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Halothane



hal′oe-thane


Trade and other names: Fluothane


Functional classification: Inhalant anesthetic



Pharmacology and Mechanism of Action


Inhalant anesthetic. Halothane is a multi-halogenated ethane. It is characterized by rapid induction and recovery, high potency, and few adverse effects. Like other inhalant anesthetics, the mechanism of action is uncertain. They produce generalized, reversible depression of the CNS. The inhalant anesthetics vary in their solubility in blood, their potency, and the rate of induction and recovery. Those with low blood/gas partition coefficients are associated with the most rapid rates of induction and recovery. Halothane has a vapor pressure of 243 mm Hg (at 20° C), a blood/gas partition coefficient of 2.3, and a fat/blood coefficient of 51. Because of high solubility in fat, its clearance from the body is slower than other agents.



Indications and Clinical Uses


Halothane, like other inhalant anesthetics, is used for general anesthesia in animals. It has a minimum alveolar concentration (MAC) value of 1.04%, 0.87%, and 0.88% in cats, dogs, and horses, respectively. However, it has been replaced by newer inhalant anesthetics (e.g., isoflurane) in many veterinary practices.



Precautionary Information



Adverse Reactions and Side Effects


Like other inhalant anesthetics, halothane produces vasodilation and increased blood flow to cerebral blood vessels. This may increase intracranial pressure. Also like other inhalant anesthetics, it produces a dose-dependent myocardial depression, with accompanying decrease in cardiac output. It also depresses respiratory rate and alveolar ventilation. Like other inhalant anesthetics, it increases the risk of ventricular arrhythmias, especially in response to catecholamines. Hepatotoxicity has been reported in people.



Contraindications and Precautions


Administer with caution to patients with cardiovascular problems.



Drug Interactions


No specific drug interactions. Use of other anesthetics in conjunction with halothane will lower the requirement for halothane dose.



Instructions for Use


Use of inhalant anesthetics requires careful monitoring. Dose is determined by depth of anesthesia.



Patient Monitoring and Laboratory Tests


Monitor patient’s heart rate and rhythm and respiration during anesthesia.



Formulations


Halothane is available in a 250-mL bottle.



Stability and Storage


Halothane is highly volatile and should be stored in a tightly sealed container.



Small Animal Dosage



• Induction: 3%

• Maintenance: 0.5%-1.5%


Large Animal Dosage



• MAC value: 1%


Regulatory Information


No withdrawal times are established for food animals. Clearance is rapid, and short withdrawal times are suggested. For extralabel use withdrawal interval estimates, contact FARAD at 1-888-USFARAD (1-888-873-2723).



Hemoglobin Glutamer (Oxyglobin)



hee′moe-gloe-bin gloot′am-er


Trade and other names: Oxyglobin


Functional classification: Iron supplement, hemoglobin substitute



Pharmacology and Mechanism of Action


Hemoglobin glutamer (bovine) is used as oxygen-carrying fluid in dogs with varying causes of anemia. Oxyglobin is an ultrapurified polymerized bovine hemoglobin. The molecular weight is 64,000-500,000 (average 200,000). Osmolality is 300 mOsm/mL. Colloid osmotic pressure is higher than other colloids, with a colloid osmotic pressure of 43.3. Half-life in dogs is approximately 24 hours (range 18-43 hours). It is metabolized by macrophages, and 95% of a dose is eliminated in 5-9 days.



Indications and Clinical Uses


Hemoglobin glutamer has been used to treat anemia caused by blood loss, hemolysis, or decreased blood cell production. Although approved for dogs, it also has been used in cats.



Precautionary Information



Adverse Reactions and Side Effects


Circulatory overload is possible, especially with high doses and rapid administration. Patients at the most risk of circulatory overload are those with cardiac disease, respiratory disease, risk of hypertension, cerebral edema, oliguria/anuria caused by renal failure, and cats. Pulmonary hypertension has been observed because of depletion of nitric oxide (NO) and volume overload. Because cats are more sensitive to the adverse effects than dogs, lower dose rates should be used in cats. Other adverse effects have been skin and mucous membrane discoloration, vomiting, diarrhea, and anorexia. Discoloration of skin and mucous membranes can persist for 3-5 days.



Contraindications and Precautions


Hemoglobin glutamer should not be used in dogs with advanced heart disease. Administer with caution to cats because of an increased risk of pulmonary hypertension.



Drug Interactions


Do not administer with other drugs via the same infusion set. Do not mix with other drugs.



Instructions for Use


Administer using aseptic technique. In 5-7 days, 90% of dose is eliminated.



Patient Monitoring and Laboratory Tests


Patients receiving hemoglobin glutamer should be monitored carefully. Use of Oxyglobin does not require cross-matching. Monitoring packed cell volume (PCV) or hematocrit is not useful for assessing response to Oxyglobin therapy. Oxyglobin will interfere with other monitoring tests, such as blood chemistry analysis (colorimetric assays). Doses of 30 mL/kg are listed by manufacturer, but many veterinarians use 10-15 mL/kg.



Formulations


Hemoglobin glutamer is available in 13 g/dL polymerized hemoglobin of bovine origin in 125-mL single-dose bags. Availability from manufacturer may be limited.



Stability and Storage


At room temperature, hemoglobin glutamer has a 3-year shelf-life. Once opened, a 125-mL bag should be used within 24 hours because of oxidation of hemoglobin to methemoglobin. Do not freeze.



Small Animal Dosage



Dogs



• One-time dose of 10-30 mL/kg IV or up to a rate of 5-10 mL/kg/hr.


Cats



• One-time dose of 3-5 mL/kg IV, slowly. Maximum rate is 5 mg/kg/hr and not to exceed 13-20 mL/kg in 24 hours.


Large Animal Dosage


No doses reported. Do not use in race horses.



Regulatory Information


No regulatory information is available. Because of low risk of residues, no withdrawal times are suggested. However, hemoglobin glutamer (Oxyglobin) is prohibited to be on the premises of racing horses.


RCI Classification: 2



Heparin Sodium



hep′ah-rin soe′dee-um


Trade and other names: Liquaemin and Hepalean (Canada)


Functional classification: Anticoagulant



Pharmacology and Mechanism of Action


Anticoagulant. Heparin produces its action by increasing antithrombin III–mediated inhibition of synthesis and activity of factor Xa. Heparin differs from low-molecular-weight heparin (LMWH) by an equal anti-factor Xa/anti-factor IIa ratio. Heparin has a ratio of 1 : 1, but the LMWHs have ratios of 2 : 1 or higher. In people, there is an advantage of LMWH over conventional heparin because the LMWHs have longer half-lives and less frequent administration is needed. However, this may not be an advantage for dogs and cats. See the description of LMWH for more information (enoxaparin [Lovenox], and dalteparin [Fragmin]).



Indications and Clinical Uses


Heparin is administered to prevent and treat hypercoagulability disorders and prevent coagulation disorders such as thromboembolism, venous thrombosis, disseminated intravascular coagulopathy (DIC), and pulmonary thromboembolism. Use in specific situations in animals is primarily anecdotal or derived from the clinical experience in people. No outcome-based studies to evaluate efficacy have been published to support specific guidelines for therapy. Use for prevention of thrombosis in canine patients with immune-mediated hemolytic anemia has not been effective (300 units/kg q6h). In horses, it is used to prevent thrombosis in patients at risk.



Precautionary Information



Adverse Reactions and Side Effects


Adverse effects caused by excessive inhibition of coagulation result in bleeding. Heparin-induced thrombocytopenia, a problem in people, has not been cited as a problem in animals. If excessive anticoagulation and bleeding occur as a result of an overdose, protamine sulfate should be administered to reverse heparin therapy. Protamine should be administered by slow IV infusion. Protamine complexes with heparin to form a stable, inactive compound.



Contraindications and Precautions


Do not use in animals unless able to monitor bleeding because it may be life threatening. Do not inject IM because it may create a hematoma.



Drug Interactions


Use cautiously in animals that are already receiving other drugs that can interfere with coagulation, such as aspirin and warfarin. Although a specific interaction has not been identified, use cautiously in animals that may be receiving certain chondroprotective compounds, such as glycosaminoglycans for treatment of arthritis.



Instructions for Use


Dose adjustments should be performed by monitoring clotting times. For example, dose is adjusted to maintain activated partial thromboplastin time (APTT) at 1.5 to 2 times normal. For information on other forms of heparin, such as LMWHs, see dalteparin or enoxaparin. Duration of anticoagulant effect may vary among patients, but in general, a 200-unit/kg dose in dogs has a duration of effect of approximately 6 hours.


In high-risk patients, doses used include 500 units/kg SQ or IM, followed by reduced doses such as those listed in dosing section q8-12h.



Patient Monitoring and Laboratory Tests


Monitor effect using APTT or anti-Xa activity. Dose is adjusted to maintain APTT at 1.5 to 2 times normal. Target range for anti-Xa activity is 0.35-0.70 units/mL. If anti-Xa activity is greater than 70 Units/mL, reduce dose by 25%.



Formulations


Heparin sodium is available in 1000- and 10,000-units/mL injection.



Stability and Storage


Store in a tightly sealed container, protected from light, and at room temperature.



Small Animal Dosage



Dogs and Cats (low-dose prophylaxis)



• 70 units/kg q8-12h SQ.


Dogs



• 100-200 units/kg IV loading dose, then 100-300 units/kg q6-8h SQ. Adjust dose via monitoring and increase to 500-600 units/kg if necessary. In more severe cases, start with 500 units/kg SQ as initial dose, then administer 500 units/kg q12h.


Cats



• 300 units/kg SQ, q8h and increase up to 500 units/kg if necessary.


Large Animal Dosage



• 125 units/kg SQ or IM q8-12h. (Lower doses of 80 units/kg SQ, q12h also have been used in horses.)


Regulatory Information


No regulatory information is available for food animals. Because of low risk of residues, no withdrawal times are suggested.



Hetastarch



het′ah-starch


Trade and other names: HES, Hydroxyethyl starch, Hetastarch, and Hespan


Functional classification: Fluid replacement



Pharmacology and Mechanism of Action


Hetastarch is a synthetic colloid volume expander that is used to maintain vascular volume in animals with circulatory shock. It is a modified branched-chain glucose polymer prepared from hydroxyethyl starch and is derived from amylopectin. There are two hydroxyethyl starch preparations: hetastarch and pentastarch. Hetastarch (6%) has an average molecular weight of 450,000 and colloid osmotic pressure of 32.7. Pentastarch (10%) has an average molecular weight of 280,000 and colloid osmotic pressure of 40. Because hetastarch is a larger molecular weight compound than pentastarch, it tends to remain in the vasculature and prevent loss of intravascular volume and prevent tissue edema. Other colloids used are dextrans (Dextran 40 and Dextran 70).



Indications and Clinical Uses


Hetastarch is used primarily to treat acute hypovolemia and shock. It is administered IV in acute situations. Hetastarch has a duration of effective volume expansion of 12-48 hours. One of the disadvantages to use of hetastarch is the high cost.



Precautionary Information



Adverse Reactions and Side Effects


Only limited use in veterinary medicine; therefore, adverse effects have not been reported. However, it may cause allergic reactions and hyperosmotic renal dysfunction. Hetastarch suspensions may affect platelet function at clinically relevant doses for up to 24 hours. Do not use in patients with bleeding problems or preexisting coagulopathies.



Contraindications and Precautions


Do not use in animals with bleeding problems (coagulopathies) or active hemorrhage.



Drug Interactions


Hetastarch is available compatible with most fluid solutions.



Instructions for Use


Suspend in saline (0.9%) or 5% dextrose solution for use. Administer in 5-mL/kg increments to small animals, then reassess and increase the dose to rates listed in the dosing section. Hetastarch is used in critical care situations, and it is infused via constant rate infusion (CRI). Hetastarch appears to be more effective and produce fewer side effects than Dextran. Infuse slowly.



Patient Monitoring and Laboratory Tests


Monitor patient’s hydration status and blood pressure during administration. Monitor heart rate and rhythm and observe patients for evidence of bleeding. Administration of hetastarch may increase patient’s amylase for 2-3 days.



Formulations


Hetastarch is available in 6% injectable solution.



Stability and Storage


Hetastarch is stable in original packaging and is compatible with most fluid administration sets.



Small Animal Dosage



Dogs



• CRI: 10-20 mL/kg/day IV (0.4-0.8 mL/kg/hr).


Cats



• CRI: 5-10 mL/kg/day IV (0.2-0.4 mL/kg/hr).
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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on H

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