Adjustment from home time to foreign time is complicated. If you are taking oral hypoglycaemicpills, work out the total dose of pills you take in twenty-four hours. Next consider the actual number of hours between breakfast on the day you leave home and the first breakfast in the country you are visiting. By breakfast, I mean the meal eaten on getting up in the morning, whatever it is called locally. If there are twenty-four hours or more between these two breakfasts take your total twenty-four hour dose of pills split at appropriate intervals. Do not take more than this, but wait until your first breakfast in your new country before you start taking your pills during the day as you would at home. If there are less than twenty-four hours between your breakfast at home and your first breakfast in your new country, take fewer pills. Thus, if there are twelve hours, take half your pills, eighteen hours, two-thirds of your pills and so on. You will need to use a bit of common sense to arrive at a practical division. Follow a similar process on the way home.

If you are taking insulin you can use the same calculation if you wish, but their type of insulin and its duration of action have to be considered. The main concern is not to have a hypoglycemic attack in some remote corner of a foreign airport. This is not a hypothetical worry. You are tired and the food on the aero-plane was indigestible; you may have had a couple of free drinks, you have lugged two suitcases, a shoulder bag, two carriers of duty free wine and a souvenir from Barcelona through endless miles of corridors; your next flight has just been delayed for four hours and the restaurant is shut. As always, check your blood glucose and do not care if anyone sees you.

How do you calculate your insulin? If you are on one injection of very long-acting insulin a day and two or more injections of rapid-acting insulin: Calculate the number of actual hours between breakfast at home and your first breakfast in the new country. If this is twenty-four hours or more, take your usual dose of very long-acting insulin; if less than this, take an appropriate proportion (for example, for twelve hours half the dose, twenty hours 80 per cent of the dose and so on). Take your usual short-acting insulin before breakfast at home and then check your blood glucose levels before each meal you have until the first breakfast. If they are 7 mmol/1 or more (126 mg/dl) take 2 to 4 units of rapid-acting insulin to cover each meal. If they are below 4 mmol/1 (72 mg/dl), eat a bigger meal and start it with some fast-acting carbohydrate. Before breakfast in the new country have your usual insulin and continue this, with frequent blood glucose measurements and adjustments as necessary, until you come home. Then follow a similar process when you arrive home.

If you are on two injections of medium-acting or long-acting insulin with short-acting insulin a day: twenty-four hours or more between your home breakfast and your next breakfast, take your usual insulin before breakfast at home and twelve hours later (or at the meal nearest to twelve hours later) take your ‘evening’ dose. It may be wise to reduce each dose by a small proportion, for example, 10 per cent, to make sure that you do not go hypoglycemic. Then have your usual insulin before the next breakfast as above.

Less than twenty-four hours between the two breakfasts, take your usual insulin before breakfast at home (reduced a little if you wish). Then take no more long-acting or medium-acting insulin until the next breakfast. Check your blood glucose level before each main meal and give 2 to 4 units of insulin if it is 7 mmol/1 or more. Have your usual medium-acting or long-acting insulin before your first breakfast in the new country. Reverse the process for your return trip.

This advice can be modified by your personal experience. If you make regular trips across a particular time zone, you should be able to work out your best insulin dose from experience. What I have suggested may cause you to run your blood glucose level a little high for the first few days, but that is better than going hypoglycemic in a strange country.

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