Methods For Detecting Adverse Drug Reactions

Methods For Detecting Adverse Drug Reactions

Many factors are responsible for the adverse effects of drugs on patients receiving them. The adverse effects of the drug depend on its dose, duration, toxicity, and other individual factors such as sex, age, genetics, compliance of patients, and the total number of drugs administered.  Whether a patient experiences the toxicity of a drug depends on its dose. 

The pharmacokinetics of the drug may also affect drug toxicity. Alteration in the pharmacokinetics of the drug may result in an abnormally higher concentration of the drug at the receptor site, resulting in an adverse effect.

The therapeutic index of a drug is also responsible for the adverse effects. A drug with a small therapeutic index is more prone to produce adverse effects than one with a large therapeutic index e.g. therapeutic index of amphotericin B is small while that of acetaminophen is large.  Hence 75% of patients receiving amphotericin B show the adverse effect while less than 1%  of patients receiving acetaminophen show adverse effects. Infants are more prone to adverse effects because of incomplete development of the liver enzyme system. Also, the elderly patient shows a higher incidence of adverse effects. 

The common cause of the drug-induced disease is the excessive pharmacological effects of the drug which is readily predictable whereas other types of drug-induced disease are more difficult to detect and quantify (Non-predictable). The various methods are given below:

Spontaneous Case Reports 

It is the common method of affecting doubts about drug-related diseases. A prescriber suspects that a condition arising in a patient may be drug-related. He, therefore, reports either in a letter to the medical journals or to the manufacturer of the drug. This means other prescribers are alerted to the possibility of a drug-disease relationship. “Spontaneous  Reporting Agencies” are set up to collect and gather such case reports. Although the resulting information collected gives no idea of the frequency with which a given event is caused by a drug, it indicates that several prescribers feel that the event is possibly drug-related. 

In recent years, national registers have been established in several countries with the main aim of providing an early warning that a dug is capable of causing a serious adverse effect. Their registers in general depend upon the voluntary spontaneous reporting of suspected adverse drug reactions by doctors. The British registrar of Adverse Drug Reactions was established in 1964. 

Most physicians fail to report many adverse drug reactions which may be due to the following reasons. 

• The misconception that ADR reflects poor therapeutic agent selection. 

• Lack of interest. 

• Lack of understanding of what to report. 

• Belief that the reaction is unimportant or has been previously reported in the literature.

Vital Statistics and Record Linkage Studies 

The details of the cause of death (as recorded on the death certificate) or of hospitalization (as recorded on the discharge letter) are routinely collected and analyzed. It gives early warning of an epidemic of drug-related disease. Record linkage studies may be used to great effect in the search for drug-induced disease.

Cohort Studies 

The ‘Cohort’ means identifying a group of recipients of a drug of interest and observing these patients for varying lengths of time for what happens to them. This type of study is used for short-term clinical trials of a new drug. Cohort studies involving long-term clinical trials are more difficult to organize. Thus, this method is of great value for detecting predictable adverse effects due to excessive pharmacological effects arising during or immediately after short-term treatment.

Case-Control Studies 

It involves the comparison of a group of patients with a disease that is thought to be due to a drug (the ‘cases’) with a group of patients who do not have the disease (the ‘control’).  The drug histories of the cases and controls are obtained and compared. If a drug is causing the disease then its use in the cases will be far more than that found in the controls.  Case-control studies can be conducted rapidly and efficiently at a relatively low cost. However,  it must be conducted correctly, and the resulting data must be interpreted correctly. The following precautions should be taken while conducting case-control studies:


• The cases must be selected carefully. The disease must be defined clearly, precisely, and accurately. The disease under study must have a reasonable risk of being drug-induced. 

• The controls obtained should be from a similar population of cases with the exception that controls do not have the disease of interest. Controls are usually hospitalized, patients. They should not include patients admitted for conditions that are indications of a drug of interest or which are caused or prevented by the drug of interest. 

• The method used to describe drug use must be identical in cases and controls. 

• Interpretation of results must be accurate.

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