Disease Modifying Drugs are a very individual topic. What is right for one person is not necessarily right for another (although you will find some people who are positively evangelical about the particular drug that they are on.)
Different factors do come into play when choosing which of the drugs offered are best for you. Initially, I was going to be offered Rebif or similar but I was reluctant about this because of my lifestyle at the time (eg I was working regular shifts which made taking very regular medications difficult – added to which my appalling memory meant that I was prone to miss doses).
Tysabri appeared to be the best option for me right from the beginning and I was very relieved/pleased when I changed neurologist and my new neuro turned out to have a very “go in hard, go in quickly” approach to DMDs and she immediately suggested Tysabri.
I have been on Tysabri for 3 years now and, although my existing symptoms have not lessened and I do have occasional “flare ups” or “pseudo-relapses” if I get an infection, I have (touch wood) not had any major relapses since starting.
After about 18 months, I was found to be JCV+. Fortunately, improvements in the blood testing regime, now mean that they can assess how much of the virus one is carrying and they can assess how great is the risk of developing serious side-effects are. In my case, my current load is low enough that the risk of developing PML is almost the same as it would be where I not carrying the virus at all. They keep the situation under very careful monitoring; taking blood for analysis every three infusions and doing a basic screening MRI scan every six months or so.
In my case, I don’t find the regime on Tysabri onerous in any way. I go in to the neuro ward every 28 days. My BP etc checked, I have a very quick medical examination by the registrar and then I am hooked up to the infusion. I sit on a comfy couch reading my Kindle for a couple of hours and then head home stop I am not affected in any way by the infusion and I am perfectly fine afterwards.
New medications do come onto the market relatively regularly - for example Tecfidera (a tablet-based option which has some very vocal supporters here) and Lemtrada were not options available when I started my medication regime. In my case, I still think that I would have opted for Tysabri (at least in the first instance) but, as I keep saying, everybody is different (!!!)
The MS Trust website has some very useful information about DMDs including a decision-making tool that might help your dad clarified his thoughts MS Decisions | MS Trust.
Best wishes to you and your dad as he makes what seems like a very difficult decision at the time you have to make it. Don’t worry he will be fine.