Good choice for antigens likely to induce anaphylactic reaction if absorbed into the bloodstream. Often relied upon to provide rapid uptake into the bloodstream and lymphatics. However, this is dependent upon the size of the antigen. Good site for small molecular weight drugs that are irritant as they are rapidly absorbed into the blood and the inflammatory response distributed. Large molecules are more likely to be absorbed primarily by the lymphatic system which lie only in the fascial planes.
Advantage is that larger amounts can be injected intramuscularly.
Disadvantage is the more prolonged absorption and spread of antigen-adjuvant preparation along the fascial planes. Major disadvantage is the ability to monitor the injection site. Use of this method in rodents is discouraged due to the small muscle mass available. Use of complete Freund's in the route is controversial. Antigen is taken up by the lymphatic system rapidly and transferred to draining nodes, the thoracic duct and hence the vascular system.