Study of local anesthetics by Infiltration anaesthesia in guinea pig

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BACKGROUND

Local anaesthesia is a technique to create loss of sensation in specific region of the body.¹ Usually they are used in minor surgeries, dental procedures, cesarean section with reduced pain and distress. This technique is safer and superior to general anaesthesia.²

Local anaesthetic drugs produce reversible effect and a loss of nociception. When these drugs are used on specific nerve pathways they show effects such as analgesia and paralysis. Local anaesthetics differ in their pharmacological properties and are used in various techniques such as surface (topical) anaesthesia, infiltration, epidural block, plexus block and spinal anaesthesia.²

The aim of the present study is to determine the activity and tolerability of new local anaesthetics after infiltration anaesthesia in guinea pig.

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REQUIREMENTS

Animals required:
Adult guinea-pigs of either sex weighing 250-300 g

Drugs:
Lignocaine 0.2%, test drug (0.05% and 0.1%)

Instruments used:
Razor, Sterile sharp needle (26gx 3/8 inch needle)

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PROCEDURE

Select adult guinea pigs for the experiment. One day before the experiment, clip the hair on the back of guinea pigs and shave areas of diameter 4-5 cm on either side of the lower back. This produces a certain amount of irritation but disappears overnight. The skin will be more sensitive in the midline then in front than the back area. Hence the action of local anaesthetic should be tested in both areas. Stretch the lower back of the guinea pig by holding the animal with the hand by pulling the skin taut with thumb and forefinger. Then inject the standard drug and the test at a dose of 0.1 ml intracutaneously each side respectively, enough to rise the wheal. Mark the size of the wheal with pen. Test the reaction to prick after 5 minutes of injection.

Observe the animals normal reaction to a prick given outside the wheal. Then give six pricks inside the wheal and count the number of pricks to which the guinea pig reacts and fail to reacts are noted. Apply each prick at an interval of about 3-5 seconds. Apply similar procedure for every 5 minutes for about 30 minutes.³

Observation

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CONCLUSION

Responses at the site of injection indicate the degree of anaesthesia. Failure to squeek (6/6) indicates maximum anaesthesia and 0/6 indicates no anaesthesia.

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REFERENCES

1. William A, Catterall A, Kenneth M. Local Anesthetics. In: Laurence Bruton L,Goodman and Gilmans The Pharmacological Basis of Therapeutics, 12 th ed. New Delhi: Mc Graw Hill Medical; 2011: 564.
   
2. Local anesthesia. Available at: https://en.wikipedia.org/wiki/Local_anesthesia. Accessed on 17 October 2017.
   
3. Vogel GH. Study of Infiltration anaesthesia in guinea pig’s wheals. Drug Discovery and evaluation-Pharmacological assays. 2nd edition. Newyork: Springer-Verlag; 2002: 655.