H
Short-term treatment of duodenal ulcer (DU), active benign gastric ulcer (GU), maintenance therapy of DU, pathologic hypersecretory conditions (e.g., Zollinger-Ellison syndrome), gastroesophageal reflux disease (GERD), and prevention of upper GI bleeding in critically ill pts.
Inhibits gastric acid secretion by interfering with histamine at the histamine H2 receptors in parietal cells. Also inhibit acid secretion caused by gastrin. Inhibition occurs with basal (fasting), nocturnal, food-stimulated, or fundic distention secretion. H2 antagonists decrease both the volume and H2 concentration of gastric juices.
| Name | Availability | Dosage Range | Side Effects |
| Cimetidine (p. 249) (Tagamet) | T: 200 mg, 300 mg, 400 mg, 800 mgL: 300 mg/5 mlI: 150 mg/ml | Treatment of DU: 800 mg at bedtime, 400 mg 2 times/day or 300 mg 4 times/dayMaintenance of DU: 400 mg at bedtimeTreatment of GU: 800 mg at bedtime or 300 mg 4 times/dayGERD: 1,600 mg/dayHypersecretory: 1,200–2,400 mg/day | Headaches, fatigue, dizziness, confusion, diarrhea, gynecomastia |
| Famotidine (p. 473) (Pepcid) | T: 10 mg, 20 mg, 40 mgT (chewable): 10 mgDT: 20 mg, 40 mgGelcap: 10 mgOS: 40 mg/5 mlI: 10 mg/ml | Treatment of DU: 40 mg/dayMaintenance of DU: 20 mg/dayTreatment of GU: 40 mg/dayGERD: 40–80 mg/dayHypersecretory: 80–640 mg/day | Headaches, dizziness, diarrhea, constipation, abdominal pain, tinnitus |
| Nizatidine (p. 862) (Axid) | OS: 15 mg/mlC: 150 mg, 300 mg | Treatment of DU: 300 mg/dayMaintenance of DU: 150 mg/day | Fatigue, urticaria, abdominal pain, constipation, nausea |
| Ranitidine (p. 1036) (Zantac) | T: 75 mg, 150 mg, 300 mgC: 150 mg, 300 mgSyrup: 15 mg/mlI: 25 mg/ml | Treatment of DU: 300 mg/dayMaintenance of DU: 150 mg/dayTreatment of GU: 300 mg/dayGERD: 300 mg/dayHypersecretory: 0.3–6 g/day | Blurred vision, constipation, nausea, abdominal pain |
C, Capsules; DT, disintegrating tablets; I, injection; L, liquid; OS, oral suspension; T, tablets.
Functions of the body are regulated by two major control systems: the nervous system and the endocrine (hormone) system. Together they maintain homeostasis and control different metabolic functions in the body.
Hormones are concerned with control of different metabolic functions in the body (e.g., rates of chemical reactions in cells, transporting substances through cell membranes, cellular metabolism [growth/secretions]). By definition, a hormone is a chemical substance secreted into body fluids by cells and has control over other cells in the body.
Hormones can be local or general:
• Local hormones have specific local effects (e.g., acetylcholine, which is secreted at parasympathetic and skeletal nerve endings).
• General hormones are mostly secreted by specific endocrine glands (e.g., epinephrine/norepinephrine are secreted by the adrenal medulla in response to sympathetic stimulation), transported in the blood to all parts of the body, causing many different reactions.
Some general hormones affect all or almost all cells of the body (e.g., thyroid hormone from the thyroid gland increases the rate of most chemical reactions in almost all cells of the body); other general hormones affect only specific tissue (e.g., ovarian hormones are specific to female sex organs and secondary sexual characteristics of the female).
Endocrine hormones almost never directly act intracellularly affecting chemical reactions. They first combine with hormone receptors either on the cell surface or inside the cell (cell cytoplasm or nucleus). The combination of hormone and receptors alters the function of the receptor, and the receptor is the direct cause of the hormone effects. Altered receptor function may include the following:
Altered cell permeability, which causes a change in protein structure of the receptor, usually opening or closing a channel for one or more ions. The movement of these ions causes the effect of the hormone.
Activation of intracellular enzymes immediately inside the cell membrane (e.g., hormone combines with receptor that then becomes the activated enzyme adenyl cyclase, which causes formation of cAMP).
ALERT 
cAMP has effects inside the cell. It is not the hormone but cAMP that causes these effects.
Regulation of hormone secretion is controlled by an internal control system, the negative feedback system:
• Endocrine gland oversecretes.
• Hormone exerts more and more of its effect.
• Target organ performs its function.
• Too much function in turn feeds back to endocrine gland to decrease secretory rate.
The endocrine system contains many glands and hormones. A summary of the important glands and their hormones secreted are as follows:
The pituitary gland (hypophysis) is a small gland found in the sella turcica at the base of the brain. The pituitary is divided into two portions physiologically: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). Six important hormones are secreted from the anterior pituitary and two from the posterior pituitary.
• Adrenocorticotropin (corticotropin)
• Thyroid-stimulating hormone (thyrotropin) (TSH)
• Follicle-stimulating hormone (FSH)
Almost all secretions of the pituitary hormones are controlled by hormonal or nervous signals from the hypothalamus. The hypothalamus is a center of information concerned with the well-being of the body, which in turn is used to control secretions of the important pituitary hormones just listed. Secretions from the posterior pituitary are controlled by nerve signals originating in the hypothalamus; anterior pituitary hormones are controlled by hormones secreted within the hypothalamus. These hormones are as follows:
• Thyrotropin-releasing hormone (TRH) releasing thyroid-stimulating hormone
• Corticotropin-releasing hormone (CRH) releasing adrenocorticotropin
• Growth hormone-releasing hormone (GHRH) releasing growth hormone and growth hormone inhibitory hormone (GHIH) (same as somatostatin)
• Gonadotropin-releasing hormone (GnRH) releasing the two gonadotropic hormones LH and FSH
• Prolactin inhibitory factor (PIF) causing inhibition of prolactin and prolactin-releasing factor
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