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Verapamil decreases MAC for halothane in dogs
Insights
Verapamil hydrochloride, a cardiovascular drug, was found to reduce anesthetic requirements. This study shows verapamil significantly lowers the minimum alveolar concentration (MAC) for halothane anesthesia in dogs.
Area of Science:
- Anesthesiology
- Pharmacology
Background:
- Verapamil hydrochloride is increasingly used for cardiovascular conditions during surgery.
- Verapamil exhibits non-selective calcium channel blocking activity, also affecting sodium channels.
- Sodium channel blockers are known to influence anesthetic needs.
Purpose of the Study:
- To investigate the effect of verapamil on the minimum alveolar concentration (MAC) of halothane in dogs.
- To determine if verapamil alters anesthetic requirements due to its sodium channel activity.
Main Methods:
- The study measured the MAC for halothane in canine subjects.
- Halothane MAC was assessed before and after administering a therapeutic dose of verapamil (0.5 mg/kg).
- Verapamil plasma levels were monitored to ensure a therapeutic concentration was achieved.
Main Results:
- A statistically significant 25% reduction in halothane MAC was observed (from 0.97% to 0.72%, P < 0.01).
- This reduction occurred when dogs reached a therapeutic plasma level of verapamil (64 ng/mL).
Conclusions:
- Dl-verapamil may reduce anesthetic requirements for halothane, potentially due to its local anesthetic-like sodium channel blocking properties.
- Clinical adjustments in anesthetic dosage might be necessary for patients receiving verapamil during perioperative care.
Abstract:
Verapamil hydrochloride is a calcium entry blocking drug that is being prescribed with increasing frequency for cardiovascular disorders in the perioperative setting. Verapamil's calcium channel blocking effect is not selective, because it also exerts activity on the sodium channel. Because of the well-described effects of sodium channel blockers on anesthetic requirements, the authors studied the MAC for halothane in dogs before and after a therapeutic dose of verapamil 0.5 mg . kg-1. There was a 25% reduction in halothane MAC from 0.97-0.72% (P less than 0.01) when a therapeutic plasma level of verapamil (64 ng . ml-1) was present. Anesthetic requirements for halothane are reduced by dl-verapamil possibly on the basis of its local anesthetic-like sodium channel blocking properties. Adjustments in anesthetic dosage may be necessary in patients receiving verapamil.