Venous equilibration model equation:
Drugs can be classified into three types
depending on the intrinsic clearance and
Flow limited drugs:
Examples include:- lidocaine, propranolol, morphine.
High fU • CLint (= CLtotal int) value
Capacity limited drugs:
Examples include:- phenytoin, warfarin, and quinidine.
Very low total intrinsic clearance. [fU • CLint << QH].
The three parameters; QH, fU, and CLint are important
determinants of drug elimination
Examples include:- Theophylline, antipyrine.
Between these two extremes.
Capacity-limited but binding-insensitive drugs.
Large polar molecules (MW > 400)
The mechanisms of transfer of drugs in milk:
both active and passive and influenced by the variations of the
composition of milk
Danger for the neonate.
The percentage of the dose given passing into milk ( 1%-5%)
The determination of drugs in saliva is done to
avoid the sampling of blood, could be used in
The salivary concentration of liposoluble drugs is the
reflection of their plasma concentration in free form.
But certain compounds such as iodide and
spiramycin, reach salivary concentrations higher than
those in plasma.
• Follows passive diffusion ( Non-ionized)
• Weak acids ( Sulphonamides)
• Weak bases ( Thiamine )
• Metals (Iron)
• For Gases (Anesthetics)
• Two types according to solubility.
• Prostate secretion
• Seminal fluid
• Vaginal fluid
• Eg: Doxycycline
• Alternative route in case of renal failure .