Managing Drug Interactions & ADR's: Drug interactions 1

Question 1

Define: Drug Interaction

Answer 1

An interaction occurs when the effects of one drug are changed by the presence of another drug, food, drink, or an environmental chemical agent

Question 2

list the factors that can increase the Incidence of Drug Interactions (6)

Answer 2

1) Age
2) Number of medicines
3) Number of physicians involved in patient care
4) Other medical conditions
- Hepatic impairment
- Renal impairment
5) Use of Over The Counter (OTC) medication
6) Herbal medication

Question 3

what can be the patient outcomes of ADRs?

Answer 3

1) Adverse or undesirable: Toxicity & Reduced efficiency
3) Beneficial: additive effect
4) Not Clinically Significant

Question 4

ADR’s can affect the pharmacokinetic properties of a drug. outline the types of pharmacokinetic interactions it can lead to. (4)

Answer 4

Affects ADME

1) Absorption: rate, extent
2) protein binding: Free drug, bound drug
3) metabolic: enzyme inhibition or induction
4) renal: excretion increased or decreased

Question 5

list some enzyme inducing drugs (5)

Answer 5

1) Rifampicin
2) Phenytoin
3) Carbamazepine
4) Phenobarbitone
5) St John’s Wort

Question 6

list some enzyme inhibitors (5)

Answer 6

1) Amiodarone
2) Erythromycin
3) Grapefruit juice
4) Ketoconazole
5) Cimetidine

Question 7

List some drugs with Narrow Therapeutic Indexes (6)

Answer 7

1) Warfarin
2) Digoxin
3) Ciclosporin
4) Phenytoin
5) Carbamazepine
6) Theophylline
- A combination of a narrow therapeutic index drug with an enzyme inducer/inhibitor is likely to be a problem

Question 8

what are Pharmacodynamic Interactions?

Answer 8

1) the effects of ONE drug is/are changed by the presence of ANOTHER drug at its SITE of action
- Competition for specific receptors
- Interference with physiological systems

Question 9

what are Additive / Synergistic pharmacodynamic Interactions and give examples

Answer 9

1) Not “true interactions” more “combined toxicity”

2) K-sparing diuretics & ACE-Inhibitors

Question 10

what are Antagonist / Opposing pharmacodynamic Interactions and give examples

Answer 10

1) Pairs of drugs with activities which are opposed to one another
2) E.g. Beta Blockers (Propranolol) & Beta2 Receptor Agonist (Salbutamol)

Question 11

give an example of an Electrolyte Disturbance

Interaction

Answer 11

↓K+ due to loop diuretics increases risk of digoxin toxicity

Question 12

list the 3 types of Pharmacodynamic Interaction

Answer 12

1) Additive / Synergistic Interactions
2) Antagonist / Opposing Interactions
3) Interactions due to Electrolyte Disturbances

Question 13

what should pharmacists ask patient about the Herbal remedies they are taking?

Answer 13

1) Health professionals should routinely ask patients about their use of herbal medicines because of potential interactions
2) St John’s Wort: Induces cytochrome P450 isoenzyme CYP3A4

Question 14

explain the relevance of drug-Food Interactions and give examples

Answer 14

1) Food can cause clinically important changes in drug absorption through effects on gastrointestinal motility or by drug binding
2) Tyramine may reach toxic concentrations in patients taking MAOIs
3) Grapefruit juice itself markedly increased felodipine levels

Question 15

explain the relevance of Drug-Alcohol Interactions and give examples. additionally state what the two cautionary labels would say

Answer 15

1) Additive / synergistic interactions: CNS depressants / drugs with sedating actions
2) Metronidazole leads to disulfiram-like effect
3) cautionary label: BNF Advisory labels 2 & 4
- Warning: This medicine may make you sleepy. If this happens, do not drive or use tools or machines. Do not drink alcohol
- Warning: Do not drink alcohol