3 Medical Mathematic: Distribution of Drugs Flashcards
What factors affect the distribution of drugs?
Physicochemical properties of the drug (Lipid solubility, degree of ionization) Concentration gradient Plasma protein binding Blood flow Tissue barriers Affinity of drugs to certain tissues
Describe plasma binding proteins
Acidic drugs bind mainly to albumin.
Basic drugs bind mainly to acid alpha 1-glycoproteins and lipoproteins.
Some drugs bind to globulin (e.g., steroids).
Generally reversible.
Prolongs the half-life of the drug.
The bound form is inactive, can not be distributed, metabolized or excreted by glomerular filtration.
The rate of binding depends mainly on the amount of the drug.
Binding can be modified by disease.
Drugs can compete on the binding sites.
Plasma protein binding depends on the species.
Describe blood flow as it affects the distribution of drugs
The rate of tissue perfusion relative to the tissue mass – Highly perfused tissues Brain, liver, kidney, endocrine glands – Moderately perfused tissues Muscle, skin – Poorly perfused tissues Bone, adipose tissue • Alteration of blood flow – Physiological factors – Drugs – Disease
List the tissue barriers
The blood-brain barrier Eye Testicles Placenta Mammary gland
Describe The blood-brain barrier
Tight capillary endothelial junctions
The presence of glial cells
Flow of the CSF into venous drainage
Active transport mechanisms for extrusion of organic acids or bases
What factors influence the blood-brain barrier?
Age Inflammation (meningitis) Trauma Allergic reactions Severe hypotension Hypoxia High doses of organic solvents (alcohol) High doses of heavy metals (lead, mercury)
Examples of the Affinity of drugs to certain tissues
Tetracycline to calcium in skeletal tissues
Aminoglycosides to kidney tissue
Trapping of iodine by the thyroid gland
What is the Redistribution of drugs?
Is the movement of the drug from the tissues to the blood
The example of thiopental versus phenobarbital
What is distribution of drugs?
Is the transport of drugs from the plasma to the tissues (site of action, site of storage, site of biotransformation)