Prescribing - T Year Flashcards
1.1 Prescribing drugs for inpatients
What are once-only prescription?
*LOB: Describe the principles of once-only, regular, as required and infusion prescriptions for inpatients
Does not reccur.
“One Dose Only”
In a paper drug chart they have their own section.
Medication that needs to be given once
1.1 Prescribing drugs for inpatients
What are as required prescription?
*LOB: Describe the principles of once-only, regular, as required and infusion prescriptions for inpatients
Also known as PRN
Can be given for the listed indications such as an antiemetic prescribed incase the patient continues to feel nauseous.
May show maximum frequency
And maximum duration
-this enforces a level of medical review
1.1 Prescribing drugs for inpatients
What are infusion prescription?
*LOB: Describe the principles of once-only, regular, as required and infusion prescriptions for inpatients
Using a drip or pump over a period of time
Rate of substance is a crucial determinant of its clinical affect.
The rate can be titrated to change the effect of the drug.
Rate of Infusion
And Duration is required.
1.1 Prescribing drugs for inpatients
What are the different types of prescriptions?
*LOB: Describe the principles of once-only, regular, as required and infusion prescriptions for inpatients
Typical
Scheduled (regular and once only)
As Required
Titratable
IV, NG, some drugs
Atypical
Oxygen
1.1 Prescribing drugs for inpatients
What are the components of a prescription?
*LOB: Describe the essential components of each prescription type
Drug Name
Date and Time
Patient name and details
Allergies noted
Dose
Route
(Max) Frequency
Duration
Indication/ order comments
You can add a stop.
1.1 Prescribing drugs for inpatients
Pros and Cons of Electronic and Paper charting
*LOB: Discuss the differences between paper and electronic prescribing for inpatients
Pro Electronic
Can colour code given, due etc
Can show doses that have been given and which time
Can time doses specificaly.
Can flag allergies etc.
Access to patient data
Pro Paper
Seperate section for One Dose Only
Doesnt rely on systems if outages occur
Con Electronic
Technical outage, must have skill to prescribe on paper
Poorly designed systems show too much data
Con Paper
Increased error risk
Handwriting
Time consuming
Not as much data.
1.1 Prescribing drugs for inpatients
How do you review existing prescriptions?
*LOB: Describe an approach to the critical appraisal of existing prescriptions for inpatients
PAIRS
- Prescription Writing
- legible, legal, correct, complete, indications
- Adverse Effects
- allergies, intolerance, adverse effects
- Interactions
- Drug-drug, drug-disease, OTC, recreational, cautions and contras
- Rational Treatment
- appropriate drug and dosage, can any others be stopped/ tapered?
- Similarities
- Pharmacologically similar drugs, are they on more than 1 drug?, sometimes appropriate to intensify therapy but worth double-checking risks.
1.1 Prescribing drugs for inpatients
Sources for Prescribing
*LOB:Describe the sources of information available to guide prescribing for inpatients
Local Support and written guidance incl senior colleagues
Formularies- BNF
National Guidance
Peer Review Literature
Senior Colleagues
Other respected guidace
Textbook (informal support)
Online resources (informal support)
1.1 Prescribing drugs for inpatients
What is the prescribing process?
*LOB: Demonstrate safe and effective (simulated) prescription writing for common inpatient prescribing tasks
- Define the problem
- Define the therapeutic object/ drug
- Choose a Tx
- Efficacy
- Safety
- Tolerability (cost) - Start a Tx
- prescription writing
- administration
- proving patient information - Monitor Effects
- Stop if appropriate.
1.1 Prescribing drugs for inpatients
How can you ensure safe prescribing?
*LOB: Demonstrate safe and effective (simulated) prescription writing for common inpatient prescribing tasks
Review PAIRS when prescribing
Positive patient identification
Use formularies and local advice.
Check frequency- methotrexate and alendronic acid are accidental daily not correctly weekly.
Check you NSAIDs- make sure they are balanced well and not overtly prescribed. Set a limit (ie 7 days)
Double check if brand name doesnt include same medication ie) CoCodamol and Paracetamol
1.1 Prescribing drugs for inpatients
Best practice for abbreviations etc.
*LOB: Demonstrate safe and effective (simulated) prescription writing for common inpatient prescribing tasks
If using a brand name which is essential, in comments give the drug components.
Combined drugs may have approved names such as 30/500, you MUST use this.
ALWAYS complete the allergies field.
1.2 Prescribing intravenous fluids
What are crystalloids?
*LOB: Define crystalloid and colloid fluid solutions and give examples of each
True solutions
Small molecules dissolved in water- salts and sugars
Sodium Chloride 0.9%
Glucose 5% (dextrose)
Hartmann’s Solution (compound sodium lactate)
Hartmann’s potassium is fixed, the others can be modified.
1.2 Prescribing intravenous fluids
Why is Hartmann’s used?
*LOB: Define crystalloid and colloid fluid solutions and give examples of each
- Balanced pbysiological solution
- More closely approximate serum and ECF electrolytes
- Doesnt change the concentration of serum that much
- Lactate is a source of bicarbonate
- Potassium of Hartmanns is fixed.
The 5mmol K+ is not to have a therapuetic affect but to make hartmanns indifferent to the serum potassium concentration. Doesnt matter how much Hartmann;s that infused, it shouldnt cause a K+ error.
1.2 Prescribing intravenous fluids
What is the consequence of changing the potassium chloride.
*LOB: Define crystalloid and colloid fluid solutions and give examples of each
The amount of potassium chloride can vary but is fixed at manufacture.
By changing the potassium, you also change the chloride amount.
For example, Sodium Chloride 0.9% has a Cl- of 154, but Sodium Chloride 0.9% with potassium chloride 0.3% has a Cl- of 194.
Remember this is concentration- so 40mmol/L at 0.5L = 20mmol given
1.2 Prescribing intravenous fluids
What are colloids?
*LOB: Define crystalloid and colloid fluid solutions and give examples of each
Has a crystalloid base like Sodium chloride .
Includes large osmotically active molecules
such as albumin and gelatin
These make it a colloid.
Understand where the volume will go.
1.2 Prescribing intravenous fluids
Where does the volume of infused fluids go?
5% Glucose
*LOB: Define crystalloid and colloid fluid solutions and give examples of each
THINK: 5% Glucose
A way to infuse pure water
Isotonic in the immediate location just at the point it starts mixing with blood, prevents water moving into cells (prevent lysis)
The Glucose is taken up by cells
Pure water is left,
Nothing stops the water moving so water distributes evenly across the 3 spaces.
1.2 Prescribing intravenous fluids
Where does the volume of infused fluids go?
Sodium chloride 0.9%
*LOB: Define crystalloid and colloid fluid solutions and give examples of each
Sodium cannot pass to cells.
It has the same concentration as serum
Therefore the sodium and water stays in the intersitium and intravascular spaces.
The water doesnt move into cells as it stays in the extracellular compartments, ensuring the osmolality is preserved and does not change with the increase of sodium.
Losing about 80% into interstitium but useful for increasing circulating volume in the intravascular space.
1.2 Prescribing intravenous fluids
Where does the volume of infused fluids go?
Albumin 4.5%
*LOB: Define crystalloid and colloid fluid solutions and give examples of each
Colloid
Large osmotically active moleucle cannot cross the intravascular membrane
The fluid can also not cross the membrane and retained intravascular and expands volume
HOWEVER, in sick pateints, this barrier is leaky and the colloid escapes in the interstitium, taking water with it.
Balance pharmacy risks (hypersensitvity) with effectivity.
Crystalloids are still favoured.
1.2 Prescribing intravenous fluids
What are daily maintenance requirements?
*LOB: Describe the essential principles of maintenance fluid prescriptions, accounting for sodium, potassium and water requirements
lost per day
25-30ml water lost per kg of body
Sodium and potassium 1mmol each per kg of body
1.2 Prescribing intravenous fluids
How to plan maintenance fluids.
*LOB: Describe the essential principles of maintenance fluid prescriptions, accounting for sodium, potassium and water requirements
Using the 25ml/Kg rather than the 30 as you end up dividng by 24 hours.
You can be approximate.
This person needs 80mmol of sodium, 80mmol of potassium
Half a litre of Sodium chloride 0.9% will give 72mmol (close enough) of sodium and gives half a litre of water
Give the rest of the water with Glucose 5%
This provides the daily glucose.
1.5L of glucose
For potassium, hers is normal, so need to give the potassium chloride.
The potassium chloride 0.3% is the closest.
1.2 Prescribing intravenous fluids
Maintenance fluids Prescription
*LOB: Describe the essential principles of maintenance fluid prescriptions, accounting for sodium, potassium and water requirements
2L of water 24 hours
77mol Sodium
80mmol Potassium
1.2 Prescribing intravenous fluids
How to prescribe maintenance fluids (stepwise).
*LOB: Describe the essential principles of maintenance fluid prescriptions, accounting for sodium, potassium and water requirements
1) decide how to provide 1mmol/kg/day of sodium
2) Calculate and prescribe the hourly infusion rate (1ml/kg/h)
3) Make up the rest of water with 5% glucose
4) Make up potassium if renal fucntion and serum potassium is normal
1.2 Prescribing intravenous fluids
What is fluid resuscitation?
*LOB: Describe the essential principles of fluid resuscitation
Sequential fluid challeneges
Most be assessed and responded afterward.
By increasing fluids, we increase LV filling, therefore stroke volume should increase.
And therefore can help with Cardiac output
HOWEVER this has a limit if the LV is overstretched, increased filling can reduce stroke volume.
1.2 Prescribing intravenous fluids
What to prescribe?
*LOB: Describe the essential principles of fluid resuscitation
Volume 250-500ml (500 easier)
Infuse rapidly ~5min
Children 20ml/Kg
1.3 Calculations in prescribing
What units are used in prescribing?
*LOB: Describe (in overview) the International System of units (including base units, derived units and prefixes) as this relates to the use of medicines
Majority are SI units (if in doubt think base 10)
Meter, second, mole, kilogram
Some drugs, such as insulin and heparin, are dosed in units of biological activity.
1.3 Calculations in prescribing
Abbreviations in prescribing
*LOB: Describe (in overview) the International System of units (including base units, derived units and prefixes) as this relates to the use of medicines
Liters are always an uppercase L
g (gram), L (litre) and mol (moles), and their ‘milli’ counterparts (mg, mL and mmol).
1.3 Calculations in prescribing
How to quanitfy body size?
*LOB: Demonstrate the calculation of ideal body weight and adjusted (dosing) body weight, and describe their interpretation and use
- Total body weight- TBW
- Calculated derivatives of weight
- Estimate of Body surface area (haematology and chemo drugs)
BUT TBW shoudl be capped, because 50% extra weight doesnt always mean 50% more drug but can soemtimes nearly double the drug- not likely to occur.
We can cap the drug. (Crude)
**Using Ideal body weight from height ** which is ideal as is easy to calculate and presumes what the liver capacity excretion capacity probably is
1.3 Calculations in prescribing
What is the ideal body weight formula?
*LOB: Demonstrate the calculation of ideal body weight and adjusted (dosing) body weight, and describe their interpretation and use
(0.91 x (height in cm-152.4)) +45.5
You can round slightly
+50 for men
1.3 Calculations in prescribing
How much of excess weight important to drug dosing?
CALCULATING ADJUSTED BODY WEIGHT
*LOB: Demonstrate the calculation of ideal body weight and adjusted (dosing) body weight, and describe their interpretation and use
Crudely divide into lipid and lean
IBW + (0.4 x Excess weight)
Why? Insoluble in lipid
Lean volume does effect distribution.
1.3 Calculations in prescribing
Which body weight method is used when?
*LOB: Demonstrate the calculation of ideal body weight and adjusted (dosing) body weight, and describe their interpretation and use
Why? Total body weight for the demo patient claculated 560mg, capped weight 500mg, adjusted 420g, ideal 300mg all for the same drug.
1.4 Prescribing drugs for outpatients
What is an outpatient prescription?
*LOB: Describe the essential components of an outpatient (FP10) prescription
FP10 and inpatient. FP10 is a complete record in itself- must have a lot more details. Age is required in under 12 years old.
Prescribers address, signature and date are legally required.
