Page 167 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

• Thus, there is a gradual concentration of the drug filtrate as it passes through the

tubules.

• Hence, a concentration gradient develops that will increase drug concentration

the further down the tubules that the solute passes.

 Thus a large concentration gradient exists between the drug in renal tubules

and the free drug in plasma.

 This will favor the reabsorption of drug molecules from the luminal fluid into the

blood.

Passive reabsorption

• Tubular reabsorption occurs after the drug is filtered through the glomerulus.

• Although reabsorption by simple diffusion is theoretically possible for all drugs,

it is most significant for non-polar drugs.

• If a drug is completely reabsorbed (eg, glucose), then the value for the clearance

of the drug is approximately zero.

• For drugs that are partially reabsorbed, clearance values are less than the GFR of

125–130 mL/min.

• Factors affecting tubular reabsorption

1. Urine pH

2. Urine flow rate

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