EBM and Biologies

Biologics are quite new drugs. The pre-marketing studies follow the high present standards of good clinical practice. Therefore, it is not surprising that the level of evidence is better for biologics than for many of the other older treatments of psoriasis, e.g. methotrexate. On the other hand, for most available biologics the clinical experience is limited and issues such as rare side effects and the results of long term treatment cannot be discussed conclusively.

Comparison of the published trials on the efficacy of biologics will lead to the assumption that there is nothing like "THE" biologic. The biologics differ in efficacy and safety. Based on the recommended dosages, the highest efficacy can be found for infliximab, followed by etanercept and efalizumab. The Number Needed to Treat (NNT), an established EBM tool to clarify efficacy, gives numbers from 1.22 (1.10-1.37) for infliximab, 3.30 (2.62-4.44) for etanercept at the low dose and 2.18 (1.65-2.66) at the higher dose, to 4.49 (3.62-5.91) for efalizumab (Table 18.1).

So what does it mean? For infliximab it means that if you treat approximately four patients with infliximab

Time of evaluation/dosing Number of patients Source needed to treat to reach a 75 % PASI reduction

Table 18.1. Efficacy of biologics: comparison of "Number Needed to Treat" according to biologic and dosage

Infliximab

Etanercept

Efalizumab 12 weeks; 1 mg/kg; 1/week 4.49 (3.62-5.91)

Gottlieb et al. 2004 Leonardi et al. 2003

Menter et al. 2005

three will achieve a reduction of the PASI of 75 % or more. This means that only one patient will fail the benchmark of a reduction of the PASI of 75 %.

However, it should be taken into account that efficacy is not everything. Effectiveness that means "How well does the drug do in clinical practice" is very important. The next most important factor is safety. You want to have a drug that is safe for this chronic inflammatory disease. Other factors to consider are the practicability for patients and doctors as well as costs. When talking about costs it is important to remember that it is just not the price of the drug but also the cost of laboratory investigations, other investigations such as X-rays and in addition the days not lost to hospitalisation.

We would like to finish this chapter with some thoughts on safety. It is important to remember that safety cannot be measured effectively by clinical trials. Only a limited number of patients are included in clinical trials. If 3,000 subjects are exposed prior to drug marketing, one can only be 95% certain that any event which does not occur in this population will occur in no more than 3 in 3,000 subjects or has an incidence rate of less than 0.001. Therefore, post-marketing surveillance is very important to discover rare and also delayed reactions, especially in biologics, which apart from a few exceptions have not been on the market for long.

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