Acute physical dependence: time course and relation to human plasma morphine concentrations

Area of Science:

• Pharmacology
• Neuroscience
• Clinical Research

Background:

• Assessing the time course of acute dependence effects in humans after opioid administration is crucial for understanding opioid withdrawal.
• Previous studies lacked a comprehensive assessment of the post-agonist time course of opioid dependence effects.

Purpose of the Study:

• To characterize the time course of precipitated withdrawal responses following morphine administration.
• To compare this time course with opioid agonist effects and plasma morphine concentrations.

Main Methods:

• 10 non-dependent, opioid-experienced subjects received a single intramuscular dose of morphine (18 mg/70 kg).
• Opioid agonist effects, plasma morphine levels, and naloxone-precipitated withdrawal were assessed at multiple intervals up to 42 hours post-morphine.
• Naloxone (10 mg/70 kg) was administered intramuscularly to precipitate withdrawal symptoms.

Main Results:

• Precipitated withdrawal effects peaked at 6 hours post-morphine, significantly later than peak agonist effects (1 hour).
• Agonist effects (pupil constriction, subjective ratings) lasted up to 12 hours; detectable morphine persisted in plasma for up to 30 hours.
• Withdrawal symptoms like temperature dysregulation lasted up to 36 hours, with significant effects observed for 24 hours post-morphine.

Conclusions:

• Acute physical dependence from a single morphine dose peaks later and persists longer than agonist effects.
• Neuronal adaptations underlying physical dependence develop and decay gradually during receptor occupancy.
• Detectable morphine supports competitive displacement in precipitated withdrawal, but noncompetitive actions are possible.