A clinical trial, which is the investigation of a new drug for its medical potential, consists of four phases. Although the number of steps may vary according to the context of the clinical trial being conducted, it is generally observed that four phases are involved in the entire investigation starting from safety assessment of the sales and marketing phase. The aims of these four phases can be broadly described in the following manner:
PHASE - 1
A new drug that reaches this stage has crossed the pre-clinical research stages. It has been tested on other life forms to rule out extreme fatalities prior to human clinical trials. In phase 1 the focus is on analyzing the safety aspects of the drug. Usually, healthy volunteers, who are paid for their participation, are administered these drugs. An outline of how the drug reacts with a human system upon entering until it exits the body is created and analyzed. Using these details, doses are also estimated for use in other levels. A majority of drugs in development pass this stage, especially those drugs which undergo pre-clinical tests have a better chance of success. It is a relatively short phase due to a small number of subjects and it being an introductory phase.
PHASE - 2
This phase is considered a true pilot trial since the drug is administered for the first time to patients who suffer from the condition that the new drug is proposed to treat. The number of patients who participate is usually kept to a minimum for health reasons. While the small sample size of testing will not show the beneficial nature of a drug, it does help provide additional safety details about side-effects and adverse reactions. This phase also helps in formulating better doses for further trials. This phase, like phase 1, is relatively short and can last up to two years due to a small population of subjects. But due to monitoring of safety and analyzing dosages, time taken may increase.
PHASE - 3
This is the last phase of the clinical trial before the drug and its associated reports is sent to a regulator for approval. This phase involves a large number of trial subjects from 300 to 3000. All of the trial subjects suffer from the condition that the new drug is supposed to treat and cure. Due to the large sample size and the additional monitoring procedures involved, the duration of this phase is the longest taking from one year up to four years and beyond in some cases.
PHASE - 4
This phase of clinical trial involves several thousand volunteers and at this stage, the drug has been received by the regulator and has either been approved to be marketed or has been rejected. Due to the need for extensive surveillance to uncover any side-effects or adverse reactions that did not express during the trials the duration of these trials vary from one trial to another. Usually, it is less than the time taken for a phase 3 of a clinical trial .i.e., less than four years.
Thus on an average, the entire process of clinically testing a drug can take anywhere from a minimum of three to a maximum of eight. This is an estimate and actual durations of clinical trials almost always vary for each trial. This is due to the complex nature of testing a drug on equally complex biological systems like humans.