Effects after occurring after repeated drug administration.
Repeated drug administration can lead to several physiological and pharmacological changes in the body, affecting both the efficacy and safety of the drug.
Tolerance
- Definition: Tolerance is a decreased response to a drug after repeated administration, necessitating higher doses to achieve the same effect.
- Mechanisms:
- Pharmacokinetic Tolerance: Changes in drug metabolism (e.g., enzyme induction) that reduce drug concentrations at the site of action. For example, chronic alcohol use induces CYP2E1 enzymes, increasing alcohol metabolism.
- Pharmacodynamic Tolerance: Changes at the drug's target site (e.g., receptor downregulation or desensitization) that reduce drug effectiveness. For instance, repeated opioid use leads to decreased opioid receptor sensitivity.
- Examples: Opioids (e.g., morphine), benzodiazepines, alcohol, and certain antidepressants.
Dependence
- Definition: Dependence is a physiological or psychological state characterized by the need for continued drug administration to prevent withdrawal symptoms.
- Types:
- Physical Dependence: The body adapts to the drug, leading to withdrawal symptoms upon cessation.
- Psychological Dependence: Cravings and compulsive drug use driven by psychological factors.
- Examples: Opioids, benzodiazepines, nicotine, alcohol, and certain stimulants like cocaine and amphetamines.