Induction

There are many lists that outline properties of an ideal induction agent.  Once example of such a list is given by Dugdale.49  Alfaxan exhibits most of the attributes that the list describes, including:

  1. Rapid onset of action192023
  2. Smooth induction192023
  3. Smooth recovery2650
  4. Non-irritant 21
  5. Short duration of action1920
  6. Non-cumulative 51
  7. Rapid metabolism2351
  8. Non-toxic or no metabolites51
  9. Does not cause histamine release5354
  10. Minimal cardiorespiratory side effects192023
  11. Produces a degree of muscle relaxation1920
  12. Stable in storage 30
  13. Stable in solution30
  14. High therapeutic index1155

In a number of studies confirming dosage pharmacokinetics, efficacy and safety in dogs and cats the onset of anesthesia from commencement of administration was found to be approximately 60 seconds.

Modern techniques for induction of anesthesia indicated that optimum results are obtained if the agent is injected slowly.  This effectively allows the patient to choose the dose it requires to produce unconsciousness.  Alfaxan does not cause pain on injection or excitement on induction,1920 so rapid bolus administration is not required.

Alfaxan dosage

To optimize results with Alfaxan, remember the following points:

  • The rate of intravenous injection should result in the total dose, if required, being administered over a period of 60 seconds.  This can be achieved by administering one-quarter of the calculated dose every 15 seconds;
  • Administration should proceed until the patient is fully anesthetized and can be intubated.  The patient's reflexes (palpebral, limb withdrawal, corneal, gag and perineal), its vital signs and the ease of passage of the endotracheal tube, indicate the depth of anesthesia;
  • If, 60 seconds after complete delivery of this first induction dose, intubation is not possible, one further similar dose may be administered to effect;
  • Alfaxan is a short-acting induction agent and anesthesia can lighten and the patient may regain consciousness if the transition period is prolonged through delaying connection to maintenance systems and administration of maintenance agents;
  • Once the endotracheal tube is placed, the patient should be immediately attached to the breathing system.  Patients administered Alfaxan in accordance with the above recommendations generally ventilate spontaneously and will transition to maintenance with gaseous agents quite smoothly.  Should apnea of more than 60 seconds occur, positive pressure ventilation (PPV) should be delivered to the patient;
  • When using Alfaxan, patients should be continuously monitored and facilities for the maintenance of a patient airway, artificial ventilation and oxygen supplementation must be immediately available.

 

Alfaxan induction dose guidelines for dogs and cats

 

PREANESTHETIC

Average Alfaxan Induction Dose
(and range) in MG/KG

Dog

Cat

No preanesthetic

2.2 (1.5 – 4.5)

4.0 ( 2.2 – 9.7)

Benzodiazepine + opioid + acepromazine

1.7 (0.9 – 3.5)

2.3 (1.15 – 5.0)

Opioid + acepromazine

1.6 (0.6 – 3.5)

3.2 (1.1 – 10.8)

Alpha, -agonist

1.1 (0.21 – 2.0)

3.6 (1.1 – 5.0)

(See full prescribing information, including some other combinations of premedicants)

The dosing syringe should be prepared to contain the calculated dose.  Administration should continue until the clinician is satisfied that the depth of anesthesia is sufficient for endotracheal intubation, or the entire dose has been administered.  Additional doses of Alfaxan, similar to those used for maintenance may be administered to facilitate intubation.