Antiparkinsonism-Anticholinergic Drugs - Pharmacology

Antiparkinsonism-anticholinergic drugs are used to treat the early stages of Parkinson’s disease. These are typically combined with levodopa to control parkinsonism or alone to treat pseudoparkinsonism. These are the parkinsonism-like side effects of phenothiazines, which is an antipsychotic medication.

Drugs for Parkinsonism

Parkinsonism, better known as Parkinson’s disease, is a chronic neurological disorder that affects balance and locomotion at the extrapyramidal motor tract. It is considered a syndrome because it has a combination of symptoms. Parkinsonism has three major features. These are rigidity, bradykinesia (slow movements), and tremors.

Rigidity is the abnormal increase in muscle tone that causes the patient to make postural changes such a shuffling gate, the chest and head is thrust forward, and knees and hips are flexed. The patient walks without swinging his arms. These movements are slow (bradykinesia) and the patient exhibits involuntary tremors of the head and neck which may be more prevalent at rest and pill-rolling movements of the hands. Another characteristic symptoms is the masked facies (no facial expression) common in patients with Parkinson’s disease.

There are four types of drugs used to treat Parkinson’s disease: dopaminergics, dopamine agonists, MAO-B inhibitors, and anticholinergics which have been discussed previously in this chapter.

Dopaminergics decrease the symptoms of Parkinson’s disease by permitting more levodopa to reach the nerve terminal where levodopa is transformed into dopamine and the tremors are reduced.

Dopamine agonists stimulate the dopamine receptors and reduce the symptoms of Parkinson’s disease. MAO-B inhibitors inhibit the catabolic enzymes that break down dopamine thereby extending the effects of dopamine. However they can cause a hypertensive crisis if taken with certain foods (see MAO inhibitors can cause a hypertensive crisis if taken with these foods).

MAO inhibitors can cause a hypertensive crisis if taken with these foods.

TABLE : MAO inhibitors can cause a hypertensive crisis if taken with these foods.

MUSCLE SPASMS AND PAIN

Muscle spasms and pain are associated with traumatic injuries and many chronic debilitating disorders such as multiple sclerosis. Spasms are caused by hyperex-citable neurons stimulated by cerebral neurons or from lack of inhibition of the stimulus in the spinal cord or at the skeletal muscles.

Muscle relaxants are used to treats muscle spasms. There are two groups of muscle relaxants: centrally acting and peripherally acting. Centrally acting muscle relaxants depress neuron activity in the spinal cord or in the brain. They are used to treat acute spasms from muscle trauma, but are less effective for treating spasms caused by chronic neurological disorders.

Centrally acting muscle relaxants

Carisoprodol (Soma), Cyclobenzaprine (Flexeril) and Methocarbamol (Robaxin).

These drugs decrease pain, increase range of motion and have a sedative effect on the patient. Centrally acting muscle relaxants should not be taken concurrently with central nervous system depressants such as barbiturates, narcotics, and alcohol.

Diazepam (Valium) and Baclofen (Lioresal)

These are used to treat acute spasms from muscle trauma and for treating spasms caused by chronic neurologic disorders.

Dantrolene sodium (Dantrium)

This is a peripherally acting muscle relaxant. Peripherally acting muscle relax¬ants depress neuron activity at the skeletal muscles and have a minimal effect on the central nervous system. These are most effective for spasticity or muscle contractions caused by chronic neurologic disorders. This is also used to treat malignant hypertension which is an allergic reaction to anesthesia.

MYASTHENIA GRAVIS

Myasthenia gravis is a disease where nerve impulses don’t reach the nerves in muscle endings (myoneural junction) because of an inadequate secretion of or loss of acetylcholine due to action of acetylcholinesterase, an enzyme that destroys acetylcholine at the myoneural junction.

Patients experience fatigue and muscle weakness—particularly in respiratory muscles, facial muscles, and muscles in the extremities. They have drooping eyelids (ptosis) and difficulty in chewing and swallowing and their respiratory muscles become paralyzed which leads to respiratory arrest. Acetylcholinesterase (ACE inhibitors) are used to treat the symptoms of this disease. They include ambenonium (Mytelase), edrophoniumCl (Tensilon), Neostigmine bromide (Prostigmin), and Pyridostigmine bromide (Mestinon).

MULTIPLE SCLEROSIS

Multiple sclerosis (MS) is an autoimmune disease affecting the central nervous system. Multiple lesions of the myelin sheath that surround the nerve fibers occur that are called plaque. Myelin enables nerves to conduct impulses.

Because some axons are spared, symptoms are different in each patient. The absence of the myelin causes impulses to jump or not transmit at all. MS patients can live a normal life span. At times patients don’t experience symptoms and other times symptoms can become severe and debilitating. These patients are said to have relapsing-remitting multiple sclerosis. Other patients have no periods of remission.

There is no cure for MS. However, the disease is treated symptomatically using several medications.

Corticosteroids

These are used for treating periods when the patient experiences symptoms of MS (exacerbations). These are also known as attacks, relapses and flare-ups.

Interferonß-1B (betaseron) and interferonß-1a (avonex)

These are used to reduce the frequency and severity of relapses.

Copolymer 1

This drug is in clinical trials and appears to decrease the disease’s activity.

Copaxone (glatiramer acetate injection)

This drug reduces new brain lesions and the frequency of relapses in people with relapsing-remitting multiple sclerosis.

ALZHEIMER’S DISEASE

Alzheimer’s disease is a form of dementia common in older people that affects the patient’s ability to carry out daily activities. Part of the patient’s brain that controls thought, memory, and language becomes impaired.

Four and a half million Americans are afflicted with Alzheimer’s disease. Alzheimer’s disease affects 5% of people between 65 and 74 years of age and half of those older than 85 years. Alzheimer’s disease is not part of the aging process.

Although the cause of Alzheimer’s disease remains unknown, investigators have discovered Alzheimer’s patients have abnormal clumps of amyloid plaques and tangled bundles of fibers called neurofibrillary tangles in parts of their brain.

There are also low levels of chemicals that carry messages between nerve cells in the brain. Amyloid plaques, neurofibrillary tangles, and decreased chemical levels impair thinking and memory by disrupting these messages and causing nerve cells to die. The course of the disease varies from person to person. Eventually, the patient loses mental capacity and the ability to carry out daily activities. This can range from mild memory problems to severe brain damage. Although there isn’t a treatment that stops Alzheimer’s disease, there are medications that provide some relief to patients who are in the early and middle stages of the disease.

Tacrine (Cognex), donepezil (Aricept), rivastigmine (Exelon), and galantamine (Reminyl)

These drugs prevent some symptoms from becoming worse for a limited time.

Memantine (Namenda)

This medication is used to treat moderate to severe cases.

Tranquilizers, mood elevators, and sedatives

These can help control behavioral symptoms such as sleeplessness, agitation, wandering, anxiety, and depression.

Effects-of-Cholinergic-and-Anticholinergic-Drugs

EPILEPSY

Epilepsy is a seizure disorder where there is an abnormal electric discharge from the cerebral neurons that result in loss or disturbance of consciousness and convulsion (abnormal motor reaction). Epilepsy affects 1% of people in the United States.

Half the epilepsy cases are secondary to trauma, brain anoxia, infection, lesions, or cerebrovascular disorder (CVA) [commonly referred to as a stroke]. Cause of the other half is unknown (idiophatic). Seventy-five percent of persons with seizures had their first seizure before 18 years of age. There are various types of seizures defined by the international classification of seizures. These include grand mal (tonic-clonic), petit mal (absence), and psychomotor seizures. Epilepsy is treated by using anticonvulsant medication.

Hydantoins (phenytoin, mephenytoin, ethotoin)

These treat grand mal (tonic-clonic) seizures and psychomotor seizures.

Barbiturates (Phenobarbital, mephobarbital, primidone)

These are used for treating grand mal and acute episodes or status epilepticus; meningitis, toxic reactions, and eclampsia

Succinimides (ethosuximide)

These are used to treat absence seizures and may be used in combination with other anticonvulsants.

Oxazolidones (trimethadione)

This is used to treat petit mal seizures and may be used in combination with other drugs or singly for treating refractory petit mal seizures.

Benzodiazepines (diazepam, clonazepam)

These are effective in controlling petit mal seizures.

Carbamazepine

This is effective in treating refractory seizure disorders that have not responded to other anticonvulsant therapies. It is also used to control grand mal and partial seizures and a combination of these seizures.

Valproate (valproic acid)

This is used to treat petit mal, grand mal, and mixed types of seizures.

Anticonvulsant medication works one of three ways:

  1. It can suppress the sodium influx by binding to the sodium channel pro¬longing the channel’s inactivation and preventing neurons from firing.
  2. It suppresses the calcium influx preventing stimulation of the T calcium channel.
  3. It increases the action of the gamma-aminobutyric acid (GABA) inhibiting neurotransmitters throughout the brain and thereby suppressing seizure activity.

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