Biopharmaceutics and Pharmacokinetics

Q: The rectal route of administration may be preferred over the oral route for some systemic-acting drugs because

(a) :  the drug does not have to be absorbed
(b) :  absorption is predictable and complete
(c) :  a portion of the absorbed drug does not pass through the liver before entering the systemic circulation
(d) :  inert binders, diluents, and excipients cannot interfere with absorption
(e) :  the dissolution process is avoided
Answer:  a portion of the absorbed drug does not pass through the liver before entering the systemic circulation
Explanation:  Although it is desirable for certain drugs rapidly metabolized by the liver to bypass absorption into the portal circulation, the value of using the rectal route for this pur- pose is limited. This is due to the fact that whereas three principal veins drain the blood supply to the rectum, only the middle and inferior hemorrhoidal veins actually bypass theliver. The superior hemorrhoidal vein enters the portal circulation via the inferior mesenteric vein.

Q: The volume of distribution (Vd) of a particular drug will be

(a) :  greater for drugs that concentrate in tis- sues rather than in plasma
(b) :  greater for drugs that concentrate in plasma rather than in tissues
(c) :  independent of tissue concentration
(d) :  independent of plasma concentration
(e) :  approximately the same for all drugs in a given individual
Answer:  greater for drugs that concentrate in tis- sues rather than in plasma
Explanation:   Following a given dose of a drug, the greater its concentration in various tissue compartments, the smaller its concentration in plasma. Therefore, according to the rela- tionship Ab = Vd Cb , the Vd of a particular drug will be greater for those drugs that tend to con- centrate in tissues as opposed to plasma.

Q: What maintenance dose is appropriate in the above patient if the clearance is estimated to be .35 mL/min/kg?

(a) :  10 mg/hr
(b) :  14 mg/hr
(c) :  17 mg/hr
(d) :  20 mg/hr
(e) :  25 mg/hr
Answer:  17 mg/hr
Explanation:  onverting the clearance to L/hr and eliminating the kg weight, .35 mL/min/kg x 60 min/hr x 70 kg = 1470 mL/hr or 1.47 L/hr (F) (Maintenance dose) = (Plasma Cone.) (Clearance) (.85) x= (10 mg/L) (1.47 L/hr) x= 17.3 mg per hour

Q: Bioavailability and pharmacokinetic data either is or may be required when pharmaceutical companies submit I. new drug applications II. abbreviated new drug applications III. supplemental applications

(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:  Unless a special waiver is granted, the FDA expects to see human bioavailability and pharmacokinetic data on all applications. Possible exceptions will be for intravenous solutions, topicals, and inhalation products.

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