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A kick in the kidneys

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Another quarter, another batch of NICE guidance arrives on ourdoorstep.  This month sees the release of the headline grabbing ADHDguidelines, but also NICE's take on the management of Chronic Kidney Disease.

Alas, one key area for clinical pharmacists remains ignored - what todo in routine practice about drug dosing when a patient has impaired renal clearance. 

Forthe uninitiated, renal function is important as the kidneys are one ofthe two main ways that the body excretes drugs and other wasteproducts.  If renal function is impaired, we have to either reduce thedose of the drug to allow for the resulting accumulation or chooseanother drug that is eliminated by other routes.

Until recently the Cockroft and Gault creatinine clearance equationwould be routinely used for estimating renal drug handling (The numberof years of age under 140 divided by the serum creatinine, multipliedby the weight in kilos and a factor of 1.23 or 1.04 depending onwhether the patient's a man or woman respectively).  Depending on whatthis approximation to the renal clearance of creatinine comes back at,we can make an informed choice about how much accumulation is likelyfor a particular drug. 

DoH guidance in 2003 brought in the MDRD eGFR equation - morecomplicated but capable of being worked out automatically by thecomputer in the biochemistry lab.  The eGFR's purpose is to screen thepopulation for kidney disease, so they can be treated earlier and leadhappier healthier lives - which is a very very good thing. Unfortuately for us pharmacists it's also frequently used by doctorsfor the purposes of adjusting drugs - a use for which it is at bestunvalidated.  No-one knows if an eGFR can be used for anything otherthan screening and monitoring caucasians and afro-carribeans for kidneydisease. 

Now NICE at one point seems to recognise this, but suggests usinginulin or other "gold standard" markers for adjusting nephrotoxicdrugs.  I don't know about other hospital pharmacists but I can't seeus injecting radioactive tracer molecules into every patient that needsto receive chemotherapy, let alone other nephrotoxic drugs, or evendrugs like nitrofurantoin which are either toxic or ineffective at mild renal impairment. 

Creatinineis measured in nearly every patient that crosses our threshold, and wehave years of practice and research (admitedly this is of variablequality) to back up the use of Cockroft and Gault in patients.

Looking through the authors, I see many doctors and health economists but no pharmacists.  Why weren't the UK renal pharmacy group involved, so that we could get in black and white that this issue exists and needs resolving?

25-9-8

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