Currently there are 22 diuretics listed in the BNF and this does not include combination products. Pharmacists who are advising local GPs on formulary development need to consider which diuretics to include on a prescribing list. With so many products to choose from, there is intense competition between companies and claims can often be very persuasive. A diuretic is any substance that increases urine and solute production.
Diuretics can work outside the kidney.
For example, by inhibiting the release of anti-diuretic hormone which happens with alcohol. However, in clinical practice, the kidney is the most important organ through which diuresis is effected. The normal glomerular filtration rate is about 300 litres daily, yet the daily volume of urine is just over 1 litre. Clinically-useful diuretics act on the renal tubule and not on the glomerulus, since effects here would have major cardiovascular repercussions. As a result, there is no change in sodium concentration in the fluid remaining in the tubule.