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[IP] Humalog and Heat

I recall that it has been claimed that Humalog doesn't stand up to  
heat as well as Novolog. Although this may be true, I have a recent  
experience with Humalog and heat that tells me Humalog does pretty  
well with the heat. I live in Phoenix, Arizona, which is one of the  
hottest summertime cities in the USA. I am 73 years old, and I use a  
Deltec Cozmo pump with Humalog. And I do a lot of bicycle riding.

On Sunday 23 July I got up at 4 AM and, because my cartridge was  
almost empty, installed a full 300 ml cartridge of Humalog and a new  
infusion set in my Cozmo. This cartridge was expected to last me for  
six days. At 5:45, after a partial breakfast of oatmeal (24 carbs,  
3.00 units) I drove about 2 miles to the starting point of the  
regular Sunday morning bike ride of the Arizona Bicycle Club. The  
only reason for driving was that I had a large box filled with  
clipboards to be used for signing in the participants of the ride.  
The digital thermometer in my car reported the temperature as 93F,  
pretty hot for 6AM.

I unloaded my bicycle and spent the time until 6:30 getting all the  
participants (47) to sign in. We left in five groups about 6:30 for  
the US Egg restaurant in Scottsdale, about 10 miles by the most  
direct route. The faster groups  took a longer route, so we all got  
there about 7:30. After breakfast of a ham and cheese omelette,  
potatoes, english muffin, and jelly (100 carbs, 4.00 units), we left  
about 8:30 to return to our starting point. It had gotten hotter, and  
continued to do so. I arrived at my car about 9:45, and after loading  
my bike on the rack, got in the car and turned on the ignition. The  
digital thermometer reported 106F. It's very seldom that I ride in  
that kind of heat, but I realized that this would be a good  
opportunity to evaluate the behavior of Humalog.

On Tuesday 25 July I went for a solo bike ride of 14.55 miles,  
starting at 6:30 AM, spending 45 minutes at a restaurant, and  
returning home at 8:45. I checked the digital thermometer in my car  
both before and after the ride, and the temperature was 93F both  
times, so this wasn't nearly as much heat as I had encountered on  

On Wednesday morning I replaced the infusion set (Polyfin QR) on  
schedule. The Humalog remained effective until Saturday morning when  
I put in a new full cartridge. During the six days of the cartridge  
being studied, I recorded 45 BG tests. The highest was 231 on  
Thursday evening, and it responded properly to a correction bolus. As  
the end of the 300 ml was being reached early Saturday morning, the  
last two BGs were each 111. So in this case, at least, the Humalog  
did not show any detectible evidence of deterioration after six days  
in the cartridge, in spite of being exposed to temperatures of >100F  
for about one hour on the first day.

In case you're wondering about the carb/insulin ratios on Sunday, the  
ratio was 1u/8g before starting the ride, but it was 1u/25g during  
the ride. These are ratios that I have worked out during 28 years of  
riding, 63 years of T1, and 11 years of pumping.

Tom Beatson
dx 12/1942, 506 1995, 508 2000, Cozmo 2005
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