Veterinary Drug Handbook (VDH) is the reference veterinarians turn to when they want an independent source of information on the drugs that are used in veterinary medicine today.

ATRACURIUM BESYLATE

Chemistry - A synthetic, non-depolarizing neuromuscular blocking agent, atracurium, is abisquaternary, non-choline diester structurally similar to metocurine and tubocurarine. It occurs aswhite to pale yellow powder. 50 mg is soluble in 1 ml of water, 200 mg is soluble in 1 ml ofalcohol, and 35 mg is soluble in 1 ml of normal saline.
The commercially available injection occurs as clear, colorless solution and is a sterile solution ofthe drug in sterile water for injection. The pH of this solution is 3.25 - 3.65. Atracurium besylatemay also be known as: atracurium besilate.

Storage, Stability, Compatibility

Atracurium injection should be stored in the refrigerator andprotected against freezing. At room temperature, approximately 5% potency loss occurs eachmonth; when refrigerated, a 6% potency loss occurs over a years time.
Atracurium is compatible with the standard IV solutions, but while stable in lactated Ringer's for 8hours, degradation occurs more rapidly. It should not be mixed in the same IV bag or syringe, orgiven through the same needle with alkaline drugs (e.g., barbiturates) or solutions (sodiumbicarbonate) as precipitation may occur.

Pharmacology - ATRACURIUM BESYLATE

Atracurium is a nondepolarizing neuromuscular blocking agent and acts bycompetitively binding at cholinergic receptor sites at the motor end-plate, thereby inhibiting theeffects of acetylcholine. Atracurium is considered to be 1/4 to 1/3 as potent as pancuronium. Inhorses, atracurium is more potent than in other species tested and more potent than other nondepolarizing muscle relaxants studied.
At usual doses, atracurium exhibits minimal cardiovascular effects, unlike most other nondepolarizing neuromuscular blockers. While atracurium can stimulate histamine release, it is consideredto cause less histamine release than either tubocurarine or metocurine. In humans, less than onepercent of patients receiving atracurium exhibit clinically significant adverse reactions or histaminerelease.
Uses, Indications - Atracurium is indicated as an adjunct to general anesthesia to produce musclerelaxation during surgical procedures or mechanical ventilation and also to facilitate endotrachealintubation. Atracurium can be used in patients with significant renal or hepatic disease.

Pharmacokinetics - ATRACURIUM BESYLATE

After IV injection, maximal neuromuscular blockade generally occurs within3-5 minutes. The duration of maximal blockade increases as the dosage increases. Systemicalkalosis may diminish the degree and duration of blockade; acidosis potentiates it. In conjunctionwith balanced anesthesia, the duration of blockade generally persists for 20-35 minutes. Recoverytimes do not change after maintenance doses are given, so predictable blocking effects can beattained when the drug is administered at regular intervals.
Atracurium is metabolized by ester hydrolysis and Hofmann elimination which occurs independently of renal or hepatic function.
Contraindications/Precautions - Atracurium is contraindicated in patients who are hypersensitive to it. Because it may rarely cause significant release of histamine it should be used with cautionin patients where this would be hazardous (severe cardiovascular disease, asthma, etc.). Atracuriumhas minimal cardiac effects and will not counteract the bradycardia or vagal stimulation induced byother agents. Use of neuromuscular blocking agents must be done with extreme caution, or not atall, in patients suffering from myasthenia gravis. Atracurium has no analgesic or sedative/anestheticactions.

Adverse Effects, Warnings

Clinically significant adverse effects are apparently quite rare inpatients (<1% in humans) receiving recommended doses of atracurium and usually are secondary tohistamine release. They can include: allergic reactions, inadequate or prolonged block, hypotensionvasodilatation, bradycardia, tachycardia, dyspnea, broncho-, laryngo- spasm, rash, urticaria, and areaction at the injection site. Patients developing hypotension usually have preexisting severecardiovascular disease.
Overdosage - Overdosage possibilities can be minimized by monitoring muscle twitch response toperipheral nerve stimulation. Increased risks of hypotension and histamine release occur withoverdoses, as well as prolonged duration of muscle blockade.
Besides treating conservatively (mechanical ventilation, O2, fluids, etc.), reversal of blockade maybe accomplished by administering an anticholinesterase agent (edrophomium, physostigmine, orneostigmine) with an anticholinergic (atropine or glycopyrrolate). Reversal is usually attempted (in humans) approximately 20-35 minutes after the initial dose, or 10-30 minutes after the lastmaintenance dose. Reversal is usually complete within 8-10 minutes.

Drug Interactions

The following agents may enhance the neuromuscular blocking activity ofatracurium: procainamide, quinidine, verapamil, aminoglycoside antibiotics (gentamicin, etc), lincomycin, clindamycin, bacitracin, polymyxin B, lithium, magnesium sulfate, thiazide diuretics, enflurane, isoflurane, and halothane.
Loop diuretics (e.g., furosemide) have been reported to both decrease and increase the effects of nondepolarizing neuromuscular blockers.
Other muscle relaxant drugs may cause a synergistic or antagonistic effect. Succinylcholinemay speed the onset of action and enhance the neuromuscular blocking actions of atracurium. Donot give atracurium until succinylcholine effects have diminished.
Theophylline or phenytoin may inhibit or reverse the neuromuscular blocking action ofatracurium.
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