Page 170 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

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

In contrast, acidification of the urine will cause:

• the amphetamine to become more ionized (form a salt).

• The salt form is more water soluble and less likely to be reabsorbed and has a
tendency to be excreted into the urine more quickly.

In the case of weak acids (such as salicylic acid),

• acidification of the urine causes greater reabsorption of the drug and

.
• alkalinization of the urine causes more rapid excretion of the drug
• Consequently, it is important, when studying the pharmacokinetics of weak acids and

bases to consider the pH of urine.

Effect of urine flow rate on tubular reabsorption

• In addition to the pH of the urine, the rate of urine flow influences the extent of

reabsorption of a drug from the distal tubule (i.e. the amount of filtered drug that

is reabsorbed).

• The normal flow of urine is approximately 1–2 mL/min.

• Nonpolar and nonionized drugs, which are normally well reabsorbed in the renal
tubules, are sensitive to changes in the rate of urine flow.

• Drugs that increase urine flow, such as:

› Ethanol

› Large fluid intake

› Methylxanthines (e.g. caffeine or theophylline),

• decrease the time for drug reabsorption and promote their excretion.

• Thus, forced diuresis through the use of diuretics may be a useful adjunct for

removing excessive drug in an intoxicated patient, by increasing renal drug

excretion.

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