APhA NAPLEX Review| 660 Questions| with complete solutions

If the pka of a weak acid is 2.5, at which pH will this drug become more ionized? A. pH 5 B. pH 2.5 C. pH 1.5 D. pH 1 correct answer: A. For a weak acid, a higher pH increases ionization Which equation describes the rate of drug dissolution from a tablet? A. Fick's Law B. Henderson-Hasselbalch equation C. Michaelis-Menten equation D. Noyes-Whitney equation correct answer: D. The Noyes-Whitney equation describes the rate of drug dissolution from a tablet. Fick's first law of diffusion is similar to the Noyes-Whitney equation in that both equations describe drug movement attributable to a concentration gradient. The Michealis-Menten equation involves enzyme kinetics, whereas Henderson-Hasselbalch equations are used for determination of pH of the buffer and the extent of ionization of a drug molecule The pH of a buffer system can be calculated with A. the Henderson-Hasselbalch equation B. the Noyes-Whitney equation C. the Michealis-Mention equation D. Yong's equation correct answer: A. The Henderson-Hasselbalch equation form a weak acid and its salt is represented as pH = pka + log ([salt]/[acid]), where pka is the negative log of the dissolution constant of a weak acid, as [salt]/[acid] is the ratio of the molar concentration of salt and acid used to prepare a buffer If the pka of a drug is 5, at which of the following pH values do the ionic and nonionic forms of the drug exist at equal ratio? A. pH 1 B. pH 5 C. pH 7 D. pH 9 correct answer: B. When the pH = pka, the ratio of ionized to un-ionized becomes the same What is bioavailability? A. Bioavailability is the measurement of the rate and extent of active drug that reaches the systemic circulation B. It is the relationship between the physical and chemical properties of a drug and its systemic absorption C. It is the movement of the drug into body tissues over time D. It is the dissolution of the drug in the GI tract correct answer: A. Bioavailability is the measurement of the rate and extent of systemic circulation of an active drug Which of the following may be used to assess the relative bioavailability of two chemically equivalent drug products in a crossover study? A. Dissolution test B. Peak concentration C. Time-to-peak concentration D. Area under the plasma-level time curve correct answer: D. The plasma drug concentration versus time curve measures the bioavailability of a drug from a product. The peak plasma drug concentration (Cmax) relates to the intensity of the pharmacologic response, while the time for peak plasma drug concentration (Tmax) relates to the rate of systemic absorption What condition usually increases the rate of drug dissolution for a tablet? A. Increase the particle size of the drug