Brand Name: Elavil

Available in 10 mg, 25 mg, 50 mg, 75 mg, 100 mg, and 150 mg tablets

Background

Amitriptyline is a member of the class of drugs called “tricyclic antidepressants.” It was originally developed as a human anti-depressant but has been found to have applications in pain management as well. Amitriptyline works by several mechanisms, the main one being increasing serotonin levels in the brain. Serotonin is a neurotransmitter that regulates mood, pain sensitivity, appetite, and other issues. The more of it you have, the more relaxed and comfortable you are. Serotonin is responsible for the sedation side effect of amitriptyline. In addition to increasing serotonin, amitriptyline also has what are called “anticholinergic” effects. An anticholinergic medication disrupts acetylcholine (another neurotransmitter) and creates side effects such as dry mouth, urinary retention, constipation, and dried respiratory secretions. Further, amitriptyline is a strong antihistamine. Amitriptyline works mostly through changes in brain chemistry. In pets, it is mostly used for behavior issues and in managing itch and pain situations.

Amitriptyline works by several mechanisms, the main one being increasing serotonin levels in the brain. Serotonin is a neurotransmitter that regulates mood, pain sensitivity, appetite, and other issues. The more of it you have, the more relaxed and comfortable you are. Serotonin is responsible for the sedation side effect of amitriptyline.

In addition to its neurotransmitter effects, amitriptyline is also a strong antihistamine. Some of its desired effects may be achieved by way of its antihistamine effects in addition to its brain effects.

How this Drug is Used

With amitriptyline becoming widely used in human psychology, small animal uses for this medication came to light not long after.

Amitriptyline has been used in animals for separation anxiety,  inappropriate urination in cats, feline lower urinary tract disease, and obsessive grooming behaviors in both dogs and cats. In many of these conditions, it is not clear which of the above-described mechanisms of action are responsible for the desired effects.

Amitriptyline is usually given once or twice daily, and can take a couple of weeks before it is possible to judge its effectiveness. It can be given with or without food. If a dose is accidentally skipped, give it when it is remembered and adjust the timing of the next dose accordingly. Do not double up on the next dose. Tablets should be stored at room temperature.

Side Effects

By blocking amine pumps in the brain, amitriptyline hampers the removal of serotonin, so any serotonin you have lasts longer. The problem is that blocking amine pumps in the brain also hampers the removal of norepinephrine, which is a fight-or-flight neurotransmitter. Having more stimulation of "fight or flight" creates what are called "anticholinergic" effects, which include dry mouth, urinary retention, constipation, and dried respiratory secretions. Such anticholinergic effects are relatively common amitriptyline side effects.

That said, the most common side effect of amitriptyline is drowsiness/sedation (caused by the increased serotonin).

Tricyclic antidepressants can alter blood sugar levels and falsely lower thyroid testing.

More serious (though rare) potential side effects can include seizures, heart arrhythmia, and/or abnormal bleeding.

Interactions with other Medications

Tricyclic antidepressants, including amitriptyline, cannot be safely used with monoamine oxidase inhibitors such as L-Deprenyl (Anipryl) or with tramadol, a pain reliever.

The use of cimetidine (Tagamet) can interfere with the desired effect of amitriptyline.

Amitriptyline is best not used in conjunction with other drugs with anticholinergic effects, drugs that stimulate the sympathetic nervous system, or with other psychoactive drugs.

The use of the intestinal motility modifier cisapride leads to heart rhythm disturbances when it is combined with certain other medications. Amitriptyline is one of those medications, so these two drugs should not be used together.

Itraconazole and ketoconazole (antifungal agents) can increase blood levels of amitriptyline, thus increasing the toxicity potential. Cyproheptadine may decrease amitriptyline levels, rendering it ineffective.

Amitriptyline should not be used in dogs that use an amitraz-based tick control product. See which products contain amitraz.

Concerns and Cautions

Amitriptyline is removed from the body through the liver. Patients with abnormal liver function may have trouble with this medication. Periodic liver enzyme evaluation (blood testing) is a good idea for patients on this medication long term.

Amitriptyline should not be used in pregnancy or lactation, in patients with seizure disorders, patients with dry eye (KCS) or in patients with cardiac rhythm disturbances.

Diabetic pets should avoid the use of amitriptyline.