Drug Interactions And Adverse Drug Reactions

Question 1

What is a drug interaction?

Answer 1

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

Question 2

What are the 4 Pharmacokinetic Interactions and how may they effect the drugs?

Answer 2

1. Absorption (rate and extent)
2. Protein Binding (may reduce the dose)
3. Metabolic (induce and inhibit)
4. Renal (excretion) (may reduce the dose, as lost through excreting)

Question 3

What are some incidence of drug interactions are proportional too?

Answer 3

1. Age- older you are more likely to happen
2. Frailty
3. Number of Medicines
4. Number of physicians involved in patient care
5. Other medical conditions- Hepatic and Renal impairment
6. Use of OTC medication
7. Herbal Medication
8. Friends and family offering medication

Question 4

What are some of the patient outcomes that may happen from ADRs?

Answer 4

1. Adverse and undesirable- toxicity and reduced efficiency
2. Beneficial- additive effect- two drugs may interact and cause the blood pressure to actually lower
3. Not clinically significant

Question 5

What is an enzyme inducer and give some examples?

Answer 5

They increase enzyme activity and reduce the efficiency of metabolism:
Examples: Rifampicin, Phenytoin, Carbamazepine, Phenobarbitone, St john’s Wort (Contraceptive pill)

Question 6

What is an enzyme inhibitor and give some examples?

Answer 6

They reduce metabolism and increase other drug levels:

Examples: Amiodarone, Erythromycin, Grapefruit Juice, Ketoconazole, Cimetidine

Question 7

What does narrow therapeutic index mean and give some examples?

Answer 7

It’s the fine margin between toxic and inefficient:

Examples: warfarin, digoxin, ciclosporin, Phenytoin, Carbamazepine, Theophylline

Question 8

What is a pharmacodynamic interaction?

Answer 8

Interactions where the effect of ONE drug is/are changed by the presence of ANOTHER drug at its site (fight for the same receptor)

1. Competition for specific receptors
2. Interference with physiological systems

Question 9

What types of pharmacodynamic interactions can you have?

Answer 9

1. Additive/Synergistic- Not “true interactions” and more “combined toxicity”- e.g. K-sparing diuretics and ace inhibitors
2. Antagonist/Opposing- Pair of drugs with activities that are opposed to one another- e.g. Beta Blockers (propanolol) and beta receptor agonist (Salbutanlol)
3. Interactions due to Electrolyte Disturbances- e.g. K+ reduction due to loop diuretics which increases risk of digoxin toxicity

Question 10

What should you as a pharmacist do about drug and herb interactions?

Answer 10

1. Routinely ask patients about their use of herbal medicines
2. The interacting constituent of the herb is not always known and is therefore not standardised for it. Could vary widely between different products and batches of the same product.
3. Example: St John’s Wort

Question 11

How does Drug-Food interactions relate to ADRS?

Answer 11

1. Food can cause clinically important changes in drug absorption through effects on the GI motility or by drug binding
2. Example Grapefruit juice may increase felodipine levels
3. Calcium with certain antibiotics bind with the same site

Question 12

How does Drug-alcohol interactions relate to ADRS?

Answer 12

1. Any drug with BNF labels 2 and 4
2. Additive/synergistic interactions- CNS depressants/drugs with sedating actions
3. Metronidazole leads to disulfiram like effect which is a sharp painful feeling when taken with alcohol

Question 13

How do you initially manage drug interactions?

Answer 13

1. Be aware of potentially interacting drugs then access clinical significance and risk to patients:
   - Avoid combination
   - Adjust dose
   - Monitor the patient
   - Continue the medication as before

Question 14

What is the pharmacists role in managing ADRS?

Answer 14

1. Identify the patients at risk of ADR
2. Identify drugs known to produce ADR (warfarin) and monitor patient
3. Avoid use of drugs that cause ADR when there’s an alternative available
4. Review patients medicines- stop any unwanted ones and check for interactions/contra-indictions
5. Make sure patient is counselled on the correct use of their medicines and the possible side effects
6. Reporting ADRs

Question 15

What is an Adverse Drug Reaction?

Answer 15

An ADR is an unwanted or harmful reaction experienced following the administration of a drug or a combination of drugs and is suspected to be related to the drug

Question 16

What are the patient groups that are most at risk from ADRs?

Answer 16

• Extremes of age
• Gender:Females
• Polypharmacy
• Incurrent diseases
• History of intolerance of hypersensitivity

Question 17

Whats the common way NSAIDS should be taken?

Answer 17

With or after food

Question 18

What do the blue boxes in the BNF represent?

Answer 18

Recommendations for dose or lowest dose

Question 19

How do you manage ADRs from NSAIDS?

Answer 19

• Paracetamol for analgesia instead
• Use Ibuprofen at lowest dose
• Don’t use more than one oral NSAID at a time (not aspirin and ibuprofen)
• Identify patients at risk- Elderly, history of ulcers
• Use PPI’s to protects the stomach from NSAIDS

Question 20

Describe warfarin in terms of ADRs?

Answer 20

Can lead to:
-GI bleeding
- Haematuria
- High INR
- Haematoma
- Watery and thick blood
Always look at the warfarin book

Question 21

What are the symptoms of Digoxin toxicity and how do you manage it?

Answer 21

Digoxin is a drug for the heart
Symptoms are: Nausea, visual disturbances, heart block, arrhythmias 
Management: 
- Stop digoxin
- Check level of drug in blood
- Check urea and electrolytes
- Monitor heart rate and pulse
- Check for Drug interactions
(try to workout what caused digoxin toxicity)