A 6.8 kg Cat, a 5 mg Tablet, and a 90-Day Request
A 6.8 kg, 13-year-old female spayed domestic shorthair cat is newly diagnosed with hyperthyroidism (T4 6.8 µg/dL, reference <4.0) and concurrent IRIS stage 2 chronic kidney disease (creatinine 2.4 mg/dL, urine specific gravity 1.022). The veterinarian writes methimazole 2.5 mg PO every 12 hours with a T4 and renal panel recheck in 3 weeks. The practice stocks only 5 mg methimazole tablets and a 5 mg/mL compounded methimazole suspension with a 14-day refrigerated beyond-use date. The owner lives alone, works 12-hour shifts, has osteoarthritis in both hands, and says she "cannot pill a cat to save her life." A second cat shares the household. She asks whether she can rub the medicine on the ear instead, and whether she can take a 3-month supply in one trip to save on gas.
1. The owner wants a single 90-day supply. Using the stocked 5 mg tablets, what do you dispense, and what do you say about the 90-day request?
Read the worked answer
The prescription is 2.5 mg q12h, so with 5 mg tablets the cat gets one-half tablet twice daily - roughly 90 tablets for 90 days. That part is arithmetic; the judgement is in whether to hand over 90 days.
Two reasons not to. First, the 3-week recheck exists precisely because the starting dose is an educated guess: T4, BUN, creatinine, and a CBC may dictate a dose change or discontinuation, and a 90-day bottle becomes either waste or an excuse to skip the recheck. Dispense 30 days with one refill, and book the recheck before the refill runs out. Second, halving tablets is not precise dosing in a 6.8 kg cat - unscored tablets crumble, and arthritic hands make consistent splitting unlikely. Ask the veterinarian whether a 2.5 mg compounded capsule or a scored product is preferable.
Do not dispense the 5 mg/mL suspension as a 90-day supply; its 14-day beyond-use date makes that unsafe. Show the owner a pill splitter, demonstrate on a spare tablet, and emphasize that consistent administration matters more than perfect precision with methimazole.
2. The owner asks about transdermal methimazole instead of pills. What do you tell her, and what handling and household safety instructions do you give?
Read the worked answer
Transdermal methimazole in a pluronic lecithin organogel is used in cats, but it is a compounded, off-label preparation and absorption varies between cats and between batches - some cats never reach a therapeutic T4. The honest answer is: possible, but it is not a like-for-like swap, and the 3-week recheck becomes mandatory rather than routine.
Practical instructions: wear gloves, apply to the hairless inner surface of the pinna, alternate ears, and keep the cat from grooming the site for 20–30 minutes. The second cat in the house must not groom the treated ear, and the owner should not sleep with the cat pressed against her face. Methimazole is a human teratogen and can cause agranulocytosis, so a pregnant or breastfeeding owner should not handle it at all, and any handling should be gloved with hand-washing afterward.
The gel is drawn in a syringe and is easy to under- or over-deliver, so demonstrate exactly how to measure the prescribed volume. Also counsel that pinnae can become red or irritated, that the formulation must not be switched back and forth without telling the veterinarian, and that any change in route needs a T4 recheck in 3 weeks.
3. On day 10 the owner calls: the cat vomited twice and is "quiet." What do you ask, what do you advise, and what must you avoid saying?
Read the worked answer
Two vomits and quietness on day 10 are not automatically an emergency, but they are a reason to gather information before advising anything.
Ask: when did the vomiting start, is the cat eating and drinking, is there jaundice, facial swelling, or scratching at the face (rare hypersensitivity), and - critically - has the owner missed doses or doubled up to "catch up"? Methimazole commonly causes self-limiting GI upset, but it can also cause hepatotoxicity and, more seriously, agranulocytosis. A quiet, vomiting cat needs a physical exam, CBC, and chemistry rather than telephone reassurance.
Advise the owner to withhold the next dose and speak to the veterinarian the same day. Do not tell her to double the next dose, do not suggest human antacids or other over-the-counter drugs, and do not promise the reaction is benign. Fever, jaundice, or oral ulcers make it same-day urgent. Document the conversation, who advised what, and when the veterinarian was notified.