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What does this study add?
- Joseph F Standing (23 May 2005)
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Dose adjustment in renal impairment
- Dinesh K Mehta (15 July 2005)
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Joseph F Standing, Research Pharmacist Great Ormond Street Hospital, WC1N 3JH
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In this study, Vidal et al highlight an important point about sources of drug information: they can only ever be used for guidance and can never replace judgements made by pharmacists and doctors working within their own field of competence/specialism/expertise. I am sure that as in paediatrics, renal doctors and pharmacists use various sources of information when determining an individual patient's dosing. These will include a knowledge of the drug's pharmacology (degree of renal clearance, therapeutic index, potential for nephrotoxicity), interpretation of primary and secondary sources. Is it reasonable to expect the BNF (probably more a tertiary source) to fully reference all of its guidelines/recommendations? This would cause it to double in size - meaning that thousands of white coats belonging to junior doctors and pharmacists would be de-commissioned for pocket-enlargement. Competing interests: None declared |
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Dinesh K Mehta, Executive Editor: British National Formulary BNF, Royal Pharmaceutical Society of Great Britain, 1 Lambeth High Street, London SE1 7JN
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Vidal et al are rightly concerned that information on dose adjustment is not as well supported by evidence as our knowledge on the effectiveness of modern interventions. But as they have found, there is a woeful lack of robust data to guide us on the precautions to take when using medicines. Therefore, their conclusions come as no surprise to compilers of drug information. Because there are few accessible studies on dose adjustment in renal impairment, the British National Formulary (BNF) has to rely on summaries of product characteristics, which reflect data submitted for gaining marketing authorisation. However, the BNF continually adjusts its position as clinically relevant information emerges; this process is summarised in Appendix 2 of Vidal et al’s paper. Vidal and colleagues’ comparison of information on drugs in renal impairment was prompted by the need to populate a computerised decision support system. On the face of it, quantitative data on dose adjustment in renal impairment appears well suited for this purpose. However, a great many factors other than renal impairment influence the choice of drug and its dose. The severity of the condition being treated, toxicity of the drug, co-morbidity, and the patient’s size, age and sex can all have a bearing on the final dose chosen, but their effect is not easily quantifiable. And even if it were possible to quantify the full effect of the clinical and demographical information, practical constraints such as the size of the available dose form sometimes make it impossible to give the calculated dose. Therefore, the most important message is often simply that renal impairment is likely to affect the dose. The clinician would still need to titrate the dose according to the patient’s clinical condition or quantitative measures (e.g. INR, blood pressure and drug concentration for drugs such as aminoglycosides and digoxin). The BNF takes the view that clinicians should understand the full range of a drug’s clinical properties. For example, the side-effects of corticosteroids include fluid retention and the reader would be expected to consider this when treating a patient with renal impairment, even though the appendix on renal impairment does not make this point. The BNF also provides formulation-specific information (e.g. electrolyte content) which may need to be taken into account for those with renal impairment. The categorisation of the degree of renal impairment often causes difficulty and, as the authors have found, there is no universal standard. The situation is further confounded by the fact that nephrologists might be interested in characterising the overall renal physiology whereas a prescriber might be interested primarily in the efficiency of drug elimination. Often, correlation between the two is poor. Vidal and colleagues’ paper gives further impetus to the BNF’s plan to review its own advice on dosage adjustment in renal impairment. The review will include close scrutiny of the individual discrepancies that they have highlighted. Dinesh K Mehta British National Formulary Competing interests: None declared |
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