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Thread: Rtx Half-Life: Another Wrinkle

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    Default Rtx Half-Life: Another Wrinkle

    Hi All,
    Quite understandably, there has been a lot of interest in Rtx over the past couple of years. It's very evident on this forum and many of us are studying it if not actually trying to get it as part of our treatment right now or contemplating the getting of it in the future. By starting this thread, I am neither advocating its use nor advocating the use of an alternative. Just looking for knowledge like all of us and pointing things out that I pick up along my merry old Wegs way - - things that I haven't already read herein on previous posts, things that might be of interest or of help to even one other on this path.
    Here's a wrinkle I haven't heard of before. In evaluating the use of Rtx vs Mtx as my next step (after six months of oral Cytox at the rate of 200mg/day - - minus one month in which I had to be off it to treat a virus), my Rheumie said she preferrred that we try Mtx first for a very specific reason. Because of the considerably different half-lifes of each of the drugs. Seems like Mtx (Cytox also) is a matter of hours and Rtx is a matter of weeks. She's of the belief that those of us prone to infections would be severely compromised in our ability to respond to treatment for the some of the very nasty ones out there, at least in our ability to respond quickly enough because the Rtx takes to long to clear out after an infusion - - such as would have been my case when dealing with the virus for which I had to temporarily suspend the Cytox.
    It makes sense when you think of some of the infections that can do us considrable harm within a handful of days, especially if one were to come our way within the first two/three weeks after getting the Rtx.
    Anyone heard of this wrinkle? Any of your doctors dismissed it? Or even mentioned it? It's not like we need another one, but we do need to know what they are. Ron
    Last edited by Thakator; 06-17-2011 at 08:29 AM.

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    I will ask my doc about this tomorrow. I have heard of this before but have not been too concerned about it. I try to minimize my exposure to possible infections and germs but I can't live in a bubble either. And I don't want to go back to using ctx for flare ups.
    Phil Berggren, dx 2003

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    After my first infusion of rtx in 2009 I had an appt with Dr Seo for some issue. I asked him how long rtx remained in the body. I wanted to take an herb and didn't want it clearing out the rtx if it was still there. I'd finished the infusions not long before that and he said it was "long gone."

    At any rate (no pun intended!) here are 2 links with specific info about the half-life. There seems to be a lot of variability in the half-life.
    Rituximab - Wikipedia, the free encyclopedia

    Medscape: Medscape Access

    I'm curious Ron-- rtx is much more powerful than mtx. Why does your doc think mtx will be strong enough? Maybe you're in an intermediate level where it's kind of a toss-up between drugs?

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    Hmm, the Medscape link doesn't want to work.It was from a Medscape article titled, "Rituximab: Pharmacology and Pharmacokinetics of Rituximab"

    Here's the part that is applicable:

    "Pharmacokinetic analysis of data from 166 patients treated with rituximab 375 mg/m 2 once weekly for four doses over 22 days revealed a steady rise in preinfusion and postinfusion serum antibody levels with each rituximab dose.[71] Moreover, detectable antibody levels were still present one, three, and six months after the end of treatment. Consistent with these findings, the elimination half-life of rituximab increased from a mean S.D. of 76.3 31.1 hours after the first infusion to 205.8 95.0 hours after the fourth and final infusion. Clearance was 38.2 mL/hr after the first dose and 9.2 mL/hr after the fourth. Prolongation of rituximab's half-life is probably due to the absence of circulating CD20-positive B cells, which bind antibodies during initial infusions. It is also likely that prior rituximab saturation of involved lymphnode sites would increase antibody availability and decrease clearance."

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    So is there any thoughts about the long term effectiveness of RTX? it sounds like it kills the defective B-cells so the body can produce healthy new ones...I wonder if that's the case for us weggies? I met with my Rheumy today and it looks like my labs have made a really good turn for the better (mostly my numbers regarding my kidneys are starting to improve) My Rheumy thinks it's the RTX working (it's been about six weeks since my first infusion). I wonder if anyone has any thoughts to how long RTX will work? When used with people with Rheumatoid Arthritis, it gets used as the problem flares up. I wonder if with RTX in place of CTX if I might be more prone to continual flare-ups that will be treated with RTX...rather than a more permanent remission with CTX? I understand the logic with RA and using it to manage flare-ups...but I think we can all agree WG flare-ups are categorically more troubling.

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    Sangye - - don't know about any intermediate stage; I'll ask about that. However, having had a major lung flare in the past because of meds not being strong enough, she's well aware of my deep concern for going too easy on the old Wegs- - she hears it from me quite often. I'll pay the price, just keep those big, hospitalizing/ICU flares away. I even got her to go along with keeping me on Cytox an extra month to make up for the month I had to take off for the virus treatment and, like most of us, I'm no great fan of the stuff, how it makes my guts feel every day and it's risks.
    Please keep in mind that, in my particular case, I nearly went down to an outbreak of cytomegalavirus that required an initial eight days of ICU treatment and which could have gotten much worse if we hadn't been able to clear my system of Cytox so quickly (or Rtx had I been on it). She was there at my side for that episode so she's apt to be a bit more cautious than others regarding this potential wrinkle. I continue to see her every three-four weeks at most and do bloodwork every two weeks; we'll be watching closely and I'm sure she won't hesitate to immediately bring out a bigger gun if needed. Besides, I'm not a bashful boy - - I'll remind her of exactly how I feel about it if I see any signs of Mtx failing to do its job.
    Take care, dear lady; hope that your days are now better than they were in the last week or so. Ron

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    Norcalian, it's all over a country mile. I've known some people who had one round of rtx and went into long-term remission. Others can go a year or more between needing a repeat round. Some of us need to do a repeat round quite often to keep the Wegs from flaring.

    Rtx doesn't kill the defective B cells so the body can make healthy ones. It kills all the B cells. B cells make antibodies, including the antibodies that attack our blood vessels. New B cells will make the antibody, too. I don't know how B cells can return and not be a problem for some people while others get into trouble as soon as their B cells repopulate. I'm not sure if the Wegs docs understand this yet, either.

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    Ron, I totally forgot about your CMV infection. Given that CMV can remain dormant it certainly makes sense that your doc would want to use mtx instead. Not only is rtx much stronger, but once it's administered it's going to work for 6 to 12 months. With ctx you can stop the meds and your blood counts will rebound fairly quickly to combat an infection.

    I'm glad you are such an active participant in your care. It's kept you alive for sure.

    As for me, I'm starting to feel a bit better. Yesterday was a Buddhist holy day and I spent the whole day at our temple. I was in good shape for a few hours and then tanked for a few hours! So today has been payback time.

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    Quote Originally Posted by norcalian View Post
    So is there any thoughts about the long term effectiveness of RTX?
    My doctor told me that the benefits of RTX can last up to a year. I suspect the benefits decrease over time from the time of its maximum effectiveness.

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