Therapeutic Drug Monitoring in the Elderly

Question 1

List factors that influence dosing of digoxin

Answer 1

• Decrease in lean body mass (decreased volume of distribution)
• Decreased renal function (decreased renal clearance)
• Na, K - ATPase functional decline enhancing arrhythmogenic effect
• Positive inotropic effects increase w/ increased dose
• Negative chronotropic effects aren’t seen until a specific total body stores threshold is met

Question 2

List factors that influence dosing of theophylline

Answer 2

• Age
• Co-morbid conditions: pneumonia, heart failure, exacerbation of pulmonary disease, liver disease (elevated bilirubin), acute severe illnesses
• Elderly are more sensitive to side effects, especially tachyarrhythmias and seizures than younger people and they occur at lower serum levels
• Clearance is changed due to factors

Question 3

What are factors that change clearance in theophylline?

Answer 3

• Factors which increase clearance: smoking, phenytoin, rifampin
• Factors which decrease clearance: Acute bronchospasm, Acute Pneumonia, old age, heart failure, severe COLD, elevated bilirubin

Question 4

List factors that influence dosing of warfarin

Answer 4

• Impaired metabolism of warfarin making them more sensitive to anticoagulant effects
• Greatest risk and greatest incidence of bleeding episodes on warfarin
• Concomitant hypoalbuminemia makes older people even more sensitive to anticoagulant effects
• Assess balance, gait and risk for falls before making a decision about warfarin therapy, especially when used for stroke prophylaxis
• High risk of drug-drug interactions

Question 5

Dosing considerations in warfarin

Answer 5

• Initiate therapy at lower doses than in younger people (i.e. 2 or 2.5 mg/day vs. 5 mg/day in younger people)(Especially important in patients with low albumin)
• Anticipate exaggerated and faster response than in younger people
• Monitor INR daily initially
• Patient education
• Aggressive monitoring for bleeding
• Aggressive monitoring for drug-drug interactions

Question 6

Discuss factors that influence the pharmacokinetics of antiepileptic drugs

Answer 6

• Metabolism of the traditional AEDs is slowed in the elderly
• Anticipate that dosing requirements will diminish with advanced age
• All three are highly protein bound thus potential for drug-drug interactions is increased and dosing requirements to exert desired effect will be decreased in those with decreased protein.
• Effects on hepatic enzymes systems is mixed leading to multiple unpredictable drug-drug interactions

Question 7

T/F, serum antiepileptic concentration correlates more closely with desired pharmacologic and toxic effects

Answer 7

true