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CVCS Interactive Case Studies
Certified Veterinary Compounding Specialist (CVCS)
The Scenario: Compounding for a Feline Patient
A veterinarian calls your pharmacy with a challenge: a 12-year-old cat with hyperthyroidism has been prescribed methimazole, but the owner is unable to administer the commercially available tablets. The cat is resistant to pilling. The veterinarian is requesting a compounded oral liquid. Your role is to formulate a palatable and stable suspension and counsel the owner on its use.
Prescription & Compounding Data
Prescription Information
- Patient: "Mittens," 12-year-old cat
- Drug: Methimazole 2.5 mg/mL Oral Suspension
- Directions: Give 1 mL (2.5mg) PO BID. Qty: 60 mL
Compounding Considerations
- Methimazole powder has a very bitter taste.
- Cats lack sweet taste receptors; savory flavors (chicken, tuna) are preferred.
- The default BUD for a non-aqueous oral formulation under USP <795> is 90 days.
Your Task
Task 1: Why is compounding a necessary intervention for this patient?
Answer:
Compounding is necessary due to a behavioral issue (the cat's refusal to take tablets) and the need for an alternative dosage form (an oral liquid) that is not commercially available for this drug.
Task 2: What is the most important factor to consider when selecting a vehicle and flavor for this compound?
Answer:
The most important factor is palatability. This requires masking the bitter taste of methimazole with a savory flavor (like chicken or tuna) that is appropriate for a cat, as they cannot taste sweetness.
Task 3: What is the appropriate Beyond-Use Date (BUD) for this prescription, assuming it is compounded in a flavored, oil-based vehicle and no specific stability study is available?
Answer:
The appropriate BUD is 90 days. An oil-based oral suspension is a "non-aqueous" formulation. According to USP <795>, the default BUD for a non-aqueous formulation is 90 days when no specific stability data is available.
Task 4: What are two critical counseling points for the cat's owner?
Answer:
1. "Shake the bottle well before every single dose." This is critical for a suspension to ensure the drug is evenly distributed and the dose is accurate. 2. "Use only the oral syringe we've provided to measure the dose." This ensures the small 1 mL volume is measured correctly.
The Scenario: Compounding for a Dog with a Drug Allergy
A 6-year-old, 10 kg dog with epilepsy is well-controlled on phenobarbital. However, the dog has developed a severe skin allergy, and the veterinarian suspects it is due to an inactive ingredient (a dye) in the commercially available tablets. The vet asks you to compound phenobarbital capsules that are free of all dyes and common allergens. The dog is also very difficult to medicate.
Prescription & Compounding Data
Prescription Information
- Patient: "Buddy," 6-year-old, 10 kg dog
- Drug: Phenobarbital 30 mg capsules
- Directions: Give 1 capsule PO BID. Qty: 60.
- Request: "Please compound in a hypoallergenic, dye-free formula."
Key Compounding & Safety Info
- Phenobarbital is a C-IV controlled substance, requiring meticulous record-keeping.
- It is a hazardous drug (NIOSH Table 3) requiring special handling (powder containment, appropriate PPE).
- Common hypoallergenic fillers include microcrystalline cellulose or rice flour.
- To improve adherence in difficult-to-medicate dogs, capsules can be opened and the contents mixed with food.
Your Task
Task 1: Why must you use pure Phenobarbital USP powder instead of crushing commercial tablets for this compound?
Answer:
You must use pure powder to fulfill the core therapeutic goal of the prescription: creating a hypoallergenic and dye-free formulation. Commercial tablets contain numerous inactive ingredients, including binders, fillers, and the suspected dye. Crushing them would re-introduce the very allergens the veterinarian is trying to avoid.
Task 2: Phenobarbital is a NIOSH Table 3 hazardous drug. What specific handling precautions are required during compounding?
Answer:
According to USP <800>, at a minimum, this requires: 1) Wearing two pairs of chemotherapy gloves and a protective gown; 2) Handling the powder in a way that contains it, such as in a powder containment hood (ventilated enclosure); and 3) Using a dedicated set of counting trays and spatulas that are immediately decontaminated after use.
Task 3: To make 60 capsules, you will need 1800 mg of phenobarbital. Your electronic balance has a sensitivity requirement of +/- 5%. What is the minimum weighable quantity (MWQ) for your balance, and can you weigh 1800 mg directly?
Answer:
The MWQ is typically calculated as $$\frac{\text{Sensitivity}}{\text{Error Rate}}$$. Assuming a standard sensitivity of 6 mg, the MWQ would be $$\frac{6 \text{ mg}}{0.05} = 120 \text{ mg}$$. Since the required amount (1800 mg) is much greater than the MWQ (120 mg), you can weigh it directly and accurately on the balance.
Task 4: What important counseling tip can you provide the owner to help with administering the capsules to a difficult-to-medicate dog?
Answer:
"Since Buddy is hard to pill, we've used a filler that is safe to mix with his food. You can carefully open the capsule and sprinkle the powder contents directly onto a small amount of his favorite wet food or a treat like peanut butter. Just make sure he eats the entire portion to get his full dose."
The Scenario: Unique Dosage Form for an Exotic Patient
A veterinarian from a local zoo calls with a prescription for a 100 kg Gorilla named "Zola" who has arthritis. Zola will not accept an oral liquid and is too dangerous to inject daily. The vet asks if you can compound a transdermal gel to deliver the medication. As the CVCS, you must evaluate the feasibility of this request and formulate an appropriate compound.
Prescription & Formulation Data
Prescription Information
- Patient: "Zola," 100 kg Gorilla
- Drug: Ketoprofen 10% Transdermal Gel
- Directions: Apply 2 mL to the inner ear once daily.
Key Compounding Information
- Transdermal Base: A Pluronic Lecithin Organogel (PLO) is a common base used to enhance the absorption of drugs through the skin.
- Safety for Handler: The person applying the transdermal gel must wear gloves to avoid absorbing the medication themselves.
- Excipient Toxicity: Some common pharmaceutical excipients are toxic to certain species (e.g., xylitol is highly toxic to dogs). Propylene glycol can be toxic to cats.
Your Task
Task 1: What is a transdermal gel, and why is it a good potential dosage form for this patient?
Answer:
A transdermal gel is a dosage form designed to deliver a drug through the skin into the systemic circulation. It is an excellent choice for Zola because it bypasses the need for oral administration (which she refuses) and daily injections (which are dangerous for the staff).
Task 2: What is the most appropriate compounding base for this formulation?
Answer:
A Pluronic Lecithin Organogel (PLO) base. This is the industry standard for compounded transdermal preparations as it has properties that enhance the permeation of drugs through the skin barrier.
Task 3: Why is the inner ear the recommended site of application?
Answer:
The skin on the inner flap of the ear (the pinna) is very thin and highly vascularized (has many blood vessels), which facilitates good drug absorption. It is also an area that is difficult for the animal to lick or rub off, ensuring the dose remains in place.
Task 4: What is the single most important counseling point for the zookeeper who will be applying this medication?
Answer:
The most important point is handler safety. The zookeeper must be counseled to wear gloves during every application. Because the gel is designed to be absorbed through the skin, the handler could absorb a significant dose of the ketoprofen themselves if they apply it with a bare hand, leading to unintended side effects.
