Editorials

Safer prescribing for children

BMJ 2005; 331 doi: http://dx.doi.org/10.1136/bmj.331.7518.646 (Published 22 September 2005) Cite this as: BMJ 2005;331:646

BNF calculator for estimating creatinine clearance is unsafe in children.

It is tempting to calculate the glomerular filtration rate (GFR) in
children, in whom the accurate measurement of GFR is challenging. The BNF
for children fails to spell out the hazards of estimations based on the
Schwartz formula. 1 Renal impairment is overlooked, where serum
creatinine is not raised.2 In addition, the BNF Extra offers a serum
creatinine, age and sex-based calculator on-line without comment on its
use in children.3

We compared creatinine clearance estimated by Schwartz formula and
BNF Extra calculator from contemporaneous serum creatinine to laboratory
GFR (by single injection 2 sample 99Tc-DTPA methodology) in 114 paediatric
urology patients aged 1-14 years (Figure 1).

Figure 1.


Frequency distribution of measured GFR (light grey), Schwartz estimate (dark grey) and BNF on-line calculator (black) in 114 paediatric urology patients aged 1-14 years. The Schwartz estimate produced an absolute error of 19.4% +/-65.2% as compared against the measured GFR. The BNF on-line calculator compared against the measured GFR resulted in an absolute error of 84.3% +/-114%.

The Schwartz formula identified patients with a laboratory GFR <_80 ml="ml" min="min" _1.73m2="_1.73m2" with="with" _91="_91" specificity="specificity" but="but" only="only" _60="_60" sensitivity.="sensitivity." schwartz="schwartz" missed="missed" those="those" in="in" whom="whom" the="the" remaining="remaining" number="number" of="of" functioning="functioning" nephrons="nephrons" was="was" sufficient="sufficient" for="for" a="a" normal="normal" serum="serum" creatinine.="creatinine." as="as" this="this" group="group" patients="patients" nevertheless="nevertheless" requires="requires" special="special" attention="attention" including="including" use="use" medicines="medicines" formula="formula" is="is" unsafe.="unsafe." p="p"/> The on-line BNF calculator overestimated creatinine clearance in
every case (Figure 2): mean overestimate 82 ml/min/1.73m2, range 4.5 to
156 ml/min/1.73m2. It should therefore never be used in children.

Figure 2.


Bland/Altman plot of the difference between the BNF on-line calculator and measured GFR against the mean of the measured GFR and BNF on-line calculator in 114 paediatric urology patients aged 1-14 years. The on-line BNF calculator overestimated creatinine clearance by a mean 82 ml/min/1.73m2, range 4.5 to 156 ml/min/1.73m2.

In reply to Dr Marcovitch, who comments that the BNF for children has
been validated against emerging evidence, guidelines on best practice and
advice from a network of clinical experts, we would caution the use of
either of these mechanisms for estimations of GFR in children.4 We
suggest that the BNF Extra on-line calculator should exclude its use in
children.

Nas Al-Jafari, F2 Trainee in Paediatric Surgery,
Naima Smeulders, Specialist Registrar in Paediatric Surgery and
Rowena Hitchcock, Consultant Paediatric Surgeon and Urologist.
Department of Paediatric Surgery and Urology, John Radcliffe Hospital NHS
Trust, Oxford, OX3 9DU.
naima.smeulders@btopenworld.com

References:

1 Costello, I ed. BNF for children. London: Pharmaceutical Press,
2005:12-13.
2 Seikaly MG, Browne R, Bajaj G, Arant BS Jr. Limitations to body
length/serum creatinine ratio as an estimate of glomerular filtration in
children. Pediatr Nephrol1996; 10:709-11.
3 BNF Extra. Calculators: Creatinine clearance. 2005
http://www.bnf.org/bnf/extra/current/noframes/450019.htm (accessed 17
March 2006)
4 Marcovitch H. Safer prescribing for children. BMJ 2005;331:646-47.

FIGURES 1 and 2 emailed to Sharon Davies

Competing interests:
None declared

Competing interests: No competing interests

07 April 2006
Naima Smeulders
SpR Paediatric Surgery
Nas Al-Jafari and Rowena Hitchcock
Department of Paediatric Surgery and Urology, John Radcliffe Hospital NHS Trust, Oxford, OX3 9DU.
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