Lecture 18: Clinical Pharmacology and Prescribing Flashcards
Importance of Prescribing
something you will do daily
must do safety and effectively
Rational prescribing
Selection of the most appropriate therapeutic regimen for a specific patient
4x Steps prior to writing a prescription
- Make a diagnosis
- Make a therapeutic decision
- Choose a medicine
- Choose a dose regimen
- Making a diagnosis: Examples of patients who come in with symptoms and not diagnoses
- please give me pain relief for a sever headache
- i have a cough that wont go away
- I am constipated. can you prescribe something
* * May think it is something, but also need to be weary that it is something you should be worried about
* * You would use a different treatment if you knew the underlying cuase
- Make a therapeutic decision
Treatment Goals:
1. Identify key management issues with patient (diagnosis, symptom control, disease modification (long-term consequence)
2. Are current symptoms modifiable by symptomatic treatment or disease modifying treatment
- are you going to treat the underlying cause of the disease or the symptoms? e.g Lose ovaries a). hormone replacement therapy with oestrogen. b). antidepressants/anti-epilepsy treatment
- e.g. to long w/o periods - may avoid period symptoms, but can be at risk of endometrial thickening and hence endometrial cancer
Overall: Dialogue with patient and treating the important factors
- Choosing a medicine
a. Efficacy
b. Safety
c. Appropriateness
Note: can choose less effective mechanism due to safety profile or appropriateness
e.g. Oestrogen HRT, even though most effective treatment to relieve symptoms, there is an increased risk of breast cancer, heart attacks and strokes in older woman, therefore people wont take as aren’t happy with the safety profile (esp. important for someone with family history, diabetic, hypertension and are already at risk)
Efficacy of a medicine
How effective are the treatment alternatives?
- what is the evidence to support these treatment alternatives (get advice from boss, reading journals, meetings, public guidelines) (annoying “well informed” patients)
Patient related factors which affect efficacy
age
disease state (e.g. worsened renal function, may handle medication differently)
pregnancy
genetics
other medications (e.g. hot flush medications interfere with breast cancer treatment)
other substances
compliance (wont work if you dont take the medicine)
Safety of medicine
- what are the contradictions for using these drugs in general and specifically in the patient?
-allergies
-concomitant disease including major organ failure - What are common and potentially serious adverse effects that can occur with this drug
- will these side effects affect my choice for this patient - What drug interactions need to be considered?
- drug-drug, drug-food, drug-disease - Is the patient pregnant or lactating
Overall: weigh up the risks and benefits to the treatment
Examples of contradictions for drugs and drug interactions
Dont give osteoporosis medication (which is renally cleared) to a patient with significantly reduced GFR
2x antihypertensive medications causing hypotension
Appropriateness of a medication
Can the patient afford it
Are there any considerations that need to be made for compliance
- more than once a day
- empty stomach
- needs blood test and dose adjustments
e.g. thinking of getting pregnant, patients needs to be aware of teratogenic effects of Topiramate
e.g. wont take meds if makes them feel drowsy (cant drive car etc.)
- Choose a dosing regimen
available in multiple forms
Start at high dose an have lots of side effects vs. start at low dose and work way up to effective dose
e.g. topiramate + gabapentin: pain medication for menopause, but if start at correct treatment dose, people often become too tired and nauseous to continue
there are methods of choosing the dose
5x Routes of delivery (considered when choosing a dosing regimen)
- IV injection
- Skin patches and gels
- Oral tablets
- Depot preparations
- Local delivery
IV injections
high concentrations in blood rapidly
instant and complete absorption
potentially more dangerous
- avoids problems wiht patient compliance
e.g. osteoporosis medication: more effective partially due to levels in the system and partially due to compliance
Skin patches and gels
Lower peak concentration and extended duration of effect
Can bypass first pass metabolism (e.g. in liver)
skin reaction is potential adverse effect
Depot preparations
Release contents slowly over hours-months
May improve compliance
Require a deep injection
e.g. Contraceptive Depovaro, high concentration of progesterone
Local delivery
Site of action can be targeted
reduced systemic effects
e.g. hormone containing IUD + Asthma Medications
Oral tablets
Slower rise to a later peak concentration
May be less complete absorption
May be subject to first pass metabolism
Manners of Choosing the dose
- Population: the same dose for everyone
- Group: the same dose for similar group (e.g. weight, renal function)
- Individual: the dose is determined by the individual response
or
A. The dose response relationship and therapeutic index
B. Disease sates that influence the response
C. Potential drug interactions
Legal prescription information requirements
- Doctors name (name and initials)
- Signature
- Physical address
- MCNZ registration number
- Contact phone number
- Patients name
- Full residential address
- Age if under 13 years
* *all must be legible
Three parts to the prescription
- R / Recipe (take thou)
- Sig/ Signa (mark /write)
- M/ Mitte (send to a total of)
Requirements for R component of prescription
- Name of medicine
- formulation e.g. caps, tabs, syrups
- strength of medicine
Rx Amoxycillin 500mg tabs
Requirements for S component of prescription
Instructions to the patient Sig: 2mg o.d. p.o Take the dose prescribed by your doctor or nurse. you need a regular INR tests to make sure this dose is safe for you abbreviations: one, twice, three, four times daily morning, middy, night time as required, before food, after food orally, rectally, subcutaneously, intramuscular, intravenous, sublingual
Requirements for M component of prescription
Instructions for the pharmacist
Specifics the quantity to be dispensed
M: 7 days supply
Note: maximum period of supply is 3 months, with an exception to:
1. oral contraceptive pill which has a 6 month supply
2. Controlled drugs (opiates) only allowed for a few weeks
3x steps after writing a prescription
- Counsel the Patient
- Monitor the response
- Review the Medicine
- Counsel the patietn
You are the patients main source of information:
1. Medicine name and dose
2. How and when to take it
3. Reason(s) for prescribing medicine
4. Benefits of treatment and when they should occur
5. Possible adverse effects and how to manage them
6. Possible interactions with food, drinks and medicines
7. Timing of follow up
Note: do not provide too much information when patient is not able to assimilate it (e.g. when worrying about other issues)
- should provide them the info and then walk them through it
- schedule a follow up
Additionally:
1. Provides sources of further information
2. Discuss aids to adherence (e.g. medicine cards)
- Monitor the response
Know the abnormality you are going to follow during treatment. Pick something you can monitor
- what signs, symptoms and laboratory parameters should I monitor in the patient –> when and how often do i measure them
- dont measure something idiosyncratic, do something that is more common at a certain time of treatment
e. g. blood test for iron levels so not anaemic before end treatment
e. g. osteoporosis: monitor bone density to prevent fractures, instead of checking for fractures alone
e. g. RBC: full blood count so not developing cytopenias
e. g. Thyroid treatment: early risk of deranged liver –> therefore do liver tests
Different monitoring strategies for different medicines
- Clinical response (if clinical end point is easily measured) : treatment of cancer, cure of infection, resolution of nausea
- Biomarkers (if biomarkers can predict the clinical response (cost, time, ease of measurement))
-PSA (surrogate measure of prostate cancer treatment)
- CD4 count (HIV)
- Full blood count (bone density for osteoporosis) - Drug concentration (if there is no endpoint. if the effects correlate better with drug concentration than the drug dose)
- Digoxin (arrhythmias, heart failure)
- Phenytoin (epilepsy)
- Lithium (mood disorders)
Note: narrow therapeutic index, dont want to be too close to either side (adverse effects or no treatment). If get in therapeutic range more likely to treat w/o side effects.
Indications for therapeutic drug monitoring
- an event is potentially serious but occurs infrequently e.g. epileptic seizure or cariac arrythmias
- check due to pot severe consequences of over/under treatment. e.g. warfarin: too low= people have fits (cant drive + social consequences) too high = sedation - narrow therapeutic index and small increase in dose can lead to toxicity
- effects correlate better with blood concentrations than they do with dose
- deciding whether or not a symptom is due to an adverse effect (due to toxicity). detecting non compliance
- Review the medicine
- Efficacy and safety (desired effects and adverse effects)
- Appropriateness (clinical changes and changes in medicine)
- Patient view (patient knowledge, understanding and concern. adherence) - insures compliance
Tips to Review the medicine
Review medicines in regular intervals:
1. offer repeat information and review to patients, especially when treating long term conditions with multiple medications
2. any plan should include a date for a follow up review
- reiterate adverse effects
-may not need any more or at a lesser dose
Check: if prescription is still the correct medicine for the disease, is still at the correct dose, and isnt causing any problems
OVerall 8 steps involved in precribing
- Diagnosis
- Therapy
- Medicine
- Dose regimen
- Prescribe
- Communicate
- Monitor
- Review
