PSA Flashcards
components of pharmacokinetics
absorption, distribution, metabolism, elimination
give some examples of enzyme inducers
enzyme inducers - reduce effect of drugs
PC BRAS:
phenytoin
carbamazepine
barbituates
rifampicin
alcohol excess (chronic)
sulphonylureas
Also St John’s wort
what is 1FTU
1 finger tip unit - 1 FTU is the amount of medication needed to squeeze a line from the tip of an adult finger to the first crease of the finger, and provides enough to treat one side of both hands.
examples of enzyme inhibitors
enzyme inhibitors - increase effects of drugs and hence toxicity risk
AODEVICES
allopurinol
omepraozole
disulfiram
erythromycin
valproate
isoniazid
ciprofloxacin
ethanol (acute intoxication)
sulphonamides
Don’t forget grapefruit juice!!
what drugs must be continued during surgery?
CCBs, beta blockers
general rule with regards to stopping drugs during surgery
As a general rule for all surgery, most drugs should be continued during surgery (i.e. not stopped beforehand) because the risk of losing disease control outweighs the risk posed by drug continuation.
what are the drugs to stop before surgery and when to stop them?
- COCP and HRT - 4 weeks before surgery
- lithium - Lithium should be stopped 24 hours before major surgery but the normal dose can be continued for minor surgery (with careful monitoring of fluids and electrolytes)
- postassium sparing diuretics day of surgery (risk of hyperkalaemia)
- ACEi/ARB - 24 hrs before surgery (risk of severe hypotension)
- anticoagulants and antiplatelts - variable acc to local policy (occasionally continued eg In patients with stable angina, perioperative aspirin should be only continued where there is a high thrombotic risk (e.g. patients with a recent acute coronary syndrome, coronary artery stents, or an ischaemic stroke).)
- oral hypoglycaemics, metformin and insulin - variable acc to local policy - since pts NBM, if these are continued metformin will cause lactic acidosis and the others hypoglycaemia if contd. usually sliding scale insulin is started instead. sliding scale now called Variable Rate Intravenous Insulin Infusion (VRIII)
- MAY be stopped - MAOIs can have important interactions with some drugs used during surgery, such as pethidine hydrochloride. Tricyclic antidepressants need not be stopped, but there may be an increased risk of arrhythmias and hypotension (and dangerous interactions with vasopressor drugs); therefore, the anaesthetist should be informed if they are not stopped.
**there is a BNF pg in treatment summaries - Diabetes, surgery and medical illness AND Surgery and long-term medication**
drugs to change arnd surgery
Patients on long-term corticosteroids - to be given IV steroids at induction of anaesthesia in addition to usual dose and to be given more steroids in the post operative period
sections of PSA
over 2hrs
safe routine for prescribing
ensure correct patient
notice and record allergies
consider CIs for each drug
consider best route
consider need for IV fluids, VTE prophylaxis, pain relief and antiemetics
sign
CIs and interactions for anti platelets and anticoagulants
CIs - bleeding, suspected bleeding, at risk of bleeding (liver disease with prolonged PT) (prophylactic heparin generally not appropriate in acute ischaemic stroke due to risk of bleeding into the stroke)
Interactions - enzyme inhibitors can inc PT and INR and warfarin’s effect (eg erythromycin)
side effects and possible CIs for steroids
STEROIDS -
stomach ulcers
thin skin
edema
right and left heart failure
osteoporosis
infection (eg candida)
diabetes (hyperglyccaemia and diabetes)
syndrome (cushing’s)
CIs for NSAIDs
indigestion
asthma
heart failure
renal failure
clotting abnormality
**aspirin at low doses given for CVD and cerebrovascular disease is not subject to same level of caution as other NSAIDs
CIs and side effects of antihypertensives
hypotension (incl postural)
bradycarida - beta blockers and CCBs
electrolyte disturbances - ACEi/ARB and diuretics
dry cough - ACEi
asthma - b blockers
peripheral oedema and flushing - ccbs
renal failure - diuretics
gout - thiazide diurteics
gynaecomastia - k+ sparing diuretics
for pts NBM, what shd be done with regards to PO medications?
Prescribed regular oral medication and pre-medication, unless contraindicated and excepting oral hypoglycaemic medicines, should be administered pre-operatively. Adults can have up to 30ml of water.
general rules for choice of replacement IV fluids
generally give IV 0.9% saline unless -
- hypernatraemic or hypoglycaemic - give 5% dextrose
- ascites - human albumin solution
- shocked from bleeding - blood transfusion but crystalloid first if no blood immediately available
how to decide quantity and speed of replacement fluids?
assess HR, BP and UO.
if tachycardic or hypotensive - give 500mL bolus (250mL if hx/risk of heart failure). then re-assess.
if oliguric (<30mL/h) (not due to obstruction) - give 1 L over 2-4h then reassess.
in general -
- reduced UO - 500mL of fluid depletion
- reduced UO + tachycarida - 1L of fluid depletion
- reduced UO + tachycardia + hypotnesion - >2L of fluid depletion
** never prescribe more than 2L of fluid for a sick pt. always reassess and review subsequent fluid prescriptions.
**IV potassium should not be given at more than 10mmol/hr
maintenance fluid choice
general rule - adults require 3L in 24 hrs and elderly require 2L.
usually 1 salty and 2 sweet - 1L of normal saline and 2L of 5% dextrose
to provide potassium - always check U&E before deciding how much to give. bags of dextrose or saline containing KCl can be used. in someone with normal potassium lvls - roughly 40mmol KCl per day so 20mmol KCl in 2 bags.
**remember do not give KCl IV at more than 10mmol/hr
**Fluids may come with an additional 20 mmol or 40 mmol of potassium in a 1 litre bag. Potassium should not be added to fluids. The mixtures should come ready-made from the manufacturer.
***When prescribing routine maintenance fluids for obese patients you should adjust the prescription to their ideal body weight. You should use the lower range for volume per kg (e.g. 25 ml/kg rather than 30 ml/kg)
***For the following patient groups you should use a more cautious approach to fluid prescribing (e.g. 20-25 ml/kg/day):
Elderly patients
Patients with renal impairment or cardiac failure
Malnourished patients at risk of refeeding syndrome
The NICE guidelines give approximate requirements of maintenance IV fluids:
25 – 30 ml / kg / day of water
1 mmol / kg / day of sodium, potassium and chloride
50 – 100 g / day of glucose (this is to prevent ketosis, not to meet their nutritional needs)
The NICE guidelines suggest starting with 25-30 ml/kg/day of 0.18% sodium chloride in 4% glucose with 27 mmol/l of added potassium. This is available as a ready-made solution. They point out that more than 2.5 litres of this fluid increases the risk of hyponatraemia as it is hypotonic.
Nasogastric fluids or enteral feeding is preferable when maintenance needs are more than 3 days.
how fast to give maintenance fluids?
If giving 3 L per day = 8-hourly bags (24 ÷ 3).
If giving 2 L per day = 12-hourly bags (24 ÷ 2).
every time you prescribe fluids in real life, you must assess the pt.
Check the patient’s U&E to confirm what to give them.
Check that the patient is not fluid overloaded (e.g. increased jugular venous pressure (JVP), peripheral and pulmonary oedema).
Ensure that the patient’s bladder is not palpable (signifying urinary obstruction) if giving replacement fluids because of ‘reduced urine output’.
CIs for blood clot prophylaxis
bleeding, risk of bleeding (incl recent ischaemic stroke) - CIs for anticoagulants
peripheral arterial disease - absent foot pulses - CI for compression stockings
main indications for IV fluids
resuscitation eg sepsis or hypotension
replacement eg vomiting and diarrhoea
maintenance eg NBM due to bowel obstruction
Generally, IV fluids should be avoided if the patient can adequately meet their fluid requirements with oral fluids.
examples of crystalloid fluids
0.9% sodium chloride (“normal saline”)
5% dextrose
0.18% sodium chloride in 4% glucose
Hartmann’s solution
Plasma-Lyte 148
contents of Hartmann’s solution
water
sodium
chloride
potassium
calcium
lactate (helps to buffer the solution – reducing the risk of acidosis)
plasmalyte contents
water
na
cl
K
Mg
acetate (helps to buffer the solution – reducing the risk of acidosis)
gluconate (helps to buffer the solution – reducing the risk of acidosis)
give examples of isotonic, hypotonic and hypertonic solutions
Isotonic solutions (e.g., 0.9% saline, Hartmann’s and Plasma-Lyte) match the concentration of solutes (osmolality) in the plasma.
Hypotonic solutions (e.g., 5% dextrose and 0.18% sodium chloride) have a lower concentration of solutes than the plasma.
Hypertonic solutions (e.g., 3% saline) have a higher concentration of solutes than the plasma.
**Theoretically, if you dilute the blood with a hypotonic solution, water will flow out of the blood into the interstitial space. This is why hypotonic solutions (e.g., 5% dextrose) are not used for fluid resuscitation. Hypotonic solutions also carry a risk of hyponatraemia (low sodium) by diluting the sodium content of the blood.
signs of hypovolaemia
Hypotension (systolic < 100 mmHg)
Tachycardia (heart rate > 90)
Capillary refill time > 2 seconds
Cold peripheries
Raised respiratory rate
Dry mucous membranes
Reduced skin turgor
Reduced urine output
Sunken eyes
Reduced body weight from baseline
Feeling thirsty
IV fluid resuscitation general guideline -
The NICE guidelines suggest:
An initial 500 ml (250mL if elderly/HF) fluid bolus over 15 minutes (“stat”), followed by reassessment with an ABCDE approach
Repeat boluses of 250 – 500 mls of fluid if required, each time followed by a reassessment
Seek expert help if the patient is not responding, particularly after 2 litres of fluid
*generally IV normal saline is used
a more cautious approach to fluid resuscitation used in pts with HF, RF, elderly
adverse effects of overprescribing IV fluids
Too much fluid can lead to dilution of important components of the blood:
Sodium (with hypotonic solutions)
Potassium (if potassium is not included)
Other electrolytes, e.g., calcium or magnesium
Haemoglobin and haematocrit (red blood cells in the blood) causing anaemia
Clotting factors, platelets and fibrinogen causing coagulopathy (clotting problems)
which pts need additional caution and senior guidance ini order to avoid fluid overload
Elderly or frail patients
Significant oedema
Sodium imbalance (hyponatraemia or hypernatraemia)
Heart failure
Renal impairment
Liver impairment
practicality of prescribing maintenance fluid during normal working day
When prescribing maintenance fluids during a normal working day, try to ensure enough bags of fluid are prescribed to last through to the next working day (unless you want the fluids to stop). If the bag of fluid runs out at 2 AM and no further bags are prescribed, the on-call junior doctor will get a bleep to attend the ward and prescribe more fluids. Not only does this interrupt whatever that doctor is doing at the time, but they have to work out what to prescribe for a patient that they don’t know. This might involve waking the patient up, disturbing important rest. If the fluids are being stopped out of hours, remember to give clear instructions to the nurses and in the notes.
eg of loop diuretics
furosemide and bumetanide
nephron diagram
what is countercurrent multiplier in the nephrons? how do loop diuretics work?
the system of secreting solutes (Na+, K+ and Cl-) from the thick ascending loop (impermeable to water movement) to draw water out of the thin descending loop is called countercurrent multiplier. the loop of Henle is responsible for reabsorbing abt 20% of filtered sodium and 15% of filtered water.
loop diuretics work by blocking the function of the membrane Na-K-2Cl (NKCC2) cotransporter at the apical membrane of the thick ascending limb of the loop of Henle.
onset of action and duration of action for loop diuretics
start working within 1 hr if given PO and within 5 mins if given IV
effects last abt 6 hrs
best to give them earlier in the day and giving at night disrupts sleep, inc risk of falls.
adverse effects of loop diuretics
hypokalaemia
hypotension
AKI
urinary retention (where there is outflow restriction)
can worsen diabetic control and cause hyerglycaemia (hyperglycaemia is less likely than with thiazides)
exacerbate gout
ototoxicity
cautions/CIs for loop diuretics
hepatic encephalopathy
hypokalaemia
dehydrated/hypovolaemic pts
hyponatraemia
lithium treatment - can increase lithium lvls
eg of thiazide diuretics
bendroflumethiazide
indapamide
target of action of thiazide diuretics?
thiazide sensitive sodium chloride cotransporter on the luminal side of the epithelial cells in the distal convoluted tubules.
adverse effects of thiazide diuretics
dehydration and AKI
postural hypotension (esp in older, frail multimorbid pts)
hyponatraemia
hypocholraemia
hypokalaemia
hyperglycaemia - esp in diabetic pts
hypercalcaemia
raised urea - gout
thiazide diuretics to be used with caution in which pts?
frail pts
gout
diabetes
hypercalcaemia
onset of action and duration of action of thiazide diuretics
They act within 1 to 2 hours of oral administration and most have a duration of action of 12 to 24 hours; they are usually administered early in the day so that the diuresis does not interfere with sleep.
which diuretic can interact with which antihypertensive to cause severe hyperkalaemia
Administration of a potassium sparing diuretic to a patient receiving an ACE inhibitor or an angiotensin-II receptor antagonist can cause severe hyperkalaemia.
eg of situations where pt might need acute fluid resuscitation?
hypovolaemia -
eg
haemorrhage
severe D&V
burns
sepsis
eg of situations where pts may need maintenance fluids
reduced oral intake
eg bowel obstruction
perioperatively
AND
Patient unable to meet their fluid and/or electrolyte needs orally/enterally
what are the IV fluids available on the PSA database?
what are the diff blood products that can be used?
packed red cells
platelets
FFP
classic signs of hypovolaemia
tachycardia
low UO
low BP
initial fluid choice for fluid resus?
normal saline
what are the monitoring req when prescribing fluids?
fluid status
FBC and U&Es
BP, HR and UO
the 5Rs of prescribing IV fluids
Resuscitation
Routine maintenance
Replacement
Redistribution
Reassessment
wht pts will require fluid replacement and/or redistribution rather than fluid maintenance
Complex fluid issues - existing fluid/electrolyte deficits/excess
Electrolyte replacement issues
Abnormal fluid distribution issues (seek senior input)
ongoing abnormal fluid or electrolyte losses - how to prescribe fluids in these cases
Estimate amount of ongoing fluid or electrolyte losses
Add or subtract these estimates from the standard routine maintenance fluid regimen discussed in the last section to provide a more tailored fluid prescription.
what signs on clinical examination may suggest hypovolaemia
cool peripheries
prolonged CRT>2s
tachycardia
hypotension (incl postural)
dry mouth
reduced UO (but could be from hx rather than clinical exam unless pt has active fluid monitring)
metoclopramide to be avoided in -
CI: 3–4 days after gastrointestinal surgery; epilepsy; gastro-intestinal haemorrhage; gastro-intestinal obstruction; gastro-intestinal perforation; phaeochromocytoma
caution:
- pts with parkinson’s disease - due to risk of exacerbating symptoms as metoclopramide is a
dopamine antagonist - young women due to risk of dyskinesia, ie, unwanted movements especially acute dystonia
antiemetic choices?
check bnf before prescribing
pain relief options
An NSAID may be introduced at any stage regularly or ‘as required’ if not contraindicated. With neuropathic pain the first line treatment is amitriptyline (10 mg oral nightly) or pregabalin (75 mg oral 12 hourly); duloxetine is indicated in painful diabetic neuropathy.
practicalities of prescribing morphine sulphate
In order of increasing effectiveness, morphine sulphate may be given orally (as Oramorph®), subcutaneously or intravenously. Oramorph® is a liquid and comes in two strengths thus the strength must be specified and is usually 10 mg/5 mL. Remember, do not use trade names in prescriptions: if you wish to prescribe Oramorph you should still write MORPHINE SULPHATE 10mg/5ml.
rule with paracetamol prescribing
In ADULTS - ensure that no more than 4 g of paracetamol each day are given in total (look at co-codamol and paracetamol prescriptions)
NOTE in patients <50kg the MAXIMUM dose of Paracetamol is 500mg 6-hourly (2g in 24hrs).
why is domperidone safe to use in PD?
Metoclopramide and domperidone are both dopamine antagonists. Metoclopramide crosses the blood-brain barrier (BBB), and so exacerbates parkinsoninan symptoms by acting on central dopamine receptors. Domperidone does not cross the BBB, and so is safe to use in Parkinson’s disease.
why is combination of NSAIDs and ACEinhibitors threat to renal perfusion?
Ibuprofen inhibits prostaglandin synthesis which reduces renal artery diameter (and blood flow) and thereby reduces kidney perfusion and function. Ramipril, an ACE-inhibitor, reduces angiotensin-II production necessary for preserving glomerular filtration when the renal blood flow is reduced. In effect, NSAIDs combined with ACEi are a double threat to renal perfusion. The combination nips tight the afferent artery (the way in) and opens up the efferent artery (the way out).
typical presentation of antimuscarinic toxicity
Antimuscarinic drugs can cause confusion, particularly in the elderly. antimuscarinic agents commonly cause pupillary dilation, with loss of accommodation, dry mouth, and tachycardia (after a transient bradycardia)
drugs that can exacerbate/cause confusion (part in the elderly)?
oxybutynin (reduced doses are recommended in the elderly)
tramadol
cyclizine can cause drowsiness and confusion (reduced doses are recommended in the elderly)
BDZs
CIs and cautions for MTX
NSAIDs shd be used with caution in pts on MTX due to inc risk of nephrotoxicity
Methotrexate is contraindicated in active infection
Trimethoprim is a folate antagonist, and is a direct contraindication to patients taking methotrexate (another folate antagonist) due to the risk of bone marrow toxicity. This can lead to pancytopenia and neutropenic sepsis.
in prescription review section, what can be the problems with the medications?
- pt allergic to meds
- meds CI in pts conditions
- meds given wrong route, dose, freqeuncy
- meds interact with each other
- meds causing SEs/toxicity
- meds interact with each other
what shd ppl with migraine with aura NOT take?
Patients who have migraine with aura should not take the COCP as it significantly increases their risk of stroke
general rule for route of administration for insulin
as a rule all insulin is s/c except for sliding scales using short-acting insulin (e.g. Actrapid® or NovoRapid®) given by IV infusion OR in hyperkalaemia where actrapid is used WITH glucose
how much time to spend on prescribing and prescription review sections?
can spend 60 mins on them as they carry 112/200 marks
most worrying SE of clozapine
agranulocytosis resulting in neutropaenia
if an asthmatic pt is currently on NSAIDs but doesn’t have a wheeze with it, shd it be continued or stopped?
the NSAID could be continued as it would suggest her asthma was not NSAID-sensitive.
causes of anaemia
causes of high and low WCC
causes of thrombocytosis and thrombocytopaenia
thrombocytosis -
- reactive: bleeding, postsplenectomy, tissue damage (infection, inflammation, malignancy)
- primary: myeloproliferative disorders
Thrombocytopaenia:
- reduced production:
- infection (usually viral)
- drugs (eg penicillamine used in RA)
- myelodysplasia, myelofibrosis, myeloma
- increased destuction:
- heprin
- DIC
- ITP
- HUS/TTP
causes of hyponatraemia
assess fluid status
causes of hypernatraemia
causes all begin with ‘d’: dehydration; drips (i.e. too much IV saline); drugs (e.g. effervescent tablet preparations or intravenous preparations with a high sodium content); diabetes insipidus