Q:I had a hip replacement in 1986. Since then every time I have my dental treatment I am advised to take amoxycillin. This has the effect of upsetting me for some seven to 10 days, and I question its value. What evidence is there that it prevents septicaemia? What do people who have other bits of steel in their bones not need to take antibiotics for dental treatment? S. M. R., Cumbria and also How defensible is the practice of giving a large dose of penicillin prophylactically before dental treatment or surgical procedures to people with heart murmur/prolapsed mitral value, "to prevent the development of bacterial endocarditis"? N.L, Hastings.

A:We asked our one of our resident dental experts, Jack Levenson, to comment on these questions. His reply: "In the first instance, the hip replacement patient should question his surgeon and possibly get a second opinion about the automatic use of an antibiotic for routine dental treatment as I have never heard of such a practice."The second instance, the practice of giving penicillin prophylactically for a heart murmur patient, is defensible. Any time there is a surgical procedure, bacteria can be released into the blood stream. When a patient has a heart murmur, there is a danger that bacteraemia released into the blood stream could settle on the value creating the murmur, causing acute bacterial endocarditis.

"This is what antibiotics are for, during o to prevent emergencies when there is a good indication, and not to be used indescriminately as they are today."

We would only add that you should be very cautious about the frequency and the dosage of penicillin. One other reader wrote that her entire family has suffered from recurrent upper respiratory tract infections this past winter and has each taken several courses of antibiotics. "Are we all reinfecting each other, and is there any way to break the vicious circle?"

In this case, the family may have got itself into what health author Geoffrey Cannon calls a chemical treadmill, where the drugs are lowering resistence to infection, particularly as they don't work on colds, anyway. Allergies and weakened immunity could be causing the infections. The case study describes just what injudicious use of antibiotics can do.