Adverse drug reactions are unwanted, unexpected and harmful effects resulting from administration of a drug in its usual therapeutic doses. Adverse drug reactions are the major challenge faced in modern day drug therapy. Even Though adverse reactions are present throughout the history of drug treatment, now people and authorities are more concerned about it. There are different types of adverse drug reactions. A better knowledge about them helps in giving more effective and safe medication to patients.
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Adverse drug reactions are not a simple matter. These reactions are becoming one of the major causes for morbidity and mortality in the world. Some studies indicate that adverse drug reactions are the cause for one in every 16 hospital admission, and 4% of total hospital bed capacity.
The World Health Organization ( WHO ) definition for Adverse drug reaction is “a response to a drug which is noxious and unintended and which occurs at doses normally used in man for prophylaxis, diagnosis, or therapy of disease or for the modification of physiologic function.”
How Adverse drug reactions affects drug therapy
- Adverse drug reactions are the main reason for the discontinuation of medication
- It decreases trust of common people towards physicians and medications.
- Sometimes it leads patients to change dosage regimen on their own wish or abrupt discontinuation of treatment, which results in more adverse effects.
- Increases burden of hospitals and healthcare professionals.
- It increases morbidity and mortality
- Increases cost of treatment.
Medicine companies are spending millions of dollars for clinical and non clinical research to find and remove adverse drug reactions on the development stage. But still we can see that some medicines are banned and withdrawn after marketing and use by a large number of patients. This increases the trend of un acceptance of new medicines by common people.
Adverse drug event is another term which sometimes gets confused with adverse drug reaction. Adverse drug events is a broader term which includes all unwanted and harmful effects of drugs within or outside the normal therapeutic dose. This includes all types of adverse reactions, medication errors, drug toxicity, drug abuse etc.
Types of adverse drug reactions
- Dose related adverse drug reactions:
It is also known as type A or Augmented reactions. These are common types of adverse drug reactions. Here the unwanted effect results from the exaggerated pharmacological actions of the drug. Most of these reactions are not life threatening and controlled by some measures.
Examples are,
Tiredness and sleepiness while taking antihistamines
Increased hair growth while taking minoxidil as anti hypertensive.
Dose related adverse drug reactions are predictable and managed by proper patient education and dosage adjustments.
Here are useful measures to control these types of adverse drug reactions.
- Some reactions are unavoidable. For example tiredness and dry mouth feeling while taking tricyclic antidepressants. Here proper patient counseling about these effects and informing the importance of following dosage regimen assures patients to continue treatment.
- Some reactions like tremor during salbutamol treatment may be due to increased sensitization of patients to particular drugs. It can be controlled by dose adjustments.
- In cases like hypoglycemic shocks induced by some anti diabetic medications, inform patients to keep something like chocolates with them every time and eat that when they feel hypoglycemic symptoms.
- Some reactions may be due to concomitant administration of some food or other medicines. Here finding the interacting food or drug and avoiding them or making some time gape with medication helps.
- Non dose related adverse drug reactions
This is also called Type B or Bizarre reactions. These are not common but very important types of adverse drug reactions. These reactions are sometimes serious and lead to morbidity and mortality. Major causes of these reactions include
- Immunological reactions between medicines or its metabolic products with the human immunological system. Example is anaphylaxis shock caused by penicillins.
- Pseudo allergic reactions caused by mast cell activation by some drugs. Example is Red man syndrome caused by Vancoycin.
- Drug intolerance resulting from inability to tolerate adverse effects of medications given at therapeutic doses. Example is liver failure to some patients when they are treated with normal doses of paracetamol.
- Idiosyncratic reactions, where some patients react to medications which cannot be explained by any of the known pharmacological actions of the drug. This is found in a very small proportion of patients. One example is hemolytic anemia caused by some antimalarial drugs in glucose in 6 phosphate dehydrogenase deficient ( G6PD ) patients.
- Dose related and time related reactions
It is also known as Type C or Chronic reactions. Here the adverse reactions produced by long term use of a specific drug. Here drug particles or its metabolites accumulate in the body and produce these effects. A classic example for these types of adverse drug reactions can be seen in the long term treatment with Corticosteroids. When corticosteroids are used for long term they produce a wide variety of adverse reactions like osteoporosis, suppression of the hypothalamic-pituitary-adrenal axis, hypertension, hyperglycemia etc.
These types of adverse reactions can be managed by
- Adjusting dosage regimen in a way that there should be a medicine free gap to prevent accumulation
- Frequent serum analysis to find level of drug in the body
- Monitor other health conditions of patients like renal or hepatic diseases which affect drug clearance in the body.
- Time related reactions
These are also known as Type D or Delayed reactions. Here adverse reactions occur only after some period of time. Example is bladder cancer induced by cyclophosphamide therapy. Here bladder cancer is occurred after a lag time of 1 to 10 years of termination of treatment.
Other examples include teratogenic effects induced by phenytoin, Travide dyskinesia induced by some antipsychotic drugs etc.
- Withdrawal reactions
These types of adverse reactions are also known as Type E or End of the treatment reactions. This is common with drugs which creates a physical addiction in patients. In this case when these drugs are removed from the treatment, unwanted physical or psychological reactions occur. Examples are withdrawal symptoms of Opioids, benzodiazepines etc. this type of reactions can be managed by slowly removing drugs and giving some other non addictive medicines to replace them.
- Failure of therapy
This is also known as Type F reactions. It can be described as failure to produce required results from some drugs in some patients when it is given in normal therapeutic doses. Major reasons for this may be drug resistance, concomitant administration of other medicines etc.
Examples are failure of therapy with some antibiotics. This may be because of the development of drug resistance mechanisms in microbes. It can be managed by increasing the dose or using a combination of other antibiotics of different mechanisms of action.
Conclusion
Adverse drug reactions are unwanted, unexpected and harmful effects resulting from administration of a drug in its usual therapeutic doses. There are different types of adverse drug reactions. A good knowledge of different types and methods to prevent them are necessary to provide a good and safe treatment to patients.
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