Pharmacology quickfire Flashcards
CYP450
a) Inducers - CRAP GPS (induce me to madness)
b) Inhibitors - SICK FACES OMG
c) Effect of each on warfarin concentration
d) Effect of each on INR
CRAP GPS:
Carbamazepine
Rifampicin
Alcohol
Phenytoin
Griesofulvin (inhibits the mytotic spindle)
Phenobarbital
St John’s Wort, Sulfonylureas
SICK FACES OMG:
Sodium valproate
Isoniazid
Clarithromycin
Fluconazole
Alcohol
Ciprofloxacin
Ethambutol
SSRI
Omeprazole
Metronidazole
Grapefruit juice
Inducers -> induce CYP450 -> break down warfarin –> lower warfarin concentration –> lower INR
Inhibitors –> inhibit CYP450 –> warfarin accumulates –> higher warfarin concentration –> higher INR
Danger of thiazides + macrolides
Hypokalaemia, causing QT prolongation
Drugs causing vision disturbance
a) Yellow tinge
b) Blue tinge
a) Digoxin
b) Sildenafil (blue pills)
Methanol poisoning
Rx: fomepizole, or ethanol
Antibiotics with good anaerobic cover
Penicillin
Erythromycin
Metronidazole
Clindamycin
Doxycycline
Chloramphenicol
(gentamicin, ciprofloxacin, cephalosporins - all have poor anaerobe cover)
NSAID overdose
a) Presentation
b) Diagnosis
c) Treatment
a) GI upset, CNS depression, seizures (most likely with mefenamic acid), metabolic acidosis, multi-organ failure
b) Clinical. NSAID screens not done routinely
c) No antidote
Charcoal if within 1 hour
PPI
Supportive
Digoxin
a) pharmacokinetics
b) loading doses and monitoring
c) who to avoid in?
d) interactions
a) - Oral bioavailability 65%
- Peak serum concentration takes around 6 hours
- Highly protein bound
- Wide tissue distribution
- Hydrophilic
- Renally excreted
- Half life 30-40 hours in normal renal function
b) - In stable arrhythmia - loading with 125-250 mcg usually
- In unstable arrhythmia - loading with 750-1000 mcg (oral or IV)
- In chronic heart failure - loading not needed
- Routine monitoring not indicated. Levels taken if toxicity suspected
c) - WPW
- Heart block
- VT
- Caution in the elderly/poor renal impairment
- Hypokalaemia
- Recent MI
d) Amiodarone, verapamil. diltiazem, macrolides, spironolactone
Digoxin toxicity
a) Therapeutic range for digoxin
b) Toxicity can occur at what levels?
c) RFs - patient, metabolic, interactions
d) Explain relationship between potassium and digoxin
e) Signs and symptoms of toxicity
f) Investigations
g) Management
a) 0.7 - 2.0
b) Can occur within therapeutic range
<1.5 unlikely unless there is significant hypokalaemia
1.5 - 3.0 digoxin toxicity is possible
>3.0 digoxin toxicity is likely
c) - Elderly, poor renal impairment, dehydration, hypothyroidism
- Hypokalaemia, hypomagnesaemia
- Concurrent use of drugs which can increase digoxin levels (amiodarone, verapamil, diltiazem, macrolides, spironolactone)
d) - Digoxin binds to Na/K/ATPase channel on cardiac myocytes, at the same receptor as K+ ions, leading to reduced K+ ions entering the cells
- HYPOkalaemia increases risk of toxicity as there are fewer competitive K+ ions for digoxin
- Digoxin toxicity leads to HYPERkalaemia as fewer K+ ions are able to bind to Na/K/ATPase and enter the cells
e) - GI upset - nausea, vomiting, abdo pain, diarrhoea
- Vision - yellow colour vision (xanthopsia)
- CNS - confusion
- CV - AV block causing bradycardia, increased automaticity causing tachyarrhythmias (atrial and ventricular)
f) - Digoxin level (take 8-12 hours after the last dose)
- U&E (renal function, K+)
- Cardiac monitoring
g) - If stable - supportive, correct any electrolyte imbalance
- If unstable - Digibind (may try atropine first if bradyarrhythmias)
First order vs. zero order kinetics
a) Explain difference
b) If drug concentration = 500 mmol/L, and half life is 5 hours, what is the concentration after 20 hours in a drug with first vs. zero order kinetics
First order:
- Drug elimination rate depends on the drug concentration
- Concentration reduces by half with every half life
Zero order:
- Drug elimination at same rate irrespective of drug concentration
- “They give ZERO f*cks about the drug concentration”
b) Drug concentration = 500 mmol/L at T0
First order kinetics:
- 20 hours = 4 half lives
- 500 –> 250 –> 125 –> 62.5 –> 31.25 mmol/L
Zero order kinetics:
- Half drug is gone after 5 hours
- So all the drug is gone after 10 hours
- (no drug present at 20 hours)
Warfarin and high INR: management
a) Major bleeding if INR above therapeutic range
b) INR >8 with minor bleeding vs no bleeding
c) INR 5-8 with minor bleeding vs no bleeding
a) Major bleeding:
- Stop warfarin
- Urgent 1-3mg IV phytomenadione
- Urgent Beriplex (PTC), or FFP if Beriplex is unavailable
b) INR >8 with minor bleeding:
- stop warfarin
- 1-3mg IV phytomenadione
- The dose of phytomenadione may be repeated after 24 hours if the INR is still too high.
- Restart warfarin when the INR is less than 5.
INR >8 with no bleeding:
- stop warfarin
- 5mg ORAL phytomenadione (using the intravenous preparation orally
- The dose of phytomenadione may be repeated after 24 hours if the INR is still too high.
- Restart warfarin when the INR is less than 5.
c) INR 5–8 with minor bleeding:
- stop warfarin
- 1-3 mg IV phytomenadione
- Restart warfarin when the INR is less than 5.
INR 5–8 with no bleeding:
- withhold 1 or 2 doses of warfarin and reduce subsequent maintenance dose.
Ethylene glycol ingestion
a) Biochemical findings
b) Management
a) HAGMA
b) - Fomepizole (Acetaldehyde dehydrogenase inhibitor)
- ITU Care
- Sodium bicarb if pH <7.2
Sodium nitroprusside infusion for malignant hypertension. Has deterioration with nausea, vomiting, chest and abdo pain, hypotension and tachycardia. VBG shows significant metabolic acidosis - cause?
Cyanide poisoning
(from denaturing of the sodium nitroprusside)
Allopurinol - dangerous interaction
Azathioprine or 6-mercaptopurine
- Xanthine oxidase is needed to metabolise thiopurines
- So allopurinol may cause toxic levels of thiopurines
Benzodiazepine overdose - when to use flumazenil and when not to
If on long-term benzos, do not use flumazenil as this increases the risk of benzo-withdrawal seizures
If acute benzo overdose without long-term use, can use flumazenil
Cocaine body packing - management
If symptomatic - urgent surgical referral as this indicates packet rupture
If asymptomatic - laxatives and observe with repeat X-rays
