Assays / Trace Metals/ Gold

The attractive appearance and relative immutability of gold has resulted in a long history of economic, decorative and artistic use. The element has also been used as a treatment for many medical conditions. More recently, gold compounds have been demonstrated to have an anti-bacterial activity e.g. in the treatment of tuberculosis and syphilis. The element has also become prominent in the treatment of rheumatoid arthritis, where gold compounds are among the so-called 'second line' agents for the condition. Much of the emphasis has been on the development of compounds which retain therapeutic value but minimise the toxic side effects. Currently the most popular is Aurothiomalate administered by intramuscular injection. This drug has also been used for a number of other conditions with a possible auto immune basis, such as psoriatic arthritis, juvenile chronic polyarthritis (Stills disease) and pemphigus.

Toxicity
A range of side effects occurs with gold therapy from the relatively trivial to the severe. Early signs may be the development of pruritis or dermatitis which will respond to the withdrawal of the gold. Treatment can often be reintroduced without further problems. More severe consequences include proteinuria which may develop into nephrotic syndrome. Progression of the renal lesion is generally avoided by the withdrawal of the therapy. The most serious side effect of gold therapy is bone marrow dysplasia. Other less common side effects include cholestatic jaundice , colitis and a diffuse interstitial lung disease.

Laboratory Indices
The peak plasma gold concentration is reached some six hours following injection of aurothiomalate; but the concentration reached is extremely variable between individuals. The half -life in plasma is approximately 5 days and if weekly injections are given, the concentration will gradually rise. Most of the gold in blood is confined to the plasma where the majority is bound to albumin. It has been argued that the binding is not tight, as measurable amounts of gold are found in the urine during chrysotherapy. Urinary gold excretion follows a similar pattern to that of the plasma gold concentration. Some 60% of gold that is injected is retained. Although toxicity associated with gold therapy may be related to gold accumulation in the tissues, there is no apparent relationship between serum or urinary gold concentrations and the onset of toxicity. Therefore regular measurement of plasma gold in patients on gold therapy is not recommended, but the assay has some value in the assessment of patients being treated for toxicity by chelation therapy.

References:
Taylor A. Therapeutic uses of trace elements. Clinics in Endocrinology and Metabolism 1985; 14: 703-724

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