Introduction
This guide covers four drug groups that technicians handle every week: hormone drugs for diabetes, thyroid and adrenal disease; anticonvulsants for seizures; gastrointestinal (GI) drugs for vomiting, ulcers and slow gut movement; and reproductive drugs such as prostaglandins and oxytocin.
The technician's job is practical. You store and mix insulin correctly, match the syringe to the insulin, time the blood draw for drug monitoring, give sucralfate at the right time, and protect yourself and coworkers from drugs that are dangerous to handle, especially during pregnancy. These are also the details the VTNE likes to test.
Key facts
- Insulin syringes are not interchangeable. U-40 insulin needs a U-40 syringe and U-100 insulin needs a U-100 syringe.2
- Unopened insulin is stored in the refrigerator at 2 to 8 °C (36 to 46 °F). Do not freeze it.23
- ProZinc is mixed by gently rolling the vial. Vetsulin is the exception: its label says to shake the vial thoroughly.34
- Trilostane is monitored with an ACTH stimulation test started 4 to 6 hours after dosing, 10 to 14 days after each dose change.7
- Phenobarbital reaches steady state in about 2 weeks. Bromide can take up to 4 months, so a loading dose is often used.9
- Potassium bromide is no longer recommended as a maintenance anticonvulsant in cats because it can cause severe bronchial disease.9
- Metoclopramide must not be given if a GI obstruction or perforation is suspected.10
- Dinoprost is absorbed through the skin and can cause abortion or bronchospasm in people who handle it.14
How the VTNE tests this
- Classify a named drug and match it to its mechanism and main side effect (Domain 1 Task F; K8, drug classification).1
- Store and handle drugs correctly: insulin temperature, mixing and in-use life (Domain 1 Task G).1
- Protect staff from drugs that are hazardous to handle, such as methimazole, trilostane and prostaglandins (K11, safe handling practices).1
- Calculate insulin volumes and spot syringe mismatch errors.
- Time monitoring samples: trough phenobarbital levels, post-dose ACTH stimulation tests and post-pill T4.
Core concepts
Endocrine drugs
Insulin lowers blood glucose. Veterinary insulins are labeled by concentration: U-40 means 40 units per mL and U-100 means 100 units per mL.2 ProZinc (protamine zinc insulin; the label cited here is for cats) and Vetsulin (porcine insulin zinc suspension, for dogs and cats) are both U-40.34 The 1-unit mark on a U-40 and a U-100 syringe both deliver 1 unit of the matching insulin, but the volume is different.2 Figure 2 shows why mixing them up causes a large dosing error.
Methimazole treats hyperthyroidism in cats by blocking thyroid hormone production. Felanorm (methimazole oral solution) starts at 2.5 mg every 12 hours. Hematology, biochemistry and total T4 (TT4) are checked before treatment, at 3 and 6 weeks, then every 3 months.5
Levothyroxine (synthetic T4) treats hypothyroidism in dogs. Therapeutic monitoring is generally done after 4 to 8 weeks. With once-daily dosing, the peak T4 4 to 6 hours after the pill should sit at the high end of, or slightly above, the reference interval. Signs of overdose (thyrotoxicosis) include panting, nervousness, polyuria, polydipsia and a fast heart rate.68
Trilostane (Vetoryl) blocks cortisol production in dogs with hyperadrenocorticism (Cushing syndrome). Capsules are given with food. Owners stop the drug and call if the dog vomits, has diarrhea, stops eating, becomes weak or collapses, because too much cortisol suppression can occur.7
Anticonvulsants
Phenobarbital is a first-line maintenance drug in dogs and the usual first choice in cats. It is metabolized mainly by the liver. Long-term use in dogs has been linked to liver toxicity, especially at serum levels above 35 mcg/mL. It is a potent inducer of liver microsomal (cytochrome P450) enzymes, so serum levels and liver values are both monitored.9
Potassium bromide (KBr) is not metabolized by the liver. It is excreted unchanged in urine, so it is useful in dogs with liver concerns. Its half-life in dogs is 25 to 46 days. High-chloride diets increase bromide loss and lower serum levels, so diet changes matter.9
Levetiracetam binds the SV2A protein and reduces glutamate release. It is used as an add-on drug in dogs and in cats, and tolerance with long-term use has been reported in dogs.9 Only drugs with a known toxic level, phenobarbital and bromide, need routine serum monitoring once seizures are controlled.9
GI drugs
- Maropitant (Cerenia) blocks NK-1 receptors, where substance P triggers vomiting. It works against many vomiting triggers in dogs and cats.10
- Ondansetron blocks 5-HT3 serotonin receptors and is used for chemotherapy-induced vomiting.10
- Metoclopramide is a dopamine (D2) antagonist and prokinetic (it speeds stomach emptying). It can cause extrapyramidal signs (tremors, abnormal movements) and is not very effective as an antiemetic in cats.10 Cisapride is a 5-HT4 agonist prokinetic.11
- Omeprazole is a proton pump inhibitor (PPI). It irreversibly blocks the acid pump of the stomach's parietal cells. Famotidine is an H2 blocker.12
- Sucralfate breaks down in stomach acid into a sticky paste that binds to ulcers. It is not absorbed.12 Because it can bind other drugs in the gut, the human label advises giving the other drug 2 hours before sucralfate when absorption matters, and dosing on an empty stomach.13
Reproductive drugs
Dinoprost (Lutalyse) is a natural prostaglandin F2-alpha. It is used in cattle and horses to manage the estrous cycle. Its label warns that women of childbearing age, people with asthma and people with breathing problems should use extreme caution, because it is absorbed through the skin.14
Oxytocin increases the frequency of uterine contractions. In small animals it is used when the cause of dystocia is uterine inertia (weak labor). It is not used in obstructive dystocia, where a puppy or kitten is physically stuck, and it can cause early placental separation.15
| Drug | Class | What the technician monitors | Handler or client warning |
|---|---|---|---|
| ProZinc, Vetsulin | Insulin, U-40 | Blood glucose, appetite, signs of hypoglycemia | Use a U-40 syringe only |
| Methimazole | Antithyroid | CBC, biochemistry, TT4 at 3 and 6 weeks, then every 3 months | Pregnant or nursing people wear gloves for drug, litter and body fluids |
| Levothyroxine | Thyroid hormone | Post-pill T4 at 4 to 6 hours | Report panting, restlessness, increased thirst |
| Trilostane | Adrenal enzyme inhibitor | ACTH stimulation test 4 to 6 hours after dosing; electrolytes | Do not handle capsules if pregnant; wash hands |
| Phenobarbital | Barbiturate anticonvulsant | Serum level at steady state; liver values | Schedule IV controlled drug: log and count |
| Potassium bromide | Halide anticonvulsant | Serum bromide after about 3 months | Do not change diet salt content without asking |
| Metoclopramide | D2 antagonist, prokinetic | Tremors or abnormal movements | Not if obstruction is suspected |
| Sucralfate | Mucosal protectant | Timing with other oral drugs | Give other drugs first |
| Dinoprost | Prostaglandin F2-alpha | Treated animal for expected response | Skin absorption: abortion, bronchospasm; wash spills with soap and water |
Sources: product labels for ProZinc, Vetsulin, Felanorm, Vetoryl and Lutalyse (DailyMed); Merck Veterinary Manual chapters on hypothyroidism, anticonvulsants and antiemetics; FDA Carafate label.345679101314
Procedure or technique
Drawing up a U-40 insulin suspension
- Check the label: product name, concentration (U-40), expiry and the date the vial was first punctured.
- Pick up a U-40 syringe. If only U-100 syringes are on hand, stop and ask. Do not convert on the fly.
- Mix the suspension the way the label says. ProZinc: roll gently, do not shake.3 Vetsulin: shake thoroughly until uniformly milky, then let any foam settle.4
- Look at the suspension. If clumps or white particles remain after mixing, do not use the vial.3
- Draw up the ordered units, have a second person check if your clinic uses double checks, and inject subcutaneously.
- Return the vial upright to the refrigerator and record the dose.3
Timing monitoring samples
- Trilostane: give the dose with food, then start the ACTH stimulation test 4 to 6 hours later.7
- Levothyroxine once daily: draw T4 4 to 6 hours after the pill.6
- Anticonvulsants: if seizure control is poor, draw a trough sample, taken just before the next dose is due.9
| Feature | ProZinc | Vetsulin |
|---|---|---|
| Labeled species | Cats (label cited) | Dogs and cats |
| Concentration | 40 IU/mL | 40 IU/mL |
| Mixing | Roll gently; do not shake | Shake thoroughly; let foam disperse |
| Storage | Upright, 2 to 8 °C, do not freeze, protect from light | Upright, 2 to 8 °C, do not freeze, protect from light |
| Use after first puncture | 10 mL vial: 60 days; 20 mL vial: 80 days | 42 days |
Sources: ProZinc and Vetsulin labels on DailyMed.34
Flowchart
Species differences
- Cats: phenobarbital is the usual first anticonvulsant. Potassium bromide is avoided because of a potentially fatal bronchial disease with cough and lung infiltrates.9 Metoclopramide is a weak antiemetic in cats.10 Felanorm (methimazole) is labeled for hyperthyroidism in cats.5
- Dogs: phenobarbital and bromide are first-line maintenance anticonvulsants. Vetoryl (trilostane) is labeled for dogs, and the levothyroxine monitoring above is described for dogs.976
- Cattle and horses: dinoprost is labeled for estrous cycle control in these species.14 In dogs and horses, one dose of omeprazole suppresses acid for 3 to 4 days.12
- Pregnant patients: trilostane is contraindicated in pregnant and nursing animals and in animals intended for breeding.8
Calculation
Problem. A cat is ordered 10 units of a U-40 insulin. What volume is that, and what happens if the dose is drawn to the 10-unit mark on a U-100 syringe?
Correct volume: 10 units ÷ 40 units/mL = 0.25 mL (units cancel, leaving mL).
Wrong syringe: the 10-unit mark on a U-100 syringe holds 10 units ÷ 100 units/mL = 0.10 mL. That 0.10 mL of U-40 insulin contains 0.10 mL × 40 units/mL = 4 units.
Result: the cat gets 4 units instead of 10, a 60% underdose. The reverse error (U-100 insulin drawn to 10 on a U-40 syringe) gives 0.25 mL × 100 units/mL = 25 units, 2.5 times the dose, with a risk of hypoglycemia.
Safety, legal and client education
- Methimazole is a teratogen (causes birth defects) and passes into breast milk. Pregnant women, women who may become pregnant and nursing mothers should wear gloves when handling the drug, the cat's litter or body fluids.5
- Trilostane: do not handle the capsules if pregnant or trying to conceive. Wash hands after use.7
- Dinoprost: avoid skin contact, and wash skin spills immediately with soap and water. Early pregnancy may not be known, so any woman of childbearing age should take care.14
- Insulin: teach owners to use only the matching syringe, to store the vial in the refrigerator, and to bring the insulin and syringes to rechecks.2
- Potassium bromide: during loading, warn owners about marked sedation. Raising food and water bowls can help prevent aspiration.9
- Phenobarbital is a Schedule IV controlled substance, so it is logged and counted like other scheduled drugs.16
Common mistakes and exam traps
- "Always roll, never shake" is true for most insulin suspensions, but Vetsulin's label says shake. Follow the label.4
- Drawing U-40 insulin into a U-100 syringe underdoses; drawing U-100 into a U-40 syringe overdoses.
- The trilostane ACTH stimulation test starts 4 to 6 hours after dosing, not at a random time.7
- Bromide is renally excreted, not liver metabolized; phenobarbital is the liver-metabolized one.9
- Give oral drugs before sucralfate, not with it.13
- Oxytocin is for uterine inertia, never for obstructive dystocia (a fetus stuck in the birth canal).15
Quick review
- U-40 insulin is 40 units/mL; U-100 is 100 units/mL; match the syringe.
- Store insulin upright at 2 to 8 °C; never freeze.
- Roll ProZinc; shake Vetsulin; discard if clumps persist.
- Methimazole: CBC, biochemistry, TT4 at 3 and 6 weeks, then every 3 months.
- Levothyroxine: post-pill T4 at 4 to 6 hours.
- Trilostane: ACTH stimulation 4 to 6 hours post dose, 10 to 14 days after each change.
- Phenobarbital: steady state in about 2 weeks; watch the liver.
- Bromide: steady state up to 4 months; avoid in cats.
- Maropitant is an NK-1 antagonist; ondansetron a 5-HT3 antagonist.
- Metoclopramide: no use if obstruction is suspected.
- Sucralfate: other oral drugs go 2 hours before it.
- Dinoprost, methimazole and trilostane carry pregnancy handling warnings for staff.