Histamine 2 Blockers Famotidine — Transcript

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1. 0:00hi there and welcome back to
2. 0:02understanding medications
3. 0:05so far in this chapter we've introduced
4. 0:07the histamine II receptor blockers like
5. 0:10famotidine
6. 0:12which are used for decreasing stomach
7. 0:15acid and our last lesson went through
8. 0:18some exercises to help you predict the
9. 0:21kind of side effects that you'd expect
10. 0:24from decreasing stomach acid for a long
11. 0:27period of time given the role of the
12. 0:30acid in the stomach
13. 0:31and right now we're going to make sure
14. 0:35that you really picture the histamine 2
15. 0:38receptor blockers like simethidine and
16. 0:41famotidine
17. 0:42and how they exert their effects in
18. 0:45other words we're going to look at their
19. 0:48mechanism of action
20. 0:51the histamine II receptor blockers like
21. 0:54cimetidine and famotidine bind to the
22. 0:57histamine II receptor in the stomach
23. 1:01so let's take a look at where they act
24. 1:05if we go down the esophagus into the
25. 1:08stomach and took a microscopic view of
26. 1:12the lining of the stomach we would find
27. 1:15that the lining of the stomach has
28. 1:17gastric pits and in those pits some of
29. 1:21those cells are called parietal cells
30. 1:25now the parietal cells are the ones that
31. 1:28secrete the acid they secrete hydrogen
32. 1:32ions or in other words protons into the
33. 1:36Lumen of the stomach and they do that by
34. 1:40using an enzyme called the hydrogen
35. 1:42potassium atpase pump
36. 1:46the parietal cell is the same cell that
37. 1:49we affect as we take a proton pump
38. 1:52inhibitor like Omeprazole which will
39. 1:55investigate in the next chapter
40. 1:58so how do the histamine 2 receptor
41. 2:01blockers work
42. 2:03well when there's a stimulation of the
43. 2:05parietal cell from gastrin histamine and
44. 2:10also acetylcholine all three of those at
45. 2:13the same time not just one of them the
46. 2:16proton pumps in the parietal cells start
47. 2:19secreting the protons or in other words
48. 2:22the hydrogen ions the acid
49. 2:27the histamine II antagonists are
50. 2:30competitive antagonists so they compete
51. 2:34with the histamine tube that's trying to
52. 2:37bind to that same receptor
53. 2:40as you can imagine if there's less
54. 2:42histamine 2 binding onto its receptor
55. 2:45there will be fewer hydrogen ions
56. 2:47secreted and a reduced acidity in the
57. 2:51stomach
58. 2:52in fact the histamine II receptor
59. 2:55blockers can be about 80 percent
60. 2:57effective in reducing the acid secretion
61. 3:00from the parietal cells in the stomach
62. 3:07we said that histamine 2 antagonists are
63. 3:11not as effective at decreasing stomach
64. 3:14acid as the proton pump inhibitors but
65. 3:17why is that proton pump inhibitors
66. 3:20decrease the stomach acidity by 99 and
67. 3:24yes that is difficult to beat but why
68. 3:28can't the histamine 2 antagonists reach
69. 3:31that level even if we take a maximum
70. 3:34dose
71. 3:35the way that the histamine 2 blocker
72. 3:39like Ranitidine works is to bind to and
73. 3:45block the histamine II receptor and that
74. 3:48binding is not permanent
75. 3:51the tadine medications the histamine II
76. 3:55blockers work by competitive antagonism
77. 3:59they're competitive antagonists
78. 4:02there's still some histamine too that's
79. 4:05being released and there's still some
80. 4:08binding of that histamine too to The
81. 4:10receptors on the parietal cells
82. 4:11regardless of how much drug is in the
83. 4:14system
84. 4:15and every time that the histamine 2 gets
85. 4:18its spot on that parietal cell receptor
86. 4:21as long as there's acetylcholine binding
87. 4:23and gastrin binding at the same time
88. 4:25there will be acids secreted
89. 4:30and the last thing that we need to
90. 4:31discuss with respect to the histamine II
91. 4:34antagonists such as famotidine is a
92. 4:37thing called selectivity
93. 4:40you may be wondering what's the
94. 4:42difference between an
95. 4:45antihistamine that you take for a runny
96. 4:47nose and allergic conditions
97. 4:51and a histamine 2 blocker or are they
98. 4:56the same is a histamine tube blocker a
99. 4:59antihistamine
100. 5:01well we reserve the term antihistamine
101. 5:04for a group of medications that block
102. 5:07the histamine one receptor
103. 5:11so while you could argue that histamine
104. 5:142 antagonists should really be called an
105. 5:17antihistamine we don't use that term
106. 5:20because the antihistamines are the ones
107. 5:22for the runny nose the ones that bind to
108. 5:26the histamine one receptor
109. 5:28and this diagram depicts that there's
110. 5:33three subsets of histamine receptors and
111. 5:36they're located in different organs when
112. 5:38you take a normal dose of a histamine 2
113. 5:41receptor blocker like Ranitidine there
114. 5:44is very little crossover onto that
115. 5:47histamine one receptor so it's a very
116. 5:50little use in allergic rhinitis
117. 5:54so we say that the histamine II receptor
118. 5:58blockers are fairly selective for the
119. 6:01histamine II receptor and the
120. 6:04antihistamines that work in allergic
121. 6:06rhinitis are fairly selective for the
122. 6:10histamine one receptor although
123. 6:14interestingly enough the histamine one
124. 6:17antihistamines some of those actually
125. 6:20bind to
126. 6:22acetylcholine receptors which gives them
127. 6:25some side effects