4.2
Adverse effects
Adverse effects are defined as any undesirable or unintended consequences of medicine administration. They can include all kinds of noxious effect: trivial, more serious or even lethal. All drugs are capable of producing such effects. These can develop immediately, after prolonged medication or even after stoppage of the drug. Adverse effects show the incidence of 10 – 25 %. They are more common in elderly patients and with multiple drug therapy. They can be classified in many ways, for example:
  • Predictable (augmented) reactions – which are based on the pharmacological properties of the drug, are more common, related to the dose and mostly reversible. (side effects, toxic effects, drug withdrawal effects)
  • Unpredictable (bizarre) reactions – are more connected with the uniqueness of a patient rather than the drug´s known actions. They usually include allergies, are less common, more serious and in most cases require withdrawal of the drug.
Severity of adverse effects can be graded as:
  • Minor – no therapy or antidote is needed.
  • Moderate – requires change in drug therapy and sometimes specific treatment.
  • Severe – potentially life-threatening condition, which can cause permanent damage, usually requires intensive medical treatment.
  • Lethal – contributes to patient’s death (directly or indirectly).
4.2.1
Adverse drug effects categories
Side effects are unwanted but unavoidable effects occurring at therapeutic doses. They are predictable and known from the pharmacological profile of a drug.
Secondary effects are indirect consequences of a drug´s primary action, e.g. bacterial flora elimination by antibiotics.
Toxic effects result from excessive pharmacological action of a drug due to prolonged use or overdose. These effects are predictable and related to the dose taken. The most commonly involved organs in drug toxicity are kidneys, liver, skin, blood, central nervous system and cardiovascular system.
Intolerance indicates a low threshold of a patient to the drug action. It is similar to toxic effects at therapeutic doses.
Idiosyncrasy is genetically determined abnormal reaction to a drug. This type of reaction is restricted to individuals with a particular genotype.
Drug allergy is immunologically mediated reaction that is not related to the pharmacodynamics profile of a drug. They can occur even with small doses, vary in duration and onset. It is also called drug hypersensitivity.
Drug dependence is a state in which a drug is used for personal satisfaction rather than medical needs. It can be divided into psychological, when the patient believes that the state of wellbeing can be only achieved via the drug action. Physical dependence is similar to drug addiction and discontinuation of the drug results in withdrawal syndrome.
Teratogenicity is defined as the capacity of a drug to cause foetal abnormalities to pregnant women.
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Video 4. Medication side effects