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pharmacokinetics (excretion (factors affecting excretion (ionization (pH…

- - - - pH of the urine
        
        high carbs/acidifying agents (oranges, vitamin C, etc) = low pH = high reabsorption since most antibiotics = acidic
        
        high protein diet/alkalinizing agents = high urine pH = more ionized drug = less re-absorption = more excretion
  - - - passive via urine pH
      - active transport @ descending loop
        
        vitamins
  - - - penicillin preferred by enzyme over glucuronic acid
      - probenecid: competes for active transport in membrane sp decreases secretion of penicillin
- - - - duodenum
        
        down the gut and excreted
        
        re-absorbed and another chance to act
        
        back into the biliary cycle
- - - - ionization: ionized molecules cannot cross lipid membranes
        
        pH dependent; stomach = pH2; gut range pH 8-9; small section of duodenum has pH <7, allowing absorption in to the blood
        
        Donnan effect: alkaline blood (pH 7.4) encourages ionization of acidic drugs
        
        ionized drug = reservoir of potentially available drug
      - affinity for proteins: molecule bound to a protein will not be free/avail for transport
        
        serum proteins (primarily albumin): reservoir of drug; releases drug when total free drug concentration decreases
      - lipophilicity: lipophobic/hydrophilic repealed by membrane; too lipophilic never leaves the membrane/fatty tissues
        
        partition coefficient (Kd) : ratio fo drug concentration in lipid to concentration in water; mathematically = the rate of molecular movement into lipid divided by the rate of movement into water; higher Kd = more lipophilic