Which factor can cause a type A adverse drug reaction for Digoxin?

Type A adverse drug reactions, also known as predictable or dose-dependent reactions, occur as a result of the pharmacologic actions of a drug. Digoxin, which is used primarily for heart conditions such as atrial fibrillation and heart failure, has a narrow therapeutic index. This means that there is a small margin between the therapeutic dose and the dose that can cause toxicity. Thus, the closer a patient's dose approaches the toxic level, the higher the likelihood of experiencing an adverse reaction.

Given that type A reactions are typically predictable based on the drug's known pharmacological effects, the narrow therapeutic index of digoxin is significant. It increases the risk of toxicity, especially in at-risk populations like the elderly or those with renal impairment, leading to issues such as digoxin toxicity, which can manifest as cardiac arrhythmias, gastrointestinal symptoms, and neurological effects.

In contrast, options related to idiosyncratic effects, teratogenicity, or carcinogenicity pertain more to type B reactions, which are unpredictable and not directly related to the pharmacological actions of the drug. Type B reactions can arise from unique individual responses rather than the drug's inherent properties. Thus, focusing on the narrow therapeutic index accurately addresses the core reason for type A adverse