Prescribing

Prescribing

Legal Requirements of a Prescription

 Must be issued by a registered medical practitioner, dentist or nurse
 Prescriptions must comply with the legal requirements outlined below
and an appropriate record must be made:
o Typed or written in black pen (written only for controlled
prescriptions)
o Be signed by the prescriber with his/her usual signature
o Include the prescriber’s registration number
 Doctors: medical council number
 Nurses: registration number
o Be dated by the prescriber
o Specify the patient's name and address
o Specify the patient's age if under 12 years of age
o Specify the patient’s date of birth
o Specify the patient’s medical record number (if hospital
prescription)

Principles of Good Prescribing

 State patient details clearly: name, address, date of birth, age-
children/elderly
 Take account of any allergies and complete relevant paperwork
 Use generic drug names
 State drug, dose, strength, route and frequency
 Avoid abbreviations where possible
 Avoid multiple route prescribing (i.e. IM/SC/PO)
 State dose as grams, mg, micrograms.
 Make administration of once weekly drugs clear

Route of Administration
 Oral (PO)
 Injections
o Intramuscular (IM)
o Intravenous (IV)
o Subcutaneous (S/C)
o Intra-articular (IA)
 Topical (top)
 Transdermal
 Inhalation (Inh)
 Intranasal (Nasal)
 Rectal (PR)
 Buccal
 Sublingual (S/L)
 Vaginal (PV)
 Ophthalmic
 Implant
 Prescribing

Abbreviations of Frequency
 Once daily (OD)
 Twice daily/Twelve-hourly  Once in the (BD/BID)
 Three times daily/8-hourly morning (mané) (TDS/TID)
 Four times daily/6-hourly (QDS)  As
 Once at night (nocté) required/needed
(PRN)
 One dose (T)

  Inpatient prescriptions (aka kardexes) differ from hospital to

hospital
 Medication reconciliation forms are to keep a list of the patient’s
regular medications. This is usually filled by the pharmacist/team
member when a patient is admitted to hospital.
 Regular outpatient/discharge prescription:
o All regular/PRN medications (including warfarin and
antimicrobials) are prescribed using this type of prescription
o Exceptions: controlled drugs
 Controlled Drug Prescription
o Separate Outpatient/discharge prescription for controlled
medications (e.g. opioids)
o Please note a doctor must undergo special training before
registering to prescribe methadone
o 2 weeks maximum duration for any controlled drug prescription
o Controlled drug prescriptions may not be repeated, but may be
dispensed in instalments.

Medications most Commonly Prescribed in Hospitals

 Analgesia
 Antibiotics
 Anticoagulants
 Anti-emetics
 Anti-hypertensives
 Sedatives
 Steroids
 Intravenous fluids
 Oxygen
 Prescribing

 Blood products

Analgesia
 WHO pain ladder
 Paracetamol: avoid in hepatic impairment
 Non-steroidal anti-inflammatories ex. ibuprofen, diclofenac,naproxen
o Avoid in elderly patients as higher risk of side effects
(gastrointestinal bleeding, peptic ulcer disease)
o Avoid in renal impairment

 Opioids
o Codeine
 Important to reduce dosing in elderly patients
 Side effect: constipation (can precipitate delirium in elderly
patients)
o Morphine
 Types: modified release preparations or instant release
preparations
 NB to reduce dose in elderly patients
 Avoid in renal impairment (consider fentanyl as alternative)
 Best practice to prescribe laxative with morphine in elderly
patients to reduce risk of constipation

Antibiotics
 Penicillin
o Examples: amoxicillin, ampicillin, co-amoxiclav, piperacillin-
tazobactam
o NB allergies
o Risk of clostridium difficile
 Cephalosporins
o Examples: cefotaxime, ceftriaxone, cefuroxime, cefixime
o Cross-reactivity with penicillins
o Risk of clostridium difficile
 Macrolides
o Examples: clarithromycin, erythromycin, azithromycin
o Interact with statins (increases risk of rhabdomyolysis)
 Aminoglycosides
o Examples: gentamicin, tobramycin, amikacin, streptomycin
o Best given once daily; need close monitoring of levels
o Side effects: nephrotoxicity, ototoxicity
 Glycopeptides
o Examples: vancomycin, teicoplanin
o Need close monitoring of levels
o Side effects: nephrotoxicity, ototoxicity
 Others
 Prescribing

o Trimethoprim: teratogenic
o Nitrofurantoin: avoid if eGFR <45; can cause pulmonary fibrosis if
used long-term
o Metronidazole: metallic taste; disulfiram-like reaction with alcohol

Novel/Direct Oral Anticoagulants (NOACs/DOACs)

 Dabigatran 110-150mg BD
o A direct thrombin inhibitor
o Avoid if creatinine clearance <30ml/min
 Apixaban 2.5-5mg BD
o Direct factor Xa inhibitor
o Avoid if creatinine clearance <15mls/min
 Rivaroxaban 15-20mg OD
o Avoid if creatinine clearance <15mls/min
 Edoxaban 30-60mg OD
o Reduce dose to 30mg in moderate/severe chronic kidney injury and
avoid in end-stage CKD/dialysis
 Positive benefits of NOACs: no regular blood tests (need renal profile at
beginning of treatment and at routine intervals), less interactions with
other medications
 Negative benefits of NOACs: more expensive, no reversal agent (except
for Dabigatran [idarucizumab]but very expensive), sometimes twice
daily dosing, cannot monitor compliance

Heparins
 Low molecular weight heparins (LMWH)
o Enoxaparin
 Prophylactic dosing (20 or 40mg) vs therapeutic dosing by
weight
o Tinzaparin
 Prophylactic dosing (4,500 IU) vs therapeutic dosing by
weight
 Unfractionated heparin
o Used only in specialist cases (e.g. metallic heart valve patients
undergoing procedures/surgeries, dialysis etc.)

Warfarin
 Indicated in valvular atrial fibrillation
 Requires regular INR monitoring
 Reversed by vitamin K
 Dose dependent on INR

Anti-emetics
 Domperidone: prolong QT interval
 Metoclopramide: cause extrapyramidal side effects
 Prescribing

 Cyclizine: addictive, avoid in severe heart failure (can reduce cardiac

output)
 Prochlorperazine: cause parkinsonism
 Ondansetron: used in chemo patients, can exacerbate movement
disorders

Antihypertensives
 Angiotensin-Converting Enzyme Inhibitors (ACE-I)
o Examples: ramipril, perindopril, enalapril, lisindopril
o Side effects: dry cough, worsen renal impairment (+
hyperkalaemia)
 Angiotensin-II Receptor Antagonists/Blockers (ARB)
o Examples: valsartan, candesartan, olmesartan, telmisartan
o Side effects: renal impairment, hyperkalaemia
 Beta-adrenoceptor blocking drugs (Beta blockers)
o Examples: bisoprolol, atenolol, metoprolol, propranolol
o Side-effects: bradycardia, hypotension, fatigue
o Avoid in asthmatic patients
 Calcium-Channel Blockers
o Non-dihydropyridine: verapamil (anti-arrhythmic agent)
 NB avoid beta-blockers with verapamil (high risk of severe
bradycardia)
o Dihydropyridine: amlodipine, lercanidipine, nifedipine
o Side-effects: lower limb/peripheral oedema, facial flushing,
palpitations
 Thiazides & Thiazide-Related Diuretics
o Thiazide: bendroflumethiazide, hydrochlorothiazide
o Thiazide-Related: indapamide, metolazone (specialised)
o Side-effects: hypokalaemia, gout exacerbation (hyperuricaemia),
hypochloraemic metabolic alkalosis
 Alpha-Adrenoreceptor Blockers
o Examples: doxazosin, prazosin
o Side-effects: dizziness, postural hypotension, nausea

Sedatives
 Low dose benzodiazepines are the safest sedatives to give elderly
patients
 Remember: avoid anti-psychotics (risperidone, haloperidol, quetiapine)
in patients with Parkinsonism

Steroids
 Acute exacerbations of inflammatory conditions (few examples):
o Rheumatoid arthritis
o Ulcerative colitis
o Chronic obstructive pulmonary disease

 Chronic auto-immune/inflammatory conditions

 Prescribing

o Adrenal insufficiency
o Systemic lupus erythematosus (SLE)
o Polymyalgia rheumatica

 Tapering of steroids
o Patients may be at risk of developing adrenal insufficiency if on
long-term steroids and they are stopped too soon
o Patients who are unlikely to develop this:
 A patient who has received any dose of glucocorticoid for
less than three weeks
 Patients treated with alternate-day prednisone at a dose of
less than 10 mg (or its equivalent)
o Tapering usually depends on regular dose
 >40mg prednisone daily: reduce by 5-10mg every 1-2 weeks
 5-10mg prednisone daily: reduce by 1mg every 2-4 weeks

 Types of corticosteroids:
o Mineralocorticoids: Fludrocortisone
o Glucocorticoids: Dexamethasone, methylprednisolone,
betamethasone, prednisone, prednisolone (low mineralocorticoid
activity)
o Hydrocortisone: equal mineralocorticoid and glucocorticoid
activity

 Best practice
o Consider proton pump inhibitor (PPI) prophylaxis with long-term
steroids to prevent gastric discomfort (increase risk of peptic
ulcer disease)
o Prescribe mané if once daily dosing (steroids can cause insomnia)
o NB know steroid side-effects

How to Use the BNF

 Practical, evidence-based information for healthcare professionals who

prescribe, dispense, and administer medicines.
 Prescribing

 Published in updated book form twice a year, in March and September.

 Comprehensive list of medications
 Available both online and in book form
 For each medication, the BNF provides a description of:
o Indications and dosages
o Important safety information
o Contraindications
o Cautions, incl. breast feeding and pregnancy
o Side-effects
o Dose adjustment in e.g. renal/liver impairment
 Also provides information on medicinal forms and UK pricing guidance
 Evidence grading (A->E) to reflect the strength of recommendations

Structure
 Drug classes and treatment summaries divided into chapters based on
specific aspects of medical care.
 Within each chapter, content is organised alphabetically
 Appendices cover drug interactions, cautionary/advisory labels, wound
care

Appendix- interactions
 Provides a detailed list of a medication and its interactions
 Listed alphabetically and within its drug class
 Level of severity of interaction described
 Specific tables of side effects and drugs which can cause these

Index
 Located at the back of the BNF, provides a quick way to find a specific
drug or medical condition
 Emergency protocols also located here e.g. ACLS, Anaphylaxis,
Hypoglycaemia

Personal Formulary
 Useful for you to develop your own personal drug formulary for common
medical conditions you will encounter
 Allowing you to build up your own knowledge around a number of key
drugs.
 Will improve rational prescribing skills
 Prescribing

Prescribing for Common Medical Conditions

Asthma
Inhalers:
 Short-acting beta agonists (SABA)
o Examples: salbutamol
o Reliever, use PRN (inhaler, nebuliser)
o Side-effects: fine bilateral tremor, hypokalaemia (high doses)
 Long-acting beta agonists (LABA)
o Examples: formoterol, salmeterol, indacaterol, vilanterol
o Maintenance therapy; can be combined with ICS or AMA
o Side-effects: tremor, palpitations, hypokalaemia (high doses)
 Long-acting muscarinic antagonists (LAMA)
o Examples: ipratropium, gylcopyrronium, tiotropium, umeclidinium
o Maintenance inhalers, can use ipratropium as nebuliser for acute
asthma; can be combined with LABA
o Side-effects: cough, arrhythmias, dry mouth
 Inhaled corticosteroids (ICS)
o Examples: beclomethasone, fluticasone, budesonide
o Maintenance; can be used in combination with LABA, LAMA or
both
o Side-effects: oral candidiasis (nb to rinse mouth after use),
paradoxical bronchospasm, increase risk of infections

Oral medication:
 Leukotriene receptor antagonists
o Example: montelukast
o Additive effect with ICS
o Side-effects: headache, diarrhoea, nausea & vomiting
 Xanthines
o Examples: theophylline, aminophylline
o Requires plasma concentration levels to ensure in therapeutic
range (theophylline levels used to check aminophylline
concentration)
o Side effects: arrhythmias, gastric discomfort, risk of hypokalaemia
with SABA (high doses)

COPD

 Prescribing

Coronary Heart Disease

 Anti-platelet therapy
o Examples: aspirin, clopidogrel
o Low dose aspirin is treatment of choice
o Clopidogrel offered if patient intolerant of aspirin or aspirin is
contra-indicated
o Side-effects:
 Aspirin: dyspepsia, bleeding, thrombocytopaenia
 Clopidogrel: diarrhoea, bleeding, dyspepsia,
thrombocytopaenia
 Anti-hypertensive
 Lipid Lowering therapy

Diabetes Mellitus
 Biguanides
o Examples: metformin
o Can be monotherapy or combination with other therapies
o Side-effects: lactic acidosis, diarrhoea, nausea, vomiting (nb does
not cause hypoglycaemia)
 Dipeptidylpeptidase-4 inhibitors (DPP-4 inhibitors/gliptans)
o Examples: linagliptin, sitagliptan, saxagliptan
o Commonly in combination with metformin
o Side-effects: headache, cough, skin reactions, pancreatitis (rare)
 Glucagon-like peptide-1 receptor agonists (GLP receptor agonists)
o Examples: exenatide, liraglutide
o Given subcutaneously (NB not insulin)
o Side-effects: decreased appetite, gastrointestinal disturbances,
belching
 Sodium glucose co-transporter 2 inhibitors (SGLT2 inhibitors)
o Examples: canagliflozin, dapagliflozin, empagliflozin
o Can be used in combination with metformin
o Side-effects: increase in urinary frequency in first 2 weeks of use,
urinary tract infections, polydipsia, hypoglycaemia, “euglycaemic”
diabetic ketoacidosis
 Sulphonylureas
o Example: gliclazide
o Need to check capillary blood glucose (CBG) level before driving
as risk of hypoglycaemia
o Side-effects: hypoglycaemia (caution if used with insulins),
abdominal pain, diarrhoea, nausea

Insulins
 Short-acting
o Examples: insulin (actrapid®, humulin®), insulin aspart
(novorapid®), insulin glulisine (apidra®), insulin lispro (humalog®)
o Actrapid usually given intravenously (treatment of diabetic
ketoacidosis or if patient fasting and is Type 1 DM)
 Prescribing

o Rest are given subcutaneously for basal-bolus regime (as bolus

doses; before meals)
o Side-effects (all insulins): oedema, lipodystrophy, hypoglycaemia

 Intermediate-acting
o Examples: bophasic isophane insulin (Humulin M3®), isophane
insulin (insulatard®)
 Intermediate-acting combined with rapid-acting insulin
o Example: biphasic insulin aspart (Novomix 30®)
 Long-acting insulin
o Examples: insulin degludec (tresiba®), insulin detemir (levemir®),
insulin glargine (lantus®)g
o Used as basal dose in basal-bolus regime
o Usually given at bedtime

Dyslipidaemia
 Includes hypercholesterolaemia and hypertriglyceridemia
 Cholesterol absorption inhibitors
o Example: ezetimibe
o Adjunct to statin therapy
o Side-effects: diarrhoea, arthralgia
 Fibrates
o Examples: bezafibrate, fenofibrate, gemfibrozil
o Usually used to treat hypertriglyceridaemia; given as alternative if
contra-indication to statin in hypercholesterolaemia
o Side-effects: decreased appetite, gastrointestinal disorders,
flatulence, diarrhoea
 Statins
o Examples: atorvastatin, rosuvastatin, simvastatin
o Used as mainstay treatment for hypercholesterolaemia
o Side-effects: rhabdomyolysis (rare but can occur if patient on
concomitant medications such as macrolides), myalgia,
gastrointestinal disturbances, pancreatitis (rare)

Hypertension
 Prescribing

Hypothyroidism
 Levothyroxine
o Dosing increased/decreased by 25-50 micrograms every 3-4 weeks
o Side-effects: thyrotoxicosis (palpitations, tremors, etc.), angina
pectoris, weight loss

Prescribing for Acute Medical Conditions

Anaphylaxis STEMI Acute Asthma

Status Epilepticus
 Prescribing

DKA
Community Acquired
Pneumonia

SVT

Paediatric Prescribing

 Children are not little adults

o Multiple physiological and anatomical differences give rise to
pharmacokinetic differences in children (especially those under 2
years) compared with adults.
o Wide variability in pharmacokinetic handling and
pharmacodynamic response to medicines occurs from birth to
adulthood
o Medication adherence dependant on formulation, taste,
appearance and ease of administration
o Many medicines used in pediatrics may not have been investigated
in children in the same way as in adults.
o Children represent >25% of the population and receive an average
of three prescription medications before 5 years of age

Drug dosing in Children

 Refer to BNFc or hospital formulary (available on intranet/app)
 Beware of different preparations (amoxicillin)
 Tables to calculate dose for BSA
 Prescribing

Drug dosing in children

 Dose calculation can be based on:
o Age
o Weight (usually most accurate)
o Body surface area (BSA)
 Weight based (mg/kg)
o If weight is unknown (or in an emergency) estimate weight (kg):
 (Age years) + 4) x 2 [for children <8 years of age]
 (Age years) x 3) + 7 [for children >8 years of age]
o Dose varies dependent on route (IV/PO/PR)

Prescribing fluids in paediatrics

 Type of fluids used varies in different centres:
o Maintenance fluid: (0.9% sodium chloride, 5% dextrose)  10% dex
in neonates
 100mls/kg for the 1st 10kgs
 50mls/kg for the 2nd 10kgs
 20mls/kg for the 3rd 10kgs and beyond
o Bolus fluid (0.9% sodium chloride)
 20 ml per kg (10mls/kg in trauma patient)
 Can be repeated

Commonly prescribed drugs

 Paracetamol:
o 15mg/kg 4-6 hourly po (max 60mg/kg in 24 hours) OR 20mg/kg 12
hourly PR
 Prednisolone:
o 1mg/kg/day max of 40mg orally for 3 days
 Cefotaxime:
o 50mg/kg every 6-8 hourly intravenously
 Gentamicin:
o 7mg/kg every 24 hours intravenously

 Co- amoxiclav:
 Prescribing

 Amoxicillin:

10 MC prescribed drugs in children and adults ranges

Different formulations of medications

 Liquid versus tablet
 Unpleasant taste- how do we overcome this??!
 At what age can a child generally take a tablet?
 Do we use PR medication commonly in paediatrics?

Dosing errors
 More common in paediatrics: children estimated to have a threefold
greater risk of suffering an adverse drug event than adult patients.
 Children more vulnerable to harm from these errors
 Such errors occur in up to 25% of drug charts in paediatric hospital
wards
 Why children are more at risk of dosing errors:
o Prescribing in mls rather than mg (refer back to amoxicillin-
different preparations)
o Prescribing more that the recommended daily total dose (an issue
in obese children)
o Childs weight constantly changing e.g. a medicine, which is
commenced in a neonate would need its dose adjusted several
times over a few months while adults can continue for years
without changing the dose of a drug.
 Prescribing

o Need to calculate doses individually based on age, weight, body

surface area
o Different clinical conditions, different medication dose (meningitis
Vs sepsis)
o Immature clearance systems in certain age-groups
o Paucity of trial data for children
o Poor handwriting!!

 The developmental stage of a child influences their response to a

medicine
 The age of the child determines the formulation required
 Doses of medications and fluids are calculated using a child’s weight
(mg/kg)
 Weight can be estimated in an emergency (formula)
 All doses should be checked in BNFc or hospital formulary, if in doubt,
always check dose with a senior colleague.
 Prescribing

Planning Management
 Do I have:
o The Right Drug
o The Right Diagnosis
o The Right Patient
o The Right Dose
o The Right Time
 All are involved in planning management when prescribing
 Knowledge of the management of acute and chronic medical conditions
is necessary for safe prescribing.
 Planning management of a condition requires various steps:
o Step 1: ABC
o Step 2: History and thorough physical exam
o Step 3: Review any available investigations
o Step 4: Medication review and allergy review
o Step 5: Action

Acute medical conditions: planning management

 Cardiac emergencies:
o ST elevation Myocardial Infarction (STEMI)
o Non-ST elevation Myocardial Infarction (NSTEMI)
o Unstable angina
o Tachycardias (a.fib/v.tachy/SVT)
o Bradycardias
o Acute heart failure
o Cardiac arrest
 Respiratory Emergencies:
o Anaphylaxis
o Acute asthma
o Chronic obstructive pulmonary disease exacerbation
o Type 1 and 2 respiratory failure
o Pulmonary embolism
o Pneumonia
 Gastroenterology emergencies:
o Acute gastrointestinal bleed
 Neurological emergencies:
o Stroke
o Meningitis
o Epilepsy
 Metabolic Emergencies:
o Hyperosmolar hyperglycemic state (HHS)
o Diabetic Ketoacidosis (DKA)
 Prescribing

o Electrolyte abnormalities (K/Na/Ca)

o Addisonian crisis
o Myxoedema coma
o Thyrotoxicosis
 Acute kidney injury
 Acute poisoning
 Infections
o Cellulitis
o Sepsis (resp/urosepsis/infective endocarditis)

Chronic medical conditions: planning management

 Cardiac
o Congestive cardiac failure
o Arrhythmias (e.g. a.fib)
o Stable angina
o Hypertension
 Respiratory
o Chronic obstructive pulmonary disease
o Stable asthma
o Cystic fibrosis
o Bronchiectasis
 Endocrine
o Diabetes (type 1 and type 2)
o Conns
o Cushing’s
 Neurological
o Parkinson's
o Stroke
o Epilepsy
o Dementia
 Gastroenterology
o Inflammatory bowel disease (Crohn’s disease/ulcerative colitis)
o Peptic ulcer
o H.Pylori
 Rheumatological
o Osteoporosis
o Rheumatoid arthritis
o Gout

Chronic Conditions
 Need to follow national and international guidelines or local hospital
policies
 Most chronic conditions have recommended treatment options outlined
by numerous bodies:
o NICE
o AHA/ASA (American Heart/Stroke Association)
o European guidelines
 Prescribing

o Irish Heart Foundation

o Information also in BNF

Prescribing in Chronic Conditions

 Most prescribing in chronic conditions needs regular review either by
the general practitioner or by the hospital specialist
 Drug requirements may change as the chronic disease progresses:
o Example: addition of steroid inhaler in COPD or alteration of anti-
Parkinson's medication in Parkinson's
 Organ function may need to be monitored in chronic diseases as some
medications can affect organs in the long-term (see Drug Monitoring
lecture)
 Drug dosage may need to be reviewed in the long term
o May need to be reduced if eGFR reduces or body weight decreases
(e.g. NOACs/DOACs need to be reduced if eGFR reduces)
o May need to be increased if disease not adequately controlled (e.g.
anti-hypertensive therapy may need to be optimised if blood
pressure poorly controlled)
Communication

 Adequate information should always be conveyed to patients when

prescribing medications
 Prior studies show poor knowledge of patients about their medications
and side-effect profile- this can lead to poor compliance
o 35% patients knew side-effects of medications1
o 30-50% of patients do not take their medication for chronic
conditions as prescribed2(WHO)
 A paper published in 2001 showed response rates of patients to a major
drug for a selected group of therapeutic areas. Alzheimer’s drugs had
an efficacy of 30%, asthma (60%), diabetes mellitus(57%), rheumatoid
arthritis (50%)
o Emphasises need for communicating with patients about the
possibility of the medication being ineffective and requiring a
change

Doctors and pharmacists should communicate with patients :

 Indication for the drug
 How to take the medication
 Potential adverse drug reactions
 Interactions (food/drink or drug interactions)
 Drug monitoring required
 Contraindications
 Alternative options if available
 Need for monitoring if applicable
 Caution with certain drugs in pregnancy should be conveyed to females

Barriers to effective communication

 Prescribing

 Ensure the patient has no sensory impairment that can affect

communication.
o If hearing impairment ensure hearing aids/written communication
given.
o If sight is poor may have difficulty with medications (e.g.
identifying them/reading side effects/directions etc) hence good
oral communication very important and blister packs or supervised
administration may be required.
 Translators if language barriers
 If cognitive deficits may need family member or carer involved in
medication communication

Data Interpretation

 Data can provide us with important clues as to the underlying cause of

illness
 Abnormal data results may be a result of the disease/illness or it may
be due to a medication/treatment
 Very important to try and differentiate between these
 Many investigative tests can help with your diagnosis
 Data should always be used in conjunction with the clinical history and
examination
 Always use clinical history and examination as a base for your
investigations
 Appropriate testing should be ordered for the suspected condition,
avoid wasting resources by ordering unnecessary tests

FBC:
 Prescribing

U+ E:

LFT, TFTs:

Investigations:
CXR
 Need to identify abnormalities linked with common conditions:
o Pulmonary infiltrate: ?pneumonia
o Interstitial Oedema: ?CCF
o Cardiomegaly: ?Heart failure
o Fluid: ?Pleural effusion
o Tracheal deviation or collapse lung? Pneumothorax/obstructing
tumour
 Prescribing

o Fibrotic changes:? Pulmonary fibrosis (may be drug related)

 Identifying changes on CXR will help you to decide on the appropriate
management and prescription
 Drugs can also cause certain lung changes which can be seen on CXR
e.g. interstitial lung disease (amiodarone, chemotherapy agents,
methotrexate)

ABG
 Check for type 1 versus type 2 respiratory failure
 Metabolic acidosis/alkalosis (these will guide your management and
prescription decisions)
 Type 1 respiratory failure (p02 <8kPa, pC02 <6kPa):
o Pneumonia
o Pulmonary embolism
o Congestive cardiac failure
o Acute asthma
 Type 2 respiratory failure (p02 <8kPa, pC02 >6kPa):
o COPD exacerbation
o Chest wall deformities
 Type 1 progressing to type 2 respiratory failure
o Drugs: sedation/reduced breathing effort e.g. opioids, overdose of
sedative medication

ECG
 Bradycardia : heart block or drug related e.g. beta-blocker, donepezil,
digoxin
 Tachycardia: sinus tachycardia/arrhythmias (e.g. infections) or drug
related e.g. salbutamol
 Wide QRS: Bundle-branch blocks, hyperkalaemia, ventricular
tachycardia or drug related: antiarrhythmics (amiodarone, sotalol),
antibiotics (e.g. clarithromycin, ciprofloxacin, levofloxacin,
ketoconazole), antidepressants (e.g. amitriptyline, sertraline,
venlafaxine), antipsychotics (e.g. haloperidol, quetiapine)

 Methotrexate can cause pulmonary fibrosis/pneumonitis

o CXR findings show reticular (net-like) shadowing of the lung
peripheries which is typically more prominent towards the lung
bases
o It may cause the contours of the heart to be less distinct on CXR
 Prescribing

Adverse Drug Reactions and Prescribing in the Elderly

 ADR= An appreciably harmful or unpleasant reaction, resulting from an

intervention related to the use of a medicinal product, which predicts
hazard from future administration and warrants prevention or specific
treatment, or alteration of the dosage regimen, or withdrawal of the
product

Types of ADR’s
 They occur due to pharmacologic properties of the drug.
 Adverse drug reactions may be broadly divided into two types, Type A
and B.
 Type A reactions:
o Common, make up 85 to 90% of all adverse drug reactions.
o They can occur in any individual, given sufficient dose and
exposure, and are predictable from the known pharmacologic
properties of a drug.
o Example: constipation secondary to opiate use or dry mouth and
blurred vision due to the anti-cholinergic effect of tricyclic
antidepressants.
o These reactions are predictable and usually dose-dependent.

 Type B reactions:
o 10 to 15% of adverse drug reactions and are not predictable.
o These are hypersensitivity reactions, mediated by immunologic
or other types of mechanisms, which occur in a susceptible
subgroup of patients, have signs and symptoms that are different
from the pharmacologic actions of the drug.
o Example: development of a rash secondary to penicillin.
o These reactions are unpredictable and not usually dose-
dependent.

How can we reduce ADRS

 At each patient outpatient or inpatient encounter, the doctor should
ideally review the medication list and consider the following points
o Is this drug indicated?
o Is the medication effective for the condition?
o Are we using the correct dose and are the prescription
directions correct?
o Can the patient follow the prescription directions and take the
drug as directed?
o Are there any drug-drug interactions?
o Are there any significant drug-disease interaction?
o Is there unnecessary duplication with other drugs? Can we stop
unnecessary drugs?
o Is the duration of therapy acceptable?
 Prescribing

o Avoid treating side effects with another drug

 “Prescribing cascades’’ (example): a patient commenced on
furosemide now develops gout and is prescribed allopurinol
 Correct action would be to discontinue the inciting drug
and replacing with alternative therapy
 Be aware of common ADR of frequently prescribed of drugs- could
drugs be a cause of any new symptom?

Common drugs and their ARDS

 Anti-diabetic medications
 Anticoagulation/Anti-platelets
 Anti-arrhythmic drugs:
o Digoxin: vomiting/nausea/blurred vision/confusion,
drowsiness/yellow-green vision (low potassium potentiates
digoxin effects)
o Amiodarone: pulmonary fibrosis / thyroid disease / skin greying /
corneal deposits / liver toxicity
 Antibiotics
 Anti-hypertensives
 Corticosteroids
o Gastric ulcers
o Diabetes/hyperglycaemia
o Thin skin
o Cushing's syndrome
o Oedema
o Hypertension
o Osteoporosis
o Infection
 Non-steroidal anti-inflammatory drugs (NSAIDs)
o Examples: diclofenac, ibuprofen.
o Contraindications: asthma, severe heart failure.
o Side effects: renal impairment, gastrointestinal bleeding
 Drugs associated with prolongation of QTc interval
o Macrolide antibiotics: clarithromycin, azithromycin,
erythromycin.
o Anti-arrhythmic’s: amiodarone, sotolol
o Antipsychotic medications: haloperidol, chlorpromazine
o Lithium
o Tricyclic antidepressants
 Opioid analgesia
o Constipation, sedation, confusion, cardiorespiratory depression,
seizures
 Benzodiazepines:
o Associated with as much as a 60% increase in fall risk
 Psychiatric medications
o Lithium: tremor, fatigue, arrhythmias, seizures, renal failure,
diabetes insipidus, prolonged QTc interval
 Prescribing

o Haloperidol: extrapyramidal side effects, dyskinesia, prolonged

QTc interval
o Clozapine: agranulocytosis
o Olanzapine: hyperglycaemia (obtain blood glucose before
starting)

Investigation abnormalities associated with drugs

 Hyponatremia: diuretics, carbamazepine, antipsychotics,
antidepressants
 Hypokalaemia: loop/thiazide diuretics
 Hyperkalaemia: ACE-I, spironolactone
 Thrombocytopenia: penicillamine, heparin, quinine, linezolid
 Acute kidney injury: nephrotoxic antibiotics, NSAIDS, ACE-I
 Deranged LFTs: flucloxacillin, Co-Amoxiclav, Nitrofurantoin, Steroids,
Statins, Sulphonylureas, Paracetamol overdose, Rifampicin
 Deranged TFTs: amiodarone, lithium
 Neutrophilia: steroids
 Neutropaenia: carbimazole, clozapine
 Leucopaenia: methotrexate
 Acidosis: Metformin (lactic acidosis), salicylate poisoning (metabolic
acidosis)

Clinically important drug interactions

 Drugs with a narrow therapeutic index:
o Warfarin, digoxin, phenytoin, theophylline, lithium,
aminoglycosides
 Others:
o Methotrexate and trimethoprim: both are both folate antagonists
and should not be prescribed together as they can cause bone
marrow suppression
o Clarithromycin and statins: adding clarithromycin significantly
increases statin serum levels and therefore increase risk of
rhabdomyolysis
o NB omit statins during course of clarithromycin
 ALWAYS CHECK BNF BEFORE PRESCRIBING

Cytochrome P45- enzyme inducers/inhibitors

 Many drugs are metabolized to inactive metabolites by the cytochrome
P450 system in the liver.
 Some other drugs or other substances can alter these the function of
these enzyme systems resulting in an increased or decreased target
drug metabolism.
 Cytochrome P450 enzyme inducers
o Increase the enzymes in the P450 system and increase the
metabolism of their target drug
o As a result the serum level of this drug falls and the effect of this
drug may be reduced
 Prescribing

o Dose increase of this drug may be needed.

 Cytochrome P450 enzyme inhibitors:
o Decreases the activity of the P450 enzyme system and decrease
the metabolism of their target drug.
o Serum levels of this drug will be increased and the effect of this
drug may be increased.
o Dose reduction in certain drugs may be needed.
 Note: Enzyme induction takes days to weeks to develop, whereas
enzyme inhibition only takes hours to days.
 Inducers of P450: ↑Enzyme Activity, ↓Drug Concentration
 Inhibitors of P450: ↓Enzyme Activity, ↑Drug Concentration
 P450 Inducers: SCRAP GP
o Sulphonylureas
Carbamazepine
Rifampicin
Alcohol (Chronic)
Phenytoin
o Griseofulvin
Phenobarbital
 P450 Inhibitors: SICKFACES.COM
o Sodium valproate
Isoniazid
Cimetidine
Ketoconazole
Fluconazole
Alcohol
Chloramphenicol
Erythromycin/Clarithromycin
Sulfonamides
o Ciprofloxacin
Omeprazole
Metronidazole + Grapefruit Juice
 Note: Acute alcohol consumption can decrease warfarin metabolism
and increase warfarin effect whereas chronic alcohol consumption can
induce warfarin metabolism and decrease warfarin effect
What patients are at most risk of ARDS
 The elderly and the young: adjusting appropriately for age is
particularly important in pediatric and geriatric populations
 Patients with pre-existing renal impairment (impaired excretion)
 Patients with pre-existing hepatic impairment (impaired metabolism)
 Women: appear to be at an increased risk (unclear why)
 Pregnancy, women of child bearing age and breast feeding all need to
be considered to be increased risk of ADRs
 Polypharmacy: drug- drug interactions and drug ADRs increase with
increasing numbers of drugs taken
 History of previous ADRs
 Prescribing

General medication cautions in the elderly

 x3 greater incidence of ADRs in patients > 65yrs compared to those
<30yrs
 Majority of ADRs are dose-dependent and therefore predictable and
preventable
 Relatively small numbers of older adults recruited in clinical trials
impedes collection of drug safety data in this group of patients
 Be aware that older patients have reduced renal function, must
calculate eGFR before dosing
 Must consider timing of medications (i.e. diuretics) and address
potential compliance issues
 In cognitive impairment, must ensure that what you are prescribing will
not cause a deterioration in cognitive function, and ensure the
medication is taken correctly.
 Consider that the older patient may have swallowing difficulties- is the
preparation suitable?

 Elderly patients have a higher risk of adverse drug reactions due to

polypharmacy but also due to alterations in pharmacokinetics and
pharmacodynamics
 Pharmacokinetics – what body does to drug – how the body absorbs,
distributes, metabolises and eliminates the drug
 Pharmacodynamics – what drug does to body – how the drug interacts
with receptor or target

Adjust dosing based on age and creatinine clearance

 A common cause of ADRs is failure to properly adjust doses for age and
renal insufficiency
 Renal impairment can occur at any age but becomes more common
with advancing age
 For patients with stable renal function, creatinine clearance can be
estimated according to published formulas which factor age into the
calculation
 Due to decreased muscle mass in older adults, however, serum
creatinine levels may not adequately reflect renal function. As a
general rule, the initial dose for starting medications in older adults
should be significantly reduced, and titrated up as tolerated by
monitoring side effects or drug levels (“Start low and go slow”)
 Prescribing

Drug Monitoring

 Involves a doctor effectively monitoring for both beneficial and

potential harmful effects of a particular drug using clinical history,
examination and investigations
 Drug monitoring will involve:
o Careful evaluation of the patient’s history and examination
o Performing appropriate investigations to ensure no
contraindications to the new medication
o Follow-up to assess for any potential side effects or adverse drug
reactions
o Monitoring the effectiveness of the new drug with appropriate
investigations/examination/history
 Drugs may need to be stopped/held/altered/increased accordingly
depending on the monitored response

 Note: Macrolide antibiotics (e.g. Clarithromycin) increase plasma levels

of statins (therefore statin should be discontinued while on the
macrolide). Statins and Fusidic Acid (used to treat osteomyelitis)

should be avoided.

Therapeutic Drug Monitoring

 Prescribing

 A certain number of drugs require an appropriate monitoring strategy to

endure they are having an appropriate therapeutic effect and to
minimize risk of toxicity
 These drugs with a narro w therapeutic window (range) need
therapeutic drug monitoring e.g. digoxin, lithium, gentamicin
 This is commonly done by measuring the serum concentrations of
specific drugs at designated time interval to ensure the drug is
maintained within its therapeutic window
When do we monitor drug levels?
 Drugs with a narrow therapeutic window
o e.g. gentamicin, warfarin, digoxin,
phenytoin, theophylline, lithium
 Drugs whose therapeutic effect is not readily
assessed by clinical observation/examination
alone
o e.g. immunosuppressive drugs
 To evaluate for suspected toxicity or abuse of a
specific drug
o e.g. paracetamol
 Drugs with a steep dose response curve such
that a small change in drug dose may lead to a significant rise in drug
levels/effect
o e.g. theophylline, aminophylline
 When another drug is added to a patients drug regimen which may have
a drug interaction leading to either an elevated drug level or a reduced
drug level
o e.g. addition of a cytochrome p450 enzyme inducer to a patient
on warfarin will lead to increased warfarin metabolism and
reduced INR levels
 In patients with pre-existing renal or liver disease which can alter that
patients ability to metabolize and excrete drugs leading to toxic drug
levels
o e.g. using gentamicin in renal failure

What drugs do we monitor using therapeutic drug monitoring?

 Antibiotics:
o Glycopeptide antibiotics: vancomycin and teicoplanin
o Aminoglycosides antibiotics: gentamicin, neomycin,
streptomycin, tobramycin and amikacin
 Anti-arrhythymics
o Digoxin
 Anti-epileptics:
o Phenytoin, sodium valproate, carbamazepine
 Immunosuppressive agents
o Ciclosporin
 Lithium
 Theophylline
 Prescribing

 Paracetamol in overdose- Treatment: N-Acetyl cysteine (NAC)

Timing of drug levels in therapeutic drug monitoring

 Many serum samples sent for therapeutic drug level sampling are
useless as they fail to have the information in relation to the time the
sample was taken in relation to the last administered dose of the drug
under evaluation

Vancomycin monitoring

Gentamicin

Prescribing in renal impairment

 Ways to calculate renal impairment when deciding on drug dosing:
o MDRD eGFR: only good for advanced renal failure- not good for
eGFR>60
o Cockcroft Gault equation (commonly
used)
o Cystatin C-based estimate of GFR
 Prescribing

o eGFRCystatinC (NICE recommends: eGFR 45- 59 for >90 days and

no proteinuria)
 In renal failure pharmacokinetic and pharmacodynamics changes
accompany renal impairment
 Be aware drugs excreted by the renal route may be affected and need
dose changing
 Toxic effects more likely with renal failure due to build-up of
metabolites
Calculation Skills

 Occasionally, when writing a prescription, calculation of the dose

required for your specific patient may be required
 The common calculations encountered are:
o Dose calculation by body weight
 e.g. enoxaparin, gentamicin
o Converting doses between common unit types
 e.g. converting micrograms to milligrams
o Converting doses expressed as percentage
o Drug infusion calculations (the most complex form of calculations
where errors commonly occur)

Converting doses between common unit types

 The most common dosing units are expressed as either grams (g),
milligrams (mg) or micrograms (mcg)
o Conversion factor
 1g = 1000mg
 1mg = 1000 micrograms
 When writing a prescription for micrograms, the
full word ‘micrograms’ is used, not mcg due to
the risk of misinterpretation
 For volume:
o Conversion factor
 1L = 1000ml
 1ml = 1000 microliters
 Similarly, when writing a prescription for microliters, the full word
‘microliters’ is used, not mcl due to the risk of misinterpretation

Converting doses expressed as a percentage

 Many medicines in solution formulations or in ointment form are
expressed as a percentage
 For example:
o Lignocaine (lidocaine) 2% solution
o Hydrocortisone 1% ointment
 1% = 1g in 100ml
o When we are dealing with solutions
o Expressing a weight of drug diluted in a volume of liquid =
weight/volume (w/v)
 Prescribing

 1% = 1g in 100g
o When we are dealing with ointments
o Expressing a weight of drug which has been ‘diluted’ in another
amount mass = weigh/weight (w/w)
Drug infusion calculations:
 Adrenaline (epinephrine) is expressed in 2 formats in the emergency
trolley
o 1 in 1000 adrenaline (epinephrine) = 1g in 1000ml (Most common
solution type used to treat anaphylaxis)
o 1 in 10,000 adrenaline (epinephrine) = 1g in 10,000ml (Most
common solution type used in cardiopulmonary
arrests/resuscitation)

Drug calculations- Enoxaparin

 Enoxaparin comes in pre-filled syringes containing a particular dose of
enoxaparin which is expressed in both mg amount and international
units (IU) of anti-Xa activity and includes water they are diluted in
 NB to select the appropriate syringe size to deliver the appropriate
dose
 Syringe sizes:
o 20mg (2,000 international units (IU)) enoxaparin injection in 0.2ml
water
o 40mg (4,000 international units (IU)) enoxaparin injection in 0.4ml
water
o 60mg (6,000 international units (IU)) enoxaparin injection in 0.6ml
water
o 80mg (8,000 international units (IU)) enoxaparin injection in 0.8ml
water
o 100mg (10,000 international units (IU)) enoxaparin injection in 1
ml water
 Remember each syringe contains 10 mg ( or 1,000 international units
(IU)) per 0.1 ml of water.