Parkinsons And Myasthenia Gravis Flashcards
Describe the synthesis of dopamine
L- tyrosine to L-DOPA using tyrosine hydroxylase
L-DOPA to dopamine using DOPA decarboxylase
Dopamine to norepinephrine using dopamine B hydroxylase
Norepinephrine to epinephrine
Outline the breakdown of dopamine
Dopamine to 3 O methyldopa using catechol O methyl transferase (COMT)
3 O methyldopa to homovnailic acid using MAO
Or
Dopamine to 3,4-dihydrophenyl acetic acid using MAO
3,4-dihydtophenyl acetic acid to homovanilic acid using COMT
How can you measure dopamine uptake?
DAT scan
What is the standard treatment for Parkinson’s?
Levodopa + DOPA decarboxylase inhibitor (to prevent peripheral conversion)
What are the major ADRs for Levodopa?
Psychosis, schizophrenia, hallucinations, delusion, nausea, hypotension
What are the main DDIs for Levodopa?
Vit B6 increases peripheral L-DOPA
With MAO inhibitors risks hypertensive crisis
Antipsychotic drugs block dopamine receptors
What are some of the ADRs for dopamine receptor agonists?
Sedation, hallucination, nausea, hypotension
Impulse disorders e.g. Pathological gambling
How do MAO inhibitors work?
Enhance the effect of dopamine by reducing the breakdown
How do COMT inhibitors work?
Reduce the peripheral breakdown of L-DOPA to 3 O methyldopa which competes with L-DOPA for transport across to the CNS
What is the pathophysiology of myasthenia graves and what are the symptoms?
IGG receptor antibodies bind to ACh receptors so that ACh can not bind and broken down by acetylcholinesterase. Symptoms include fatigueable muscles, weak muscles e.g. Lid drooping
What drugs acting at neuromuscular transmission can exacerbate myasthenia graves?
Aminoglycosides, beta blockers, quinine, ACE inhibitors
What drug class is used to treat myasthenia graves and name an example
Acetylcholinesterase inhibitors e.g. Pyridostigmine
What are the cholinergic side effects?
Salivation, sweating, lacrimation, urinary incontinence, diarrhoea, GI upset, emesis (vomiting)
