prescribing - simply finals - simply revision
TRANSCRIPT
PrescribingThe PSA, Finals and Beyond…
Dr Andrew Smith
OutlinePlus:
• Some practical tips for the PSA• Slides on
Prescribing Theory
• There is a lot of overlap of knowledge which may be tested in
various way•A number of other Simply Finals talks
have useful prescribing info
• The knowledge is useful for Finals too!
How to Prepare for the PSA
Firstly, know thy enemy!
www.prescribingsafetyassessment.ac.uk
Contains lots of information on the PSA, as well as practice questions.
In particular:
www.tinyurl.com/PSAblueprint
Provides an overview of the exam content, question types, possible topics etc.
How to Prepare for the PSA
• Learn treatment algorithms
• Available in OHCM and BNF (your friend in the exam!)
CTRL + F
How to Prepare for the PSA• Practise!
• Example questions on PSA website
• Also free questions at: www.prepareforthepsa.com
• BL tutorial: www.tinyurl.com/BLprescribingtutorial
• I’m informed that this book is useful:
Prescribing
• Remember to sign and print your name on all prescriptions
– don’t lose easy marks in the exam!
• Consider the most appropriate formulation/route/timing
etc. – you get marks for these too!
• A reminder that for Controlled Drugs, you must:
• Include the name and address of the patient.
• State the name and strength of the formulation
• State the dose and frequency
• State the total amount to be supplied in words and figures
What dose should you prescribe?
A. SMITH
What dose should you prescribe?
A. SMITH
How would you improve this prescription?
FUROSEMIDE
PREDNISOLONE16/1/19
PO
16/1/19PO
40mg
40mg
A. SMITH
A. SMITH
FUROSEMIDE
PREDNISOLONE16/1/19
PO
16/1/19PO
40mg
40mg
Should be given in morning – will keep patient awake!
Should be given in morning – will keep patient awake!
A. SMITH
A. SMITH
Prescribing Controlled Drugs – Which is correct?
MORPHINE SULPHATE 10mg oral tabletsTake one tablet, three times dailyPlease supply 28 (TWENTY-EIGHT) tablets.
MORPHINE SULPHATE 10mg oral tabletsTake one tablet, three times daily.Please supply 28 10mg(TEN MILLIGRAM) tablets.
30 Will Dooley
20/6/86 Perrin Lecture Theatre
30 Will Dooley
20/6/86 Perrin Lecture Theatre
A. SMITHA. SMITH16/01/2019 16/01/2019
Prescribing Controlled Drugs – Which is correct?
MORPHINE SULPHATE 10mg oral tabletsTake one tablet, three times dailyPlease supply 28 (TWENTY-EIGHT) tablets.
MORPHINE SULPHATE 10mg oral tabletsTake one tablet, three times daily.Please supply 28 10mg (TEN MILLIGRAM) tablets.
It’s the ‘total amount’ that you need to specify
30 Will Dooley
20/6/86 Perrin Lecture Theatre
30 Will Dooley
20/6/86 Perrin Lecture Theatre
A. SMITHA. SMITH16/01/2019 16/01/2019
Prescribing Controlled Drugs – Which is correct?
MORPHINE SULPHATELiquid (10mg/5ml)
Take 10mg when required
Please supply 100ml(ONE HUNDRED)
MORPHINE SULPHATELiquid (10mg/5ml)
Take 10mg (TEN MILLIGRAM) when required
Please supply 100ml
30 Will Dooley
20/6/86 Perrin Lecture Theatre
30 Will Dooley
20/6/86 Perrin Lecture Theatre
A. SMITHA. SMITH16/01/2019 16/01/2019
Prescribing Controlled Drugs – Which is correct?
MORPHINE SULPHATELiquid (10mg/5ml)
Take 10mg when required
Please supply 100ml(ONE HUNDRED)
MORPHINE SULPHATELiquid (10mg/5ml)
Take 10mg (TEN MILLIGRAM) when required
Please supply 100ml
A. SMITHA. SMITH15/01/2019 16/01/2019
It’s the ‘total amount’ that you need to specify – Including the units. It should read:
Please supply 100ml (ONE HUNDRED MILLILITRES)
30 Will Dooley
20/6/86 Perrin Lecture Theatre
30 Will Dooley
20/6/86 Perrin Lecture Theatre
Spot the mistakes
DOOLEY
WILL
Spot the mistakes
DOOLEY
WILL
No details of reaction
No unique patient identifier or DOB
Allergy No signature
How many charts? Good practice to fill this in
Spot the mistakes
A. SMITH
A. SMITH
A. SMITH
Spot the mistakes
Incorrect dose – Should be 62.5 MICROgrams
Write Units (not just ‘U’) – technically should be prescribed on the insulin area of the chart!
Write “micrograms” in full
What type?
A. SMITH
A. SMITH
A. SMITH
Fluid chart errors
16/1/19 0.9% Saline 1 litre STAT A.L.S
16/1/19 Red Blood Cells 2 units ----------------- 4 hours A.L.S
16/1/19 50% Dextrose 1 litre 12 hours A.L.S
A. SMITH
A. SMITH
A. SMITH
Potassium Chloride
40mmol
Fluid chart errors
16/1/19 0.9% Saline 1 litre KCl 40mmol STAT A.L.S
16/1/19 Red Blood Cells 2 units ----------------- 4 hours A.L.S
16/1/19 50% Dextrose 1 litre 12 hours A.L.S
This amount of potassium must be given over at least 4 hours due to risk of arrhythmias
A. SMITH
A. SMITH
A. SMITH
Each unit needs to be prescribed separately
Has to be discarded after 4 hours (from leaving the lab)
50% Dextrose is irritant to veins. It should only be given in small volumes and ideally
via a central line10% or 20% should preferably be used if
trying to reverse hypoglycaemia
Potassium Chloride
40mmol
Familiarise yourself with management of:Acute Conditions:• STEMI• NSTEMI• Acute left ventricular failure • Tachycardia with pulse • Anaphylaxis• Acute asthma exacerbation • Pneumonia• PE• GI bleed• Bacterial meningitis • Seizure • Status epilepticus • Stroke • Hyperglycemia • DKA and HHS• AKI• Poisoning
Chronic Conditions:• Hypertension
• Chronic Heart Failure
• Stroke Prevention
• Stable Angina
• Chronic Asthma
• COPD
• Diabetes
• Insomnia
• Constipation
• Diarrhoea
• Pain
Some examples
Drug Important points of information
Ramipril Stop in pregnancy – teratogenic
Gliclazide Eat regularly, don’t skip meals – hypo risk
Methotrexate Regular FBC – neutropenia risk
Warfarin Monitor INR – bleeding
Long Term Steroids
Take bisphosphonate – osteoperosis risk
Don’t stop suddenly
May need to increase dose when unwell
SSRI Contact doctor if thoughts of self harm
Insulin Don’t stop taking when unwell, you may need more
Bisphosphonate Take with full glass of water and remain upright for 1 hour
Drug Calculations
• Always convert to the same units and then:
D (What you want) x V (volume it is in) = Dose
H (What you’ve got)
For example, a baby needs 200mg of Cefotaxime.
Vials contain 500mg and are made up to a total volume of 2ml.
What volume do we need to give?
200mg x 2ml = 0.8ml
500mg
Some reminders
1% means
• 1g in 100ml or 10mg in 1ml for weight/volume (w/v)
calculations
• 1g in 100g for weight/weight (w/w) calculations
• E.g. 5ml of 1% Lidocaine contains 50mg Lidocaine
Drugs Expressed as Ratios
weight (g) : volume (ml)
1:1000 = 1g in 1000ml = 1000mg in 1000ml
Therefore, 1mg in 1ml → 0.5mg in 0.5ml
1:10000 = 1g in 10,000ml = 1000mg in 10,000ml
Therefore, 1mg in 10ml
Higher concentrations are given IM so less volume has to be given
(IM injections are unpleasant)
Used in
anaphylaxis
Used in
cardiac
arrest
E.g. Adrenaline
Adverse Drug Reactions
• Unwanted reactions that occur with normal use of the
drug
• Two main types:
• Type A (Augmented) – Common, predictable and often
dose dependent. Can be severe and delayed.
• Type B (Idiosyncratic) – No link to expected
pharmacological effects. Often serious but rare.
Adverse Drug Reactions - Examples
Drug Reaction
Type A (Augmented)
Anticoagulants Bleeding
Insulin Hypoglycaemia
Antipsychotics Parkinsonism
Cytotoxics Bone Marrow Suppression
Type B (Idiosyncratic)
Penicillin Anaphylaxis
Isoniazid Hepatotoxity
Anaesthetics Malignant Hyperthermia
Sulphonamides Toxic Epidermal Necrolysis
Allergies• Type 1 allergy (IgE-mediated) to medications is not as common as
patients report
• It’s important to discern the exact reaction as else important
medications may be unnecessarily withheld
• True allergic symptoms: urticaria, swelling, wheeze, laryngeal
oedema, anaphylaxis.
• Common culprits: Penicillin, Sulfa drugs, Tetracycline, Codeine,
NSAIDs, Phenytoin, Carbamazepine.
Penicillin Allergy• Which of the following are safe, or useable with caution, in a
patient with true penicillin allergy?
AugmentinAmikacinCeftriaxoneGentamicinTazocinDoxycyclineFlucloxacillinMetronidazoleTrimethoprimMeropenem
Adverse Reactions – Management Examples
• 76 year old on warfarin for recurrent DVTs. Recent check showed an INR of 7. She is otherwise well• Withhold warfarin. Recheck in 24 hours. If patient is high risk
consider oral/IV Vit K.
• 64 year old on warfarin for atrial fibrilliation. Recent check showed an INR of 8.4. He is suffering from epistaxis.• Withhold warfarin. IV Vitamin K.
• 83 year old on warfarin for a replacement heart valve. Recent check shows INR of 8.7. She is suffering from an upper GI bleed.• Withhold Warfarin. Immediate reversal with Vit K and PCC.
Consider why the INR was so high!?drug interaction
Warfarin Overtreatment ManagementDepends on patient factors:• High risk patients are age >65, severe hypertension, organ failure,
falls risk, trauma, etc.
and Bleeding Factors• Minor bleeding, e.g. haematuria, epistaxis.• Major bleeding, e.g. intracranial, intra-abdominal etc.• Any bleed can be major if deemed so by the clinician
Mx Options include:• Withold Warfarin• Vitamin K – oral (effect within 24 hours), or IV (4-6 hours)• Prothrombin Complex Concentrate (PCC. E.g. Beriplex/Octaplex)
– immediate action (still need to give Vit K)• Fresh Frozen Plasma generally not recommended
Drug Level Monitoring• For some drugs, the therapeutic range (or window) is narrow.
I.e. They can be easily under-or-overdosed.
• Other indications for monitoring include:• Potential compliance issue• Benefit (and adverse reactions) which cannot be judged by clinical
parameters alone• Drug levels in overdose/self-harm
• Drug levels are typically measured as a trough level (pre-dose). However, for drugs with short half-lives peak and trough levels should be taken.
• They should be taken once a steady-state has been achieved (typically after 3-5 doses)
Drug Level Monitoring - Examples
DrugHalf-life
TimingTherapeutic
Range*ToxicLevel*
Extra CareMajor Toxic
Effects
Gentamicin 2h TroughAfter 2-3
doses<2mcg/ml >2mcg/ml
Renal disease, elderly, obesity
Nephrotoxity,irreversible ototoxicity
Phenytoin 20-40h TroughAfter 2-3
days
Total 10-20mcg/ml
Free 1-2mcg/ml
Total >20mcg/ml
Free>2mcg/ml
NB: Zero-orderkinetics. Elderly,
pregnancy, altered protein states
Nystagmus, diplopia, ataxia,
confusion, hyperglycaemia
Aminophylline4-16hr
N/A4-6hrs after starting IV infusion
10-20mcg/ml
>20mcg/ml
Inc. in: Liverdisease, elderly
Dec. in: Smokers, alcohol
Arrhythmias, convulsions, hypotension
Theophylline Trough 5 days
Digoxin 24-36h Trough 1 week0.5-
1.9ng/ml>2ng/ml
Elderly, hypokalaemia
Arrhythmias, visual disturbance,
anorexia
*can vary between labs/assays
Some detail on specific drugs: http://tinyurl.com/druglevels
Other Drug Monitoring
• The effects of other drugs need to be monitored also.
For example:
• Warfarin – monitor INR
• Levothyroxine – monitor TFTs
• When starting, monitor TFTs every 4 weeks and titrate
dose up in increments of 25-50micrograms.
• ACE Inhibitors/Diuretics – monitor U+Es
• Clozapine – monitor FBC
Drug InteractionsDrug interactions may be caused by a variety of effects:• Drug Absorption• Altering gastric pH, e.g. Omeprazole/Ranitidine• Chelation, e.g. Aluminium salts• Gastric motility, e.g. Metoclopromide
• Drug Distribution not typically clinically significant• Drug Excretion • Urinary pH, e.g. Salicylates, Diuretics, Sodium Bicarbonate
• Additive effects of drugs• E.g. Multiple anticoagulants• Increased side-effects, ACE inhibitors and K-sparing diuretics
• Antagonistic effects• Competing effects, e.g. Steroids and anti-hypertensives• Confounding effects, e.g Furosemide and Digoxin, Metronidazole and
Alcohol
• Enzyme Induction/Inhibition
Enzyme Inducers/Inhibitors• A major cause of drug interactions is the inhibition/induction of the
cytochrome P450 family of enzymes (there are 6 main subtypes).
• Inhibition/induction may occur via direct action on the enzymes or by altering the genes involved in their expression.
• Inhibitors increase the levels of drug metabolised by the enzymes.
• Inducers decrease the levels of drugs metabolised by the enzymes.
Inducers Inhibitors
Carbamazepine Macrolides (e.g. Clarithromycin)
Phenytoin Grapefruit juice (flavinoids)
Omeprazole Imidazoles (e.g. Fluconazole)
Nifedipine Quinolones (e.g. Ciprofloxacin)
Rifampicin Amiodarone
Smoking Isoniazid
Chronic Alcohol Use Acute Alcohol Use
Interactions listed in BNF. Or check out www.webmd.com/interaction for interactive checker
Courtesy of www.apotential.wordpress.com
What should you monitor in this patient?
Spot the mistake.
A. SMITH
A. SMITH
What should you monitor in this patient?
Spot the mistake.
POTASSIUM – both drugs can cause hyperkalaemia
Dose alteration is not signed for and previous dose not ruled out
A. SMITH
A. SMITH
What should you monitor in this patient?
Spot the mistake.
POTASSIUM – both drugs can cause hyperkalaemia
Dose alteration is not signed for and previous dose not ruled out
Some drugs causing HYPERKALAEMIA• ACE Inhibitors• Amiloride• Angiotensin Receptor Blockers (ARB)• Antifungals (Ketoconazole, Fluconazole)• Beta Blockers• Cyclosporine• Digoxin• Heparin• NSAIDs• Spironolactone• Tacrolimus• Transfusions of RBC• Trimethoprim
What is this patient at risk of ?
A. SMITH
A. SMITH
What is this patient at risk of ?
PHENYTOIN TOXICITY
Enzyme inhibitor
Enzyme inducer(but relatively less so)
What is this patient at risk of ?
OMEPRAZOLE
PAROXETINE16/1/19
PO
16/1/19PO
20mg
40mg
A. SMITH
A. SMITH
What is this patient at risk of ?
OMEPRAZOLE
PAROXETINE16/1/19
PO
16/1/19PO
20mg
40mg
Drugs commonly causing HYPONATRAEMIA
• Thiazide diuretics• Amiloride• Carbamazepine• Sulphonylureas (but not
Gliclazide)• Proton pump inhibitors• Antidepressants, particularly
SSRIs• ACE inhibitors and ARBs• Opiates
Gentamicin DosingHartford nomogram: guides when to give patient next dose, based
on blood concentration and the time the measurement was taken
Answer: 36h
Q: If concentration is
8mg/ml, 8h after
giving drug – what is
correct dosing
interval?
Activated charcoal: consider if >150mg/kg* has been taken in the last 1hr
*for all Paracetamol overdose, the maximum weight that should be used
is 110kg – this is to avoid underestimating toxic levels in obese patients
N-acetylcysteine (NAC):
• Single overdose, >75mg/kg – presenting <4 hours since ingestion – wait
until 4 hours to take level and use nomogram
• Single overdose, >75mg/kg – presenting within 4-8 hours – measure level
and use nomogram
• Single overdose, >75mg/kg – presenting >8 hours – commence NAC, take
level and discontinue treatment if below Tx line
• Staggered overdose (>1h) – presenting within 24 hours of last dose –
commence NAC. Can discontinue if level undetectable and patient
asymptomatic
Paracetamol Overdose
Q: A patient has taken
200mg/kg of
Paracetamol at 13:00.
A paracetamol level at
20:00 is 80mg/L.
Should NAC be
started?
Paracetamol Overdose
A: Yes
Q: A patient has taken
90mg/kg of
Paracetamol at 09:00.
They present at 21:00.
Should NAC be
started?
Paracetamol Overdose
A: Yes
Q2: A level taken at
presentation was
<0.1mmol/L.
Should NAC be
continued?
A: No
Q: A patient has taken
180mg/kg of
Paracetamol at 15:00.
They present at 15:30.
Should NAC be
started?
Paracetamol Overdose
A: No
Q2: What could be
started?
A: Activated Charcoal
Some of the theory summarised…
Rules of Prescribing• Prescriptions must be written legibly, ideally in CAPITALS!
• Ensure the patient’s name, DOB and hospital/NHS number is present
• The dose and route of administration should be specified
• Avoid using decimal places. If mandatory, make them clear e.g. 0.5
rather than .5
• “Micrograms” should be written in full. Not mcg or µg
• Write “Units” in full. Not “U”
Rules of Prescribing Continued
• Some drug charts will have specific places for insulin, antimicrobials
and anticoagulants – use them!
• If stopping a drug, make it clear and sign and date it
• Avoid abbreviations in drug names e.g. “Isosorbide Mononitrate”
rather than “ISMN”
• Accepted abbreviations for routes of administration are often printed
on the drug chart
Rules of Prescribing Continued
• Trade-names should be avoided apart from in special circumstances
(e.g. modified release preparations)
• Ensure special instructions are clear, especially if it is an uncommon
drug (e.g. Methotrexate weekly)
• Use the BNF – including the appendices on interactions, and info on
hepatic/renal failure, pregnancy and breast-feeding
• Don’t prescribe a drug you don’t know (read about it first)
Common AbbreviationsAbbreviation Meaning Abbreviation Meaning
PO Orally/By mouth OD Once Daily
IV Intravenous BD Twice Daily
IM Intramuscular TDS X3 Daily
SC Subcutaneous QDS X4 Daily
TOP Topical PRN When Required
SL Sub-lingual MANE Morning
INH Inhaled NOCTE At Night
NEB Nebulised Others routes (e.g. buccal, intradermal) should be written in full. It is good practice to try and avoid using the Latin frequency
abbreviations on formal prescriptions.
PV Vaginally
PR Rectally
Prescribing in Liver Disease• Many drugs are metabolised by the liver, but there is a large
hepatic reserve. LFTs are a poor indicator of drug metabolism.
• Some drugs, e.g. Rifampicin, are excreted unchanged in bile and can accumulate in obstructive disorders
• Hypoalbuminaemia is associated with decreased drug binding and therefore increased free toxic levels of highly protein bound drugs, e.g. Phenytoin, Prednisolone.
• Patients with abnormal clotting will be more sensitive to anticoagulants
• In severe disease, sedative drugs, opioids, and drugs causing constipationwill increase the risk of encephalopathy
Prescribing in Liver Disease
Some examples of Hepatotoxic drugs:
• Amiodarone
• Isoniazid
• Coamoxiclav
• NSAIDs
• Statins
• Anti-fungals
• Anti-retrovirals
• Consult the BNF for dose alterations
Prescribing in Renal Failure• Dose adjustments required in renal failure vary depending on the
extent of renal excretion and toxicity of the drug
• For many drugs, empirical dose reductions will suffice. For drugs with narrow therapeutic ranges, or in patients with extremes of weight, doses based on creatinine clearance should be used. Plasma levels should then be monitored.
• Some drugs should be avoided altogether• Consult the BNF!
Some examples of nephrotoxic drugs: • ACE Inhibitors• Aminoglycosides• NSAIDs• Methotrexate
Prescribing in Pregnancy• Harm can be caused at any time during
pregnancy
• Teratogenesis occurs in the first trimester
(during organogenesis), but growth and
functional disorders can occur throughout
pregnancy
• Even those prescribed just prior to labour can
have an effect on foetus and neonate, e.g.
pethidine, labetalol
• Drugs should be prescribed only if the
expected benefit is thought to be greater than
the risk to the foetus.
Prescribing in Pregnancy• Tried and tested drugs should be used before
newer ones, and at lower doses
• There is some impact on fertility and risk of paternal teratogenesis for certain medications used by the father near the time of conception (mostly chemotherapeutic agents)
Examples of teratogens:
• Sodium Valproate
• Warfarin
• ACE inhibitors
• Tetracyclines
• Lithium
• Alcohol
Prescribing in Breast Feeding• The amount of drug transferred to the infant via breast-milk is often very
small; especially for drugs with poor enteral absorption• ‘Basic’ drugs transfer more easily due to the more acidic nature of breast
milk compared to plasma• Large molecules (e.g. heparin) do not transfer into the milk• Some drugs are known to be present in high levels, e.g. Fluvastatin• Some medications can have effects on lactation, e.g. Bromocriptine, or on
the sucking reflex, e.g. phenobarbital• Insufficient evidence does not equal safety!
Examples of drugs to avoid:• Aspirin• Carbimazole• Tetracyclines• Fluoroquinolones• Lamotrogine• Diazepam.
Prescribing in the Elderly - Issues• Polypharmacy increases the risk of drug interactions (but polypharmacy
does not just occur in the elderly!)
• Patient compliance decreases as the number of drugs increases
• Hepatic and renal excretion decline with age. These are exacerbated by acute illness.
• There may be exaggerated pharmacodynamic effects on certain systems. E.g.:• ß-blockers and bradycardia• Nitrates/diuretics and postural hypotension• Anticholinergics/hypnotics/opioids and confusion/sedation• NSAIDs and gastric erosions.
• It may be appropriate to change the formulations of medications.
Prescribing in the Elderly - Guidelines• Always consider whether a drug is indicated at all• Limit the range from which you prescribe so your knowledge of
each increases• Reduce drug doses (consider starting 50% of recommended dose)• Review the need for medications regularly• Simplify regimens, minimises doses. Blister packs may help.• Explain clearly.
Good Luck!
Any Questions?