McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 2 Cholinergic agonists

■ ■ Evaluate the effectiveness of the teaching plan (person can name drug, dosage, adverse effects to watch for and specific measures to avoid them, and proper administration of ophthalmic drugs). ■ ■ Monitor the effectiveness of comfort and safety measures and compliance with the regimen.

to determine the effectiveness of therapy and evaluate for any potential adverse effects. ■ ■ Assess vital signs, including pulse and blood pressure, and cardiopulmonary status, including heart and lung sounds, to evaluate for changes related to cardiovascular effects of parasympathetic activity ; obtain an electrocardiogram (ECG) as indicated to evaluate heart rate and rhythm. ■ ■ Assess abdomen, auscultating for bowel sounds ; palpate bladder for distension. ■ ■ Monitor intake and output, noting any complaints of urinary urgency, to monitor for drug effects on the urinary system. Implementation with rationale ■ ■ Ensure proper administration of ophthalmic preparations to increase the effectiveness of drug therapy and minimise the risk of systemic absorption. ■ ■ Administer oral drug on an empty stomach to decrease nausea and vomiting. ■ ■ Monitor response closely, including blood pressure, ECG, urine output and cardiac output, and arrange to adjust dose accordingly to ensure the most benefit with the least amount of toxicity. Maintain a cholinergic blocking drug on standby such as atropine to use as an antidote for excessive doses of cholinergic drugs (see Focus on safe medication administration in discussion of Agents for myasthenia gravis in this chapter) to reverse overdose or counteract severe reactions (see Chapter 33 for further discussion of atropine). ■ ■ Provide safety precautions if the person reports poor visual acuity in dim light to prevent injury. ■ ■ Monitor urinary output to evaluate effects on the bladder ; ensure ready access to bathroom facilities as needed with GI stimulation. ■ ■ Provide thorough teaching, including drug name, dosage and schedule of administration; administration of oral forms before meals or without food; proper administration for ophthalmic preparations as indicated; measures to prevent or minimise adverse effects; need for readily available access to toileting facilities; warning signs of problems; and importance of follow-up and evaluation. Evaluation ■ ■ Monitor response to the drug (improvement in bladder function, increased salivation, miosis). ■ ■ Monitor for adverse effects (cardiovascular changes, GI stimulation, urinary urgency, respiratory distress).

KEY POINTS

■■ Cholinergic agonists stimulate the parasympathetic nerves, some nerves in the brain and the neuromuscular junction at the same site that ACh does. ■■ Cholinergic agonists are used topically in the eye to produce miosis (pupillary constriction) and treat glaucoma. ■■ Systemically, these agents are used to increase bladder tone (e.g. postoperative or postpartum) and to increase secretions to relieve dry mouth associated with Sjögren’s syndrome.

INDIRECT-ACTING CHOLINERGIC AGONISTS

The indirect-acting cholinergic agonists do not react directly with ACh receptor sites; instead, they react chemically with acetylcholinesterase (the enzyme responsible for the breakdown of ACh) in the synaptic cleft to prevent it from breaking down ACh. As a result, the ACh that is released from the presynaptic nerve remains in the area and accumulates, stimulating the ACh receptors for a longer period of time than normally expected. These drugs work at all ACh receptors, in the parasympathetic nervous system, in the central nervous system (CNS) and at the neuromuscular junction. Most of these drugs bind reversibly to acetylcholinesterase, so their effects pass with time when the acetylcholinesterase is released and allowed to break down ACh. However, there are certain indirect-acting cholinergic agonists that irreversibly bind to acetylcholinesterase. These drugs are not used therapeutically; they are being developed as nerve gas to be used as weapons (Box 32.2). Because these drugs might be encountered in a war situation, it is important to have an antidote readily available to military personnel and any civilian who might be affected. Pralidoxime is the antidote developed for the irreversible indirect-acting cholinergic agonists and is also used to reverse poisoning associated with organo- phosphate pesticides (Box 32.3). The reversible indirect-acting cholinergic agonists fall into two main categories: (1) agents used to treat myasthenia gravis; and (2) agents used to treat Alzheimer’s disease.