Absorption of Drugs Part 2 — Transcript

Full transcript

1. 0:00yeah
2. 0:01right now we need to understand more
3. 0:03about the basics of absorption and for
4. 0:06that discussion we're going to take the
5. 0:08example of an oral medication
6. 0:11as you take an oral medication the
7. 0:13medication goes down the esophagus into
8. 0:16the stomach there's generally very
9. 0:19little absorption that occurs in the
10. 0:21stomach even aspirin which has chemical
11. 0:24properties that favor absorption in the
12. 0:27stomach doesn't normally have a very
13. 0:30high percentage of absorption from the
14. 0:33stomach because of a couple things first
15. 0:36of all aspirin isn't in the stomach very
16. 0:39long and secondly there's very little
17. 0:42surface area for absorption in the
18. 0:44stomach compared to that of the
19. 0:46intestines
20. 0:48so most of the absorption of orally
21. 0:51administered medications usually occurs
22. 0:53in the small intestines
23. 0:56there are a lot of factors involved in
24. 0:58the absorption of orally administered
25. 1:01medications and a lot of those have to
26. 1:03do with the properties of the drugs
27. 1:06themselves for instance the molecular
28. 1:09size of the drug the acidic or Alkali
29. 1:12nature of the drug and whether the drug
30. 1:15generally has a lipophilic or
31. 1:18hydrophilic property
32. 1:20for instance lipophilic or fat soluble
33. 1:23drugs are normally absorbed faster and
34. 1:27more completely because they can simply
35. 1:30diffuse across these cell membranes of
36. 1:35the gastrointestinal tract wall
37. 1:38other factors that affect the absorption
38. 1:41of medications include the specific
39. 1:44conditions of the gastrointestinal tract
40. 1:46at the time
41. 1:48for instance drug absorption is affected
42. 1:51by the rate at which the contents are
43. 1:54moving through the git
44. 1:57another factor that affects absorption
45. 2:00is blood flow through that area
46. 2:03and this is an interesting one a meal
47. 2:06increases the blood flow through the git
48. 2:09so you'd probably predict that it's best
49. 2:12to take medications with food
50. 2:16but in reality food often decreases the
51. 2:20bioavailability of the drugs or in other
52. 2:22words decreases the fraction of the drug
53. 2:24that ultimately reaches systemic
54. 2:26circulation unchanged so although taking
55. 2:30the drugs with food generally speeds up
56. 2:33the absorption of drugs It generally
57. 2:36decreases that bioavailability and
58. 2:39therefore in general oral drugs are best
59. 2:42taken about an hour before or two hours
60. 2:45after a meal
61. 2:47after the drug has dissolved into tiny
62. 2:50little fragments in the stomach and is
63. 2:52in the small intestine the drug is going
64. 2:55to be absorbed into the bloodstream by a
65. 2:58number of different mechanisms
66. 3:00and the most common way for a drug to
67. 3:03get absorbed is by simple diffusion in
68. 3:06that process the water soluble products
69. 3:09will move across channels in the cell
70. 3:12surface and they're going to move from
71. 3:14the area of higher concentration to the
72. 3:17area of lower concentration but if it's
73. 3:20a lipid soluble drug or in other words
74. 3:23lipophilic that drug can simply diffuse
75. 3:27from one side of the cell membrane to
76. 3:30the other and once that medication is
77. 3:33absorbed that medication is ready for
78. 3:35the next process of pharmacokinetics
79. 3:37which is the distribution of drugs
80. 3:42recall what we were saying about the
81. 3:44absorption of medications generally the
82. 3:47best absorption in other words the
83. 3:50fastest and most complete absorption
84. 3:53normally comes with a lipophilic or fat
85. 3:57soluble drugs or B hydrophilic or
86. 4:02water-soluble drugs
87. 4:06and you would have been correct if you
88. 4:08had recalled that lipophilic drugs are
89. 4:11generally absorbed the best
90. 4:13and this is especially important in some
91. 4:16types of administration such as topical
92. 4:18administration because the cells on the
93. 4:21skin have a protein called keratin that
94. 4:24protects the skin from absorbing
95. 4:27water-soluble products
96. 4:29this is the reason that ingredients
97. 4:31within creams which are fairly water
98. 4:33soluble are poorly absorbed they
99. 4:36generally stay in that local area
100. 4:40conversely
101. 4:41transdermal patches are made with
102. 4:44lipophilic drugs to make sure that they
103. 4:47permeate the skin to the deeper layers
104. 4:49where they can access the blood supply
105. 4:52the lipophilic nature of drugs is also
106. 4:55important in sublingual sprays so sprays
107. 4:59that are administered under the tongue
108. 5:00and for rectal suppositories
109. 5:04and the important thing to remember
110. 5:06about those applications is that the
111. 5:08drug is applied in a very limited area
112. 5:11remember water soluble drugs can be
113. 5:14absorbed from the intestines but these
114. 5:17small intestine is made for absorption
115. 5:20it has over 30 square meters of area
116. 5:23with the Villi and the microvilli that's
117. 5:27about 320 square feet
118. 5:31so using that information what would you
119. 5:34predict would happen if you for instance
120. 5:37crushed a medication
121. 5:39suspended it in an ointment and applied
122. 5:43it rectally and by the way ointments are
123. 5:47oil-based substances that are topically
124. 5:50applied
125. 5:52and the answer to that question is
126. 5:55variable depending on the properties of
127. 5:57the drug itself a very lipophilic drug
128. 6:01May indeed be absorbed fairly well but
129. 6:04remember that oral medications are
130. 6:06exposed to many thousand times the
131. 6:09surface area as compared to rectally
132. 6:11administered medications so the result
133. 6:15is going to be unpredictable
134. 6:18always administer medications in the way
135. 6:21they've been proven to be absorbed
136. 6:23effective and safe