by Marvin Somers

Created on: April 17, 2010

The most basic way to ascertain which antidepressant to prescribe is to use a flow chart, which ascertains the best antidepressant based on the answer to certain questions. Factors which may dictate which antidepressant is best include the kind of illness being experience – for example, anxiety, major depression or manic depression – the severity of the illness and the kind of symptoms that the patient is manifesting. Doctors may also be guided by clinical trials - if there is an existing clinical trial for a new drug which may effective then they will often recommend this.

Most modern doctors however will use computer technology and a program known as an algorithm. An algorithm is basically a flowchart in computer form – rather than following the chart on paper the doctor will click through multiple choice questions on a screen. You can get information about and view examples of algorithms for depression and other mental disorders, such as schizophrenia, at the Mental Health Connections algorithms page.

It should be noted however that many such algorithms exist and they are constantly being updated as new evidence is presented from new clinical trials. The algorithm that your doctor uses may be very different from any that you find on the web.

Before using an algorithm, the doctor will generally go through an in depth discussion with the patient about their symptoms and medical history. A patient who has had previous episodes of depression or who exhibits other symptoms not normally associated with clinical depression, such as mania or hallucination, may be referred for further psychiatric treatment and analysis before an antidepressant is prescribed.

This is because periods of depression or anxiety associated with mood disorders such as bipolar and schizophrenia are qualitatively different from similar episodes experienced by patients not suffering from such disorders. As such, they will respond better to different types of drugs and it is important to understand the causes of depression before making a prescription.

Once the type of depression is better understood and the symptoms are analysed, the doctor will begin the algorithm. The algorithm that doctor uses will be different depending on whether the patient is suffering from depression, anxiety or schizophrenia. Examples of questions that the doctor might have to answer are:

- What is the patient’s DSM-IV diagnosis?

- Is the patient psychotic?

- Does the patient’s medication include a mood stabilizer?

Overall, there are hundreds of potential factors. Each factor will indicate a different type of drug. The indications are based on clinical trials where the performance of individual drugs was measured for particular types of condition or symptom. Conclusions regarding the effectiveness of performance are generally based on statistical assessment alone – if drug A was found to be effective for 50% of people with a particular symptom and drug B was found to be effective for 40%, drug A will be preferred. However, if the patient exhibits another symptom for which drug B is 20% more effective on average then drug B may be preferred.

Flow charts and algorithms are complex tools that combine a great deal of medical knowledge from clinical trials. Rather than make assessments himself a doctor will generally rely on these algorithms when making a choice. Often a treatment will not work in the first instance, in which case the doctor will return to the algorithm to make a second selection. While no process is 100% successful, these programs are generally more efficient than humans at making decisions because they can incorporate a vast wealth of historical clinical knowledge.

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