example,  insulin  cannot be given orally because upon being administered in this manner, it is extensively  metabolized  in the  gastrointestinal tract  (GIT) before reaching the  blood stream , and is thereby incapable of sufficiently reaching its therapeutic target destinations. Contents  [ hide ] 1 Types 1.1 Oral 1.2 Inhalational 1.3 Parenteral Injection 1.4 Topical 1.5 Suppository 2 See also