OSCE Flashcards
what is the mechanism of action amiodarone
Target: non-selective for Na channel, Ca channel and α-adrenoceptors
Action: Non-selective inhibitor of the above channels and receptor Effect: prolongs the cardiac action potential seen as an increase in the QT interval on the ECG
Overall effect: Class III antiarrhythmic effect
what are the side effects of amiodarone
Common side effects: Corneal microdeposits
Important:
Thyoid disorders – hypothyroidism, hyperthyroidism
Pulmonary fibrosis
Phototoxicity
Peripheral neuropathy
Optic neuritis/neuropathy (can lead to blindness)
Hepatotoxicity
Slate-grey skin discolouration
what are the interactions of amiodarone
Other anti-arrhythmic (increased myocardial depression)
Digoxin (amiodarone increases plasma digoxin concentration – halve digoxin dose)
Warfarin (increased anticoagulant effect)
Beta blockers, calcium channel blockers (increased risk of bradycardia, AV block and myocardial depression)
Simvastatin (increased risk of myopathy)
Tricyclic antidepressants (increased risk of ventricular arrhythmias)
Phenytoin (increased plasma phenytoin concentration)
Lithium (increased risk of ventricular arrhythmias)
what is the therapeutic indication of amiodarone
Starting dose – 200mg 3 times daily for 1 week then twice daily for the following week Maintenance dose – 200mg once daily
what formulations does amiodarone come in
Tablet, injection, solution
how is amiodrone metabolised
This drug is metabolized to the main metabolite desethylamiodarone (DEA) by the CYP3A4 and CYP2C8 enzymes.
Metabolised in the liver
how is amiodarone excreted
Via the liver and bile
what are the contraindications of amiodarone
Caution in heart failure and the elderly
Avoid in sinus bradycardia, sino-atrial heart block, thyroid dysfunction and iodine sensitivity
Avoid intravenous amiodarone in severe respiratory failure, circulatory collapse and severe arterial hypotension
Discontinue if patient develops optic neuritis/neuropathy
what are brand names for amiodarone
Cordarone, Nexterone
what is the absorption of amiodarone
The bioavailability is between 35-65%
what is the MoA of Amitriptyline
Target: Noradrenaline and serotonin reuptake transporters on the pre-synaptic neuronal membrane
Action: Inhibitor
Effect: Prevent re-uptake and subsequent degradation of the monoamine neurotransmitters serotonin and noradrenaline from the synaptic cleft
Overall effect: Prolonged presence of serotonin and noradrenaline in the synaptic cleft leads to prolonged neuronal activity – in mood disorders such as depression there are low levels of these neurotransmitters in the brain. TCAs therefore restore the concentration to normal levels.
what is the absorption of Amitriptyline-
The bioavailability is between 30-60%
what is the distribution of amitriptyline
Widely distributed around the body. The protein binding is around 95%
how is amitriptyline metabolised
Metabolised in the liver and CYP2D6, CYP2C19, CYP3A4
how is amitriptyline excreted
Excreted as urine around 12-80%
what formulations does amitriptyline come in
Tablets, solutions, capsule
what is the therapeutic indication for amitriptyline
Starting dose – 75mg daily (30-75mg if elderly) (lower doses for indications other than depression)in divided doses or as a single dose nocte
Maintenance dose – varies depending on drug; for amitriptyline 150-200mg
what are the side effects for amitriptyline
Antimuscarinic effects – dry mouth, blurred vision, constipation, urinary retention
CNS side effects (particularly in elderly) e.g. anxiety, dizziness, agitation, confusion
Weight gain
Important:
**Cardiotoxic in overdose – caution in patients at risk of suicide
Neuroleptic malignant syndrome
Hyponatraemia (particularly in elderly)
what are the interactions for amitriptyline
**MAOIs (risk of hypertensive crisis and hyperthermia) – do not start a tricyclic until 2 weeks after stopping an MAOI and vice versa, do not co-prescribe
Antiepileptics (seizure threshold lowered)
Alcohol (increased sedative effect)
Anti-arrhythmics (increased risk of ventricular arrhythmias)
what are the contraindications for Amitriptyline
Caution in cardiovascular disease, hepatic impairment (avoid if severe), hyperthyroidism, epilepsy, diabetes, prostatic hypertrophy, chronic constipation, urinary retention, glaucoma, the elderly and those at high risk of falls and of suicide
Avoid following MI, in heart block and in the manic phase of bipolar disorder
Discontinue if patient enters a manic phase
what is the brand name for amitriptyline
Elavil
what is the MoA of Azathioprine
Azathioprine is metabolised to the 6- mercaptopurine, which is then converted intracellularly to purine analogues. These purine analogues are incorporated into DNA and inhibit clonal expansion of B lymphocytes during the induction phase of the immune response. This results in suppression of the antibody-mediated response.
what is the absorption of Azathioprine
The bioavailability is 60%
what is the distribution of Azathioprine
Protein binding is between 20-30%