Aspirin is a weak acid drug (pKa 3.5) and propranolol is a weak base (pKa 9.5). Which ONE of the following statements regarding their in vivo disposition is correct?

Question

BlackTom AI · Accepted Answer

Question restatement: The prompt asks which statement about the in vivo disposition of aspirin (a weak acid, pKa 3.5) and propranolol (a weak base, pKa 9.5) is correct, focusing on ionization and plasma protein binding.
Option A: 'Compared to propranolol, aspirin is more extensively ionized in the stomach and highly bound to serum albumin.' While aspirin is indeed bound to albumin, its ionization depends on pH. In the stomach, which has a very low pH, a weak acid tends to be largely non-ionized, not extensively ionized. Therefore this option is inconsistent with the pH-dependent ionization behavior of aspirin in the gastric environment, making it unlikely to be correct.
Option B: 'Compared to propranolol, aspirin is more extensively ionized in plasma and highly bound to serum albumin.' In plasma (pH ~7.4), aspirin (a weak acid) is mostly ionized, which increases its tendency to bind to serum albumin. Propranolol, a weak base, tends to remain more non-ionized in plasma and can bind to alpha-1-acid glycoprotein as well as albumin, but the key comparison is that aspirin is more ionized in plasma and highly albumin-bound relative to propranolol. This option captures the correct trend about ionization in plasma and albumin binding, aligning with well-known pharmacokinetic principles.
Option C: 'Compared to propranolol, aspirin is more extensively ionized in plasma and highly bound to α1-acid glycoprotein.' Although basic drugs like propranolol interact with α1-acid glycoprotein, aspirin is a weak acid and primarily binds to albumin, not α1-acid glycoprotein. This makes the statement inaccurate regarding the binding partner.
Option D: 'Compared to propranolol, aspirin is more extensively ionized in the stomach and highly bound to α1-acid glycoprotein.' In the stomach, aspirin would not be more ionized; weak acids are less ionized in the highly acidic stomach. Moreover, binding to α1-acid glycoprotein is more characteristic of basic drugs, not aspirin. Thus this option misstates both the ionization environment and the binding protein.
Summary of reasoning: The core concepts are the pH-dependent ionization of acids vs bases and the differential plasma protein binding patterns (albumin for many acidic drugs like aspirin; α1-acid glycoprotein for many basic drugs like propranolol). Therefore, the option stating that aspirin is more extensively ionized in plasma and highly bound to serum albumin correctly reflects these pharmacokinetic principles, while the other options misstate the ionization environment (gastric pH) or the primary binding protein (α1-acid glycoprotein) for aspirin or misattribute ionization.

Aspirin is a weak acid drug (pKa 3.5) and propranolol is a weak base (pKa 9.5). Which ONE of the following statements regarding their in vivo disposition is correct?Single choice

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