Factors predisposing to ADRs may relate either to the properties of the drug or to the characteristics of the individual. Different factors predisposing to ADRs are discussed below:
1. Multiple drug therapy: The incidence of ADRs has been known to increase sharply with the number of drugs taken. E.g. occurrence of synergistic effects and additive effects.
2. Age: The very old and the very young are more susceptible to ADRs. In the elderly, physiologic changes due to ageing and chronic disease states often contribute to impaired drug metabolism, which can lead to increased incidence of ADRs. Neonates and children also differ from adults in the way they handle and respond to drugs, making them more susceptible to ADRs. E.g. neonates are more prone to adverse effects of chloramphenicol, Ryes syndrome due to aspirin in children and increased ADRs due to hypnotics, diuretics, etc in elderly.
3. Gender: women are generally more susceptible to ADRs then men. E.g. women are more susceptible to blood dyscrasias due to phenylbutazone and chloramphenicol than men.
4. Intercurrent diseases: Patients with impaired renal or hepatic function are at substantially increased risk of developing ADRs to drugs metabolized and eliminated by these organs. Other specific
disease states like human immunodeficiency virus (HIV) positive patients are also known to suffer an increased incidence of ADRs. E.g. increased occurrence of ADRs due to antitubercular drugs in human immunodeficiency virus (HIV) positive patients.
5. Race and genetic polymorphism: Inherited factors that affect the pharmacokinetics of drugs can also predispose to an individual’s risk of ADRs. E.g. increased incidence of ADRs due to isoniazid and other cytochrome P450 metabolized drugs in poor metabolizers.