Principles of Prescribing Flashcards
Definition of adherence
the extent to which a patient’s behaviour matches agreed recommendations from the prescriber. Based on shared decision making between the prescriber and the patient
Definition of compliance
the extent to which a patient’s behaviour matches the prescriber’s recommendations (OLD TERM – criticised for relegating role of patient to one of a passive recipient of medical advice)
Definition of concordance
a belief that decisions about medicines should be shared by a prescriber and a patient so that they can arrive at a harmonious agreement (a concord) regarding therapeutic decisions that incorporate their respective views. Based on:
o Knowledge … education will empower patients to manage their own health. Information should be tailored, clear, accurate and accessible.
o Partnership … invite patients to talk about their medicines
o Support … review medicines regularly with patients
Scale of non-adherence
- In developed countries adherence to long-term therapies as low as 50%
- In UK less than 50% recieve optimal therapy for their condition
- Patients with asthma least compliant - most likely to say costs outweigh the benefits
- In UK, unused/unwanted medicines total £100-300 million annually
Reasons for non-adherence (WHO five factors)
1) Socioeconomic factors - age, geneder, inability to pain for medicines
2) Health system/healthcare team factors - e.g. poor quality of instructions provided to the patient
3) Therapy-related factors - adverse effects, complexity of regimen
4) Patient-related factors - patient disagreement with the necessity for treatment, low self-esteem, low motivation
5) Condition related factors - e.g. dysphagia in myasthenia gravis
Adherence in age groups
- Adolescents less adherent to meds than <12s
- The classic ‘adult’ cohort tends to be ost adherent
- To improve adherence, children <12 should be given the choice of drug formulation
- To improve adherence liquid dosage forms should be first choice preparations for people over 80 years of age
Interventions to improve shared decision making
- Improve communication - aids to improve communication, patient information leaflets (PILs), brail, Yellowcard app (reporting adverse effects) etc
- Increase patient involvement
- Understand the patient’s perspective
- Provide information
Assessing adherence
No agreed gold standard for measuring adherence. Number of approaches adopted:
- Subjective strategies - patient self-reporting
- Objective strategies - measurement of a biomarker or metabolite in blood or urine, e.g. lithium
Interventions to increase adherence
- Simplification of the medication regimen
- Counselling
- Reminders
- Close follow-up
- Supervised self-monitoring - e.g. blood glucose readings, HBPM
- Rewards for success
- Family therapy
- Couple-focused therapy
- Psychological therapy
- Crisis intervention
- Manual telephone follow-up
- Suggest using a Monitored Dosage System (MDS)
Prescription pre-payment certificates (PPCs) and help with healthcare costs
If patient not entitled to free prescriptions (bc they have to pay for >11 prescribed medicines each year or >3 in 3 months), patient can purchase a PPC online
If patient on low income they may be elegible to recieve financial help through NHS low income scheme. HC1 –> HC2 (free prescriptions)/HC3 (help with prescription costs).
New Medicines Service (NMS)
Pharmacy based intervention which provides support for people with long-term health conditions who are newly prescribed a medicine. Patient groups include: Asthma/COPD, T2DM, antiplatelet/anticoag therapy, HTN.
2 intervention dates are set up - 7/14 days and 14/21 days post prescription
Standards for dosing and calculating medications
- SECOND CHECK: good practice to get a second practitioner to check your calculations independantly (especially in case of paediatrics)
- SENSE CHECK: check the calculated dose does not exceed the adult dose or max daily dose, does dose seem reasonable?
- DOCUMENTING WEIGHT REGULARLY: actual body weight (ABW) - stand a pt on a set of scales; Ideal body weight (IBW) - for pts at the extremes of weight as proportions of fat, muscle, bone etc are distorted compared to normal (seek dosing info for these pts); Lean body weight (LBW) - calculated by subtracting body fat weight from ABW
- BODY SURFACE AREA (BSA): some drugs e.g. IV aciclovir rely on this calculation
Paediatric weight calculations
Paediatrics: weight (kg) = (age + 4) x 2
OR
0 to 12 months = (0.5 x age in months) + 4 (kg)
1 to 5 years = (2 x age in years) + 8 (kg)
6 to 12 years = (3 x age in years) + 7 (kg)
These formulas are only to be used in an emergency situ until a measured weight can be obtained
Preparation strengths
Solid dosage forms (e.g. tablets/capsules): expressed as weight per unit e.g. 50mg/tablet
Liquid preparations: expressed as weight per ml e.g. 50mg/ml or 50mg/5ml
Injectable preparations:
- Percentage (% w/v, v/v).
- Amount per ml.
- Total quantity of drug per total volume.
- Ratio (e.g. 1: 1000) = 1g in 1000ml
Conversion factors in dosing
1 kilogram (kg) = 1000 grams (g)
1 g = 1000 milligrams (mg)
1 mg = 1000 micrograms
1 microgram = 1000 nanograms
**micrograms should always be written out in full
Percentage concentrations
%w/w = percentage weight per weight
e.g. hydrocortisone 0.5% w/w contains 0.5 g of hydrocortisone in 100 g of the cream
%w/v = percentage weight per volume
e.g. sodium chloride 0.9% w/v contains 0.9 g of sodium chloride in 100 ml of the infusion.
%v/v = percentage volume per volume
e.g. in a 1% v/v solution there is 1 ml of liquid drug/chemical in 100 ml of the final product.
Conversions from imperial to metric
For weight:
- 1 stone contains 14 pounds (lb).
- 1 lb is equivalent to 450 g.
- 1 stone is equivalent to 6.35 kg.
For height:
- 1 foot contains 12 inches.
- 1 inch is equivalent to 25.4 millimetres (mm).
- 1 foot is equivalent to 304.8 millimetres (mm).
Opioids drug dose equivalents
*Use the lowest dose in the conversion range and then adjust according to response and tolerance
Patients sometimes need to change to alternative opioids because of adverse reactions, intolerance or lack of efficacy.
A table is available in the BNF for converting morphine to fentanyl patches for example… > Prescribing in Palliative Care
Benzodiazepine drug dose equivalents
If a patient is being withdrawn from a benzo, standard practice is to change to an equivalent dose of diazepam then titrate down to zero.
The BNF provides equivalent doses of benzos, all compared to diazepam 5mg > Hypnotics and Anxiolytics
Corticosteroid drug dose equivalents
BNF will base conversion on glucocorticoid activity of drug, disregarding mineralocorticoid activity.
All corticosteroid conversions in the BNF are compared Prednisolone 5mg > Glucocorticoid therapy
Prescribing infusions/medicines for infusion info required
- The name of the active drug
- The total quantity of the active drug to be added to the infusion (if applicable)
- The name and concentration of the diluent (if applicable)
- The total volume of the syringe or infusion bag
- How long the infusion is to be administered over.
- The infusion rate (e.g. ml/hour)
- The infusion rate range (usually in ml/hour) (where applicable)
- The intended dose (e.g. microgram/kg/hour) (where applicable for continuous infusions)
- The route of administration
Prescribing Acetylcysteine in paracetamol overdose
- Calculate dose using actual body weight (ABW), although dose is capped at 110kg body weight
- The diluent - preferably diluted in glucose 5%
- Total dose regimen to be prescribed in 3 parts
- 1st or loading dose given over 1 hour in 200ml of glucose 5%
- 2nd is given over next 4 hours in 500ml of glucose 5%
- 3rd given over next 16 hours, in 1 litre of glucose 5% - Dose of acetylcysteine varies at each step:
- For the first you need 150 mg/kg.
- For the second you need 50 mg/kg.
- For the third you need 100 mg/kg.
- That’s a total dose of 300 mg/kg over 21 hours!
Patient with speech and swallowing problems
- Review meds with advice from a pharmacist. If oral route is used they may be at risk of aspiration or chewing tablets. Drugs can be given enterally via an NG tube if need be
- Decide whether drugs can be easily manipulated, e.g. crushed; discontinued; temporarily withheld; switched to an alternative medicine in same class; switched to alternative route or formulation
- Not always appropriate to crush tablets or open capsules - particularly for MR tablets (drug will be released quickly) or any med that may cause irritation to stomach if coating is broken (i.e. enteric coating, EC). This aso renders drugs off label.
Parenteral routes
- intravenous (IV)
- intramuscular (IM)
- intrathecal (IT)
- subcutaneous (SC)
- topical drops/jel/patch
- intranasal spray
Enteral routes
- enema
- capsule
- (coated) tablet
- MR tablet
- oral solution/syrup/suspensions
- rectal suppository
- soluble tablet
Problems with formulation/administration
Patient - e.g. arthritic?
Where is medicine absorbed? - most oral meds absorbed in small bowel which may cause problems if there is ileus etc.
Where does medicine act? - Vancomycin is not absorbed from GI tract therefore needs to be administered IV if treating systemic infection
Excipients
Most drugs - 10% active ingredient, 90% excipients i.e. pharmacologically inactive substances that are added to improve acceptability, shelf-life, administration, stability etc.
May be easy for patient to recieve something that isn not appropriate for them:
- Pt with DM recieving sugar
- Allergy sufferer recieving allergen
- Baby recieving alcohol
- Pt receiving large amounts of sodium from effervescent tablets
- Gelatine for veggies
Practical pharmacokinetics (ADME)
1) Absorption
2) Distribution
3) Metabolism
4) Excretion
Factors affecting oral absorption
- CHELATION - drugs can be bound to some electrolytes which will reduce absorption; e.g. tetracycline antimicrobials and Ca2+, antacids and iron preparations; Quinolones and iron preparations
- SOLID or SOLUTION - drugs given as solution tend to act faster
- MR - not always appropriate for patients who have had bowel resections (e.g. ileostomy)
- ENTERIC COATING (EC) - bypass the stomach and enter small intestine, therefore not good for pts with ileostomy
Factors affecting absorption from other routes
- Poor blood flow will slow rate of drug absorption
- Very well perfused muscle will have rapid drug absorption
- Absorption through skin can be affected by simple actions such as having hot bath which dramatically increases blood flow to the skin
Timing of certain drugs
Antibiotics > need to achieve a consistent therapeutic concentration throughout the day
Insulin > understand how quickly the differing insulin regimens take effect
Nitrates > should be prescribed so that there is a “nitrate-free period” of at least 8 hours preventing pt developing tolerance
Parkinsons meds > must be administered according to the pt’s usual dosing program. Late administration may result in a return of symptoms
MR morphine sulphate > has a short half-life
Timolol eye drops > short half-life - failure to administer may mean glaucoma worsens and pt loses eyesight
Prescription documentation in primary care
FP10(green) > GPs, hospitals
FP10(lilac) > nurse independant
FP10(yellow) > dentists
FP10(blue) > used to prescribe drugs of misuse to manage opioid dependance
FP10(pink) > used in private sector to prescribe schedule 2/3 controlled drugs
Basic prescription requirements
- Patient details > includes name and address. Age/DOB requirement for anyone under 12 years
- Signature of prescriber > handwritten
- Prescriber identifier > e.g. address
- Valid date on the prescription
- Indelible ink
Additional legal requirements for controlled drugs (CDs)
- Dose
- Form (e.g. tablets, capsules)
- Strength
- Total quantity of the preparation or the number of dose units in both words and figures
- Cross out all other areas of prescription not filled
**CDs in BNF: CONTROLLED DRUGS AND DRUG DEPENDENCE
Unlicensed drugs
Drugs that do not have UK marketing authorisation
Off-label - unlicensed drugs that are used outside the terms of its license. Maybe at a different dose, indication, or pt group outlined in the summary of product characteristics (SPC).
Do not prescribe off-license meds unless asked to by senior clinician. Must be satisfied that:
- no suitable alternatives that would meet pts needs
- sufficient evidence base and/or experience for its use
- prepared to take responsibility for prescribing unlicensed medicine and for overseeing pts care
- decision has been documented including rationale
- inform pt and gain consent where possible
As required medications (PRN)
- State maximum dose within 24 hours
- Minimum dose interval - length of time bt doses to avoid doses being given in quick succession
- Indication - assist nursing staff in administering meds appropriately
Medicines reconciliation
Df. the aim of medicines reconciliation on hospital admission is to ensure that medicines prescribed on admission correspond to those that the pt was taking before admission
Verification> Clarification > Reconsilliation
Asking about drugs specifically in drug history (DRUGS/CASES)
D - drugs prescribed by doctor
R - recreational, alcohol, illicit drugs
U - user, OTC, complementary and alternative meds
G - gynecological e.g. contraceptives
S - sensitivities and the nature of reaction
C - contraception A - anticoagulation S - steroids E - ethanol S - smoking
Monitored dosage systems (MDS)
MDS contains ‘prescribed’ drug treatments, however if self-filled may contain herbal meds etc too.
MDS should not contain:
- PRN meds
- Cytotoxic meds
- Once weekly doses (e.g. methotrexate)
- Variable doses (e.g. warfarin)
- Dispersable or effervescent formulations (e.g. aspirin)
- Buccal or sublingual formulations
Problem drugs (when it comes to dosing)
- WARFARIN - check INR etc etc., confirm warfarin dose with GP and the Yellow Oral Anticoagulation Book; brown tablet (1mg); blue (3mg); pink (5mg)
- INSULIN - following sources are useful: insulin passport (NPSA), clinical nurse specialist, community pharmacist
- CYTOTOXICS - alert oncologist/haematologist, only cancer specialists should prescribe these
- DRUGS NOT TAKEN DAILY : > Bisphosphonates > Vitamin B12 > Injectable antipsychotics > Methotrexate > Implants
General guidance sections in BNF
- How BNF publications are constructed
- Changes (since last print)
- Guidance on prescribing
- Prescription writing requirements
- Emergency supply of medicines
- Controlled drugs and drug dependence
- Adverse drug reactions
- Guidance on IV infusions
- Prescribing in special patient groups
