Second Semester Exam - 1995 - Answers

Section THREE

Question 1.

Intramuscular Injection.

• Injection into the larger muscle of arm, buttock.
• Advantages
  • Larger volumes can be given (compared with s.c.)
  • Depot effect possible
  • By-passes the liver. No first-pass effect
• Disadvantages
  • May cause local tissue damage
  • Absorption is sometimes erratic, incomplete
  • Personal administering dose must be trained
  • Painful

Question 2.

Clearance, CL, is the volume cleared per unit time; relates rate of elimination to plasma concentration

CL = kel * V = Dose/AUC

UNITS: vol/time i.e. ml/min or L/kg

Question 3.

Fick's first law can be summarized as dM/dt = - D * A * (Ch-Cl)/X

• D is the diffusion coefficient. Depends on the size of the molecule and the viscosity of the dissolution medium
• A surface area. Smaller particles mean more particles, larger overall surface area and faster dissolution
• Ch is the drug solubility. Higher solubility generally means faster dissolution
• Cl is the concentration in the bulk phase. May approach zero ('sink' conditions) with a larger volume or if the drug is being removed by absorption
• X is the thickness of the stagnant layer surrounding each drug particle. Increased agitation or use of a reactive medium will reduce the effective value of X and increase dissolution.