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HLT-VET42-07 · Lesson 9 · 22 clock hours · theory

Drug Classification III: Cardiovascular, Endocrine, GI, and Dermatologic Agents

Objective. Students will describe the pharmacologic management of common veterinary medical conditions (heart failure, diabetes mellitus, hyperthyroidism, GI disease, and allergic skin disease) and identify the monitoring parameters and owner education points relevant to each drug class.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

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Cardiovascular Agents

Heart failure in dogs (most commonly dilated cardiomyopathy in large breeds) and cats (most commonly hypertrophic cardiomyopathy) requires drugs that reduce the heart's workload and manage fluid accumulation.

Diuretics — Furosemide is the most commonly used diuretic in veterinary medicine. It acts on the kidney to promote excretion of sodium and water, reducing the fluid congestion that accompanies congestive heart failure. Monitor patients for dehydration, electrolyte imbalances (especially low potassium), and increased thirst and urination. Owners should be taught to watch for labored breathing at rest, which may signal worsening fluid accumulation.

ACE Inhibitors — Drugs such as enalapril and benazepril block the renin-angiotensin-aldosterone system, reducing blood pressure and easing the workload on a failing heart. They are often combined with furosemide in dogs with dilated cardiomyopathy. Monitoring includes blood pressure, kidney values (BUN, creatinine), and electrolytes.

Positive Inotropes — Pimobendan is a positive inotrope and vasodilator widely used in dogs with dilated cardiomyopathy and certain cases of mitral valve disease. It strengthens cardiac contractions and is typically given twice daily on an empty stomach. Owners must understand the importance of consistent timing.

Digoxin is an older cardiac glycoside that slows the heart rate and strengthens contractions; it has a narrow therapeutic index, meaning toxicity can occur close to therapeutic doses. Signs of toxicity include vomiting, anorexia, and arrhythmias. Regular blood level monitoring is required.

Endocrine Agents

Diabetes Mellitus — Dogs typically require insulin therapy because they usually have insulin-deficient (Type 1-like) diabetes. Cats more commonly have Type 2-like diabetes and may respond to diet and oral agents in some cases, but many also require insulin. Insulin is never shaken — vials are gently rolled to mix without denaturing the protein. Insulin must be stored per label instructions (most require refrigeration). U-100 insulin syringes must match the insulin concentration to ensure accurate dosing. Hypoglycemia (low blood glucose) is the most dangerous acute complication of insulin therapy; owners must recognize signs such as weakness, trembling, disorientation, and seizures and know to offer food or a glucose source and contact the clinic immediately.

Hyperthyroidism (Cats) — Feline hyperthyroidism is caused by a benign tumor of the thyroid gland producing excess thyroid hormone. Methimazole is the most common medical management. It is available as an oral tablet or as a compounded transdermal gel applied to the inner ear pinna. Transdermal gel is often preferred in cats that resist pilling. Owners applying the gel must wear gloves to avoid self-exposure, rotate application sites between ears to prevent skin irritation, and wash their hands after application. Methimazole can rarely cause bone marrow suppression or liver changes; regular bloodwork monitoring is required.

Hypoadrenocorticism (Addison's Disease) in Dogs — Addison's disease results from insufficient production of adrenal hormones (glucocorticoids and mineralocorticoids). Long-term management typically involves mineralocorticoid replacement (such as fludrocortisone acetate or injectable desoxycorticosterone pivalate, DOCP) and often a low-dose glucocorticoid (such as prednisone). During physiological stress (illness, surgery, travel), glucocorticoid doses are commonly increased on veterinary advice — this is called stress-dosing. Owners must never abruptly stop steroid therapy.

Gastrointestinal Agents

GI disease in small animals spans vomiting, diarrhea, ulcers, and motility disorders.

Antiemetics — Maropitant (Cerenia) is a neurokinin-1 receptor antagonist widely used to control vomiting in dogs and cats. Metoclopramide is a prokinetic antiemetic that also aids gastric motility.

Antidiarrheals and GI Protectants — Metronidazole has anti-inflammatory GI effects and antiprotozoal activity. Sucralfate is a mucosal protectant used for ulcers and esophagitis; it should be given on an empty stomach and separated from other medications because it can impair their absorption. Famotidine is an H2 blocker that reduces gastric acid.

Parvoviral Enteritis — Treatment is supportive: IV fluids, antiemetics, and antibiotics (because the damaged intestinal barrier allows bacterial translocation). Maropitant is commonly used for vomiting control. Owners of puppies with parvovirus should understand strict isolation protocols and the importance of the full vaccination series for prevention.

Dermatologic Agents

Atopic Dermatitis (Allergic Skin Disease) — Atopy is one of the most common dermatologic conditions in dogs. Several drug classes are used:

Safety and Scope of Practice

Veterinary assistants do not prescribe or independently dispense drugs. Your role is accurate drug preparation, clear owner education, and thorough documentation. Always confirm the drug, dose, patient weight, and route with the supervising veterinarian before preparation. Report any owner-reported signs of adverse effects promptly.

Key terms10

Positive inotropeA drug that increases the force of cardiac muscle contractions, used to strengthen a weakened heart.
Narrow therapeutic indexA property of drugs (such as digoxin) where the difference between an effective dose and a toxic dose is very small, requiring careful monitoring.
U-100 insulinInsulin with a concentration of 100 units per milliliter; insulin syringes must be matched to this concentration to ensure accurate dosing.
MethimazoleAn antithyroid drug used to manage feline hyperthyroidism by blocking the production of thyroid hormone; available orally or as a transdermal gel.
MineralocorticoidAn adrenal hormone (such as aldosterone) that regulates sodium and potassium balance; deficient in dogs with Addison's disease.
Stress-dosingTemporarily increasing a patient's glucocorticoid dose during illness, injury, or other physiological stress, as directed by a veterinarian, to compensate for the adrenal gland's inability to respond normally.
Maropitant (Cerenia)A neurokinin-1 receptor antagonist antiemetic used to control vomiting in dogs and cats.
Oclacitinib (Apoquel)A JAK (Janus kinase) inhibitor used to control itch and inflammation associated with atopic dermatitis in dogs.
SucralfateA GI mucosal protectant used for gastric and esophageal ulcers; it should be given on an empty stomach and separated from other medications.
HypoglycemiaAbnormally low blood glucose; a life-threatening risk of insulin therapy whose signs include weakness, trembling, disorientation, and seizures.

Worked examples4

1. A dog with diabetes mellitus is ordered 8 units of U-100 insulin. Using a U-100 insulin syringe marked in units, what volume in milliliters does 8 units represent, and how do you confirm the correct mark on the syringe?
  1. Step 1: Recall that U-100 insulin contains 100 units per 1 mL.
  2. Step 2: Calculate the volume: 8 units ÷ 100 units/mL = 0.08 mL.
  3. Step 3: On a U-100 insulin syringe, each unit mark corresponds to 0.01 mL. Count to the line labeled '8 units' on the syringe barrel.
  4. Step 4: Confirm by reading the syringe at eye level and verifying the plunger tip aligns with the 8-unit graduation mark.
Answer: 8 units of U-100 insulin equals 0.08 mL; draw the plunger to the '8' mark on a U-100 insulin syringe.
2. A cat is prescribed 5 units of U-100 insulin twice daily. The owner asks how many days a 10 mL vial will last. Calculate the answer.
  1. Step 1: Determine daily dose in units: 5 units × 2 doses = 10 units per day.
  2. Step 2: Determine total units in vial: 10 mL × 100 units/mL = 1000 units.
  3. Step 3: Divide total units by daily dose: 1000 units ÷ 10 units/day = 100 days.
  4. Step 4: Note that most insulin vials carry a manufacturer's recommendation for use after opening (commonly 28–30 days once opened, depending on the product), so the vial may need to be replaced before it is mathematically depleted. Always follow label guidance.
Answer: Mathematically, the vial contains enough for 100 days, but the opened vial's labeled discard date (often 28–30 days after opening, per product labeling) may apply first.
3. A 22 lb dog is prescribed furosemide. The veterinarian writes an order for 2 mg/kg by mouth once daily. What dose in milligrams should this dog receive?
  1. Step 1: Convert body weight from pounds to kilograms: 22 lb ÷ 2.2 = 10 kg.
  2. Step 2: Multiply weight by dose rate: 10 kg × 2 mg/kg = 20 mg.
  3. Step 3: Confirm the calculation and document 20 mg PO SID on the treatment sheet.
Answer: This dog should receive 20 mg of furosemide by mouth once daily.
4. A technician needs to prepare a 12-unit insulin dose from a U-100 vial using a 0.3 mL U-100 syringe. How many mL will be drawn, and does the syringe capacity allow this dose?
  1. Step 1: Calculate volume: 12 units ÷ 100 units/mL = 0.12 mL.
  2. Step 2: Compare to syringe capacity: 0.12 mL is less than 0.3 mL, so the syringe can accommodate this dose.
  3. Step 3: Draw to the '12' unit mark on the U-100 syringe. Verify at eye level before administration.
Answer: 12 units equals 0.12 mL; a 0.3 mL U-100 syringe is adequate for this dose.

The math in this lesson1

Learners divide 8 units by U-100 insulin (100 units/mL) to draw 0.08 mL on the syringe.
7.RP.2
In class: Disease-based drug matching exercise: students receive brief case summaries for five patients (dog with dilated cardiomyopathy, cat with hyperthyroidism, dog with Addison's disease, dog with parvoviral enteritis, dog with atopic dermatitis) and, using Plumb's, identify the primary drug class used, a representative drug name, and the most important owner-education point for home administration · Insulin handling and storage station: instructor demonstrates proper storage, vial mixing technique (gentle rolling, not shaking), and syringe selection for U-100 insulin; students then each prepare a simulated insulin dose using a training vial of saline and an insulin syringe, calculating units from a mock doctor's order, and document on a treatment sheet · Owner-education role-play: in pairs, one student plays a veterinary assistant explaining how to administer methimazole transdermal gel to a cat at home; the other plays the owner and asks scripted questions; roles are reversed; instructor evaluates clarity, accuracy, and use of lay terminology
Materials: Plumb's Veterinary Drug Handbook, case summary handouts, U-100 insulin syringes, training saline vials (labeled as training insulin), insulin storage reference, treatment sheet forms, role-play script cards
Check: Disease-drug matching exercise scored on accuracy (4 of 5 correct drug class identifications required); insulin preparation evaluated by instructor during station—correct unit calculation and volume confirmation required for pass; role-play evaluated on a 5-item rubric with a pass mark of 4 of 5

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Pharmacology
1. A dog with dilated cardiomyopathy is started on pimobendan. Which owner-education point is most important regarding this medication?
Pharmacology
2. Which of the following is the most dangerous acute complication of insulin therapy that owners of diabetic pets must be taught to recognize?
Pharmacology
3. An owner is applying methimazole transdermal gel to her hyperthyroid cat at home. Which safety instruction is essential to give her?
Pharmacology
4. A dog with Addison's disease is being managed with fludrocortisone and a low-dose glucocorticoid. The owner calls to report the dog is going to have a dental procedure next week. What action is most appropriate?
Pharmacology
5. Which drug has a narrow therapeutic index and requires regular blood-level monitoring to avoid toxicity in cardiac patients?
Pharmacology
6. Sucralfate is dispensed for a dog with a gastric ulcer. When should this medication be given relative to meals and other drugs?
Pharmacology
7. A veterinary assistant is preparing 14 units of U-100 insulin using a U-100 syringe. What volume in milliliters does this dose represent?
Pharmacology
8. Which drug class is most appropriate as a first-line treatment for pruritus associated with canine atopic dermatitis when rapid relief is needed, and which significant long-term side effect must owners understand?
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