Dialysed patients: differences in dialysis methods – clinical relevance

Oral presentation

Clinical dialysis today represents a routine life-saving procedure for patients with kidney failure. However, it is still far from being an ideal replacement for kidney function. At least three disadvantages should be mentioned:

First, while more than 90 uremic retention molecules/uremic toxins have been described, only a proportion of them are removed by dialysis, as current dialysis methods do not effectively remove compounds with a relative molecular weight above 500 and/or substances bound to plasma proteins. In case of extracorporeal dialysis, this removal is not only partial, but also only intermittent in nature.

Secondly, dialysis does not replace endocrine and regulatory kidney functions at all. As a result, renal failure is inevitably accompanied by renal anaemia and metabolic bone disease. Fortunately, due to recent advances in pharmacology, drugs in experienced hands can cure these complications.

Thirdly, patients on maintenance dialysis suffer from numerous other chronic abnormalities and diseases, whether related or unrelated to chronic renal failure and dialysis (malnutrition, chronic inflammation, cardiovascular complications etc).

For the above-mentioned reasons, most dialysis patients are prescribed a host of drugs, but the likelihood of adverse consequences can be quite high.

Appropriate drug policy in these patients is a great challenge. Chronic kidney disease may influence drug distribution, as a primary determinant of distribution volume Vd (plasma protein binding, tissue binding and total body water) may be altered in kidney failure. Drug effectiveness can be modified directly by dialysis (drug removal), but also indirectly (e.g. digoxin toxicity due to a rapid drop of serum potassium during dialysis). Some retention molecules may influence a drug's effect by competing for protein binding; these protein-bound compounds are poorly removed by dialysis. Low albumin levels due to malnutrition in dialysis patients may further aggravate this interference. Not only drugs, but also their metabolites, may accumulate and exert their own toxicity. On the other hand, some drugs may help to reduce toxin concentrations. In some of these aspects, hemodialysis and peritoneal dialysis can differ to varying degrees. These differences will be discussed.

For all these reasons, clinicians as well as researchers in pharmacology should be aware of all risks versus benefits of drug treatment in this specific patient population and an intensive cooperation in this field is warranted.

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