Methods: Using three ladders pain analgesic WHO introduced, that is the first ladder giving NSAIDs. The second weak opioid 'analgesics, the third strong opioid analgesics.
Opioid analgesics are the mainstay for treatment of moderate and severe pain. However, the clinical use of opioid drugs still faces many obstacles, such as side effects and analgesic tolerance.
阿片类药物被广泛应用于治疗和缓解各种中度及重度疼痛，但其严重的副作用极大地限制了其临床应用。
3
While receptor affinity determines the amount of opioid needed to occupy a given percentage of receptors, it is the intrinsic activity of the opioid that determines its analgesic efficacy.