Drug Interaction Flashcards
Define Drug interaction
- When the pharmacological activity of one drug is altered by the concomitant use of another drug or by the presence of some other substances.
- Interaction between a drug and another substance e.g. food
What is an Object drug?
Drug whose activity is affected by such as interaction.
What is a Precipitant?
Agent which precipitates such an interaction.
What does a drug interaction lead to?
An interaction that could manifest as an:
- INCREASE or DECREASE in drug effectiveness.
- ADVERSE REACTION or new SIDE EFFECT.
Give an example when drug interaction can be beneficial.
Penicillin and Probenecid enhances activity of Penicillin.
Factors contributing to drug interactions:
Many Malaysian People Are in Need of Drug M.
M - Multiple drug therapy and prescribers.
M - Multiple pharmacological effects of drug.
P - Poor patient compliance.
A - Advancing age of patient.
N - Narrow therapeutic index drugs e.g. Lithium, Digoxin, Warfarin.
D - Drug-related factors
M - Multiple diseases / predisposing illness.
The 6 Types of Drug Interactions:
- Drug-Food interactions
- Drug-Disease interactions
- Environment-Induced interactions
- Drug-Drug interactions
- Chemical-Drug interactions
- Drug-Laboratory test interactions.
Example of Drug-Food interaction
Mixing alcohol with some drugs may cause a feeling of tiredness or slows down reactions.
What further contributes to Drug-Food interaction?
- Lack of standardization
- Contamination
Drug-Food interaction can result in…
Impaired nutritional benefit.
When do Drug-Disease interactions occur?
When an existing medical condition makes certain drugs potentially harmful.
Example of Drug-Disease interaction
High BP can cause unwanted reaction with nasal decongestant.
What is important for a physician to know?
Patient’s entire disease profile
What patients are prone to Drug-Disease interactions?
- Frail elderly hospitalised patients
- Critically ill patients or Chronic diseased patients
Explain Drug-Disease Interactions
- may occur when an existing medical condition makes certain drugs potentially harmful
- can occur when medication has the potential to worsen disease
Example of Drug-Disease Interaction
high blood pressure can cause unwanted reaction with nasal decongestant
Explain Environment-induced interaction
- when there is an intentional or unintentional exposure to environmental chemicals that can cause pharmacokinetic and/or pharmacodynamic reactions
Examples of Environment-induced interactions
- smoking
: carcinogenic polygenic aromatic hydrocarbon in tobacco smoke are potent INDUCERS of CYP4501A1/1A2 and possibly 2E1 enzymes
: pharmacokinetic interactions with smoking occur with drugs like caffeine (substrates of CYP1A2)
Explain Drug-drug interactions
- when two or more drugs interact with each other to produce pharmacokinetic and pharmacodynamic reactions
- harmful drug-drug interactions are important as they cause 10-20% of ADR
Example of drug-drug interactions
- mixing drugs taken to sleep (sedatives) and drugs taken for allergies (antihistamines) can slow reactions and make driving dangerous
Why are the elderly patients vulnerable to drug-drug interactions?
- increasing age
- number of drugs prescribed
- frequency of potential drug-drug interactions
Examples of top drug-drug interactions
- Warfarin - Non-steroidal anti-inflammatory drugs (NSAIDs)
- Warfarin - Sulfa Drugs
- Warfarin - Macrolides, Quinolones, Phenytoin
- ACE Inhibitors - Potassium Supplements and Spironolactone
- Digoxin - Amiodarone and Verapamil
- Theophylline - Quinolones
Explain Pharmacokinetic drug-drug interactions
- what the body does to the drug
- occur when one drug alters the concentration of another drug with clinical consequences
Definition ADME interactions?
pharmacokinetic interactions (ADME interactions) occur when the absorption, distribution, metabolism or elimination process of the object drug is altered by the precipitant drug
Resultant effect of ADME interactions?
altered plasma concentration of the object drug
Explain drug absorption interactions
- interactions where the absorption of the object drug is altered
Where are interactions influencing absorption more likely to occur?
GI tract
What are the net effect of drug absorption interactions?
- faster or slower drug absorption
- more or less complete drug absorption
What are clinically significant interactions that occur due to the drug absorption effect?
- changes in GI pH and motility
- changes induced by chelation and absorption
- transporter based interactions
Explain how alteration in GI pH affects drug absorption?
- non-ionised = lipid soluble = more readily absorbed from GIT (than in ionised form)
: some drugs are absorbed from stomach (acidic media), so when the media becomes neutral or alkaline, drug absorption is affected
Example of how alterations in GI pH can occur?
- sulphanomides and aspirin when given with antiacids lead to enhanced dissolution
- tetracycline with antacid leads to decreased dissolution
How does drug interaction alter bacterial flora, ultimately affecting absorption?
- bacterial flora has a marked role in metabolism of some drugs
: long term antibiotics may kill normal flora and affect drug absorption
e. g. 40% or more of administered Digoxin dose in metabolised by the intestinal flora
- antibiotics kill a large population of intestinal flora, and thus increases the Digoxin concentration and chances of toxicity
Define complexation
the covalent or non-covalent interaction between two or more compounds that are capable of independent existence
Define chelation
a type of bonding where ions and molecules bind to metal ions
How does drug interaction cause complexation and chelation, therefore affecting absorption?
- drugs such as tetracycline / fluroquinolones with antacid / food contain divalent ions
: lead to the formation of poorly soluble chelates or complexes which cannot be absorbed
e.g. warfarin and cholestyramine lead to reduced absorption due to binding
