Download Using the BNF

Using the BNF
CWFS F1 Programme
Safe Prescribing Module
Know Your BNF
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Guidance on prescribing
- Controlled drugs and dependence
- Prescribing in palliative care/elderly/children
Emergency treatment of poisoning
General drug monographs Section 1 to 15
Appendix 1 to 9
Yellow Cards for ADR reporting
Advanced Life Support
Prescribing in children age/weight/body surface area
table
• http://www.bnf.org/bnf/bnf/current/
BNF Appendices
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1. Interactions
2. Liver disease
3. Renal impairment
4. Pregnancy
5. Breast feeding
6. Intravenous additives
• (7. Borderline substances
• 8. Wound management products and elastic hosiery
• 9. Cautionary and advisory labels for dispensed medicines)
Appendix 1 : Interactions
• Pharmacodynamic
• Similar or antagonistic pharmacological
effects or side effects e.g. opiates
• Pharmacokinetic
• When one drug alters the absorption,
distribution, metabolism or excretion
of another drug e.g. NSAIDs and
methotrexate
Appendix 1: Interactions
• Look for drugs in classes (e.g. Cardiac
glycosides not digoxin)
• Name of interacting drug in blue
• Black dot interactions indicating ‘Potentially
hazardous so avoid or use only with caution
and intensive monitoring’
Appendix 2: Liver Disease
• Dose adjustment in liver disease is more
contentious than renal impairment since liver
may retain large amounts of its metabolising
capacity despite very deranged LFTS
•Liver disease may alter response to drugs so
prescribing should be kept to a minimum
• •Hepatic metabolism is one of main routes of
elimination for many drugs
• •Appendix 2 in BNF has information regarding
dose reduction etc.
Liver disease
• Liver disease must be severe before important changes in drug
metabolism occur
• Impaired drug metabolism –Rifampicin, Fusidic acid
• Hypoproteinaemia (Hypoalbuminaemia is associated with reduced
protein binding and increased toxicity of highly protein bound drugs) –
Phenytoin, prednisolone
• Reduced clotting –Warfarin & phenindione
• Hepatic encephalopathy –some drugs can further impair cerebral
function i.e. sedatives, opioids, some diuretics
• Fluid overload –Oedema can be exacerbated by NSAIDS, corticosteroids
• Hepatotoxic drugs
Appendix 3: Renal Impairment
• The basic principles:
• Reduced renal function can cause problems
with certain drugs:
• Toxicity
• increased sensitivity
• poorly tolerated side effects
• reduced therapeutic effect
• Some of these problems can be avoided by
reducing the dose or using an alternative drug
Renal impairment
• Dose reduction depends on how drug is
eliminated
• Drugs with minor or no dose related side
effects only require simple dose reduction
• Toxic drugs require dose reduction based on
GFR
• Reduce dose or increase interval between
doses
• If possible avoid nephrotoxic drugs
Appendix 3: Renal Impairment
• Recommendations are based on severity
of renal impairment expressed as GFR
• Serum creatinine gives a very rough estimation N.B.
Elderly/ Tiny
• Grades of renal impairment:
• Grade
GFR
Serum Creatinine
• Mild
20 –50ml/minute
150 –300
• Moderate 10 –20ml/minute
300 –700
• Severe
< 10ml/minute
> 700
Appendix 3:
Renal Impairment
• Take highest severity for borderline values of GFR
• If a dose needs to be reduced in mild impairment, then
action will need to be taken for moderate/severe
impairment
• Sources of information include:
• –BNF
• –Summary of Product Characteristics
• –Ward Pharmacist
• –Medicines Information
Appendix 3:
Renal Impairment
• Example: Advice for Meropenem
• Usual dose = 500mg every 8 hours
• Mild –Increase dose interval to every 12 hours
= 500mg b.d.
• Moderate –Use half normal dose every 12
hours = 250mg b.d.
• Severe –Use half normal dose every 24 hours
= 250mg o.d.
Appendix 4:
Pregnancy
• Drugs can be harmful at any time during pregnancy
• Only prescribe if essential
• Benefit to mother needs to be >> risk to foetus
• Risks differ depending on Trimester
• 1st trimester –Congenital malformations
• 2nd & 3rd trimester –Growth & functional development
• Perinatal –Adverse effects on labour or neonate
• BNF Tables are not complete –absence does not imply safety
Appendix 5: Breast Feeding
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Drugs excreted in maternal milk; consider
Toxicity
Hypersensitivity
May inhibit lactation
May inhibit infant’s sucking reflex
• Benefit of breast feeding > need for drug?
• Use only essential drugs
Appendix 5: Breast Feeding
• Table lists:
• Drugs to be used with caution or which are
contraindicated
• Drugs that can be given to the mother –due to
small amounts in milk
• Drugs that can be given to the mother –since
not harmful even though present in significant
amounts
• NB: Information not available on many drugs
• Absence from the table does not imply safety
Appendix 6: Intravenous additives
• Details of compatible fluids and suggestions of
concentrations
• Sometimes suggests maximum rates
• Check carefully as not all drugs are compatible
with sodium chloride 0.9%
• Not exhaustive
• Doesn’t always imply need for IV infusion
• Ask Pharmacy
Not relevant to medical hospital
practice
• Appendix 7: Borderline substances
• Appendix 8: Wound management products
and elastic hosiery
• Appendix 9: Cautionary and advisory labels
for dispensed medicines
• Try the quiz to familiarise yourself with
your BNF