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Table 1 Opioid characteristics regarding constipation

From: Clinical evaluation of the efficacy of methylnaltrexone in resolving constipation induced by different opioid subtypes combined with laboratory analysis of immunomodulatory and antiangiogenic effects of methylnaltrexone

Opioid Receptor affinity Lipophilicity Distribution site Incidence of constipation1
Morphine Sulphate Mainly μ, some κ Low Peripheral 60% (range 21-70%)
Oxycodone μ, κ and δ Intermediate Central and peripheral 65% (range 25-74%)
Fentanyl μ (highly selective) High Central 35% (range 10-55%)
  1. 1Estimated incidence of constipation without laxative use and the range of this incidence found in different studies in which a proportion of patients already uses laxatives.