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Drug toxicity: Drug–Drug Interaction

Drug toxicity: Drug–Drug Interaction

Drug–drug interactions can precipitate toxicity through multiple mechanisms. Absorption interactions alter how drugs enter the body, exemplified when ranitidine increases the absorption of basic drugs, while cholestyramine decreases the levels of propranolol. Protein binding interactions occur when drugs share the same binding sites on plasma proteins. Drugs like aspirin and warfarin, when bound in excess, can lead to increased free drug concentrations, enhancing the potential for...

Pharmacokinetics: Drug–Drug Interactions

Pharmacokinetics: Drug–Drug Interactions

Drug interactions occur when the pharmacological effect of one drug is altered by another substance, either enhancing or diminishing its activity. The drug whose activity is altered is known as the object drug, and the substance causing the alteration is called the agent drug or the precipitant. The net effects of these interactions are mostly undesirable, leading to decreased effectiveness or increased adverse effects. In rare cases, interactions can be beneficial, such as the enhanced...

Pharmacokinetics: Drug–Food and Drug–Viral Interactions

Pharmacokinetics: Drug–Food and Drug–Viral Interactions

A drug interaction occurs when the concurrent use of another drug, food, or an external substance alters the pharmacological activity of a drug. This interaction can modify the action of the original drug, affecting its effectiveness and safety.Drug–food interactions are significant as they impact drug absorption, metabolism, and excretion. For example, grapefruit juice is a well-known disruptor of drug metabolism. It inhibits the cytochrome P450 3A4 enzyme, crucial for the metabolism of many...

Combined Effects of Drugs: Synergism

Combined Effects of Drugs: Synergism

Synergism is a useful mechanism where combining two or more drugs is more effective than each constituent used alone. Such combinations are also called supra-additive interactions. The drugs collectively enhance the final therapeutic effect by acting on different targets. Another advantage is that the low dose of each constituent drug is sufficient to achieve the desired effect. This helps reduce the duration of therapy and lower the adverse effects of these drugs.
Such synergistic combinations...

Combined Effects of Drugs: Antagonism

Combined Effects of Drugs: Antagonism

The combined effects of drugs can result in various interactions, of which an important type is antagonism. Antagonism is a mechanism where one drug inhibits or counteracts the effects of another drug. Antagonism can occur through various means, including receptor binding, allosteric modulation, functional interaction, chemical reactions, and pharmacokinetic processes.
The most common type is receptor antagonism, where one drug acts as an antagonist to block the effects of another drug by...

Drug-Receptor Interactions

Drug-Receptor Interactions

Drug-receptor interaction describes the binding of receptors by drugs, but not all drug-receptor interactions result in activation and tissue response. For instance, the binding of agonists activates the receptor to generate a cellular reaction, while antagonists bind to receptors without causing their activation.
Several parameters, such as the drug's affinity for its receptor and its efficacy, which is its ability to activate the receptor, determine the drug's effect on the tissue.

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Related Experiment Video

Updated: May 21, 2026

Creating Dynamic Images of Short-lived Dopamine Fluctuations with lp-ntPET: Dopamine Movies of Cigarette Smoking

Creating Dynamic Images of Short-lived Dopamine Fluctuations with lp-ntPET: Dopamine Movies of Cigarette Smoking

Published on: August 6, 2013

[Smoking and drug interactions].

Annamari Rouhos¹, Kari Raaska

¹HYKS, Meilahden Sairaal, Medisiininen Tulosyksikkö, Keuhkosairaudet.

Duodecim; Laaketieteellinen Aikakauskirja

|June 26, 2012

Summary

Smoking significantly impacts drug efficacy by inducing liver enzymes, potentially lowering medication effectiveness. Quitting smoking requires careful medication review to prevent dangerous drug level increases.

Area of Science:

Pharmacology
Drug Metabolism
Toxicology

Context:

Smoking is a widespread habit with significant health implications.
Polycyclic aromatic hydrocarbons (PAHs) in tobacco smoke are potent inducers of the CYP1A2 enzyme.
CYP1A2 plays a crucial role in metabolizing numerous clinically important medications.

Purpose:

To elucidate the mechanisms and clinical significance of drug interactions caused by smoking.
To highlight the impact of CYP1A2 enzyme induction on drug efficacy.
To emphasize the pharmacodynamic interactions between nicotine and certain drug classes.

Summary:

Smoking induces the CYP1A2 enzyme, leading to decreased efficacy of drugs like psychoactive medications, theophylline, warfarin, antiarrhythmics, and anticancer agents.

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Diagonal Method to Measure Synergy Among Any Number of Drugs

Diagonal Method to Measure Synergy Among Any Number of Drugs

Published on: June 21, 2018

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Last Updated: May 21, 2026

Creating Dynamic Images of Short-lived Dopamine Fluctuations with lp-ntPET: Dopamine Movies of Cigarette Smoking

Creating Dynamic Images of Short-lived Dopamine Fluctuations with lp-ntPET: Dopamine Movies of Cigarette Smoking

Published on: August 6, 2013

Diagonal Method to Measure Synergy Among Any Number of Drugs

Diagonal Method to Measure Synergy Among Any Number of Drugs

Published on: June 21, 2018

Nicotine can also cause pharmacodynamic interactions with beta-blockers and benzodiazepines.

Upon smoking cessation, normalization of induced metabolism increases the risk of elevated drug concentrations, particularly for drugs with a narrow therapeutic index (e.g., clozapine, theophylline).

Enzyme induction by smoking has a slower onset and offset compared to enzyme inhibition.

Impact:

Healthcare providers must screen medications and evaluate dosage adjustments during smoking cessation or hospitalization.
Understanding these interactions is critical for patient safety and optimizing therapeutic outcomes.
This knowledge aids in managing patients undergoing smoking cessation programs and those requiring hospitalization.