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Cimetidine; Uses, Dosage, Side Effects, Drug Interactions

Cimetidine is a histamine H(2)-receptor antagonist. Enhancing anti-tumor cell-mediated responses, cimetidine blocks histamine’s ability to stimulate suppressor T lymphocyte activity and to inhibit natural killer (NK) cell activity and interleukin-2 production. Cimetidine also may inhibit tumor growth by suppressing histamine’s growth-factor activity and blocking histamine-induced stimulation of vascular endothelial growth factor (VEGF), a pro-angiogenic growth factor.

Cimetidine is a histamine H₂ receptor antagonist that inhibits stomach acid production. It inhibits gastric acid secretion, as well as pepsin and gastrins output. It is available over-the-counter and is mainly used in the treatment of heartburn and peptic ulcers. The development of longer-acting H₂ receptor antagonists with fewer drug interactions and adverse effects, such as ranitidine and famotidine, decreased the use of cimetidine, and though it is still used, cimetidine is no longer among the more widely used of the H₂-receptor antagonists.

Mechanism of Action of Cimetidine

Cimetidine binds to an H₂-receptor located on the basolateral membrane of the gastric parietal cell, blocking histamine effects. This competitive inhibition results in reduced gastric acid secretion and a reduction in gastric volume and acidity.

H2 antagonists inhibit gastric acid secretion elicited by histamine & other H2 agonists in a dose-dependent, competitive manner; the degree of inhibition parallels the concentration of the drug in plasma over a wide range. The H2 antagonists also inhibit acid secretion elicited by gastrin &, to a lesser extent, by muscarinic agonists. Importantly, these drugs inhibit basal (fasting) & nocturnal acid secretion & that stimulated by food, sham feeding, fundic distention, & various pharmacological agents; this property reflects the vital role of histamine in mediating the effects of diverse stimuli. The H2 antagonists reduce both the volume of gastric juice secreted & its H+ concentration. The output of pepsin, which is secreted by the chief cells of gastric glands (mainly under cholinergic control), generally falls in parallel with the reduction in the volume of gastric juice. Cimetidine blocks H2-receptors, which in part are responsible for the inflammatory response, in the cutaneous blood vessels of humans.

Indications of Cimetidine

Gastro-esophageal Reflux Disease
Heartburn
Hypersecretion gastric
Cutaneous mastocytosis
Bronchogenic carcinoma
Duodenal ulcer prophylaxis
Erosive esophagitis
Indigestion
Stomach ulcer
Upper GI Hemorrhage
Zollinger-Ellison Syndrome
Active Duodenal ulcer
Benign gastric ulcers
Maintenance therapy Duodenal ulcer

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Contra-Indications of Cimetidine

Clostridium difficile infection
Inadequate Vitamin B12
Low amount of magnesium in the blood
Liver problems
Interstitial Nephritis
Subacute cutaneous lupus erythematosus
Systemic Lupus Erythematosus
Osteoporosis
Broken Bone
Allergies to Proton Pump Inhibitors

Dosage of Cimetidine

Strengths: 100 mg; 200 mg; 300 mg; 400 mg; 800 mg; 900 mg 300 mg/5 mL;

Duodenal Ulcer

Parenteral: 300 mg IV or IM every 6 to 8 hours. Alternatively, a continuous IV infusion may be administered at a rate of 37.5 to 50 mg/hour, or up to a maximum rate of 100 mg/hour (2.4 g/day).
Oral: 800 mg to 1600 mg once a day at bedtime. Alternatively, dosage regimens of 300 mg four times per day, with meals and at bedtime, or 400 mg twice daily, in the morning and at bedtime, have shown to be effective.

Erosive Esophagitis

Parenteral: 300 mg IV or IM every 6 hours. Alternatively, a continuous IV infusion may be administered at a rate of 50 mg/hour initially, with 25 mg/hour incremental increases up to a maximum rate of 100 mg/hour (2.4 g/day).
Oral: 800 mg twice a day, or alternatively, 400 mg four times a day.

Stress Ulcer Prophylaxis

Parenteral: 300 mg IV or IM every 6 hours. Alternatively, a continuous IV infusion may be administered at a rate of 50 mg/hour.

Zollinger-Ellison Syndrome

Parenteral: 300 mg IV or IM every 6 hours. Alternatively, a continuous IV infusion may be administered at a rate of 50 mg/hour initially. Infusion rates have ranged from 40 to 600 mg/hour, but should not exceed a daily total of 2.4 g.
Oral: 300 mg 4 times a day with meals and at bedtime.

Gastroesophageal Reflux Disease

Parenteral: 300 mg IV or IM every 6 hours. Alternatively, a continuous IV infusion may be administered at a rate of 50 mg/hour. The maximum daily dose should not exceed 2.4 g.
Oral: 800 mg twice a day, or 400 mg 4 times a day.

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Pediatric Gastroesophageal Reflux Disease

Neonatal: 5 to 10 mg/kg/day administered IV or IM in divided doses every 8 to 12 hours.
Infants: 10 to 20 mg/kg/day administered IV, IM, or oral in divided doses every 6 to 12 hours.
Children: 20 to 40 mg/kg/day administered IV, IM, or oral in divided doses every 6 hours.

Side Effects of Cimetidine

The most common

More common

Abdominal or stomach pain, discomfort, or tenderness
chills or fever
difficulty with moving
a headache, severe and throbbing
joint or back pain
muscle aching or cramping
muscle pains or stiffness
chest pressure or squeezing pain in the chest
discomfort in arms, shoulders, neck or upper back
excessive sweating
feeling of heaviness, pain, warmth and/or swelling in a leg or in the pelvis
sudden tingling or coldness in an arm or leg
sudden slow or difficult speech
sudden drowsiness or need to sleep
fast breathing
sharp pain when taking a deep breath
fast or slow heartbeat
coughing up blood
rust colored urine
decreased amount of urine

Rare

Anxiety
change in vision
seizures
abnormal or fast heart rate
tremors
weight loss
chest pain or tightness
confusion
a cough
Agitation
arm, back, or jaw pain
blurred vision
chest pain or discomfort
convulsions
extra heartbeats
fainting
hallucinations
a headache
irritability
lightheadedness
mood or mental changes
muscle pain or cramps
muscle spasm or jerking of all extremities

Drug Interactions of Cimetidine

Cimetidine may interact with the following drugs, supplements, & may change the efficacy of the drug

amiodarone
azole antifungal medications (e.g., fluconazole, ketoconazole)
caffeine
calcium channel blockers (e.g., diltiazem, nifedipine, verapamil)
carbamazepine
carvedilol
certain benzodiazepines (alprazolam, chlordiazepoxide, clonazepam, diazepam, flurazepam, midazolam, and triazolam)
clopidogrel
clozapine
dasatinib
glyburide (and other “sulfonylurea” diabetes medications)
lidocaine
metformin
metoprolol
pentoxifylline
phenytoin
propranolol
salmeterol
SSRIs (e.g., citalopram, fluoxetine, sertraline)
sucralfate
theophyllines (e.g., aminophylline, oxtriphylline, theophylline)
tramadol
tricyclic antidepressants(e.g., amitriptyline, clomipramine, desipramine, trimipramine)
warfarin

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Pregnancy Catagory

FDA Pregnancy Category C

Pregnancy

The safety of this medication for use during pregnancy has not been established. This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Lactation

This medication passes into breast milk. If you are a breastfeeding mother and are taking cimetidine, it may affect your baby. Talk to your doctor about whether you should continue breastfeeding.