Week 4 notes 3 - T reatment of Nausea Vomiting The...

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The treatment of nausea and vomiting should involve a search for the underlying condition, which may require specific therapy apart from relieving the symptoms. Frequently, there is no available treatment for the cause and in these cases effective control of the nausea and vomiting is the primary goal. List of Antihistamines for Motion Sickness Nausea diphenhydramine (Benadryl) meclizine (Antivert) (Bonine) dimenhydrinate (Dramamine) Pharmacodynamics of Antihistamines for Motion Sickness In this context, the antihistamines block histamine-1 (H-1) receptors in the Chemoreceptor Trigger Zone (CTZ) area of the brain, which is that part of the brain that detects noxious stimuli and activates the nausea and the vomiting centers. These drugs primarily block those signals coming into the CTZ from the inner ear mechanism (the labyrinth) where balance is maintained. Patients with motion sickness have an array of abnormal signals coming from this area and the antihistamine drugs block these signals and abort or prevent the motion sickness. In addition, like all antihistamines, these drugs also have anticholinergic activity and block muscarinic-type cholinergic receptors in the brainstem, which also play a role in transmitting the abnormal signals from the inner ear into the CTZ. Pharmacokinetics of the Antihistamines for Motion Sickness All of these drugs are administered orally. All except meclizine can also be given parenterally. They are metabolized in the liver and excreted in the urine. Advantages of the Antihistamines in the Treatment of Motion Sickness - Available orally; most useful for motion sickness prophylaxis. - Useful as therapeutic and prophylactic drugs. - Available over-the-counter; some brand name products are prescription only (i.e., Antivert). - Fairly rapid onset of action following oral administration. - Long duration of action for meclizine (8-24 hrs.); the remainder have a duration of action that ranges from 4-6 hrs. - Most available parenterally (I.M.); this is an advantage when treating patients who cannot take oral medications because of vomiting. - Commonly produce drowsiness; this may be an advantage in treatment of nausea. - May be safely used in pregnancy (Category B). 1
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Disadvantages of the Antihistamines for Motion Sickness - Requires q 4-6 h dosing (except meclizine, q 12-24 hrs). - All produce drowsiness, dizziness and occasionally confusion; these are typical antihistamine effects. [THE SEDATIVE EFFECTS WILL BE ADDITIVE TO THE EFFECTS OF OTHER CNS DEPRESSANT DRUGS.] - All have varying degrees of anticholinergic adverse effects including blurred vision, dry mouth, tachycardia, constipation and urinary retention. - Requires precaution in patients with glaucoma and prostatic enlargement (BPH).
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Week 4 notes 3 - T reatment of Nausea Vomiting The...

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