Amitriptyline HCl/MethimAZOLE Transdermal Pen (9mL)
Amitriptyline HCl/MethimAZOLE is a compounded formulation containing Amitriptyline HCl, MethimAZOLE, prepared by Mixlab for veterinary use. Available by prescription.
A transdermal pen is a simple way to give your pet medicine through their skin—usually used for cats by applying gel to the inside of their ear.
Step-by-Step:
- Get the pen ready – Twist the pen to dispense a small amount of gel. If it’s your first time, you will need to “prime” it first (the gel should be flush with the edge of the tip)
- Wear gloves – Always use a disposable glove or finger cot so the medication doesn’t absorb into your skin.
- Twist to dose – Follow the pen’s directions (like two full twists) to get the right amount of gel out. Always click in a clockwise direction, clicking counter-clockwise will stop you
- Pick the spot – Apply to a hairless area, usually the inside of your cat’s ear. Make sure the area is clean and dry.
- Apply the gel – Dab the gel directly with the pen or use your gloved finger to rub it in gently. Avoid the ear canal.
- Let it dry – It usually dries in a minute or two. Try to keep your pet from rubbing it off.
- Recap the pen – This keeps the medication fresh.
- Wash your hands – Even if you wore gloves, wash thoroughly after.
- Reward your pet – A treat helps make it a stress-free routine!
- Store properly – Keep at room temp, away from sunlight. Track doses so you know when it’s time to refill.
Important: Only apply where your vet has directed—usually hairless areas. Never apply over fur or broken skin. Keep other pets from licking the area until it’s dry.
This compounded formulation combines amitriptyline, a tricyclic agent, with methimazole, an antithyroid agent — two different drug classes. In compounding practice, clinicians may consider a combination like this for a multi-targeted approach. Your veterinarian determines whether it is appropriate based on your animal's diagnostic findings.
At a pharmacological level, this medication functions through two distinct pathways. Methimazole acts by inhibiting the enzyme thyroid peroxidase, which is essential for the iodination of tyrosyl residues in thyroglobulin. This action help address the synthesis of the thyroid hormones triiodothyronine (T3) and tetraiodothyronine (T4). Amitriptyline HCl acts by inhibiting the reuptake of serotonin and norepinephrine at the neuronal membrane, which increases the concentration of these neurotransmitters within the synaptic cleft. This combined activity helps stabilize the patient's metabolic rate while managing the emotional reactivity often seen in the relevant cats with a hormonal condition. Your veterinarian will determine whether this combination is appropriate based on your cat’s diagnostic testing results and previous response to single-agent protocols.
This description reflects the general pharmacology of the active ingredient's drug class; your veterinarian determines whether this approach is appropriate for your animal.
Prescription only. Use only under the direction of a licensed veterinarian. This information is not a substitute for veterinary diagnosis, prescribing or monitoring. Compounded drugs are not approved by the FDA for safety or effectiveness.
Commonly observed effects of amitriptyline HCl/methimazole administration include lethargy, sedation and gastrointestinal changes such as vomiting or a decrease in appetite. Because methimazole can influence the blood profile, your veterinarian will monitor for shifts in white blood cell counts and liver enzymes through periodic blood work. The amitriptyline component may lead to anticholinergic effects such as a dry mouth or constipation. Owners should watch for signs of persistent scratching (particularly around the face), significant weakness or behavioral shifts and contact their veterinarian promptly if these occur.
This medication is typically used with extra caution or avoided in patients with known severe liver disease, kidney impairment or pre-existing cardiac arrhythmias. It is also carefully evaluated in cats with a history of seizures or the relevant ophthalmic condition. Before starting a protocol, ensure your veterinarian has a complete history of all other prescriptions and supplements your pet is receiving, as this combination can have significant interactions with other serotonergic medications or certain heart medications. Your veterinarian is the right person to provide guidance on the necessary duration of use and the most commonly considered monitoring schedule to ensure the management approach remains suitable for your pet's individual health status.
Yes. Amitriptyline HCl/methimazole is a combination prescription medication and can only be dispensed by a licensed pharmacy upon receipt of a valid authorization from a licensed veterinarian. Mixlab verifies all authorizations before any medication is prepared or shipped to your home.
Yes. Because this specific combination of an antithyroid agent and an antidepressant is not available as a single commercial product, Mixlab compounds it into specialized strengths and dosage forms—such as flavored oral liquids or transdermal gels—to suit your cat's specific needs. The decision to use a compounded formulation rests with the prescribing veterinarian.
Veterinarians discuss this combination for the relevant cats with a hormonal condition that also experience high levels of stress or anxiety. While methimazole manages the overproduction of thyroid hormone, amitriptyline may be part of a management approach for the behavioral agitation that often accompanies the condition, allowing for a more comprehensive approach to the patient's well-being.
Commonly observed responses include mild sedation or a decrease in appetite. However, you should report any signs of intense facial itching, yellowing of the skin or eyes (jaundice) or extreme lethargy to your veterinarian immediately, as these may indicate a need to adjust the management plan.
