Basic principles of prescribing Flashcards
oxybutynin side effect
Antimuscarinic
- memory loss
- dry mouth
- constipation
- blurred vision
adherence definition
the extent to which the the pt’s behaviour matches agreed recommendations from the prescriber
compliance definition
the old term for adherence:
the extent to which the the pt’s behaviour matches agreed recommendations from the prescriber
what is concordance
a process of prescribing and medicine taking based on partnership
Diclofenac adverse effect
dyspepsia (NSAID)
indapamide adverse effect
gout (thiazide diuretic)
lisinopril adverse effect
intractable cough
prednisolone adverse effect
alter mood and behaviour
prochlorperazine adverse effect
ESPSE like dystonia (antipsychotic)
what is intentional non-adherence
the pt makes a conscious decision not to follow treatment recommendations
what is non-intentional non-adherence
the pt wants to follow treatment instructions but is prevented from doing so by certain factors
at what age are patients entitled to free prescriptions
60
how many half lives will it take to clear 97% of the drug from the body
5
how does erythromycin effect warfarin
it inhibits warfarin metabolism
how does phenytoin effect other antiepileptics
it increases metabolism of other antiepileptics
how does rifampicin affect oestrogen in the COCP
it increases the metabolism of oestrogen
what is the first pass effect
the concentration of a drug, specifically when administered orally, is greatly reduced before it reaches the systemic circulation
what is the volume of distribution
the theoretical volume of fluid that would be needed to achieve the actual plasma drug concentration
total amount of drug in the body / plasma drug conc
what is zero order elimination
Elimination of a constant quantity per time unit of the drug quantity present in the body
what is first order elimination
Elimination of a constant fraction per time unit of the drug quantity present in the body. The elimination is proportional to the drug concentration
elimination rate constant formula
k = clearance / volume distribution
what does it mean when a drug induces the P450 system e.g. phenytoin
can accelerate the metabolism of concomitant drugs
what does it mean when a drug inhibits P450 e.g. erythromycin
can slow down the metabolism of other drugs
what are pro drugs
medicines or compounds that are converted (or activated) to pharmacologically active forms within the body
what is an agonist
a chemical that binds to its target to increase its activity
what is an antagonist
a chemical that opposes the action of another chemical
define affinity
the tendency of a molecule to bind to a receptor
define efficacy
how well an agonist achieves a response
what is a partial agonist
a drug that has a lower maximal response resulting from lower efficacy
what are allosteric modulators
they bind to proteins atd site other than the site for the principal agonist
what is the greatest risk in overdose of TCA
ventricular dysrhythmias
why are statins given at bed time
the enzyme HMG CoA reductase is more active at night. Statins inhibit it which decreases synthesis of cholesterol
what is ED50
the dose required to elicit 50% of a maximal response
calculation to estimate a child’s body weight
(age + 4) x 2(kg)
how many micrograms in 1mg
1000
how many nanograms in 1 microgram
1000
what is % w/w
percentage weight per weight
e.g. hydrocortisone 0.5% w/w contains 0.5g of hydrocortisone in 100g of the cream
what is % w/v
percentage weight per volume
e.g. NaCl 0.9% contains 0.9g of NaCl in 100ml of the infusion
what is % v/v
percentage volume per volume
e.g. ChloraPrep, containing isopropyl alcohol 70% v/v contains 70ml isopropyl alcohol in 100ml solution
how much adrenaline is in 1 in 1000
1g in 1000ml
so 1mg per ml
how much adrenaline is in 1 in 200,000
1g in 200,000ml
so 5 micrograms per ml
how many lbs in a stone
14
how many grams in 1lb
450g
how many kg is 1 stone
6.35kg
how many cm in 1 inch
2.54cm
how many cm in 1 ft
30.48cm
in obese patients, gentamicin should be dosed to which body weight?
ideal body weight
on the BNF how do you find the opioid conversions?
treatment summaries –> prescribing in palliative care
on the BNF how do you find steroid conversions?
trx summaries –> glucocorticoid therapy
on the BNF how do you find the benzodiazepam conversions?
trx summaries –> hypnotics + anxiolytics
what should vancomycin be diluted up to?
5mg/ml and run at a rate not exceeding 10mg/min
what body weight should be used when calculating the dose for acetylcysteine?
actual body weight (max 110kg)
what should acetylcysteine be diluted in
glucose
describe the 3 part dose regimen of acetylcysteine
1) loading dose over 1h in 200ml glucose 5%
2) next dose over 4h in 500ml glucose 5%
3) final dose given over 16h in 1L glucose 5%
formula for volume of parenteral drug required to be administered or added to a infusion
volume required = (what you want/what you get) x what it’s in
why should alendronic acid not be crushed
Biphosphonates should not be crushed because they can cause adverse GI affects
why is diclofenac CI’d post stroke
increased risk of thromboembolic event
can indapamide be crushed
yes
can nifedipine be crushed
no
what is bioavailability
the proportion of the medicine which finally makes it to the systemic circulation where it is available to act at the ‘effector site’
what is the bioavailability of IV medicines
100%
name 3 commonly prescribed drugs where the bioavailability changes depending on the route
- morphine
- ciprofloxacin
- digoxin
how should ciprofloxacin be taken
- NOT with a glass of milk
- at different times to indigestion medication
why should there be a ‘nitrate free period’ of at least 8 hours
to prevent pts from developing a tolerance to the medicine
common drugs which interact with the enteral feed
- quinolones
- phenytoin
what can aid the absorption of iron salts
vit C (ascorbic acid)
why are enteric coated formulations CI’d in pts with an ileostomy
EC meds bypass the stomach and get absorbed in small intestine which is not possible if pt has ileostomy
are MR formulations appropriate for pts with an ileostomy
no
should you check gentamycin serum conc levels after giving 1 stat dose?
no need to unless planning to give another dose
what are bacteriostatic agents
they inhibit protein synthesis, stopping the cell from growing
they don’t kill the cell, but allow host defences to deal with the infection
Name some bacteriostatic agents
macrolides (clarithromycin)
tetracyclines (doxycycline)
what are bactericidal agents
they inhibit a vital cellular process which leads to cell death
name some bactericidal agents
aminoglycosides (gentamicin)
what infection is co-amoxiclav associated with
c.difficile infection. Diarrhoea!
c.difficile infection mnx
- send stool cultures to test for c.difficile toxin + antigen
- stop co-amoxiclav or suspected drug
- give narrow spectrum agent if needed for her pneumonia
- start empirical metronidazole whilst awaiting stool culture
why are urine dipsticks an unreliable method for catheter related UTIs
urinary catheters quickly become colonised with bac and the dipstick will only detect their presence
which group of bacteria is vancomycin affective for
gram positive
how do you know if a drug is controlled
Schedule 2 and 3 preparations are labelled as CD2 or CD3 next to the drug in the BNF
what is meant by unlicensed drugs?
do not have UK marketing authorisation
what is meant by off label
has marketing authorisation but used outside the terms of its license
should tacrolimus be prescribed a a brand or drug name?
brand - to minimise the risk of inadvertent switching between products, which has been associated with reports of toxicity and graft rejection.
what is medicines reconciliation
ensures that the medicine prescribed on admission correspond to medicine prescribed before admission
what is the max dose of simvastatin when prescribed with amlodipine
20mg
what medicines should be omitted from an MDS
- Aspirin (likely to disintegrate)
- cytotoxic drugs e.g. methotrexate as handling shold be kept to a minimum
- PRN meds
- chewable tablets
which medicines can reduce the effectiveness of the COCP
Cytochrome P450 inducers e,g, carbamazepine
equation to calculate eGFR in neonates
30 x height (cm) / serum creatinine (micromol/L)
equation to calculate eGFR in child>1y
40 x height (cm) / serum creatinine (micromol/L)
when should a Yellow card be submitted in <18y
all serious adverse drug reactions that result in harm and suspected ADRs to new vaccines/drugs
what can’t F1’s prescribe
- parenteral nutrition
- cytotoxic or immunosuppressants except corticosteroids
