McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 2 Cholinergic agonists

KEY POINTS

■■ Alzheimer’s disease is a progressive dementia characterised by a loss of ACh-producing neurons and ACh receptor sites in the neurocortex. ■■ Acetylcholinesterase inhibitors that cross the blood– brain barrier are used to manage Alzheimer’s disease by increasing ACh levels in the brain and slowing the progression of the disease.

■■ Myasthenia gravis is an autoimmune disease characterised by antibodies to the ACh receptors. This results in a loss of ACh receptors and eventual loss of response at the neuromuscular junction. ■■ Acetylcholinesterase inhibitors are used to treat myasthenia gravis because they allow the accumulation of ACh in the synaptic cleft, prolonging stimulation of any ACh sites that remain.

CRITICAL THINKING SCENARIO Indirect-acting cholinergic agonists

THE SITUATION A.J., a 75-year-old man with an unremarkable medical history, is seen in the clinic for evaluation of memory loss and confusion. Three years ago, his wife began to notice memory gaps and confusion when A.J. was driving around town. He would get lost only a few blocks from home. The problem has become steadily worse. He was diagnosed with Alzheimer’s disease after neurological tests and medical evaluation ruled out other causes for his problem. He did not want to take any drugs, but when he heard the diagnosis, he became quite frightened and agreed to try medication. His wife states that she is somewhat concerned about giving him medication because he has sometimes had trouble swallowing and chokes on his food. She excitedly tells A.J. that once he starts the medication, his memory will return and things will be normal again. A.J. is placed on rivastigmine. CRITICAL THINKING What could be responsible for A.J.’s symptoms? What modifications can be made to the prescription to ensure A.J.’s safety if he is having trouble swallowing? What important information about the disease and the effectiveness of drug therapy needs to be discussed with A.J. and his wife ? Will things return to normal? What potential adverse effects can be anticipated with rivastigmine, and how might these effects complicate the situation for A.J. and his wife? DISCUSSION Alzheimer’s disease is a chronic, progressive disease that involves the loss of neurons in the cortex of the brain that are responsible for making connections between different memories. A.J. has had the problem for at least 3 years, and his loss of memory and confusion have become worse over that period of time. Unfortunately, there is nothing available at this time that can stop the loss of neurons or restore the function that has already been lost.

One of the problems that occur with Alzheimer’s disease is difficulty swallowing. Swallowing is a complex CNS reflex that requires coordination of impulses, and with this disease, the ability to swallow in a coordinated manner is often lost. This can lead to aspiration and pneumonia, which are often the underlying causes of death with Alzheimer’s disease. Since A.J. already has some difficulty swallowing, it would be important to look into the forms in which rivastigmine is provided. In this case, the drug is available in capsule form and as an oral solution. The oral solution might be suggested because it could be much easier to swallow. As the disease progresses, this drug is also available as a transdermal system, which would eliminate the need to swallow the drug. The status of A.J.’s swallowing should be evaluated before starting therapy and periodically as time goes on to determine how safe the dosage form of the drug is for his particular situation. A.J. and his wife should receive information on Alzheimer’s disease and its progression. The drugs available at this time do not reverse the memory loss and they do not cure the disease. A.J.’s wife may be encouraged to monitor A.J.’s behaviour, ability to perform activities of daily living and other significant markers of importance to them. The drug should slow the progression of the disease and it might be helpful to monitor progress to see if the drug is being effective. She might also want to become involved in an Alzheimer’s support group or organisation, which could provide valuable support, educational materials and access to community resources. This is an overwhelming diagnosis and it might be necessary to approach these individuals over several visits to give them both time to adjust. It is important to always include a family member and provide information in writing for later reference when doing teaching with a person with Alzheimer’s disease. Many of the adverse effects associated with the indirect-acting cholinergic agonists are a result of the parasym-pathetic stimulation caused by these drugs and may complicate A.J.’s care as his disease progresses. GI effects can include increased salivation, which may further