I agree with the above post by Snodger,
(have added a bit below *)
I'm assuming that we are comparing rapid acting analogue insulin with fast acting human insulin.
Here are some manufacturers profiles
Actrapid (regular human insulin) typically has an onset of around 30min, peaks at 1.5 to 3 hours and has a duration of action of 7-8hrs
Insuman rapid (regular human insulin) typically has an onset of around 30min, peaks at 1 to 4 hours and has a duration of action of 7-9hrs
Novo rapid (rapid analogue insulin) typically has an onset of around 10-20 min, peaks at 1 to 3 hours and has a duration of action of 3-5 hours
Apridra (rapid analogue insulin)typically has an onset of around 10-20 min, peaks at 55min and has a duration of action of 1.5-4hr hours
Humalog (rapid analogue insulin) typically has an onset of around 15min, peaks at 1.5 hours and has a duration of action of 2-5 hours
The main difference is in how soon the insulin is supposed to start working and how long it stays in the body for. Rapid insulins should start working very quickly so that you can inject and then eat rather than injecting in advance.
They are also out of the body much more quickly so that if you have a gap of 5 hours between meals there shouldn't be any insulin stacking.
How quickly they work seems to depend upon the person. Most people don't seem to see much difference between Humalog and Novorapid. Apidra does seem to be quicker for most people.
Some people still find that it is better to dose a bit earlier with rapid insulins finding they still don't stop blood glucose rising high in the first hour. Conversely some people find that Apidra works too quickly for some lower glycemic index meals.
Some people with young children or even adults with uncertain appetites find that they can dose after a meal when they know how many carbs that they have actually eaten.
Calrr
It maybe that your high glucose levels are contributing to your irritability. I don't know how long you have been diagnosed but obviously there are a variety of medications and approaches to diet that may help lower your levels. Obviously it's something to discuss with your doctor.
If oral medications really aren't working then there are a lot of insulin options around and the type of regime that you start with will depend very much on what your nurse/doc thinks you need. There are also other non insulin, injectable drugs used for people with T2 (GLP 1 ie Victoza and Byetta)
If they start insulin Some T2s only need to use a long term background insulin. Some people use premixed insulins in which background and bolus insulins are mixed in the same preparation (injecting usually 2 or 3 times a day. There are others who use two separate sorts of insulin, background/basal insulin (once or twice a day) and bolus (fast or rapid) for each meals.
This PDF written for Nurses so it is fairly technical but does explain the options that are available.
http://www.rcn.org.uk/__data/assets/pdf ... 002254.pdf
*Today, both human and analogue insulins are synthetic, bioengineered versions of insulin. Human insulin is grown in bacteria according to the human genetic code for insulin.
Human insulin can be varied by the manufacturers for use as slower insulin. In this case 2 ingredients (protamine and zinc) are added to slow the action.
Analogue insulins are made in the same way as human insulin, however, the human insulin molecule is modified. The modification of the DNA acts to speed up or slow down the rate at which insulin becomes available to the body.
Slower insulins are used as a background insulin (from very slow insulins that last for more than 24 hours to an intermediate rate lasting around 12 hours)
The faster types are used as mealtime insulins.
There are still a few people that use insulin derived from animals, again these can be made slower acting by the addition of other ingredients.