According to the definition, provided by WHO, any adverse reaction to medicines, harmful and undesirable for the body, which occurs when these meds prescribed for the treatment, diagnosis and prevention of diseases, is attributed to side effects of medicinal products.
It is believed that adverse reactions occur in 4-29% of patients, who take
different medications. The incidence of side effects depends primarily on individual characteristics, sex, patient’s age, severity of the disease, pharmacodynamics and pharmacokinetics, dose, duration of using, method of medicine administration, and drug interactions.
Consequences of side effects
Side effects are the reason for seeking medical attention for 2-3% of patients; 3% of them need help in the intensive care unit. The most common causes of hospitalization are adverse reactions to cardiac glycosides, acetylsalicylic acid, corticosteroids, diuretics, antihypertensive drugs, and indirect anticoagulants. Adverse events are observed in 10-20% of hospitalized patients. 3-12% of them have extended duration of hospitalization. Side effects are the cause of death of approximately 0.27% of patients. In case of intravenous administration of drugs for severely ill individuals, this indicator can exceed 1.5%.
In most cases, cardiac glycosides, antibiotics, diuretics, potassium preparations, analgesics, tranquilizers, anti-diabetic agents are the most common causes of side effects in hospitalized patients.
Most often, side effects include the following conditions: digestive tract dysfunctions, skin changes, exceeded quantity of potassium ions in the blood plasma, hematopoietic disorders, or blood clotting, allergic reactions, as well as mental disorders.
The most common causes of fatal outcomes, caused by side effects of drugs, include gastrointestinal bleeding and peptic ulcers (when using glucocorticoids, NSAIDs, anticoagulants), other bleeding (when using anticoagulants, cytostatic drugs). Besides, aplastic anemia (taking chloramphenicol, phenylbutazone, gold preparations, cytostatics), liver damage (while using chlorpromazine, isoniazid, tetracycline), kidney damage (using NSAIDs, aminoglycosides), low resistance to infections (cytostatics, glucocorticoids), allergic reaction (penicillin preparations procaine) are side effects, which can lead to death.
Types of side effects
Adverse reactions can be divided into:
- predictable (they are expected);
- unpredictable (they are rarely developed, aren’t always related to the pharmacological action of the drug, and aren’t described in the scientific literature).
The predicted adverse reactions have a definite clinical presentation (for example, parkinsonism appears while taking aminazine; arterial hypertension is the side effect of glucocorticoids). At the same time, identic symptoms (for instance, headache, weakness, dyspepsia, changes in blood pressure, heart rate) may be side effects of drugs, which belong to different groups. For example, headache belongs to Viagra side effects and Avanafil adverse effects.
By the criterion of pathogenesis, the predicted side effects are divided into the following groups:
1) concomitant undesirable pharmacological effects (functional metabolic and toxic ones, for example toxic effects can be caused by counterfeited OTC Viagra);
2) allergic reactions;
3) drug dependence (mental, physical, withdrawal syndrome).
In some cases, the mechanism of side effects can be combined. For instance, as a consequence of the primary drug toxic effect, body proteins acquire antigenic properties, which in turn leads to an increase in antibody synthesis (AT) and hypersensitivity.
By the nature of the onset, the side effect can be direct and indirect. Depending to localization, they may be local and systemic.
According to the severity of the clinical course, side effects are divided into non-severe (there is no need to stop taking of the drug or special treatment, after decreasing dosage of the drug side effects disappear), of medium severity (drug cancellation and special treatment are necessary) and severe (there are syndromes that pose a threat to the patient’s life, for example, complete AV block).
Causes of side effects
I) Not associated with taking of medical products:
a. Associated with the characteristics of the patient’s body (age, gender, genetic characteristics, propensity to allergic reactions, features of the disease, bad habits).
b. Associated with external factors (for instance, iatrogenesis).
II) Associated with drugs:
a. Improper choice of medicines.
b. Pharmacodynamic and pharmacokinetic features.
c. ways of drug administration.
d. interaction of medicines.
Concomitant undesirable pharmacological effects are caused by the effect of drugs on the same type of receptors located in various organs and tissues, or on other types of receptors and biologically active centers sensitive to this medication. For example, sildenafil citrate (Viagra component) can affect vision as it may influence PDE6 enzyme contained in the retina. PDE6 isn’t a main target of the drug, it affects mainly PDE5, but in some persons, effect on PDE6 is also pronounced.