Download Adverse Drug Reactions - University of Bristol

Warfarin, Insulin and Digoxin are
the most Dangerous drugs in the
elderly.
Do we believe that?
No Drugs are
Dangerous if
used properly
All Drugs are
Dangerous
Some drugs
have a low
therapeutic ratio
Some drugs have a
low incidence of
horrendous effects
Some drugs are
dangerous in
acute poisoning
but not when
used
therapeutically
The most
dangerous drugs
have the greatest
potential for
benefit
Some adverse
effects occur
after a delay or
after stopping
BAD
GOOD
How dangerous a drug
is depends on the skill of
the prescriber
Some adverse
effects can be
predicted if you
know the
pharmacology
(Type A); some
are not (Type B)
The Risk to Benefit Ratio
When prescribing drugs a doctor must assess
risk to benefit ratio in the individual patient by
•Choosing an appropriate class of drug then an
appropriate individual agent
RISK
BENEFIT
•Is it effective ?
•What are the chances of adverse effect ?
•Are there features in this patient which
affect choice eg other drugs, organ failure,
aged
•Tailoring the dose
•Considering duration of treatment
The Risks when prescribing
drugs with a low therapeutic
ratio are greatly increased if
1. Pharmacokinetic process is
complicated eg high hepatic
extraction, or zero order
elimination
2. Wide interindividual
variation in kinetics and / or
response
3. Pharmacokinetics sensitive
to drug interaction, disease
or ageing
Adverse drug reactions
An ADR is any unwanted effect
resulting from a drug’s use in
treatment.
Epidemiology
4% of hospital admissions
1 in 1000 deaths in medical wards
10 to 20 % of in-patients
5% of patients in general practice
More frequent in elderly:
erratic drug taking
multiple pathology
altered pharmacokinetics
increased sensitivity of CNS
and CVS
Drugs - anti-coagulants,
NSAIDs,corticosteroids, antihypertensives, anti-biotics,
diuretics and insulin.
Occur in circumstances related to
drug’s pharmacology,
predisposing factors in the patient
and care taken in choosing the
drug and the dose.
The BNF appendices
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Drug Interactions
Liver disease
Renal impairment
Pregnancy
Breast feeding
BNF chapters of relevance
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Adverse reactions to drugs
Prescribing in the elderly
Prescribing for children
Emergency treatment of poisoning
Detecting Adverse Effects
• If a new drug causes a bizarre effect in 1 in 6000
patients it would need 18000 patients to use the
drug for it to occur in 3 patients
• It would take twice as many before there was any
suspicion that the effect was due to the drug
• If the effect also occurs naturally then it would
take many times more patients
• Most early trials involve about 2000 patients
Detecting Adverse Effects
• MRHA (Medicine and Healthcare products
Regulatory Agency) freephone service for
reporting and information about suspected
ADRs
• Self reporting by patients and relatives
using Yellow cards available at pharmacies
• Prescription event monitoring
• New drugs – black triangles and yellow
cards
• Established drugs
Measuring danger
• MHRA activity
through Yellow card
reporting and
prescription
monitoring
• Huge increase
in reports over
recent years
Who reports to the MHRA?
•Under-reporting estimated at 94% in hospital practice
(Smith et al 1996)
•MRHA activity good at detecting adverse effects
•Not very good at assessing the risk ratio
Prevention of Adverse Drug
reactions
• Never use any drug unless there is good
indication. If the patient is pregnant do not
use the drug unless the need is imperative.
• Allergy and idiosyncrasy are important
causes of ADRs. Ask if the patient had
previous reactions.
• Ask if the patient is already taking other
drugs including self medication
Preventing ADRs cont’d
• Age, hepatic and renal disease may impair clearance
of drugs so smaller doses may be needed. Genetic
factors may also predispose to certain ADRs
• Prescribe as few drugs as possible and give clear
instructions
• Where possible use familiar drugs. With new drugs
be particularly alert for ADRs and unexpected event.
• If serious ADRs are liable to occur warn the patient
Some websites
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www.yellowcard.gov.uk
http://medicines.mhra.gov.uk
www.dsru.org
http://eis.bris.ac.uk/~pmcjcr/Drug%20Safet
y.pdf