Where are you putting that Mars Bar?


I saw a recent suggestion that rectal administration of a chocolate bar could be used to reverse hypoglycaemia in a patient who was unable to take anything orally.

This led to a range of comments from colleagues mostly of surprise. There were the suggestions that maybe a Poly Woffle has a better likeness to a stool. I helpfully hinted that the wrapper needs to be removed first.

Use of rectal chocolate bars seemed a little strange but not directly counter intuitively. As a pharmacist, I had the joy of preparing suppositories albeit for my undergraduate manufacturing examination, where a pass required a homogeneous and perfectly contoured little bullet. Suppositories have a long history of medicinal uses, although in the Australian context they are not always a popular choice.

But a chocolate bar!

Mars bars contain Milk Chocolate 40%,  Nougat 33% and Caramel 27%. Specific ingredients are Sugar, Glucose Syrup (Sources include Wheat), Milk Solids, Vegetable Fat, Cocoa Butter, Cocoa Mass, Barley Malt Extract, Cocoa Powder, Emulsifier (Soy Lecithin), Salt , Egg White, Natural Flavour (Vanilla Extract). A 36 gram bar gives you 20.8 grams of sugar and 6.2 grams of fat, and reassuringly 0.5g of fibre. There is some glucose in it and that is what we need to reverse hypoglycaemia. Sucrose will do the same but it first needs to broken down to glucose and fructose by the enzyme, sucrase. Sucrase, unfortunately lives in the brush border of the small bowel not the rectum. This kind of makes sense given that the food goes into the mouth and waste comes out of the rectum and from an evolutionary perspective it is best to absorb the good stuff higher up in the bowel after it has passed the taste bud test.

The upper part of the rectum drains into the superior mesenteric vein which drains into the liver via the portal vein. The middle and inferior rectal veins in contrast drain the lower part of the rectum and venous blood is returned to the systemic circulation via the inferior vena cava and thus avoids hepatic first pass metabolism by the liver. So use of some drugs as a suppository has an advantage, although potentially toxicity is increased as liver metabolism is bypassed.

Drugs aside, is their any evidence for benefit from per rectum glucose?

Long, Geiger and Kenny published in Metabolism in 1967 a small study following radiolabelled glucose infused per rectum compared to intravenously. They showed that if you killed of gut flora with neomycin, then the expired radiolabelled CO2 following rectal administration was diminished greatly. They suggested rectally absorption of glucose was minimal and the CO2 expired was due to the effect of gut flora.

In 1984, Aman and Wranne published a small study using six diabetic children as in their words “volunteers” in Acta Paediat Scand. The title kind of gives away their findings “Treatment of Hypoglycemia in Diabetes: Failure of Absorption of Glucose through Rectal Mucosa” The authors gave their “volunteered” children aged 5 yo 10 years old, their normal insulin dose, half a serve of breakfast then exercised them to ensure hypoglyaemia. They were sent to bed and given a dose of 30% glucose solution via a rectal tube. One of the children’s glucose was 1.4mmmol/L and they were so worried that child got intravenous glucose leaving just five subjects. Two more were given milk, leaving just three subjects. One child who got 100ml of the solution up the bum, managed after an hour to get a blood sugar rise from 1.8 to 2.4 mmol/L and I suspect still symptomatic. Anal leakage was also an a problem. Aman and Wranne quite reasonably suggested that “For the unconscious hypoglycemic child, glucose intravenously or glucagon by injection is still necessary.”

A letter published in 1985 in Diabetes care by Attval, Lager and Smith used healthy volunteers, thankfully a little older and better able to consent to having tubes pushed up their bums. In this case a dose of glucose 1g/kg was dissolved in water and inserted. The mean maximal increase in serum glucose was 19%, compared to 64% per oral. The time to that increase rectally was 30 to 40 minutes after administration. Oral peak was at 20 minutes.

For historical purposes only Tallerman published a study On the rectal absorption of glucose in Quarterly Journal of Medicine in 1920. He noted the change was slow. Interestingly this was done  prior to Banting and Best introducing insulin into clinical medicine in 1922.

Interestingly, glucagon which I would normal inject in severe hypoglycaemia, has been studied by Parker etal in a suppository form and it works quite well. Unfortunately, and possibly thankfully for me and my patients, it is only available in Australia in an injectable form.

Is there an alternative for an unconscious hypoglycaemic patient?

Yes, you can given parenteral glucagon if available. And you can place glucose into the mouth. A New Zealand study by Harris et al published in the Lancet in 2013 in neonates showed that a 40% glucose gel was effective as reversing hypoglyacemia.  The gel was massaged into the buccal cavity and the babe encouraged to feed. The use of the gel was more effective than feeding alone. Now this doesn’t exactly transfer to the unconscious adult. There is the issue of teeth to contend with. But there is evidence that there are glucose transporters within the the oral cavity.

So in conclusion, and without any obvious evidence, I think hypoglycaemic bottoms are safe from chocolate bars and squirting glucose into the mouth seems a more reasonable approach if intravenous access is not readily available. Honey which contains up to 35% glucose would be a useful substitute. Except in neonates of course, because of the risk of botulism.


One thought on “Where are you putting that Mars Bar?

  1. Pingback: Where are you putting that Mars Bar? | Prehospital and Retrieval Medicine - THE PHARM dedicated to the memory of Dr John Hinds

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