Drug Interactions: Understand to Use Safely

Drug Interactions: Understand to Use Safely

Drug interaction (DI) is a phenomenon that occurs when two or more drugs are used together, resulting in altered drug efficacy or side effects. Understanding the types of DIs and their mechanisms of action is essential for safe and effective drug use.

# Classification of Drug Interactions

DIs are classified into two main types:

• Pharmacokinetic DI: Affects the absorption, distribution, metabolism, or excretion of drugs.

• Pharmacodynamic DI: Affects the mechanism of action of drugs at the site of action.

# Consequences of Pharmacokinetic DI

Pharmacokinetic DIs can lead to:

• Changes in drug plasma concentrations: Causing increased or decreased drug efficacy.

• Increased or decreased pharmacological and toxic effects: Due to changes in drug concentrations, drug side effects may also change.

• No effect on the mechanism of action: Although drug concentrations change, the mechanism of action of the drug remains the same.

# Drug Interactions Affecting Absorption Rate

• Minimal impact on chronic diseases, long-term medications: As these medications are used regularly, the total amount of drug absorbed is not significantly affected.

• Single-dose medications are affected: Changes in absorption rate can significantly affect the efficacy of the drug.

• Unchanged total absorption: Although the rate of absorption changes, the total amount of drug absorbed remains the same.

# Some examples of drug interactions affecting absorption rate:

• DI due to changes in intestinal motility: Changes in intestinal retention time lead to changes in drug absorption.

• DI due to complex formation: Complex formation between the drug and other substances in the stomach reduces the drug’s absorbability. Drugs should be taken 2 hours apart to avoid complex formation.

• DI due to changes in gut flora: Broad-spectrum antibiotics can kill essential bacteria in the gut, affecting the absorption of drugs that require bacteria to function.

• Drugs easily displaced from proteins by NSAIDs: For example, vitamin K antagonist anticoagulants (Warfarin), oral hypoglycemic sulfonamides (tolbutamide), and metabolic type anticancer drugs (methotrexate).

# Drug Interactions Affecting Metabolism

• Metabolic DI: There are two types of metabolic DIs:

• Enzyme induction: Some drugs can stimulate the activity of metabolic enzymes, leading to faster metabolism and reduced efficacy of other drugs.

• Enzyme inhibition: Some drugs can inhibit the activity of metabolic enzymes, reducing the rate of metabolism of other drugs, leading to increased drug concentrations in the blood and increased side effects.

• Changes in blood flow to the liver: Some drugs can affect blood flow through the liver, leading to changes in the rate of drug metabolism.

# Drug Interactions Affecting Excretion

• Excretion DI: Some drugs can affect the excretion process of other drugs through:

• Changes in urine pH: Affects the excretion of drugs through urine.

• Excretion competition: Two drugs compete for the same excretion system, reducing the efficiency of excretion for both drugs.

• Renal tubular flow: Affects the rate of filtration and excretion of drugs through the kidneys.

• Hepatic-intestinal cycle: Some drugs can be reabsorbed in the gut, prolonging the drug’s duration of action in the body.

# Mechanism of Pharmacodynamic DI

• DI on the same receptor: Two drugs compete for the same receptor, reducing the efficacy of both drugs.

• DI on different receptors: Two drugs act on different receptors but share the same mechanism of action, resulting in changes in overall efficacy.

# Consequences of Pharmacodynamic DI

• Synergistic effect: Two drugs act on the same mechanism, enhancing each other’s effects.

• Antagonistic effect: Two drugs act on the same mechanism but in opposite directions, reducing each other’s efficacy.

• Reversal of action: One drug can reverse the action of another drug.

# Some Common Substances with Drug Interactions

• Caffeine:

• Increases the effects of analgesics and antipyretics.

• Increases side effects when combined with some medications.

• Tannins in tea: Precipitates iron salts, alkaloids.

• Caffeine:

• Precipitates with aminazine, haloperidol.

• Increases the absorption of ergotamine.

# Advice

• Always inform your doctor about all medications you are taking, including over-the-counter medications, vitamins, and herbal remedies.

• Do not stop taking medications or change dosages without your doctor’s consent.

• Always read the medication instructions carefully and follow your doctor’s instructions.

Understanding drug interactions is crucial for ensuring safety and efficacy when using medications. Please consult your doctor or pharmacist if you have any questions about drug interactions.