McKenna's Pharmacology for Nursing, 2e

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P A R T 5  Drugs acting on the autonomic nervous system

TABLE 32.2

DRUGS IN FOCUS Indirect-acting cholinergic agonists

Drug name

Dosage/route

Usual indications

Agents for myasthenia gravis edrophonium (generic)

Diagnosis: 2 mg IV over 15–30 seconds, then 8 mg IV if response was seen or 10 mg IM, repeat with 2 mg IM in 12 hours to rule out false-negative results Paediatric (diagnosis only): 0.5–2 mg IV based on weight, or 2–5 mg IM Adult: 0.5 mg SC or IM for control; 0.022 mg/kg IM for diagnosis; 0.5–2 mg IV as antidote, maximum dose 5 mg Paediatric: 0.01–0.04 mg/kg/dose IM, IV or SC for control q 2– 3 hours; 0.04 mg/kg IM for diagnosis; 0.07–0.08 mg/kg IV, slowly, for antidote Adult: 60–180 mg PO b.d. to q.i.d Paediatric: 7 mg/day PO in five or six divided doses for myasthenia gravis

Diagnosis of myasthenia gravis; reversal of toxicity from non-depolarising neuromuscular junction–blocking drugs, which are used to paralyse muscles during surgery (see Chapter 28) Diagnosis and management of myasthenia gravis; reversal of toxicity from non-depolarising neuromuscular junction–blocking drugs, which are used to paralyse muscles during surgery (see Chapter 28) Management of myasthenia gravis; antidote to neuromuscular junction blockers; increases survival after exposure to nerve gas Management of Alzheimer’s dementia, including severe dementia Management of mild to moderate Alzheimer’s dementia delays progression of disease

neostigmine (generic)

pyridostigmine (Mestinon)

Agents for Alzheimer’s disease donepezil (Aricept)

5–10 mg PO daily at bedtime

galantamine (Galantyl, Reminyl)

4–12 mg PO b.d.; reduce dose to 16 mg/day maximum with renal or hepatic impairment; available as an oral solution 4 mg/mL; range 16–32 mg/day; extended release tablets, range 16–24 mg/day taken as a single dose 1.5–6 mg PO b.d., based on response and tolerance; transdermal system, one 4.6 mg/24 hours patch placed once a day, maximum 9.5 mg/24 hours

rivastigmine (Exelon)

Management of mild to moderate Alzheimer’s dementia; treatment of dementia related to Parkinson’s disease

■■ BOX 32.5  A new drug for treating Alzheimer’s disease

In 2003, the Therapeutic Goods Administration approved a new drug for treating Alzheimer’s disease. The drug, memantine hydrochloride ( Ebixa, Memanxa ), has been used in Europe for several years and has been reported to slow the memory loss of people with moderate to severe dementia associated with Alzheimer’s disease. Memantine has a low to moderate affinity for N -methyl- d -aspartate (NMDA) receptors with no effects on dopamine, gamma-aminobutyric acid, histamine, glycine or adrenergic receptor sites. It is thought that persistent activation of the CNS NMDA receptors contributes to the symptoms of Alzheimer’s disease.

Pharmacokinetics Anticholinesterase inhibitors are well absorbed after oral administration and distributed throughout the body. The sites of metabolism and excretion for all of these drugs are not known. It is thought that they are metabolised at the nerve synapse or in the tissues. By blocking these sites, it is thought that the symptoms are reduced or delayed. The drug is available in a tablet form, and an oral solution and is started at 5 mg/day PO, increasing by 5 mg/day at weekly intervals. The target dose is 20 mg/day given as 10 mg twice daily. Dose reduction should be considered in individuals with renal impairment. Headache, dizziness, fatigue, confusion and constipation are common adverse effects. The drug should not be taken with anything that alkalinises the urine. Sufferers and family members need to understand that this drug is not a cure but may offer some extended time with mild symptoms.

and parasympathetic crisis—and to reverse the effects of non-depolarising neuromuscular junction blockers used to cause paralysis in surgery. See Table 32.2 for usual indications for each drug.