Diabetes: tablets for type 2 diabetes
Oral hypoglycaemics
Tablets that are used to treat type 2 diabetes mellitus are known as oral hypoglycaemics or antihyperglycaemics. They are generally not suitable for people with type 1 diabetes as these people must take insulin injections one or more times daily because their insulin-secreting pancreas cells have been destroyed.
There are a number of different types of oral hypoglycaemics available for treating type 2 diabetes, and they work in different ways. They may be used on their own and some can be used in conjunction with each other, or with insulin.
Sulfonylureas
Sulfonylureas include the medications:
- glibenclamide (e.g. Daonil);
- gliclazide (e.g. Diamicron);
- glimepiride (e.g. Amaryl, Dimirel); and
- glipizide (e.g. Minidiab).
There is also a medicine called Glucovance that contains both glibenclamide and metformin (see below) in one tablet.
The sulfonylureas are an older, but very effective, group of antidiabetic agents. They are usually prescribed for people with type 2 diabetes who are not overly obese.
How do they work?
Sulfonylureas work by helping to stimulate the production of insulin by the pancreas. They may also have some effect in improving the sensitivity of the body's tissues to the action of insulin.
Side effects
Possible side effects of sulfonylureas include weight gain, skin rashes and gastrointestinal disturbances. They also increase the risk of hypoglycaemia (blood glucose levels that are too low), particularly in elderly people or people with kidney or liver problems. Many drugs may interact with sulfonylureas, so be sure to tell your doctor about any other medicines you are taking.
When should you take them?
Sulfonylureas should be taken at mealtimes to reduce the risk of hypoglycaemia.
Biguanides
Metformin (e.g. Diabex, Diaformin) is the only biguanide currently available in Australia.
Metformin is a moderately effective antidiabetic agent, and is generally prescribed for obese people with type 2 diabetes, sometimes in conjunction with sulfonylureas. It is also commonly used in non-obese people. There is a combination medicine called Glucovance that contains both glibenclamide (a sulfonylurea) and metformin in one tablet.
How do they work?
Biguanides work by reducing the amount of glucose produced by the liver, increasing the uptake of glucose by muscle and fat cells, and reducing the amount of glucose absorbed by the intestine. This in turn reduces the level of glucose in the bloodstream.
Side effects
Lactic acidosis
The most serious complication associated with metformin is lactic acidosis. This happens when lactic acid builds up in the body faster than it can be metabolised. It is a potentially fatal condition but is very rare. When it occurs in people treated with metformin it is generally associated with old age, or people with kidney, liver or heart problems, those taking more than 2 grams per day, or those drinking excessive amounts of alcohol. Anyone who may have lactic acidosis should be taken immediately to the nearest Accident or Emergency department or receive urgent medical attention. The symptoms of lactic acidosis are:
- nausea, vomiting, stomach pain;
- trouble breathing;
- feeling weak, tired or generally unwell;
- unusual muscle pain;
- sleepiness;
- dizziness or light-headedness;
- shivering, feeling extremely cold; and
- slow heartbeat.
Other side effects
More common side effects include nausea and diarrhoea. Your doctor will minimise the chance of you getting these by making gradual adjustments to your dose and by advising that you take the tablets at mealtimes. Beneficial side effects of taking metformin that have been observed include weight loss, and improved lipid (cholesterol) profile. When used on its own, metformin rarely causes hypoglycaemia.
When should you take them?
In order to reduce unwanted gastrointestinal side effects, biguanides (metformin) should be taken with or at the end of a meal.
Alpha-glucosidase inhibitors
There is only one type available in Australia: acarbose (brand name Glucobay). Acarbose is sometimes prescribed in conjunction with biguanides or sulfonylureas.
How do they work?
The alpha-glucosidase inhibitors interfere with the function of some of the digestive enzymes (alpha glucosidases) that are involved in digesting carbohydrates. The effect is to slow carbohydrate digestion in the small intestine so that glucose (sugar) is not absorbed into the bloodstream so quickly. This decreases the blood glucose peaks which happen after a meal.
Side effects
Common side effects of alpha-glucosidase inhibitors include flatulence, diarrhoea and abdominal pain, especially upon initial treatment. However, starting at a low dose and gradually increasing it to the final dosage, rather than starting with the final dose, can help avoid these problems.
When should you take them?
Alpha-glucosidase inhibitors (acarbose) must be taken immediately before your meal, or with the first couple of mouthfuls, in order for them to work.
Glitinides
Repaglinide (e.g. NovoNorm) is an oral hypoglycaemic belonging to the glitinide group of drugs. It is sometimes prescribed for people who cannot adequately lower their blood glucose levels through diet alone. It is sometimes prescribed in addition to metformin tablets or sometimes with insulin therapy in people with type 2 diabetes.
How do they work?
Glitinides work by stimulating the pancreas to produce a surge of insulin just after eating. Because it works quickly, repaglinide gives you more freedom to determine when you want to eat than other diabetes medications.
Side effects
Common side effects of glitinides include hypoglycaemia, weight gain and gastrointestinal disturbances.
When should you take them?
You should take repaglinide just before eating to ensure that it works properly, and to help reduce the risk of hypoglycaemia.
Thiazolidinediones (glitazones)
Rosiglitazone (e.g. Avandia) and pioglitazone (e.g. Actos) are examples of another group of oral hypoglycaemic drugs called thiazolidinediones. These medications may be used either on their own or in conjunction with other diabetes medications.
There is a medicine called Avandamet that contains both rosiglitazone and metformin in one tablet. These combination tablets can be prescribed for people who are already treated with both rosiglitazone and metformin, or those whose diabetes is not adequately controlled on either rosiglitazone or metformin alone.
How do they work?
Thiazolidinediones work by increasing the sensitivity of the body's tissues to the action of insulin, rather than stimulating insulin secretion. This allows glucose to be transported from the bloodstream into the body's fatty tissue, skeletal muscle and liver cells more efficiently.
Side effects
Side effects of the thiazolidinediones include fluid retention, raised lipid levels and anaemia. They may also cause weight gain and heart problems in some people. They are generally not prescribed for people with heart failure.
When should you take them?
Thiazolidinediones are taken once or twice daily, with or without food. It may take 6 to 8 weeks to get the full effect of these drugs on blood sugar levels.
Incretin enhancers and mimetics
These medicines include sitagliptin (e.g. Januvia) — an incretin enhancer — and exenatide (e.g. Byetta) — an incretin mimetic. Sitagliptin is an oral hypoglycaemic medicine, while exenatide must be injected. These medicines are used in adults, and are used in combination with other oral diabetes medications.
How do they work?
Incretin enhancers — also called dipeptidyl peptidase-4 (DPP-4) inhibitors — work by increasing the production and release of insulin by the pancreas, as well as reducing the production of glucose by the liver.
Sitaglipitin works when blood glucose levels are high, especially just after a meal, but also helps to lower blood sugar levels between meals. Sitaglipitin on its own is unlikely to cause hypoglycaemia, because it does not work when blood sugar levels are low.
Side effects
Side effects of sitagliptin include runny nose, sore throat, cough, discomfort when swallowing, headache and nausea.
When should you take them?
Sitagliptin is taken once daily, with or without food. It is taken as combination therapy with metformin, a sulfonylurea or a thiazolidinedione. It should be taken around the same time each day.
There is a medicine called Janumet that contains both sitagliptin and metformin in one tablet. These fixed-dose combination tablets can be prescribed for people who are already treated with both sitagliptin and metformin, or those whose diabetes is not adequately controlled on metformin alone. Janumet should be taken twice a day with meals.
Long-term outlook for people taking tablets for type 2 diabetes
It is not unusual for oral hypoglycaemics to control type 2 diabetes for a number of years, and then stop working. In fact, insulin treatment may be required in one-third of people with type 2 diabetes after 10-15 years of successful management using oral hypoglycaemic agents.
A healthy balance
Regardless of the type of diabetes you may have, it is important to recognise that medication is only part of the overall treatment picture. It is just as important to follow both a healthy eating plan and a regular activity programme in order to maintain relatively stable blood glucose levels.
Last Reviewed: 31 August 2009
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