Which statement correctly describes the effect of highly charged molecules on absorption (ct curve)?

Which statement correctly describes the effect of highly charged molecules on absorption (ct curve)?

• A. Slower absorption; the slope is less steep; elimination remains constant.
• B. Absorb faster and steeper slope
• C. No absorption at all
• D. Elimination increases proportionally

Answer: (A)

Absorption rate is limited by how easily a drug can cross cell membranes. Highly charged molecules have low lipid solubility, so their ability to diffuse through the intestinal epithelium is greatly reduced. This lowers the absorption rate constant (ka), causing a slower rise in the concentration-time curve during the absorption phase. The curve becomes less steep because it takes longer for the drug to enter systemic circulation, and the peak concentration is typically smaller and reached later (lower Cmax, longer Tmax). Meanwhile, elimination is governed mainly by clearance and the intrinsic disposition of the drug, which, in linear kinetics, remains unchanged by slower absorption. So the overall pattern is slower absorption with a gentler slope, while elimination stays essentially the same.

Absorption rate is limited by how easily a drug can cross cell membranes. Highly charged molecules have low lipid solubility, so their ability to diffuse through the intestinal epithelium is greatly reduced. This lowers the absorption rate constant (ka), causing a slower rise in the concentration-time curve during the absorption phase. The curve becomes less steep because it takes longer for the drug to enter systemic circulation, and the peak concentration is typically smaller and reached later (lower Cmax, longer Tmax). Meanwhile, elimination is governed mainly by clearance and the intrinsic disposition of the drug, which, in linear kinetics, remains unchanged by slower absorption. So the overall pattern is slower absorption with a gentler slope, while elimination stays essentially the same.