"all Antidepressants Are Created Equal" (some Are More Equal than Others)

"All antidepressants have a 60-70% response rate". "Nobody has ever proved that one antidepressant is better than another". How far are these statements true? Does this mean that antidepressants are interchangeable? All marketable drugs are categorized as belonging to a particular class depending upon specific biochemical or pharmacological properties. Grouping together drugs in this fashion has certain advantages and disadvantages. To assume that drugs belonging to a particular class can be used interchangeably may not be true. Interchangeability does not take into account the benefit, risk or cost of the drug. Drug selection within a class may depend on marketing strategies (Furberg et al.,1999). Drug regulating agencies assume that all drugs within a class are related by structure, activity or adverse effects. This assumption is qualitative i.e., whether the drug is effective when compared to standard drug or plecebo. The agency is not concerned with quantitative differences in terms of efficacy or safety. It is the marketing department, which often decides this issue. Certain drugs may have long term side effects, which become obvious only by post marketing surveillance or anecedotal reports by practitioners (pharmacovigilance). Why should an antidepressant be changed? The three main reasons are lack of efficacy, troublesome side effects, or the high cost of the drug Traditionally, antidepressants are classified into three group viz., tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and monoamine oxidse inhibitors (MAOIs). Drugs belonging to a particular group are supposedly interchangeable. But there are limitations. Dothiepin, doxepin and amitriptyline are all sedative tricyclic antidepressants If a switchover is made from dothiepin to doxepin or amitriptyline for some reason, there is a risk ofdeveloping acute urinary retention, or frequent falls and fractures because of marked anticholinergic and adrenargic side effects with amitriptyline and doxepin which can be disastrous (Kaplan & Sadock,1991). When changing over from a TCA to a SSRI, the SSRI may not prove as effective as the TCA (Preskorn,1994). TCAs are more effective than SSRIs, especially in severely depressed inpatients (DUAG, 1988; DUAG, 1990; Rooseetal.,1994; Anderson STomenson, 1994). Simultaneous administration of a TCA and a SSRI can increase the TCA levels and cause severe side effects like seizures or cardiotoxicity or a serotonergic syndrome during the change over period (Montgomery, 1998). In comparative drug trials between two drugs, the statistical conclusion "no significant difference between two groups" does not mean the two drugs are equally effective At periodic follow-up assessments during the trial, a patient on drug A' may say "Doctor I feel great, can I stop the pills?" In contrast, the patient on drug B' may say "Doctor, like that, I am alright, but — " . This could mean that drug B' is probably not as effective as drug A'. The two drugs may be quantitatively different though statistically not different. Statistical significance is not the same thing as clinical efficacy. Inadequate recovery