prescribing - simply finals - simply revision

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.

http://www.prescribingsafetyassessment.ac.uk/

http://www.tinyurl.com/PSAblueprint

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:

http://www.prepareforthepsa.com/

http://www.tinyurl.com/BLprescribingtutorial

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

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


A. SMITHA. SMITH16/01/2019 16/01/2019


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


30 Will Dooley


A. SMITHA. SMITH16/01/2019 16/01/2019


MORPHINE SULPHATELiquid (10mg/5ml)

Take 10mg when required

Please supply 100ml(ONE HUNDRED)


Take 10mg (TEN MILLIGRAM) when required

Please supply 100ml

30 Will Dooley


30 Will Dooley


A. SMITHA. SMITH16/01/2019 16/01/2019



Take 10mg when required

Please supply 100ml(ONE HUNDRED)


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


30 Will Dooley


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

http://www.webmd.com/interaction

Courtesy of www.apotential.wordpress.com

What should you monitor in this patient?

Spot the mistake.

A. SMITH

A. SMITH


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


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


PHENYTOIN TOXICITY

Enzyme inhibitor

Enzyme inducer(but relatively less so)


OMEPRAZOLE

PAROXETINE16/1/19

PO

16/1/19PO

20mg

40mg

A. SMITH

A. SMITH


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?


A: Yes


90mg/kg of


They present at 21:00.

Should NAC be

started?


A: Yes

Q2: A level taken at

presentation was

<0.1mmol/L.

Should NAC be

continued?

A: No


180mg/kg of


They present at 15:30.

Should NAC be

started?


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?

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