A comparison of withdrawal in rats implanted with different types of morphine pellets

Pharmacol Biochem Behav. 1976 Dec;5(6):603-7. doi: 10.1016/0091-3057(76)90299-9.


Time course and duration and physical dependence was investigated in rats implanted subcutaneously with 3 different types of morphine (M) pellets. Each was formulated according to the method of Gibson and Tingstand [8], but differed in surface area and hardness. Animals were maintained for 19 days after implantation and physical dependence was assessed every other day. Severity of naloxone (Nx)-induced withdrawal was quantified by the use of a composite symptom score and weight loss. Withdrawal severity was greatest following implantation of a pellet (Type C) of large surface area and low hardness rating, and least following implantation of a pellet (Type A) of small surface area and high hardness rating. Abstinence severity which resulted from implantation of a pellet (Type B) of moderate surface area and low hardness rating was intermediate. When 2 pellets were implanted the difference between Type C and B was amplified. It was concluded that formulation per se was not sufficient for specifying M pellet characteristics.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Body Weight / drug effects
  • Drug Implants
  • Hardness
  • Humans
  • Male
  • Morphine / administration & dosage*
  • Morphine / pharmacology
  • Morphine Dependence / complications
  • Morphine Dependence / physiopathology
  • Naloxone / pharmacology
  • Rats
  • Substance Withdrawal Syndrome / chemically induced
  • Substance Withdrawal Syndrome / etiology
  • Substance Withdrawal Syndrome / physiopathology*
  • Surface Properties
  • Tablets
  • Time Factors


  • Drug Implants
  • Tablets
  • Naloxone
  • Morphine