Medicine SC066: Am I Prescribing The Right Drug? Flashcards
Elements of a prescription
- Date
- Patient’s identity
- Rx / Please take
- Drug name
- Formulation
- Dosage amount and frequency
- Route
- Additional directions
- Signature
10 principles of good prescribing
- Be clear about the reasons for prescribing
- Take into account the patient’s medication history before prescribing
- Take into account other factors that might alter the benefits and harms of treatment
- Take into account the patient’s ideas, concerns, and expectations
- Select effective, safe, and cost-effective medicines individualised for the patient
- Adhere to national guidelines and local formularies where appropriate
- Write unambiguous legal prescriptions using the correct documentation
- Monitor the outcomes of treatment, both beneficial and adverse
- Communicate and document prescribing decisions and the reasons for them
- Prescribe within the limitations of your knowledge, skills, and experience
Prescription errors
Likely victims:
1. Children
2. Mentally handicapped
3. Elderly
- on multiple drugs
- chronic illnesses (e.g. HT, DM, COPD)
- more susceptible to adverse effects
- cognitive problems
- require assistance in taking medications
4. Nursing homes
5. ICU
2 types of errors:
1. Lack of knowledge of what is right / wrong
2. Has knowledge but makes unintentional mistake
Ways to minimise errors:
1. Double check identity
- Ask for patient’s name + one other detail such as DOB or ID number
- Check at least 2 of these (name, DOB, ID number)
- Do NOT use bed / room number
- Total amount
- State the total duration of treatment / total amount for:
—> Antibiotics
—> Steroids
—> Opioids
—> Hypnotics - Specify formulation
- Tablets / Capsules / Syrup / Injection / Drops / Inhaler / Suppository - PRN prescribing
- Above rules apply
- In addition:
—> Indication
—> Maximum dose to give
—> Minimum interval to give
—> Maximum dose to be given in 24 hour period
Patients are entitled to 5 rights
- Right patient
- Right medication
- Right dose
- Right time
- Right route
Drug safety
Swiss cheese model:
Regulatory bodies + Government
—> Pharmaceuticals
—> Hospitals + Clinics
—> Prescriber
—> Pharmacist
—> Nurse / Carer
—> Patient
Common way of bypass above safeguard: Drug store (patient buy OTC medication)
Types of medication errors
- Ordering (i.e. Prescription)
- Administration
- Dispensing
- Transcribing (check if patient is taking them in addition to looking at medical records)
Personalised medicine
Benefits and Risks of drug may be different in different patients
Complex interplay between genetic and environmental factors —> Affect fate (PK) + effect (PD) of drugs
1. Genetic
2. Demographics (e.g. sex, age, body weight)
3. Concomitant conditions (e.g. renal failure)
4. Interactions with food + other drugs
Identify responders + non-responders:
1. Using pre-treatment characteristics, including sex, age etc.
2. Using initial treatment response as a guide
3. Genetics / Mutations
4. Receptor status (e.g. breast cancer)
***Important pharmacogenetics
- **Carbamazepine: HLA-B1502 —> ***Compulsory —> SJS (highly prevalent in HK (~20% carrier rate) and Taiwan)
- Allopurinol: HLA-B*5801 (13% of HK Chinese) —> SJS (commonest drug cause of SJS) (genetic test is costly and when tested positive, an expensive alternative Febuxostat would be given)
- Abacavir: HLA-B*5701 —> SJS
- Azathioprine, 6-MP: TMPT (SpC Medicine: NOT use together with Xanthine oxidase inhibitor —> occupy TPMT —> accumulation of Azathioprine)
- Clopidogrel: CYP2C19
- Warfarin: CYP2C9, VKORC1 —> classify High, Medium, Low dose Warfarin patients
- Statin: SLCO1B1
Benefit-Risk of a drug
Good efficacy, Low risk of harm: Prescribe
Good efficacy, High risk of harm: Weigh up benefit-risk
Poor efficacy, Low risk of harm: No
Poor efficacy, High risk of harm: No
High benefit-risk ratio, Mild disease (e.g. dermatitis): Prescribe
High benefit-risk ratio, Severe disease (e.g. cancer): Prescribe
Low benefit-risk ratio, Mild disease: No
Low benefit-risk ratio, Severe disease: Prescribe with caution and discuss with patient
How to interpret safety data and inform patients:
Common, Severe SE: NOT prescribe (unless very severe disease e.g. cancer)
Common, Mild SE: Prescribe but **inform patient (e.g. ankle swelling with CCB)
Rare, Severe SE: Prescribe with caution and **warn patient (e.g. agranulocytosis with carbimazole)
Rare, Mild SE: Prescribe, NO need to inform
Cost-effectiveness of drug
Costs
- Differ depends on perspective (e.g. who is paying)
- Examples:
1. Drug price
2. Cost of administration
3. Cost of monitoring
4. Cost of adverse effects
Benefits
- Depends on perspective
- Discount (future benefits are less valuable than immediate ones) (e.g. statin prevention of heart attack in future 10 years)
- Useful measure of benefit is QALY (e.g. targeted therapy)
- Some treatment improve survival, some improve QoL
Cost-effectiveness ratio
Drugs to right of CE line (i.e. confer more benefit at same price): Better than current drug
Drugs to left of CE line (i.e. confer less benefit at same price): Worse than current drug
High cost per QALY: Haemodialysis in hospital
Low cost per QALY: Pacemaker for AV heart block
Incremental cost-effectiveness = Extra money spent / Extra patient cured
Quality prescribing
- Efficacy
- Safety
- Tolerability
- Cost-effectiveness
SC Teaching clinic: Minimising the adverse effects of drugs
Why do we need to worry about side effects?
- Principle of do no harm
- SE can be serious
- Carcinogenicity + Teratogenicity
- Compliance
- Litigation
Which drugs:
1. Toxic drugs
2. Drugs with narrow therapeutic index
3. Drugs with unpredictable pharmacokinetics
4. Drugs prone to interaction
5. Drugs with rare but serious adverse effects
6. Drug toxicity determined by genetics
7. Carcinogenic and teratogenic drugs
Warfarin
- Haemorrhage can be a serious complication of anticoagulation
- Review indications
- Monitoring of INR
- Dietary and prescription restrictions
- Patient education
- Consider new anticoagulants in non-valvular AF patients
Amiodarone
- Long half-life
- Long list of potential side effects
- Monitoring of its efficacy over long periods
- Monitoring of its SE over long periods
- Consider alternatives
