Drug Interactions: What You Need to Know

Drug Interactions: What You Need to Know

Drug interactions occur when two or more drugs affect each other, changing their effectiveness or toxicity. Understanding drug interactions helps you use medications safely and effectively.

1. Metabolism-Based Interactions:

• CYP450 Enzyme Inhibition:

• Certain medications like azole antifungals, antihistamines, and macrolide antibiotics can inhibit CYP450 enzymes, reducing the metabolism of other drugs. This leads to increased drug levels in the blood, enhancing drug efficacy and potentially causing drug toxicity with medications having a narrow therapeutic window.

• Example: Ketoconazole antifungal can inhibit the metabolism of statins, increasing the risk of rhabdomyolysis.

• CYP450 Enzyme Induction:

• Stomach ulcer medications, proton pump inhibitors (lanzoprazole, omeprazole), anticonvulsants (barbiturates), sleeping pills, tuberculosis medications (isoniazid), alcohol, and tobacco can increase the metabolism of CYP450 enzyme system. This can lead to decreased drug effectiveness.

• Example: Rifampicin, a tuberculosis medication, can decrease the effectiveness of birth control pills.

2. Pharmacokinetic Interactions:

Pharmacokinetic interactions involve changes in the absorption, distribution, metabolism, or excretion of a drug due to the effects of another drug.

• Absorption: Weak acid drugs like NSAIDs (paracetamol, ibuprofen, aspirin), sulphonamides (hypoglycemic, diuretics, antimicrobial) can be affected by the pH in the stomach.

• Distribution: Diuretics and drugs distributed in extracellular fluid (theophylline, aminoglycosides) can increase drug concentration in extracellular fluid, leading to toxicity.

• Metabolism:

• Drugs metabolized by the liver can be affected by the activity of CYP450 enzymes.

• Cimetidine can inhibit CYP450 enzymes, causing increased levels of co-administered drugs, leading to increased toxicity.

• Excretion: Vitamin C can decrease the excretion of weak acid drugs, leading to sulphonamide precipitation.

3. Pharmacodynamic Interactions:

Pharmacodynamic interactions involve interactions between drugs at the site of action, resulting in increased or decreased drug effects.

• Antagonism: Two drugs acting on the same receptor with opposing effects.

• Synergism: Two drugs acting on the same receptor or different receptors, enhancing each other’s effects.

• Example:

• Insulin and alcohol: Alcohol can increase insulin release, leading to dangerous hypoglycemia.

• Digoxin and calcium chloride: Increased heart rate, potentially leading to death.

4. Other Interactions:

• Incompatibility: Occurs when two or more drugs are mixed together, forming a precipitate or chemical reaction.

• Chelation: Large-structured antibiotics (tetracycline, macrolide), antibiotics containing fluorine can chelate with metals, reducing absorption.

5. Alcohol-Related Interactions:

• Alcohol and paracetamol: Alcohol can increase the metabolism of paracetamol, causing liver toxicity.

• Alcohol and antifungal medications, H2 blockers, macrolide antibiotics: These medications inhibit CYP450, leading to increased blood acetaldehyde, causing headache, tachycardia.

• Alcohol and sulfonamide hypoglycemic agents, insulin: Increased hypoglycemic effects, risk of hypoglycemia.

• Alcohol and nitroglycerin, calcium channel blockers: Increased vasodilation, hypotension.

6. Opioid-Related Interactions:

• Opioids and alcohol: Respiratory depression.

7. Pain Reliever-Related Interactions:

• NSAIDs and corticosteroids: Stomach ulcers.

Note:

• The above list is not exhaustive.

• Drug interactions can vary from person to person.

• Always consult your doctor or pharmacist before taking any medication.

What to Do If You Suspect a Drug Interaction:

• Report all medications you are taking to your doctor or pharmacist, including prescription, over-the-counter, herbal remedies, vitamins, and dietary supplements.

• Do not change the dosage or stop taking any medication without your doctor’s consent.

• Learn more about the medications you are taking to better understand potential interactions.

Remember, safe and effective medication use depends on understanding drug interactions. Be careful and seek information from reliable sources.