Drug Interactions Flashcards by Dua Khan

What is a drug interaction?

Modification of a drugs effect by prior or concomitant administration of another drug

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What are different things involved in drug interactions?

Drugs

Herbal

Food

Drinks

Pharmacogenetics

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What is the object drug?

Drug which is effected by these interactions

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What is the precipitant?

Agent which precipitants such a reaction

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What are examples of drug interactions which are not always decremental?

Hypertension

Parkinson’s

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What is epidermiology?

Branch of medicine that deals with incidence, distribution and possible control of disease

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What is the incidence of significant interactions?

Relatively low at 1%

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What are some examples of drug involved in serious reactions?

Lithium

Warfarin

Erythromycin

Linezolid

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What are drugs involved in serious interactions often?

Potent with a narrow therapeutic index, meaning a small change in blood levels induce toxicity

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What do lots of foods interact with?

Warfarin

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What happens to the probability of a drug-drug interaction with more medicaments?

Increases exponentially

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Who are some people more likely to suffer from a drug-drug interaction?

Elderly

Young

Critically ill

Patients undergoing complicated surgery procedures

Patients on many medications

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What kinds of conditions make people susceptable to drug interactions?

Chronic

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What are examples of chronic conditions that make people more susceptable to drug interactions?

Liver disease

Renal impairment

Diabetes mellitus

Epilepsy

Asthma

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Who usually experience severe interactions?

Patients with chronic conditions

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What is pharmacodynamics?

Study of how a drug affects an organism

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What is pharmacokinetics?

Study of how the organism affects the drug

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What can drug interactions be?

Additive or synergistic

Antagonistic

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What can interactions be due to?

Changes in drug transport

Fluid and elctrolyte disturbances

Indirect pharmacodynamics interactions

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What are the 4 stages of pharmacodynamics?

Absorption

Distribution

Metabolism

Elimination

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What can a drug do to the pharmacokinetics of another drug?

Alter it

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Why is it possible to predict potential interactions?

Due to marked inter-individual variations in pharmacodynamics process

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What is it not possible to predict?

Patients who will have a clinically significant interaction

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What do absorption interactions mechanisms include?

Formation of insoluble complexes

Altered pH

Altered bacterial flora

Altered GIT motility

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What do most absorption interactions lead to?

Change in absorption rate and not the extend of absorption

When is delayed absorption likely to have a great impact?

When the drug has a short half life or when we want high plasma levels quickly

How can absorption interactions be avoided?

2-4 hours are left between administration of drugs

What do some drugs do in the GI tract?

Bind to each other

What are examples of drugs that bind to each other in the GI tract?

Tetracycline and erythromycin complex with iron, calcium and magnesium Cholestryamine resin used to bind cholesterol in the GI tract also binds to other drugs like warfarin

What is absorption affected by (relates to acids/bases)?

Degree of ionisation which is dependant on pH

Why do drugs increase pH?

Reducing the [H⁺] ions

What are some drugs that increase pH?

H2 antagonists Proton pump blockers Antacids

What destroys normal gut flora?

Broad spectrum antibiotics

Where are most oral medicines absorbed?

Small intestine

What is the rate limiting step of most oral medicines?

Gastric emptying

What can some drugs do to gastric emptying?

Increase or decrease it and so impact absorption of other drugs

What is the drug interaction in distribution?

Protein-protein displacement

When does protein-protein displacement occur?

When there is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug

What does displacement of a drug from a plasma protein cause?

Increased bioavailability of that drug

What are the 2 most important plasma proteins?

Albumin Alpha1-glycoprotein

What protect patients from distribution interactions?

Increased metabolism and excretion

What drugs cause distribution interactions?

Ones which are highly protein bound

What are examples of drugs which are highly protein bound?

Indomethacin Warfarin Ibuprofen

When do interactions involving metabolism occur?

When one drug induces or inhibits the metabolism of another

Where does metabolism of drugs commonly occur?

In the liver via the cytochrome P450 system

What are some drugs that can inhibit the cytochrome system?

Erythromycin Cimetidine

What do drugs inhibiting the cytochrome system cause?

Inhibition of metabolism of drugs that use that cytochrome

What are drugs that can be affected by drugs inhibiting the cytochrome system?

Warfarin Diazepam

What are some drugs that are potent inducers of cytochrome P450?

Barbiturates Carbamazepine

How long does it take for the effects of enzyme induction to be seen?

2-3 weeks

What factors impact the effect of enzyme induction been seen?

Age Disease Genetics Concurrent drug therapy

What are examples of drugs inducing the production of cytochrome P450 enzymes?

Rifampicin inducing CYP 3A4 increases metabolism of Ciclosporin St John's wort induces CYP 3A4 to increase metabolism of ciclosporin

Where are most drugs excreted?

In urine or bile

What do interactions in excretion involve changes in?

Glomerular filtration rate Tubular secretion

What is glomerular filtration rate?

How much blood passes through the glomeruli each minute

What is the glomeruli?

Tiny filters in the kidney that filter waste from blood

What is an example of a drug that inhibits excretion?

Calcium channel blockers

When do pharmacodynamic interactions occur?

When the action of a drug is changed due to another drug acting directly on the same receptor or indirectly on a different receptor

What can pharmacodynamic interactions be?

Direct Indirect Antagonistic Synergistic/Agonistic

What is an example of pharmacodynamic direct antagonsm?

Beta blockers blocking the site of agonists

What is an example of pharmacodynamic synergistic interactions?

Two drugs with the same pharmacological effect acting on the same receptor are given concurrently

What is an example of a pharmacokinetic indirect agonism?

CNS depression Warfarin and NSAIDs

What is an example of pharmacodynamic indirect antagonist?

NSAIDs and antihypertensive medication NSAIDs and treatment for heart failure

What is the process of clinically dealing with an interaction?

1) Determine if the interaction is clinically important 2) Will altering the dose timing solve the interaction 3) Will using an alternative solve the interaction 4) If no for all of above, adjust the dosage and monitor the drug level and physiological function