My two-year-old daughter has been started on a new treatment for eczema called tacrolimus. It seems to be working very well, but I understand it suppresses the immune system and this makes me worry that she will suffer from other side effects. How does this drug work?

My two-year-old daughter has been started on a new treatment for eczema called tacrolimus. It seems to be working very well, but I understand it suppresses the immune system and this makes me worry that she will suffer from other side effects. How does this drug work?

Tacrolimus (trade name Protopic) has recently been licensed in this country as a treatment for eczema. It has been in use in North America for a couple of years. The same drug is also used for kidney- and liver-transplant patients to prevent them from rejecting their transplanted organs. The drug works by suppressing the body's immune reaction. In eczema, this dampens down the body's inflammatory reaction. Skin that is severely inflamed by eczema responds quite quickly to treatment with tacrolimus, and early reports say that it can have dramatic effects. The Drug and Therapeutics Bulletin, which reviews new drugs for doctors, says that it is an "effective novel treatment" for eczema. Because it is new, and because its long-term side effects are unknown, its use should be supervised by a skin specialist. The worry is that it could increase the risk of skin cancer later in life, although there is no evidence of this so far.

Hormone hype

Every week my e-mail box fills up with internet adverts for human growth hormone. They claim amazing things for the hormone, including more energy, longer life, stronger bones and an improved sex life. Is any of this true?

Human growth hormone is produced naturally by the pituitary gland. If you don't have enough if it during the growing period of childhood, you will end up very short. A child who has untreated growth-hormone deficiency may have an adult height of not much more than 4ft 6in. With growth-hormone treatment, however, these children grow normally. The role of growth hormone in adult life is much less well understood. Once a person reaches their final height, it is clearly not necessary for continued growth. But a condition called adult growth-hormone deficiency syndrome has recently been described.

People with this condition tend to have both physical and psychological problems. Physically, they are rather fat around the middle, and their bones tend to be more brittle than average. Psychologically, they suffer from low mood, lack of concentration and a reduced sex drive. They may also be at increased risk of heart disease. Most of the supplements that are advertised on the internet claim to be growth hormone "stimulants" that can be swallowed as tablets. They do not actually contain any human growth hormone. True human growth hormone can only be given by injection. Adults who are definitely deficient in growth hormone, such as people who have had surgery to their pituitary glands, usually say that they feel better if they have growth hormone injections every day. The use of growth hormone as a "supplement" has never been properly studied. You can be sure that it will be difficult to obtain on the NHS – the cost of a year's treatment is £1,000 or more, depending on the dose that is used.

Shellfish alert

I discovered in my twenties that I could not eat lobster without a violent allergic reaction. Then, in my forties, I developed an allergy to oysters. I don't regard either of these allergies as a great problem, but on holiday in Spain this year, I was very tempted to eat delicious-looking crayfish on a platter of seafood, but didn't dare – they look too much like small lobsters. Are they actually the same, and how can I know which shellfish might contain the chemical to which I am allergic and which not?

The substance that causes lobster allergy is a protein in the lobster muscle called tropomyosin. The same protein, or a very similar one, is likely to be present in related species of crustacean. Studies have shown that if someone is allergic to one member of the crustacean family, they are usually allergic to others as well. The common foods that show this type of cross-reactivity are shrimp and prawns, crabs, lobsters and crayfish. There are a small number of people who have an allergy to both crustaceans and oysters and you may be one of them. It is also possible that your reaction to oysters was actually a case of food poisoning, rather than true allergy. Unfortunately, it is difficult to find reliable tests to predict food allergies. Skin-prick tests are sometimes used, and they usually correlate well with known symptoms. But there can be "false positive" skin tests, in which the skin prick produces a reaction, but eating the food does not. For you, the safest thing is to avoid all crustaceans and oysters in the future. You may also find that you cannot tolerate clams and mussels. Food allergies can be potentially life-threatening. If they cause swelling of the tongue, wheezing or difficulty in breathing, you must seek immediate emergency medical help. People who have had a serious anaphylactic reaction are advised to carry a syringe containing adrenaline for emergency use.

Have your say

AJ, a nurse at a travel clinic in London, comments on last week's suggestion for antimalarial tablets:

It is true that Malarone can be used for children who weigh more than 11kg. The difficulty is that paediatric tablets, for children from 11kg-40kg, are not yet licensed in the UK, and probably won't be until the end of 2002 or early 2003. It is not possible simply to divide the adult dose.

Please send your questions and answers to A Question of Health, 'The Independent', Independent House, 191 Marsh Wall, London E14 9RS; fax to 020-7005 2182; or e-mail to Dr Kavalier regrets that he is unable to respond personally to questions