Biopharmaceutics and Pharmacokinetics

Q: When converting a patient from theophylline to aminophylline, a dose adjustment

(a) :  is not needed
(b) :  with an increase of 20% is suggested
(c) :  with an increase of 50% is suggested
(d) :  with a decrease of 20% is suggested
(e) :  with a decrease of 50% is suggested
Answer:  with an increase of 20% is suggested
Explanation:  The water solubility of theophylline is enhanced by combining it with ethylenediamine, forming the drug aminophylline. Because the active moiety, theophylline, con- tributes 80% of the molecular weight of aminophylline, a correction factor is needed to convert between the two drugs when predicting therapeutic activity. This conversion factor is often referred to as the "S" factor, and is expressed as a fraction. In some books, a correction of 85% is used instead of 80. This minor discrepancy is

Q: Which one of the following peroral dosage forms is likely to exhibit the longest lag time?

(a) :  delayed-release tablet
(b) :  elixir (20% alcohol)
(c) :  enteric-coated tablet
(d) :  osmotic tablet
(e) :  sustained-release capsule
Answer:  enteric-coated tablet
Explanation:  The lag time is the time delay between drug administration and the beginning of absorption, usually reflected in the appearance of drug in theplasma. Enteric-coated tablets are intended for disintegration in the small intestine, which could slow absorption for several hours. Both delayed-release and sustained-release tablets are usually designed tobegin some drug release shortly after administration.

Q: If an oral capsule formulation of the drug A produces a serum concentration-time curve having the same area under the curve as that produced by an equivalent dose of drug A given IV, it can generally be concluded that

(a) :  the IV route is preferred to the oral route
(b) :  the capsule formulation is essentially completely absorbed
(c) :  the drug is very rapidly absorbed
(d) :  all oral dosage forms of drug A will be bioequivalent
(e) :  there is no advantage to the IV route
Answer:  the capsule formulation is essentially completely absorbed
Explanation:  If the areas under the respective curves are equal, it can be concluded that the total amount of drug delivered to the body by each dosage form was equal. Because the in- travenous administration did not involve an absorption process, the fact that the same amount of drug administered in a capsule formulation delivered the same total amount of drug indicates that the absorption of the drug from the oral capsule was essentially complete.

Q: Dosage forms of nitroglycerin that are minimally affected by the first-pass effect include I. intravenous II. transdermal patches III. sublingual tablets

(a) :  I only
(b) :  III only
(c) :  I and II only
(d) :  II and III only
(e) :  I, II, and III
Answer:  I, II, and III
Explanation:  All three routes of administration are used for delivering nitroglycerin. In each case the drug enters systemic blood before significant loss occurs due to the first-pass effect.

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