therapies such as physical exercises, massage therapy, cognitive behavioral treatment, and dietary changes may help reduce the medications and help avoid possible drug interactions can be considered.

8. As many side effects are dose-related in elderly individuals, beginning the treatment with a newer medicine at a lower dose followed by gradual escalation is vital. This helps to identify the risks easily and helps in altering the dose or discontinuing the medicine at an early stage of the treatment. On gradual increase in dose, the patient must be evaluated and educated to inform the health care provider if adverse effects are observed.

9. Age-related change in memory function is quite common in elderly individuals. Burdening them with multiple medicines would do more harm than good. Hence, it is necessary to follow a dosage regimen that is simple and optimal. It is better to follow the policy approach of fewer the better in the case of medications, especially in elderly people.

Conclusion

Many biological changes take place in the body of the elderly patients due to aging, which may also affect the pharmacokinetics and pharmacodynamics of the drugs taken due to various medical conditions. The use of multiple medications, especially over-the-counter drugs (OTC) and herbal supplements, must be avoided as much as possible to avoid unnecessary complications. Therapeutic drug monitoring is an essential tool to be considered in the management of drug therapy in elderly people to achieve treatment goals and improve the quality of life of the patients.