Drug Interactions: An Overview

Drug combinations are an important part of disease treatment, but understanding the interactions between drugs is crucial to ensure effectiveness and safety. Drug interactions can be classified based on their effects on each other.

1. Synergistic interactions:

• Additive synergy: Two drugs act on the same target organ with an effect equal to the sum of the effects of each individual drug.

• Example: penicillin and streptomycin, calcium, potassium, and sodium bromide with sedative syrup.

• Synergism by mutual support: Two drugs may act on different target organs but contribute to achieving therapeutic efficacy.

• Example: adrenaline-anesthetic, amoxicillin – clavulanic.

• Multiplicative synergy: Two drugs act on the same target organ but the overall effect is greater than the sum of the effects of each individual drug.

• Example: Bactrim (sulfamethoxazole and trimethoprim).

2. Antagonistic interactions:

• Antagonism: Two drugs have opposite effects, reducing the effectiveness of each other.

• Antagonism should be avoided in drug combinations.

• Antidotation: An antidote helps eliminate or reduce the toxic effects of the main drug.

• Reducing side effects: The second drug helps reduce the unwanted side effects of the main drug.

3. Special interactions:

• Avoiding antagonism: Some drugs should not be used simultaneously as they can lead to dangerous interactions.

• Example: APAB (acetaminophen), SULFAMID.

• Reducing side effects: The second drug helps reduce the unwanted side effects of the main drug.

• Example: Atropine eliminates the sphincter spasm effect of morphine, combined in reducing spasmodic pain.

• Antidotation: There are three forms of antagonism to detoxify the main drug.

• Reversal of effect: The second drug reverses the effect of the main drug.

• Example: Ergotamine – THA of E.

• Reversal of effect with different doses: Drugs of the same type but with different dosages can cause opposite effects.

• Example: Barbiturates: low doses are stimulating, high doses are inhibitory.

• Terpin hydrate: small doses are diuretic, large doses are diuretic.

4. Biological activity of drugs:

• Affinity to receptor: The ability of a drug to bind to a receptor, the smaller the K(D), the better.

• Intrinsic activity: The efficacy of a drug when bound to a receptor, Alpha = Em/ Emax.

Understanding the different types of drug interactions is essential to ensure effectiveness and safety in disease treatment. Doctors will consider factors such as age, health status, medical history, and the types of medications being used to choose the optimal treatment regimen.