Strong agonist

Moderate agonist

Weak agonist

Agonist-antagonist (mixed)

Antagonist

Not well absorbed orally.

Cannot cross the placental barrier.

First pass effect is negligible.

Converted to non-polar metabolites.

Excreted via kidneys.

Opioids have negative effect on cardiac contractility.

Meperidine can cause bradycardia.

Methadone can prolong QT interval.

Buprenorphine can cause 2nd degree heart block.

Morphine infusion may cause increased blood pressure.

BILIARY TRACT: Contract relaxation of biliary wall smooth muscle

UTERUS: May shorten labour

NEUROENDOCRINE: Inhibit ADH release

RENAL: Increase sphincter tone can precipitate urine retention

GASTROINTESTINAL TRACT: Diarrhoea due to increased intestinal peristalsis

Not recommended for long-term use

Neurotoxic active metabolite - normeperidine

Useful in treatment of cough

In large doses it dilates pupils

All adverse effects associated with meperidine and its metabolites are reversible by naloxone

Centrally acting analgesic that binds the kappa opioid receptor

Extensive metabolism via CYP450 2D6

Active metabolite has lower affinity for opioid receptor

More respiratory depression than morphine

Naloxone fully reverses analgesia

Morphine + ethanol causes additive CNS depression

Meperidine + MAO inhibitors increase incidence of hyperpyrexia coma

Meperidine + selective serotonin reuptake inhibitor causes serotonin syndrome

Tramadol + MAO inhibitors causes dopamine syndrome

Fentanyl + NASAIDs decrease pain tolerance

Meperidine

Codeine

Diphenoxylate

Oxycodone

Nalbuphine

Has no effect on the affect of pain.

Causes severe retrograde amnesia.

Cause inhibition of the brainstem respiratory center.

Meperidine strongly suppresses cough centre in the medulla.

Nausea and vomiting is more prominent when static.