By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com
Brand Name: Elavil
Available in 10 mg, 25 mg, 50 mg, 75 mg, 100 mg, and 150 mg tablets
Amitriptyline was developed out of a need in human medicine for anti-anxiety and anti-depressant medications to treat mental illness, though in humans it has gained some popularity for treating chronic pain syndromes, especially interstitial cystitis.
This medication creates its effects via several mechanisms:
- By blocking the way cells of the nervous system transport biochemicals called amines, amitriptyline is able to increase the levels of circulating neurotransmitters, especially a neurotransmitter called serotonin. This mechanism seems to be at the route of amitriptyline's anti-anxiety and psychoactive properties. In humans, this medication is used in the treatment of anxiety, bipolar disorders, and depression. This property also is responsible for amitriptyline's sedation side effect.
- The same blockage of the amine pump leads to increased levels of the neurotransmitter norepinephrine. Norepinephrine is an important neurotransmitter in the sympathetic nervous system as described below.
- Amitriptyline is a strong antihistamine.
- Amitriptyline also has what are called anticholinergic effects, which requires some explanation. The part of the nervous system that regulates an assortment of involuntary operations is called the autonomic nervous system. It is divided into two areas: the sympathetic system, which is responsible for generating changes during a fight or flight situation (such changes include increased circulation to muscles, increased heart rate, pupil dilation etc.) and the parasympathetic nervous system, which is responsible for maintaining the body's status quo. The parasympathetic system uses acetylcholine as its chief neurotransmitter. An anticholinergic medication, disrupts acetylcholine and creates side effects such as dry mouth, urinary retention, constipation, dried respiratory secretions.
Amitriptyline is a member of the class of drugs called tricyclic antidepressants.
How this Drug is Used
With amitriptyline becoming widely used in human mental illness, it was not long before small animal uses for this medication came to light. Amitriptyline has been used in animals for separation anxiety, for inappropriate urination in cats, for feline lower urinary tract disease, and for 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 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.
Anticholinergic side effects would probably not be surprising: dry mouth (manifested in animals often as frequently licking of the lips), urinary retention, and constipation.
Tricyclic antidepressants can alter blood sugar levels.
In humans, side effects in virtually every organ system have been reported at one time or another which means that potentially any side effect could be attributed to the use of this medication.
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 cimetadine (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.
Use of the intestinal motility modifier cisapride leads to heart rhythm disturbances when it is combined with certain other medications. Amitripyline is one of those medications so these two drugs should not be used together.
Tricyclic antidepressants can alter blood sugar levels.
In humans, side effects in virtually every organ system have been reported at one time or another, which means that potentially any side effect could be attributed to use of this medication. In dogs the issues reported by National Animal Poison Control in overdose cases involve lethargy, increased heart rate, incoordination, elevated body temperature, and nausea. In cats, the issues reported are vocalizing, dilated pupils, increased heart rate, incoordination, lethargy and disorientation, and nausea.
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.
It can take up to 3 weeks to determine if amitriptyline is effective.
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