Fentanyl is a pure mu agonist. It is generally not
administered orally due to it undergoing extensive
first-pass metabolism. Preparations which
are absorbed through the oral or nasal mucosa are,however, available. It is lipophilic which facilitates
absorption through the skin. Trans-dermal administration
is useful for patients with stable pain and stable
opioid requirements. Fentanyl lacks active metabolites
and is useful in patients with renal failure.