 They can't be delivered orally because the harsh environment of the gastrointestinal tract would breakdown the drug before it could reach the diseased tissue.Because systemic administration results in blockading the same pathway in both healthy and diseased tissue, pharmacology is exaggerated leading to many side effects such as lymphoma, infections, congestive heart failure, demyelinating disease, a lupus-like syndrome, injection site reactions, and additional systemic side effects.Patients often wait till after other treatment options have failed to begin biological therapy because biologics are extremely expensive.