Low molecular wt vs. unfactionated??

[catwoman]

Al:

What is the difference between low-molecular weight and unfractionated heparin? LMW is Lovenox and warfarin is unfractionated, isn't it?

Am trying to understand differences between the two descriptions.

Have heard of low-molecular weight protein, used in Rx vet foods (Hill's z/d is one example) for cats & dogs with food allergies. LMW protein particles are so tiny the body doesn't develop allergic reactions to them.

Thanks for any explanation.

 

[Guest]

First, warfarin is neither heparin nor low molecular weight. It is an oral anticoagulant.

Heparin comes from the innards of pigs and cows. It is a rather crude product. Because of its high molecular weight, it has lots of odd actions and interactions. This means that the PTT (partial thromboplastin time) needs to be monitored closely to be sure that it is slowing coagulation in the proper amount.

There are several ways of getting low molecular weight heparin but they all boil down to getting just the active part of the molecule without the big chain part that causes all of the unpredictability. Lovenox, Fragmin and some other brands are available. Because it has less interactions, it is not usually monitored. But they do know now that people with decreased renal function only need about half of the usual dose.

The discovery about the renal function only came after about 10 years of experience looking back at why some people did not do well with them. This is the point I have been making about Exanta. Maybe 10 years from now when millions of people have taken it, they will look back and say, "Oh yeah, it looks like ___ should not have gotten that." This happens with allmost every new drug.

 

[catwoman]

Al:

Thanks. That's about the same way that LMW protein works in the Rx foods.

Am trying to understand how/why Lovenox works as a "substitute" for warfarin. It's the journalist in me, always wanting to know the 5 W's and the H -- who, what, when, where, how and why.

 

[Nancy]

Al-

That's very interesting-what you mentioned about renal function and Lovenox. Would that mean that people who were having a CHF flare-up and fluid retention and were on diuretics, could potentially have a problem with Lovenox?

 

[Guest]

Because heparin is injected and works directly on clotting factors, it works within half an hour to prevent clotting. Warfarin takes days for its onset of action because it slows the production of clotting factors, it does nothing about those already circulating in the body. Some people who cannot take warfarin stay on heparin injections forever. But most people will switch over to warfarin as the effect builds.

Fluid retention from CHF is usually caused from the blood not pumping through the kidneys at high enough pressure for for the kidneys to be able to remove water from the blood. This can lead to kidney failure but in the acute phase it is nou usually kidney failure.

The formula for kidney failure is complex and is slightly different for men and women because usually men have a greater portion of their body in muscle. However, just about every hospital pharmacist can calculate this on a hand-held calculator or have it on their central computer. You need the serum creatinine which is one of the factors that is determined by all of that blood that they are always drawing. It is not something that needs to be calculated before the first dose of LMWH is given but it is an indicator of how well your body will dispose of the drug. If it builds up over days there can be a problem. You have to be in fairly poor helath already for this factor to come into play. It is not a big issue that everyone needs to know before anything gets done to you. As a general rule if your serum creatinine is less than 1.5 and you weight over 120 pounds or so this is not a factor. There are many other drugs such as antibiotics where this also comes into play. At our hospital the in-patient pharmacists have a list of people who are on these drugs printed every morning. This is compared with a list of everyone's serum creatinine. If something looks suspicious according to the rule above, then they run the calculation. If it looks like a problem then a note is left on the chart for the doctor to consider changing the dosing. It is usually not how much you get but how far apart the doses are spaced. When i was doing in-patient pharmacy we started doing this back in the 1980s.