Drug Interactions & Its Introduction:
“The person who takes medicine must recover twice, once from the disease and once from the medicine”. – William Osler, M.D.
Drug Interaction: A mechanism by which a drug interact with the action(s) of another drug or the modification of the action of a drug by the concurrent or prior administration of another drug is known as drug interaction. When we talk about drug interaction, generally interaction between the drugs comes in mind (Drug-Drug interaction). It has been observed that interaction may also exist between drugs & foods (Drug-food interaction), as well as drugs & herbs (Drug-herbs interactions).
Mostly drug interaction should be avoided as it may produce unexpected or poor outcomes. Sometimes it is used intentionally, as it may help in retarding the excretion of useful drug molecule, who presence in the body can heal the disease during the course of the therapy.
Example of Beneficial Drug Interaction:
- Carbidopa with levodopa (Available as Carbidopa/levodopa)·
- Probenecid with penicillin·
- Reduces the risk of side effects
Types of Drug Interaction:
- Pharmacodynamic Interactions:
- Drugs acting agonistically at the same receptor sites leading to potentiation·
- Drugs acting antagonistically at the same receptor leading to antagonism
2. Pharmacokinetic Interaction:
Drugs affecting each other at sites of absorption, distribution, metabolism, and excretion
|Pharmacodynamic Interaction||Pharmacokinetic Interaction|
|Drug B Increases the effects of Drug A||Drug B Increases the effects of Drug A|
|Drug B Decreases the effects of Drug A||Drug B Decreases the effects of Drug A|
What are the outcomes of Drug Interactions?
- Increased toxicity
- Decreased Efficacy
2. No Clinical Significance
- Increased activity (eg penicillins/cephalosporin with probenecid
How do Drug Interactions occur?
There are various mechanisms by which a drug interacts with other drugs, foods, and other substances.
An interaction can only result when there is an increase or decrease in the following:
- Adsorption of a drug into the body·
- Distribution of the drug within the body·
- Alteration made to the drug by the body (Metabolism)·
- Elimination of a drug from the body
Drug interaction may occur when drugs with similar (additive) effects or opposite (canceling) effects on the body are administered together. For examples when two drugs with sedation as side effects are administered into the body, major sedation is observed (eg. narcotics and antihistamines). Drug interactions also occurs when a drug alters the concentration of a substance that is generally present in the body, this alteration of substances reduces or enhances the effects of another drug that has been administered into the body (eg. warfarin (coumadin) and vitamin k containing products) warfarin acts by reducing the concentration of the active form of vitamin K in the body. So, when Vitamin K is taken, it reduces the effect of warfarin in the body.
When drug is administered into the body, it is absorbed into the blood and then moves to their site of action. Most drug absorption that is due to the altered absorption occurs in the intestine.Some of the various potential mechanisms through which the absorption of the drug can be reduced are as follows:
- An alteration in blood flow to the intestine·
- Change in drug metabolism (breakdown) by the intestine·
- Increased or decreased intestinal motility (movement) ·
- Alterations in stomach acidity, and ·
- A change in the bacteria that reside in the intestine
Drug absorption also can be affected if the drug’s ability to dissolve (solubility) is changed by another drug or if a substance (eg. food) binds to the drug and prevent absorption.
Drug distribution defined as the movement of drug to and from the blood and various tissues of the body (for example, fat, muscle, and brain tissue) and the relative proportions of drug in the tissues.
Factors Affecting Drug Distribution
Rate of Distribution:
- Membrane Permeability
- Blood Perfusion
Extent of Distribution:
- Lipid Solubility
- pH – pKa
- Plasma Protein Binding
- Intracellular Binding
Drug metabolism can be defined as the chemical alteration of a drug by the body.
Factors affecting Drug metabolism:
- Species Differences
- Drug Dose
- Enzyme Induction
- Enzyme Inhibition
The removal of drug from the body is known as elimination. Routes of elimination includes:
- Elimination in the urine
- Elimination in the Bile
- Other forms of elimination
In India and abroad, most adults and elderly individuals consume medicines or drugs in order to treat their diseases without knowing the fact that these medicine or drug can interact with each other and can produce an adverse effect in the body. So, it is always recommended to have some knowledge about your prescribe drug and should always update your personal doctor about any side effects caused by taking any medication.