McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 2 Cholinergic agonists

Cultural considerations

Safe medication administration

BOX 32.4

Therapeutic actions and indications The indirect-acting cholinergic agonists work by revers- ibly blocking acetylcholinesterase at the synaptic cleft. This blocking allows the accumulation of ACh released from the nerve endings and leads to increased and pro- longed stimulation of ACh receptor sites at all of the postsynaptic cholinergic sites. Indirect-acting cholin- ergic agonists work to relieve the signs and symptoms of myasthenia gravis and increase muscle strength by allowing ACh to accumulate in the synaptic cleft at neuromuscular junctions. Indirect-acting choliner- gic agonists that more readily cross the blood–brain barrier and seem to affect mostly the cells in the cortex to increase ACh concentration in the area of the brain where ACh-producing cells are dying, affecting memory and the ability to access and link different memories, are used in the treatment of Alzheimer’s disease. In addition to usual indications, pyridostigmine has also recently been approved for military personnel to increase survival after exposure to particular nerve gases —irreversible acetylcholinesterase inhibitors used in warfare to cause paralysis and death by prolonged muscle contraction Alzheimer’s disease Alzheimer’s disease is a chronic, progressive disease on the brain’s cortex. Eventually it results in memory loss so severe that the person may not remember how to perform basic activities of daily living and may not recognise close family members. Although Alzheimer’s disease primarily strikes the elderly, it has a tremendous impact on family members of all ages. For example, adult children of Alzheimer’s sufferers, many of whom are busy raising children of their own, may find themselves in the role of caregivers—in essence, becoming parents of their parent.This new role can put tremendous stress on individuals who are trying to struggle with work, family and issues related to their parent’s care. When caring for an Alzheimer’s sufferer and family, the health professional must remember that the person’s cultural background can affect how the family copes. For instance, those who tend to have solid extended families or who are part of communities that offer strong social support and interdependence may be better equipped to deal with caring for the person as the disease progresses. In contrast, families that are more goal and achievement oriented and who value autonomy and independence may find themselves overwhelmed by the person’s needs and may require more support and referrals to community resources. The health professional is in the best position to evaluate the family situation. By approaching each situation as unique and striving to incorporate cultural and social norms into the considerations for care, the health professional can help to ease the family’s burden while also maintaining the dignity of the person and the family through this difficult experience.

Myasthenic crisis versus cholinergic crisis

Myasthenia gravis is an autoimmune disease that runs an unpredictable course throughout the person’s life. Often, the disease goes through an intense phase called a myasthenic crisis, marked by extreme muscle weakness and respiratory difficulty. Because of the variability of the disease and the tendency to have crises and periods of remission, management of the drug dose for a person with myasthenia gravis is a challenge. If a person goes into remission, a smaller dose is needed. If a person has a crisis, an increased dose is needed. To further complicate the clinical picture, the presentation of a cholinergic overdose or cholinergic crisis is similar to the presentation of a myasthenic crisis. The individual with a cholinergic crisis presents with progressive muscle weakness and respiratory difficulty as the accumulation of ACh at the cholinergic receptor site leads to reduced impulse transmission and muscle weakness. This is a crisis when the respiratory muscles are involved. For a myasthenic crisis, the correct treatment is increased cholinergic drug. However, treatment of a cholinergic crisis requires withdrawal of the drug. The person’s respiratory difficulty usually necessitates acute medical attention. At this point, the drug edrophonium can be used as a diagnostic agent to distinguish the two conditions. If the person improves immediately after the edrophonium injection, the problem is a myasthenic crisis, which is improved by administration of the cholinergic drug. If the person gets worse, the problem is probably a cholinergic crisis, and withdrawal of the person’s cholinergic drug along with intense medical support is indicated. Atropine helps to alleviate some of the parasympathetic reactions to the cholinergic drug. However, because atropine is not effective at the neuromuscular junction, only time will reverse the drug toxicity. The person and significant others will need support, teaching and encouragement to deal with the tricky regulation of the cholinergic medication throughout the course of the disease. Health professionals in the acute care setting need to be mindful of the difficulty in distinguishing drug toxicity from the need for more drug—and be prepared to respond appropriately. The drugs used to help people with this progressive disease are several indirect-acting cholinergic agonists that do not cross the blood–brain barrier and do not effect ACh transmission in the brain (see Table 32.2). These drugs include edrophonium (generic), neostigmine (generic) and pyridostigmine (Mestinon).

Alzheimer’s disease. This drug works in a unique way to slow the effects of this disease and is the only drug of its class that is available (Box 32.5).