M1: Ch3 Drug Absorption & Distribution Flashcards
Refers to Drug Fate
Metabolism & Excretion
Refers to Drug Disposition
Absorption & Distribution
Delivery of drug to the tissue
Distribution
Passage of drug from its site of administration into the blood
Absorption
Most important transfer mechanism for foreign substance. Down a concentration gradient. Drug molecules pass from high to low concentration.
Passive Diffusion
Pass to different pores of membrane via fenestrations. Important for small molecules.
Filtration
Example of an organ that utilizes Filtration
Kindney (Glomeruli)
Agains a concentration gradient. Energy-dependent, Selective carrier-mediated & Saturable. From Low to High concentration. Uphill and against a concentration gradient.
Active transport
Drugs that uses Active transport
Levodopa, Iron, PTU & 5-FU “LIP 5”
Drugs that uses Active transport: for thyroid problems
PTU
Drugs that uses Active transport: for parkinsonism
Levodopa
Drugs that uses Active transport: for cancer
5-FU
Drugs that uses Active transport: for blood dyscrasia
Iron
Down a concentration gradient. Does not require energy. Selective carrier-mediated. Saturable. Never against a concentration gradient. High to Low concentration.
Facilitated Diffusion
Examples of drugs using Facilitated Diffusion
Vit. B12/Cobalamin
Complexes with intrinsic factor the goes to ileum them detected by the intestinal cells
Vit. B12
Microscopic invaginations capable of cell drinking. In-pouching of cell wall.
Pinocytosis
An example of drug that uses Pinocytosis
Botulinum toxin
Important in cell absorption. Example is Albumin may not be able to pass thru smaller sized membranes.
Basement membrane
Contains tight junctions with tightly packed endothelial junction. Only drugs that have high lipid-water partition coefficient can penetrate.
Blood Brain Barrier
BBB uses what mechanism of drug transfer
Passive & Facilitated Diffusion
Can increase the permeability of BBB
Inflammation (bacterial meningitis & encephalitis)
Substances that are lipid soluble crosses the placenta with relative ease in accordance with their partition coefficient and degree of ionization
Placental Barrier
Found at the specialized sertoli-sertoli cell junction, prevents certain chemotherapeutic agents thus hinders treatment of neoplasm.
Blood-Testis Barrier
Four Parameters that Influence the rate of diffusion of drugs
Thickness, Permeability Coefficient, Surface Area & Concentration Gradient “TPS C”
Fick’s Law of Diffusion: Increase Concentration Gradient = _________ Diffusion.
Decrease
Fick’s Law of Diffusion: Increase of Surface Area = ________ Diffusion.
Increase
Fick’s Law of Diffusion: Increase of Membrane Thickness = _________ Diffusion.
Decrease
Ratio of concentration of a drug in two phases (oil & water) polar & nonpolar. Measure drug affinity to lipid and water.
Lipid-Water Partition Coefficient
Formula for Lipid-Water Partition Coefficient
Kp = Coil / Cwater
Increase in Kp means
Soluble in oil
Decrease Kp means
Soluble in water
The polarity of drug influences its
Solubility
Increase polarity of drug = _____ water solubility. Thus Kp is ______.
Increased. Decreased.
Decrease polarity of drug = _____ water solubility. Thus Kp is ______.
Decrease. Increase.
More nonpolar means
More soluble to oil
Less nonpolar means
Less soluble to oil
Drug that is polar, ionized = ______ Kp (<1); soluble in ________.
Decreased. Water.
Drug that is nonpolar, non-ionized = ______ Kp (>1); soluble in ________.
Decreased. Lipid.
Ionization extent of Drug is based on
pH solution & pKa
Formula for total drug concentration
pH - pKa = log R/RH (unprotonated/protonated)
Fully ionized in a region of acidic environment. Goes into Intestine. _______ form will dominate.
Weak bases. Unionized.
More lipid soluble substances & able to cross membranes (lipophilic)
Unionized form
Base favors basic environment. Intestine is less acidic: ___________.
Unionized form
Base favors basic environment. Stomach is acidic: ___________.
Ionized form
Causes trapping
Ionized form
Able to pass
Unionized form
Weak Base in the Intestine is
Unionized
Weak Base in the GIT is
Ionized
Weak Acid in the GIT is
Unionized
Weak Acid in the Intestine is
Ionized