Apoquel®, also known by its generic name oclacitinib, is a significant advancement in managing pruritus (itchiness) in dogs. As a Janus Kinase (JAK) inhibitor approved by the FDA, Apoquel® targets specific signaling pathways involved in inflammation and itching. This article delves into its clinical application, efficacy, potential side effects, and monitoring protocols, drawing from extensive clinical experience and updated information as of January 31, 2023.
Understanding Apoquel®’s Mechanism of Action
Apoquel® works by inhibiting JAK-1 and JAK-3 signaling. These pathways are crucial for the communication of inflammatory signals, including those triggered by cytokines like IL-2, -4, -6, and -13, which are associated with lymphocyte activation. Critically, Apoquel® also blocks IL-31, a key mediator of itch sensation. Unlike other common treatments such as steroids, antihistamines, Cytopoint®, or cyclosporine, Apoquel® offers a targeted approach to itch relief.
Rapid Efficacy and Dosing Regimen
One of the primary advantages of Apoquel® is its rapid onset of action, with most dogs experiencing a noticeable reduction in itching within 24 hours. This quick relief is often sustained daily, as the drug’s antipruritic effects typically last 12-24 hours.
The standard dosing for dogs is 0.4-0.6 mg/kg administered every 12 hours for up to 14 days. Following this initial period, the dosage is adjusted to 0.4-0.6 mg/kg once daily. It is important to adhere to these recommended doses, as exceeding them could increase the risk of immune suppression, while doses below the range may prove ineffective for many patients. While some mild cases might be managed with lower doses, it’s crucial to consult a veterinarian.
Most dogs show significant improvement within a few days of starting Apoquel®. However, underlying infections such as yeast, bacteria, or mites can impede its effectiveness. Zoetis reports that approximately 60% of dogs with moderate to severe atopic dermatitis achieve long-term control with once-daily dosing. In some severe cases, a veterinarian might consider off-label, long-term twice-daily dosing. It’s essential to remember that managing severe skin conditions often requires a multimodal therapeutic approach.
Safety Considerations and Drug Interactions
Gastrointestinal upset, a common side effect with drugs like cyclosporine, is rare with Apoquel®. While long-term studies combining Apoquel® with other immunosuppressants like steroids and cyclosporine are limited, clinical experience suggests that short-term use of steroids at anti-inflammatory doses (0.5 mg/kg twice daily, then tapered) appears safe when used concurrently with Apoquel®. However, careful evaluation of Apoquel®’s efficacy is necessary if steroids are required. Due to Apoquel®’s rapid action, a slow transition from steroids is generally not needed, though tapering may be essential to prevent Addisonian crisis in pets on long-term, high-dose steroids.
While JAK inhibitors in human medicine have potential interactions with certain drugs like ketoconazole (a CYP3A4 inhibitor), clinical observations have not revealed significant adverse effects when these are co-administered with Apoquel®. Caution is advised, however, when using other medications that might affect bone marrow function.
Age Restrictions and Potential Side Effects
Apoquel® is FDA-approved for dogs over 12 months of age. This restriction stems from studies indicating an increased incidence of demodicosis and pneumonia at higher doses in younger dogs. Furthermore, anecdotal evidence suggests Apoquel® may not be as effective for allergies in very young puppies.
In humans, JAK inhibitors can cause side effects including neutropenia, anemia, thrombocytopenia, elevated liver enzymes, increased cholesterol, urinary tract infections (UTIs), and weight gain. For dogs, the product insert lists potential side effects such as vomiting, diarrhea, lethargy, anorexia, dermal masses, decreased leukocytes and globulins, and increased cholesterol and lipase. While demodicosis, neoplasia, pneumonia, bloody diarrhea, skin and ear infections, UTIs, and histiocytomas have been reported in a small number of dogs, their direct causal link to Apoquel® requires careful consideration, especially in dogs with underlying atopic dermatitis. Some owners have reported polydipsia, increased appetite, and aggression, reminiscent of steroid side effects, though a definitive link to Apoquel® has not been established.
Clinical Experience and Monitoring
Having initiated Apoquel® treatment in over a thousand dogs, the incidence of significant side effects has been rare. Bone marrow suppression is the most serious concern, observed in approximately 1% of patients. This is typically detected through bloodwork, with no outward clinical signs. Regular bloodwork monitoring, particularly a complete blood count (CBC) at three months and then annually, is crucial. In cases of bone marrow suppression, the condition usually resolves within weeks of dose reduction. While CBC values may shift towards the lower end of normal, the clinical significance is still being evaluated.
Ear infections may not be as effectively managed with Apoquel® compared to steroids or cyclosporine. While UTIs can occur, they are often suspected to be more common in dogs with atopic dermatitis itself, rather than a direct side effect of Apoquel®. Weight gain has been observed, though generally less pronounced than with steroid therapy. Rare instances of behavioral changes, described as manic episodes, have been reported, resolving upon discontinuation of the medication. Interestingly, some dogs have shown improved mobility, possibly due to reduced inflammation or a general sense of well-being.
The product insert mentions “unspecified skin masses,” with histiocytomas and viral papillomas being more common in dogs on Apoquel®. While histiocytomas often resolve spontaneously, discontinuing Apoquel® might expedite resolution. Viral papillomas, transmissible infections, may also resolve faster if Apoquel® is stopped. Any new masses should always be evaluated by a veterinarian. Concerns about Apoquel® exacerbating neoplastic conditions are noted, but current evidence is lacking. It is important to differentiate between Apoquel® causing cancer and treating the symptoms of skin disease that is triggered by an underlying internal condition, such as cancer.
Monitoring Protocols
The standard monitoring protocol for dogs on once-daily Apoquel® involves a CBC and chemistry panel before starting the medication, followed by checks at three months and then annually. The CBC is particularly important. Ensuring the absence of liver disease before initiating Apoquel® is also recommended, with the exception of steroid-induced liver elevations.
Summary of Apoquel®
Apoquel® is a valuable therapeutic option for managing atopic dermatitis in dogs, offering rapid relief and a low incidence of gastrointestinal side effects. Its primary drawbacks include the need for bone marrow monitoring, potential lack of efficacy in some patients, and limited long-term data.
For comprehensive information and FDA-recommended use, consult the drug insert. Report any adverse side effects to the FDA or Zoetis at 1-888-963-8471. For specific medical advice regarding your pet, contact your veterinarian.
Apoquel® Use in Cats
While not FDA-approved for felines, Apoquel® can be used to manage atopic dermatitis and other immune-mediated diseases in cats. Higher doses and more frequent administration are typically required compared to dogs. Approximately 66% of cats show good control, but about 7% discontinue due to low immune cell counts within 2-5 months. In 34% of cases, Apoquel® was ineffective, with some cats experiencing vomiting, diarrhea, or lethargy. Due to the off-label use and potential side effects, management of feline cases requiring Apoquel® is best handled by a veterinary dermatologist.
