Compound Administration IV

Footpad is one of the specialized injection methods that biomedical researchers use for experiments necessitating the delivery of compounds via these atypical routes.
A footpad injection involves subcutaneous administration of the compound into the animal's hind foot. This video will illustrate the considerations, procedures and applications of this special injection technique.
Footpad injection is used in certain studies, especially those involving inflammation and tumor growth. Note that injections should be performed on only one foot and never bilaterally.
Alternatively, hock injections administered in the tarsal region are often preferred, as they target the popliteal lymph nodes while minimizing pain and preserving mobility compared with footpad injections.
Footpad injection is associated with increased discomfort, as it involves a weight-bearing surface and may impact normal ambulation. 
Footpad measurements should be taken daily once obvious swelling occurs.
Therefore, this technique should only be performed when scientifically justified and when alternative approaches are not suitable for the experimental objectives.
A 27-gauge or small-gauge needle is recommended for the injection, and the maximum volume recommended is 50 microliters or as specified in IACUC-approved institutional guidelines. 
Following any injection, all animals must be closely monitored for signs of pain, level of food consumption, and for normal ambulation. 
Humane endpoints must be established to ensure that animals are euthanized before mobility is significantly impaired or access to food and water is compromised.
Let’s learn this injection procedure in mice and rats. Attach the appropriate needle and fill the syringe with the correct volume. This procedure can be done in conscious animals.
Place the animal in a restraint tube with one hind foot isolated and extended by grasping the skin above the stifle. 
Wipe the foot with water or alcohol to remove debris before injection.
To avoid the blood vessel that runs the length of the foot, the injection landmark is at the center, but just off the midline, closer to the toes.
Place the needle bevel up at the injection site, directing it towards the heel. 
Inject the compound slowly and steadily to avoid rapid distention of the foot tissues. This will cause the footpad to swell as the injected material fills the subcutaneous space. 
In a small animal's foot, the swelling from the injection can extend to the heel, whereas in a larger animal, it will be more localized.
After the injection, observe the animals daily, and if persistent swelling is present or if there are lesions or tumors as a result of the experimental protocol, then, using a caliper, perform the footpad measurement. 
This instrument measures foot thickness in millimeters and helps in the quantification of swelling.
Now, let's discuss a few example experiments that use footpad injections.
Investigators often use footpad injection to analyze inflammatory responses. In this experiment, researchers isolated peripheral blood mononuclear cells from human blood samples, mixed them with different test antigens and injected the solutions into an animal's footpad. 
Finally, they measured foot thickness to quantify the swelling response due to different antigens.
You've just watched JoVE's final installment on the common and specialized compound administration techniques.
Just to recap, in the first part, we reviewed the most common parenteral routes. In the second chapter, we discussed the enteral and topical procedures. The third installment covered with the first set of atypical procedures, like intradermal, intranasal, and intracranial administration in neonates. 
Lastly, here we discussed one additional atypical route that biomedical researchers use in labs for specific purposes.
After watching this series, you should have a much better understanding of different administration techniques, and you should also know the general and specific considerations related to these protocols of compound administration. 
Whenever scientifically appropriate, non-animal methods, including cell-based models, organoids, organ-on-chip platforms, and other in vitro assays, should be used to reduce or replace animal use in studies involving compound administration.