I believe the answer is <span>c. absorption
</span>The phase of pharmacokinetic that happens in the intestine is when the drug absorbed. A person with old age will have lower intestine motility. This will increase the transit time which will increase the amount of drug absorbed.
Age could also influence others pharmacokinetic parameter(<span>excretion, distribution, metabolism) but it is related with another organ, not intestine.</span>
Buffers absorb the free hydrogen ions and hydroxide ions that result from chemical reactions. Because they can bond these ions, they prevent increases or decreases in pH. An example of a buffer system is the bicarbonate system in the human body.
