Pharm 2 - Exam 4

How is an arrhythmia defined?

An abnormality in the rate, regularity, or site of origin of a cardiac impulse, or a disruption in the impulse conduction.

What are the common imbalances or physiological factors associated with the mechanism of action (MOA) of arrhythmias?

Imbalances of the Parasympathetic ($PSNS$) and Sympathetic Nervous System ($SNS$), changes in electrolyte concentrations (especially $K^+$ and $Ca^{++}$), hypoxemia, and acidosis.

What is the primary MOA and typical use of Class I antiarrhythmic drugs?

They block fast $Na^+$ channels (membrane stabilizers) to enhance automaticity or prolong the refractory period; they are primarily used for ventricular tachyarrhythmias.

Which Class IA agent is specifically used for the treatment of atrial fibrillation in horses via IV administration?

Quinidine

Why is lidocaine generally not recommended for use in cats?

Due to adverse neurological and cardiac reactions.

What is the drug of choice (DOC) for boxer dogs suffering from severe ventricular tachyarrhythmias and syncope?

Mexiletine (oral equivalent) or Lidocaine.

What is the relationship between the PO dose and IV dose of Propranolol due to first-pass metabolism?

The PO dose is approximately $10 \times$ that of the IV dose.

Which Class III agent is noted for having a unique combination of Class III ($K^+$ block) and Class II ($\beta$ block) effects?

Sotalol

What must be monitored when a dog is treated with Amiodarone for DCM or atrial fibrillation, and why?

Liver enzymes must be monitored due to the risk of hepatotoxicity.

Which Calcium ($Ca^{++}$) Channel Blocker is most commonly used in veterinary medicine to control supraventricular arrhythmias?

Diltiazem

How does Digoxin exert its antiarrhythmic effects on the sinus and AV nodes?

Via parasympathetic (vagomimetic) effects.

Which oral vagolytic is used for the chronic treatment of bradyarrhythmias like sick sinus syndrome?

Propantheline bromide

What is the biggest determinant of serum osmolarity?

Sodium ($Na^+$)

What percentage of total body weight ($TBW$) is comprised of Intracellular Fluid ($ICF$), and what is its primary cation?

$ICF$ is approximately $40 \text{\%}$ of $TBW$, and its primary cation is Potassium ($K^+$).

Which force, primarily determined by albumin, pulls water into capillaries?

Oncotic Pressure ($COP$)

What is the maintenance fluid rate?

$$40–60 \text{ mL/kg/day}$$

What is the formula used to calculate the volume (L) needed to correct a fluid deficit?

$$\text{Body Weight (kg)} \times \text{\% Dehydration} = \text{Volume (L)}$$

Why should Calcium ($Ca^{++}$) NOT be added to Lactated Ringer's Solution ($LRS$)?

It will cause precipitation.

Which crystalloid is the fluid of choice for Diabetic Ketoacidosis ($DKA$) because it is acidifying?

Normal Saline ($0.9 \text{\% NaCl}$)

What is the primary use of Hypertonic Saline ($7.5 \text{\% NaCl}$)?

Small-volume resuscitation for shock/hemorrhage and the reduction of Intracranial Pressure ($ICP$).

When are colloids like Hetastarch or Vetstarch indicated based on Total Protein levels?

In hypooncotic states where Total Protein is \text{\leq 35 g/L}.

What agent is used to stabilize cardiac cell membranes during hyperkalemia by affecting threshold potential?

Calcium Gluconate

What is the maximum intravenous administration rate for Potassium ($K^+$) to prevent fatal overdose?

$0.5 \text{ mEq/kg/h}$ (or $0.5 \text{ mmol/kg/hr}$).

What is Varenzin-CA 1 (molidustat) used for in cats?

Control of non-regenerative anemia associated with Chronic Kidney Disease ($CKD$) by increasing erythropoietin production.

Describe the shift of Potassium ($K^+$) during states of acidosis.

$K^+$ moves out of cells in exchange for $H^+$, which can worsen hyperkalemia.

What is the normal pH range maintained in the body?

$7.38$ to $7.42$

What are the common causes of High Anion Gap Metabolic Acidosis listed in the notes?

Lactic Acidosis (hypoxia, shock), Diabetic Ketoacidosis ($DKA$), and Renal Failure.

Why do NSAIDs inhibit the diuresis response to Furosemide?

They block the production of $PGE_2$, which is needed for Furosemide's effect.

What is the MOA and primary therapeutic use of Acetazolamide (Diamox)?

It inhibits Carbonic Anhydrase to decrease $HCO_3^-$ formation; used primarily to decrease Intraocular Pressure ($IOP$) in glaucoma.

What is the primary therapeutic use for the osmotic diuretic Mannitol?

Reduction of Intracranial Pressure ($ICP$) and Intraocular Pressure ($IOP$).

Which diuretic blocks the $Na^+–K^+–Cl^-$ symporter in the loop of Henle and is used for $EIPH$ in horses?

Furosemide

Where do Thiazide diuretics like Hydrochlorothiazide ($HCTZ$) exert their mechanism of action?

In the Distal Convoluted Tubule ($DCT$), where they inhibit the $Na^+/Cl^-$ symport.

What is the mechanism of action of the Potassium-Sparing diuretic Triamterene?

It inhibits renal epithelial $Na^+$ channels, thereby retaining $K^+$.

How does Spironolactone assist in the treatment of refractory edema or ascites?

It binds to Mineralocorticoid Receptors ($MRs$) to antagonize aldosterone, enhancing diuresis while sparing $K^+$.

Vitamin K is a necessary cofactor for the hepatic synthesis of which clotting factors?

Factors $II$, $VII$, $IX$, and $X$.

Why is Vitamin K injection avoided via the IV route?

The vehicle (castor oil) can cause a reactivity leading to histamine release.

What drug is used as the reversal agent for a heparin overdose?

Protamine Sulfate

What is the clinical use for the antiplatelet drug Clopidogrel (Plavix) in felines?

To prevent thrombi associated with feline cardiomyopathy and other thromboembolic disorders.

How do Glucocorticoids ($GCs$) indirectly reduce the production of prostaglandins and leukotrienes?

By inhibiting phospholipase $A_2$ ($PLA_2$), which prevents the release of Arachidonic Acid ($AA$).

What effect do Glucocorticoids have on blood glucose ($BG$)?

They are antagonistic to insulin and increase $BG$, which is the mechanism for causing Diabetes Mellitus ($DM$).

How do Glucocorticoids cause Polyuria/Polydipsia ($PU/PD$)?

Via inhibition of $ADH$ (Vasopressin) release and action.

What is the relative potency of Dexamethasone compared to Hydrocortisone ($HC$)?

Dexamethasone is approximately $30 \times$ as potent as $HC$.

Why is it critical to taper Glucocorticoids after chronic use rather than stopping abruptly?

Abrupt withdrawal risks iatrogenic hypoadrenocorticism.

Which oral soft steroid is the drug of choice for inflammatory bowel disease ($IBD$) in dogs and cats?

Budesonide

What are the drugs of choice ($DOCs$) for treating Hypoadrenocorticism (Addison's) in both injectable and oral forms?

Injectable: Desoxycorticosterone pivalate ($DOCP$); Oral: Fludrocortisone (Florinef).

What is the drug of choice for canine Hyperadrenocorticism (Cushing's) and its mechanism?

Trilostane (Vetoryl); it blocks the synthesis of adrenal steroids (cortisol and aldosterone).

How is a Low-Dose Dexamethasone Suppression Test ($LDDS$) interpreted if cortisol does not change at 4 or 8 hours?

The Hyperadrenocorticism (Cushing's) is adrenal in origin.

What is the treatment for Central Diabetes Insipidus ($DI$)?

Desmopressin acetate ($DDAVP$), a synthetic $ADH$ analog.

What is the most common endocrinopathy in dogs, and what is the drug of choice for treatment?

Hypothyroidism ($HypoT4$); the drug of choice is Levothyroxine ($L\text{-thyroxine}$) ($T_4$).

What is the drug of choice for feline Hyperthyroidism, and what is considered a selective cure for the condition?

The drug of choice is Methimazole (Felimazole); the cure is Radioactive Iodine ($I\text{-}131$ therapy).