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What form is more stable?
the amorphous form is always more stable then the crystal form
When a drug gets into solution what can it do?
Enter the systemic circulation to exert a therapeutic effect
What is the rate limiting step in dissolution?
- The rate or time to dissolve in fluids at the site of absorption
- Absorption of drug into blood circulation
What is the diffusion layer of dissolution?
When a diffusion layer, stagnant layer is formed around the solid drug then mixed with the gastric juices to for the bulk of the solution then can get absorbed into the blood stream
What is the Danckwert's model of dissolution?
- Also called surface renewal theory
- Accounts for packet that are present in the agitated fluid which reach the solid-lquid interface, absorb the solute by diffusion and carry it into the bulk of the solution
- Continuously being replaced by new ones and exposed to new solid surface each time
What is the partition coefficient ?
this number indicates how readily a chemical can dissolve in fats and oils. If the octanol/water partition coefficient is high, e.g. for DDT it is about 6, then the chemical can accumulate more readily in body fat and can be stored there for a very long time, as it may be excreted very slowly
T/F Unionized/Lipophillic drug molecules are more readily absorbed
Where are weak acid and weak bases absorbed?
They are going to absorbed at a pH of their pka. If it is enteric coated and they are acidic they will not be released until the intestines, there will be a small amount of unionized and can diffuse accross the membrane then reset the equilibrium and repeat the process to slowly release an acidic drug in an a basic environment
What are four properties of excipients?
- Alter drug absorption
- Enhance solubility
- Increase retention time of drug in the GIT
- Act as carriers to increase diffusion across intestinal wall
Makes the diluent adhere to the tablet to form a compact mass
Swells up and disintegrates causing a release of active ingredients into solution
improve the flow properties, mainly during manufacturering
Decrease interfacial tension
capable of being percieved by more than one sense organ
the movement of drug between blood and tissues
What are the factors that afect drug distribution?
- Blood flow: rate of delivery to tissues
- Capilary permeability: ability of drug to pass through capillaries
- Binding of drugs to proteins and tissue components
- Hepatic first past effect
- Enterohepatic cycling
Perfusion limited distribution
- Perfusion is the process of nutritive delivery of arterial blood to a capillary bed
- THe rate of blood flow to certain organs can limited distribution to the target organ
- High Lipid solubility
- Low water solubility
Diffusion limited distribution
- drugs with charges unable to diffuse across the membranes
- Low lipid solubility
- High water solubility
What is a loading dose?
It is a dose that binds to the plasma protein such that it allows for the actual dose to get to the target tissue
Enterohepatic circulation refers to the circulation of biliary acids from the liver, where they are produced and secreted in the bile, to the small intestine, where it aids in digestion of fats and other substances, back to the liver.
enterohepatic cycling of drugs
- Enterohepatic circulation also means that some molecules which would not otherwise be very toxic can become extremely hepatotoxic as they reach unexpectedly high hepatic concentrations. Drugs may remain in the enterohepatic circulation for a prolonged period of time as a result of this recycling process.
- When taken with food increases the circulation of drug and can stay in stomach longer
- Fat solubile drugs stays into body longer than water soluble drugs
T/F Urine is the only route of excretion
- Can be secreted through sweat, milk, hair....
- Allows drugs to pass into urine
- Reduced by plasma protein binding
- Only a portion of plasma is filtered
active carrier process for cations and anions
What inhibits tubular secretions?
Of lipid soluble drugs back into body across the tubule cells
What is the first step in renal drug excretion?
Active tubular secretion
some drugs that are weak acids or weak bases undergo active tubular secretion by transport systems located in the proximal tubular cells
- Most substance can be reabsorbed if they are unionized and lipid soluble
- Manipulation of urine pH makes drugs not to be reabsorbed in overdose situations
What is the renal clearance?
Excretion rate divided by plasma drug concentration in units of L/h