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[IP] Mixing of H and V: summary report

OK pumpers, here is the result of the "scientific" study I've been doing on myself over the last 2 1/2 months comparing the effectiveness of mixing H and V on site stability. I've written it in the form of a case report. If some of the formatting gets screwed up by your email program, I'd be happy to send you a copy for your word processor as an attachment. Just email me privately if you want a copy. As you will see if you read it, I found no evidence of any benefit of adding Velosulin. There was a wide spectrum of how sites behaved, but this variability was apparent with the straight stuff or the mix. I know some will swear that the mix is better, but I think that given all the variability I saw, it would be very easy to get fooled by a few good sites with the mix. And then of course the placebo effect in medicine is known to be very potent.
At least for me, I'm off the mix. I've got a few unopened bottles of V left in the refrigerator that I'd be happy to donate to anyone who thinks that it really helps. I could mail them when the whether turns cooler.

Comparison of insulin pump infusion site stability with pure Humalog and a mixture of Humalog and Velosulin. -Wayne Mitzner. June-July-August, 1998

There have been several anecdotal reports of benefits of mixing various amount of Buffered Regular (BR) or velosulin (V) with Humalog in insulin pumps. The potential disadvantage of the additional regular insulin delaying or prolonging the action of the pumped insulin is said to be greatly outweighed by the advantage of prolonging the functioning of the subcutaneous catheter infusion sites. Some people have claimed sites with such insulin mixtures lasting as long as two weeks! The rational that has been put forth for this improved site stability is either that the unique buffering in Velosulin helps promote site stability (and that even a little bit of this buffer helps), or that the Regular insulin in some as yet unknown way helps stabilize the Humalog. This study was designed to compare the function of infusion sites with either pure Humalog or a mixture of Humalog and Velosulin.

Methods: The syringe was filled to capacity with either pure Humalog or a mixture of Humalog and Velosulin (buffered Regular) in a ratio of 5:1. The tubing was primed and connected to a newly inserted Silhouette catheter. With my insulin requirements, a full syringe lasts 11 days. Thus, I was able to go through 3 successive 4-day site with one syringe. (For the last day of the third site, I disconnected the syringe and filled it with enough insulin for one day.) A 4 day cycle was longer than I had been using, and I anticipated that there would be several sites that would fail prior to the end of the 4th day. Data were obtained from nine 4-day sites with each insulin. Sites were either abdominal or high on the hips, and the Silhouette was inserted at about a 30 degree angle. A new site was always started in the morning prior to the breakfast bolus.

Protocol: The goal was to keep each catheter in place for 4 full days, or until the site failed. Site failure was defined by either: 1) excessive redness, swelling, irritation, or pain: or 2) Unexpected blood glucose highs (greater than 250 mg/dl) that could not be corrected by a subsequent bolus. To my surprise, all 18 sites were able to last the full 4 days.

Site evaluation: I set up a plus scoring system using the following criteria:
0+ No redness of pinkness at catheter hole.
+ Slight redness at the catheter hole less than 1.5 mm in diameter. No bumps or hardness under the skin.
++ Redness at the catheter hole (less than 2 mm in diameter) with surrounding pinkness (less than 5 mm in diameter). Slight bump or subcutaneous hardness.
+++ Redness and pinkness exceeding 5 mm in diameter. Noticeable welt.

++++ Inflammation with sensitive welt and pus.

None of the sites during this experiment were 0 or 4+.

[Note: On two occasion, when I pulled out the catheter, fresh blood started flowing from the hole. Since in both cases the sites were otherwise 1 to 2+, I didn't downgrade these sites (one was with H and one with the H/V mix). I think this bleeding occurs sometimes because the catheter gets fibrosed (stuck) in place, and when you pull it out, it is possible to tear some adjacent tissue and capillaries. In both cases, the bleeding stopped easily with a little pressure.]

Results: Although there were numerous unexpected blood glucose highs (6 with H and 5 with the H/V mix), with one possible exception, there were no BG highs that could not be brought down with a subsequent bolus. On that one occasion, which occurred on the last (4th) night, the pre-bed BG was high, and was still high in the morning after a night bolus. It is a questionable failure in my mind because I generally am conservative when bolusing overnight. This one occurrence was with the H/V mix.
The following table lists the number of 1,2, and 3+ sites with either pure H or the H/V mixture.

Site evaluation pure Humalog H/V mixture
+ 6 4
++ 2 4
+++ 2 1

Discussion: At least for this experimental study on one individual, there was no obvious difference between the pure and mixed insulins. If there are any benefits of the buffer in the Velosulin, it was not apparent in my body . Would it be different if the mix was 3:1 instead of 5:1? I don't know, but I don't think it would make much difference for me personally. I think that the primary reason why a site becomes limited is the tissue reaction to the physical trauma caused by a foreign thing being stuck in it. Proof of this explanation comes from the fact that sites with the stainless steel bent needles don't last even half as long as those with the teflon catheters. Since both materials are not allergenic and don't react with body tissues, the only difference is the much greater tissue damage caused my movements of the stiff needle.
Several other points are worth noting. In my case, there was a tendency for sites to be more stable in my hip rather than my abdomen. That is, of the ten 1+ sites, seven were in the hip, and two of the three 3+ sites were in the abdomen. This is likely to be very subject dependent, or as they say, YMMV. I don't have a lot of body fat, and this may be an important factor. Another observation from this study is that there did not seem to be any problem with leaving the Humalog or mixture in the pump and tubing for as long as 11 days. There have been several anecdotal reports of Humalog degrading more readily than Regular, and this was emphasized recently on John Walsh's website (http://www.diabetesnet.com/news.html). However, despite this study being done in the summer (including a week on the beach at the Outer Banks, NC), there wasn't any clear trend associated with whether the 4-day cycle was started with fresh insulin from a new syringe or after the insulin had been in the syringe for 8 days. There number of 1+ sites were equally distributed among the three 4-day cycles for a single syringe. Two of the three 3+ site were on the last cycle, but this requires more data to determine if this is a reproducible finding.

Conclusion: There was no advantage of mixing Velosulin with Humalog (in a 1:5 ratio) on infusion site stability. Although others may believe there is some benefit of such mixing, it would be nice to see some similar experimental data in support of these anecdotal reports.
Wayne Mitzner
Department of Environmental Health Sciences
The Johns Hopkins School of Hygiene and Public Health
615 N. Wolfe St.
Baltimore, MD 21205
Tel. 410 614 5446
Fax 410 955 0299

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