Tacrine

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Tacrine

Definition

Tacrine is a drug used to treat dementia associated with Alzheimer’s disease. In the United States tacrine is sold under the brand name drug Cognex. It is also sometimes called tetrahydroaminoacridine or THA.

Purpose

Tacrine is used to treat symptoms of Alzheimer’s disease in people with mild to moderate illness. The drug may result in mild improvements in thinking for a short period. Tacrine does not cure or stop the progression of Alzheimer’s disease.

Description

The Food and Drug Administration approved tacrine in 1993 for treating Alzheimer’s disease. In Alzheimer’s disease, some cells in specific regions of the brain die. Because of this cell death, these brain cells lose their ability to transmit nerve impulses. Brain cells normally transmit nerve impulses another by secreting various chemicals known as neurotransmitters.

Brain cells that make and secrete a neurotransmit-ter called acetylcholine are affected early in the course of Alzheimer’s disease. Tacrine helps prevent the breakdown of acetylcholine in the brain, thus temporarily increasing its concentration. In doing so, tacrine may improve the thinking process by facilitating nerve impulse transmission within the brain.

Tacrine is available as capsules in several different strengths. Tacrine is broken down by the liver.

Recommended dosage

The dose of tacrine will be different for different people. An initial dosage of tacrine is usually 10 mg taken four times per day. This dose should be continued for four weeks while liver function is monitored. If no adverse liver effects are detected, the dosage should be increased to 20 mg taken four times per day. Higher dosages such as 30-40 mg given four times per day may also be used. Liver function must be monitored every other week during the first 16 weeks of treatment. After 16 weeks of tacrine therapy, liver function can be assessed every three months. Dosage increases should not occur more often than every four weeks. Tacrine should be taken on an empty stomach between meals, but if stomach upset occurs, it may be taken with food.

If problems in liver function arise, tacrine may be stopped, or the dosage reduced, until liver function returns to normal. Very specific guidelines should be followed by physicians with regard to dosage adjustments based upon the severity of liver effects. Newer drugs that work in the same manner as tacrine are not as toxic to the liver and may be preferred for patients just beginning therapy for Alzheimer’s-type dementia.

Precautions

Tacrine may cause liver damage. It may not be the best drug to treat symptoms of Alzeheimer’s disease in people with known liver damage. If these individuals take tacrine, their liver function should be closely monitored. Tacrine may also slow heart rates, increase acid secretion in the stomach, make urination difficult, cause breathing difficulties, or contribute to seizures. As a result, it should be used carefully in people with certain heart conditions, those who are prone to stomach ulcers, people with bladder obstruction, individuals with asthma, and those with a history of seizure disorders.

People should not stop taking tacrine suddenly because this could cause behavioral disturbances. The drug may be stopped slowly if improvements are not noted by caregivers or physicians.

KEY TERMS

Acetylcholine —A naturally occurring chemical in the body that transmits nerve impulses from cell to cell. Generally, it has opposite effects from dopamine and norepinephrine; it causes blood vessels to dilate, lowers blood pressure, and slows the heartbeat. Central nervous system well-being is dependent on a balance among acetylcholine, dopamine, serotonin, and norepinephrine.

Dementia —A group of symptoms (syndrome) associated with a progressive loss of memory and other intellectual functions that is serious enough to interfere with a person’s ability to perform the tasks of daily life. Dementia impairs memory, alters personality, leads to deterioration in personal grooming, impairs reasoning ability, and causes disorientation.

Milligram (mg) —One-thousandth of a gram. A gram is the metric measure that equals about 0.035 ounces.

Neurotransmitter —A chemical in the brain that transmits messages between neurons, or nerve cells.

Placebo —An inactive substance or preparation used as a control in experiments with human subjects to test the effectiveness of a drug or herbal preparation. Some patients may experience a medicinal response or experience side effects to a placebo simply because they have faith in its powers even though it contains no medicine.

Side effects

The most common side effect of tacrine is impaired liver function. This causes 8% of people to stop taking the drug. Other common side effects occurring in at least 5% of people and at twice the rate of placebo are stomach upset (nausea, vomiting, diarrhea, indigestion, or anorexia), muscle aches, and difficulty walking. Side effects affecting the stomach appear to be more severe at higher dosages.

Side effects that occur less often are behavioral disturbances, abnormal thinking, hostility, tremor, inability to sleep, slow heart rates, changes in blood pressure, urinary difficulties, rash, flushing, aggravation of asthma, or cold-like symptoms.

Health care providers should be informed immediately if nausea, vomiting, loose stools, or diarrhea occur soon after the dose of tacrine is increased or if rash, jaundice (yellow tinge to eyes or skin), or changes in stool color occur at any time.

Interactions

Many drugs can alter the effects of tacrine. Some drugs such as dicyclomine may lessen the effects of tacrine. Other drugs such as propranolol, cimetidine, ciprofloxacin, fluoxetine, fluvoxamine, neostigmine, or bethanechol may increase some of tacrine’s side effects. Rivastigmine may interact with some of the drugs used to relax muscles during surgery. The interaction increases the effects of both drugs.

Tacrine may also diminish the effects of levodopa and increase the side effects of theophylline. Smoking cigarettes may reduce the effectiveness of tacrine.