Review questions answers

Review questions

14.1 The solution instilled as eye drops into the ocular cavity may disap-pear from the precorneal area of the eye by which of the following route(s):

A.      Nasolacrimal drainage

B.      Tear turnover

C.      Corneal absorption

D.      Conjunctival uptake

14.2 After oral drug delivery, drugs are absorbed in the gastrointestinal tract, and through the portal circulation, they enter the liver, where they are destroyed by so-called:

A.      Second-pass metabolism

B.      Drug efflux metabolism

C.      First-pass metabolism

D.      Drug decomposition

E.       None of the above

14.3 The lung:

A.      Has a highly permeable membrane

B.      Has a membrane that provides an effective barrier to drug absorption

C.      Provides easy access to the bloodstream

D.      None of the above

14.4 Which layer is the major rate-limiting barrier for permeation of hydro-philic drugs across the cornea?

A.      Endothelial layer

B.      Stroma

C.      Epithelial layer

D.      A and C

14.5 Liposomes containing an anticancer drug are rapidly taken up by the cells of reticuloendothelial system on systemic administration. How can one extend the blood circulation time of this liposomal system?

14.6 Define polymeric micelles and liposomes. What is a common feature of these two carrier systems?

14.7 Why oral delivery of protein and peptide drugs is often not preferable?

14.8 How can a matrix system be differentiated from a reservoir system?

14.9 What are Peyer’s patches? How can they be exploited in drug delivery and targeting?

Answers:

14.1 E.

14.2 C.

14.3 A.

14.4 D.

14.5 PEGylation or reduction in size increases the retention time of lipo-somes in the bloodstream. Inclusion of PEG-lipid conjugates, such as polyethylene glycol–phosphatidylethanolamine (PEG–PE) reduces the uptake of liposomes by cells of the reticuloendothelial systems (RES), leading to their prolonged circulation half-life.

14.6 Polymeric micelles are small spherical structures composed of both hydrophilic and hydrophobic groups. The micelles are in dynamic equilibrium with free molecules (monomers) in solution; that is, the micelles are continuously breaking down and reforming. This fact distinguishes micellar solutions from liposomes, which are micro-scopic phospholipid vesicles composed of uni- or multilamellar lipid bilayers surrounding aqueous compartments.

14.7 The low oral bioavailability of peptide and protein drugs is primar-ily due to their large molecular size and vulnerability to proteolytic degradation in the GI tract. Most protein and peptide drugs are sus-ceptible to rapid degradation by digestive enzymes. Furthermore, most peptide and protein drugs are rather hydrophilic and thus are poorly partitioned into epithelial cell membranes, leading to their absorption across the GI tract through passive diffusion.

14.8 A microcapsule is a reservoir-type system in which the drug is located centrally within the particle, whereas a microsphere is a matrix-type sys-tem in which the drug is dispersed throughout the particle. Microcapsules usually release their drug at a constant rate (zero-order release), whereas microspheres typically give a first-order release of drugs.

14.9 Peyer’s patches belong to gut-associated lymphoid tissues (GALT) of the small intestine. Peyer’s patches are capable of internalizing particu-late matter, bacteria, and marker proteins. Localization of mucoadhe-sive polymeric delivery systems at or around Peyer’s patches has the potential of favoring the absorption of peptides and proteins.