MEDizzy - A patient with Alzheimer’s disease is taking an

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Pharmacology Of The Peripheral Nervous Systems 1

A patient with Alzheimer’s disease is taking an acetylcholinesterase inhibitor specifically approved for that indication, primarily because it is quite lipophilic and so enters the CNS well. Which of the following drugs is the patient most likely receiving?

ExplanationPatients with Alzheimer’s disease present with progressive impairment of memory and cognitive functions such as a lack of attention, disturbed language function, and an inability to complete common tasks. Although the exact defect in the central nervous system (CNS) has not been elucidated, evidence suggests that a reduction in cholinergic nerve function or receptor activation plays an important role in the etiology. At the very least, increasing central cholinergic receptor activation seems to reduce symptom severity. Tacrine has been found to be somewhat effective in patients with mild-to-moderate symptoms of this disease for improvement of cognitive functions. The drug is primarily a reversible cholinesterase inhibitor that increases the concentration of functional ACh in the brain. However, the pharmacology of tacrine is complex; the drug also acts as a muscarinic receptor modulator in that it has partial agonistic activity, as well as weak antagonistic activity on muscarinic receptors in the CNS. In addition, tacrine appears to enhance the release of ACh from cholinergic nerves, and it may alter the concentrations of other neurotransmitters such as dopamine and NE. Of all the reversible cholinesterase inhibitors, only tacrine and physostigmine cross the blood-brain barrier in sufficient amounts to make these compounds useful for disorders involving the CNS. Physostigmine has been tried as a therapy for Alzheimer’s disease; however, it is more commonly used to antagonize the effects of toxic concentrations of drugs with antimuscarinic properties, including atropine, antihistamines, phenothiazines, and tricyclic antidepressants. Neostigmine, pyridostigmine, and ambenonium are used mainly in the treatment of myasthenia gravis; edrophonium is useful for the diagnosis of this disease because of its fast onset and short duration.