Posted 8/4/2010 1:10 PM (GMT -7)
Right, personal experience first: I've been on Etanercept (Enbrel) for quite a few months, and the only side effect I've noticed is being tired the next day. Although I wouldn't describe this as fatigue, and it's nothing compared to the fatigue I get from MTX. I've had pretty good results from it, and I am continuing to do so.
You could be taking either medication for a great number of years, or not very long at all if you were lucky enough to go into partial or complete remission. The side effects last 24-36 hours usually, but depends on my level of activity and general energy levels.
TNFa stands for Tumour Necrosis Factor, and these are cytokines, which are pretty small proteins which send low-level signals between cells. TNFa cause the 'acute phase reaction' which tells your body's immune system to respond to injury at that site, which through a chain reaction from inflammatory cells to the liver, results in inflammation, and therefore pain. The aim of these meds is to inhibit the effect of the TNF alpha cytokine.
Etanercept/Enbrel is a protein that is synthesis(z)ed by splicing two genes (which produce two different proteins when separate). It acts as a decoy for the TNFa, mimicking so-called "soluble" TNF receptors in your body which inhibits the TNF's effect. These serve to 'deactivate' the TNF, whereas the receptors in your white blood cells produce cytokines which result in inflammation when they bind to TNF. The increase in these 'deactivating' sensors will reduce the overall inflammatory response experienced.
Infliximab/Remicade is an antibody (Enbrel isn't strictly an antibody, it is a fusion protein, but functions as the 'tail' of an antibody), as is Humira. Both are thought to have the same mode of action as Enbrel, but this isn't confirmed as far as I know. (Remicade also has action on a specific type of T white blood cell which results in the cells suicide, which means it also has efficacy in treating Crohn's disease. Whether Enbrel does is up for debate.)
Both are immuno-supressents, but with fairly good side-effect profiles. There will be tiredness, but how much depends on the individual.
To be honest I'm not sure how doctors choose between the two, I know some clinics will start with Enbrel, and others with Remicade. In my opinion, it doesn't really matter which you choose as there is currently no mechanism in predicting which will suit any given patient more. The NHS in England tend not to try the other if one fails, but that is because the NHS is the biggest joke in the history of comedians. (/rant)
That just about sums up my knowledge on the subject. Hope I helped a little, if not, sorry!
I'm not a doctor so this doesn't constitute medical advice!