The discovery of a new drug usually takes 10-15 years. Within this time period, the candidate drug is thoroughly screened for its beneficial as well as side effects. But the side, adverse or toxic effects cannot be detected to a full scale due to some special reasons. The beneficial effects and toxicity of new drugs and vaccines are usually studied by “Clinical trials”, which are divided into four categories ranging from clinical trial phases I to IV. During clinical trial phase-III, about 4,000-10,000 patients are involved and after passing this phase, the drug is allowed to enter into the global market. Then, billions of people, including those who were excluded in phase-III, may be administered with this drug. It is worthy to mention that these 4,000-10,000 patients may not show many of the side effects or toxic actions. The undetected adverse drug reactions (ADRs) are studied in clinical trial phase-IV, which is also known as post market surveillance. For this reason, the ADRs are compared with the tip of the iceberg, as it indicates the minor part of a major event. This phenomenon gave birth to a new branch of the pharmacology known as Pharmacovigilance.
Part of the book: New Insights into the Future of Pharmacoepidemiology and Drug Safety