**3. Risk factors for ADR in elderly**

Several factors contribute to the higher incidence of ADR. **Table 1** highlights the list of risk factors for ADR in the elderly. Older people experience greater morbidity with a corresponding increase in medication utilization resulting in a higher risk of ADRs [12].

#### **3.1 Physiological changes**

The natural physiological changes that occur due to aging and alterations in homeostatic regulation alter drug response and increase the risk of ADR in them. Drug metabolism and clearance change with alterations in pharmacokinetics [13] further increasing the risk of ADRs. The decrease in total body water alters the volume of drug distribution prolonging the half-life of a drug and increasing the risk of toxicity [14, 15].


**Table 1.** *List of risk factors for ADR.*

The filtration capacity of the glomerulus reduces as age advances, which results in the decreased excretion of drugs and an increase in adverse reactions.

### **3.2 Polytherapy**

Multi-prescription, polytherapy also increases the incidence of adverse reactions. It was estimated that more than 60% of the elderly take five or more drugs regularly. The risk of ADRs is increased with the increase in the number of medicines prescribed [16]. This has been estimated at 13% for two drugs, 58% for five drugs, and 82% for seven or more drugs [17].

#### **3.3 Nonadherence**

Complex medication regimens related to polypharmacy can lead to nonadherence in older adults [18]. Nonadherence can lead to serious sequelae, including disease progression, treatment failure, hospitalization, and adverse drug events [19].

#### **3.4 Potentially inappropriate medications**

The use of potentially inappropriate medications (PIMs) in the elderly has also been described as a potential cause of ADR [20]. PIMs use increases the risk of hospitalization, drug-related problems, and other adverse health outcomes by two to three folds [21]. For example, drug-related problems secondary to the inappropriate use of sedatives and hypnotics among older adults are found highly associated with the risk of falls, delirium, and hallucination [22].

#### **3.5 Medication errors**

Errors in medication administration and autonomous modification of medication schedules have also been reported to contribute to ADRs [23]. Another important risk factor for developing ADR is its previous occurrence. Re-exposure to offending drugs due to poor documentation can cause the same ADR.

#### **3.6 Multiple diseases**

The risk of ADRs also increases with an increasing number of chronic diseases. When medicine was given to treat one condition, it aggravates the signs or symptoms of another underlying disease. For example, beta-blockers taken for cardiovascular disease worsen asthma symptoms or metoclopramide for gastric dysmotility worsens motor symptoms of Parkinson's disease [24].
