ANY parent with a child who wets the bed knows the problems of taking them on holiday. Now there is a new tablet that can help to prevent the problem. It contains a substance known as anti-diuretic hormone, which slows down the production of urine. The medication, called desmopressin, has been available in the form of a nasal spray for several years but has not been convenient to take on holiday because it has to be stored in a refrigerator. From tomorrow it will be available in tablet form. Further information is available from the Enuresis Resource and Information Centre, 65 St Michael's Hill, Bristol BS2 8DZ.