Why does orally administered morphine exhibit significantly lower analgesic potency compared to intravenous administration in treating post-operative pain?

💡 Explanation

Morphine's oral bioavailability is low because it undergoes substantial first-pass metabolism in the liver, where enzymes like UGT2B7 conjugate it, rendering it less active; therefore, a smaller fraction of the drug reaches systemic circulation compared to intravenous injection, rather than altered receptor affinity.

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