Cimetidine Antacids

Chlorination of the antacid cimetidine leads to the formation of four major DBFs cimetidine sulfoxide, 4-hydroxyhnethyl-5-methyl-7//-imidazole, 4-chloro-5-methyl-7//-imidazole, and a product proposed to be either a jS- or (5-sulfam. The formation of the last three products resulted from unexpected reactions and more substantial structural changes than those t3q)ically observed in chlorination [93]. 

Drugs that may interact include antacids, cimetidine, aspirin, digoxin, phenytoin, and theophylline. 

Drugs that may affect gabapentin include antacids, cimetidine, hydrocodone, and morphine. Drugs that may be affected by gabapentin include oral contraceptives and hydrocodone. 

P. Regan, J. Malagelada, E. DiMagno, S. Glanzman, and V. Go. Comparative effects of antacids, cimetidine and enteric coating on the therapeutic response to oral enzymes in severe pancreatic insufficiency. N. Engl. J. Med. 297 854 (1977). 

PO. Acid pH (stomach) required for dissolution. Absoiption i by food, antacids, cimetidine. Highly plasma protein bound, low CNS levels. 

Koneru B, Bramer S, Bricmont P, Maroli A, Shiba K. Effect of food, gastric pH and co-ad-ministration of antacid, cimetidine and probenecid on the oral pharmacokinetics of Ae broad spectrum antimicrobial agent grepafloxacin. Pharm Res (1996) 13 (9 Suppl), S414. 

The absorption of cimetidine, famotidine, nizatidine, and ranitidine may possibiy be reduced to some extent by antacids, but it seems doubtful if this significantly reduces their effects. Separating the dosages by 1 to 2 hours minimises any interaction. Roxa-tidine absorption appears not to be affected by antacids. Cimetidine appears not to interfere with the effectiveness of Gaviscon (sodium alginate compound). 

Ketoconazole. For treatment of systemic mycoses with amphotericin B or miconazole, the patient must be admitted to a hospital. This is not always possible, particularly in areas where systemic mycoses occur frequently, nor is it always desirable, because of the expense. For these reasons, it was desirable to find an antimycotic that combined safety and broad-spectmm activity with oral adraiinistration. Ketoconazole (10), which is orally active, met most of these requirements. This inhibitor of the ergosterol biosynthesis is an A/-substituted imidazole, that differs from its precursors by the presence of a dioxolane ring (6,7). Ketoconazole is rapidly absorbed in the digestive system after oral adrninistration. Sufficient gastric acid is required to dissolve the compound and for absorption. Therefore, medication that affects gastric acidity (for example, cimetidine and antacids) should not be combined with ketoconazole. 

Concurrent use of the fluoroquinolones with theophylline causes an increase in serum theophylline levels. When used concurrently with cimetidine, the cimetidine may interfere with the elimination of the fluoroquinolones. Use of the fluoroquinolones with an oral anticoagulant may cause an increase in the effects of the oral coagulant. Administration of the fluoroquinolones with antacids, iron salts, or zinc will decrease absorption of the fluoroquinolones. There is a risk of seizures if fluoroquinolones are given with the NSAIDs. There is a risk of severe cardiac arrhythmias when the fluoroquinolones gatifloxacin and moxifloxacin are administered with drains that increase the QT interval (eg, quini-dine, procainamide, amiodarone, and sotalol). 

Dofetilide is not administered with cimetidine because dofetilide plasma levels may be increased by as much as 50%. When treatment for gastric disorders is necessary, patients receiving dofetilide should take omeprazole ranitidine, or antacids as an alternative to cimetidine. 

HISTAMINE H2 ANTAGONISTS. The nurse administers ranitidine and oral cimetidine before or with meals and at bedtime Nizatidine and famotidine are given at bedtime or, if twice-a-day dosing is prescribed, in the morning and at bedtime. These drugp are usually given concurrently with an antacid to relieve the pain. In certain situations or disorders, cimetidine and ranitidine may also be given by intermittent IV infusion or direct IV injection. 

Antacid/alginic acid (Gaviscon) 2 tablets or 1 5 mL after meals and at bedtime AND/OR C. Patient-directed therapy Over-the-counter H2RAs (each taken up to twice daily) - Cimetidine 200 mg - Lamotidine 1 0 mg - Nizatidine 75 mg - Ranitidine 75 mg OR Over-the-counter PPI (taken once daily) - Omeprazole 20 mg agent. 

Snepar R, Poporad GA, Romano JM, Kobasa WD, Kaye D Effect of cimetidine and antacid on gastric microbial flora. Infect Immun 1982 36 518-524. 

Intermittent, mild heartburn Lifestyle modifications plus patient-directed therapy Antacids Maalox or Mylanta 30 mL as needed or after meals and at bedtime Gaviscon 2 tabs after meals and at bedtime Calcium carbonate 500 mg, 2-4 tablets as needed and/or Nonprescription 11 receptor antagonists (taken up to twice daily) Cimetidine 200 mg Famotidine 10 mg Nizatidine 75 mg Ranitidine 75 mg or... 

Drug therapy, if necessary, may be initiated with aluminum, calcium, or magnesium antacids sucralfate or cimetidine or ranitidine. Lansoprazole, omeprazole, and metoclopramide are also options if the patient does not respond to histamine-2 receptor blockers. 

Why are cimetidine and ranitidine better antacids than sodium hydrogencarbonate or magnesium or aluminium hydroxide ... 

If 10% of patients previously receiving prescriptions for an antacid were prescribed a H2 antagonist such as cimetidine or ranitidine, this claimed savings would not have been achieved. The growth in the H2 antagonist market was rapid at this time, and some of this growth must have been due to such escalation of prescribing. 

Drugs that may affect HMG-CoA reductase inhibitors include alcohol, amiodarone, antacids, azole antifungals, bile acid sequestrants, cimetidine, cyclosporine, diltiazem, erythromycin, gemfibrozil, isradipine, nefazodone, niacin, nicotinic acid, omeprazole, phenytoin, propranolol, protease inhibitors, ranitidine, rifampin, St. John s wort, and verapamil. 

Drugs that affect all phosphodiesterase type 5 inhibitors include the following alcohol, amlodipine, angiotensin II receptor blockers, antacids, bendroflumethiazide, beta blockers, cimetidine, diuretics, enalaphl, metoprolol, nifedipine, rifampin, tacrolimus. 

Drugs that may affect benzodiazepines include alcohol, antacids, barbiturates, cimetidine, disulfiram, fluoxetine, isoniazid, ketoconazole, metoprolol, oral contraceptives, narcotics, probenecid, propoxyphene, propranolol, ranitidine, rifampin, scopolamine, theophylline, and valproic acid. 

Drugs that may be affected by sucralfate include aluminum-containing antacids, anticoagulants, diclofenac, digoxin, histamine H2 antagonists (eg, cimetidine,... 

Drugs that may interact with zalcitabine include antacids, chloramphenicol, cisplatin, dapsone, didanosine, disulfiram, ethionamide, glutethimide, gold, hydralazine, iodoquinol, isoniazid, metronidazole, nitrofurantoin, phenytoin, ribavirin, vincristine, cimetidine, metoclopramide, amphotericin, aminoglycosides, foscarnet, antiretroviral nucleoside analogs, pentamidine, and probenecid. 

Deravirdine (Rescnptor) [Antiretroviral/NNRTI] Uses HIV Infxn Action Nonnucleoside RT inhibitor Dose 400 mg PO tid Caution [C, ] CDC recommends HIV-infected mothers not to breast-feed (transmission risk) w/ renal/hepatic impair Contra Use w/ drugs dependent on CYP3A for clearance (Table VI-8) Disp Tabs SE Fat redistribution, immune reconstitution synd, HA, fatigue, rash, T transaminases, N/V/D Interactions T Effects W/ fluoxetine T effects OF benzodiazepines, cisapride, clarithromycin, dapsone, ergotamine, indinavir, lovastatin, midazolam, nifedipine, quinidine, ritonavir, simvastatin, terfena-dine, triazolam, warfarin effects W/ antacids, barbiturates, carbamazepine, cimetidine, famotidine, lansoprazole, nizatidine, phenobarbital, phenytoin, ranitidine, rifabutin, rifampin effects OF didanosine EMS Use of benzodiazepines and CCBs should be avoided may cause a widespread rash located on upper body and arms OD May cause an extension of nl SEs symptomatic and supportive Deferasirox (Exjade) [Iron Chelator] Uses Chronic iron overload d/t transfusion in pts >2 y Action Oral iron chelator Dose Initial 20 mg/kg... 

Un, acute exacerbation of chronic bronchitis prophylaxis in transurethral procedures Action Quinolone antibiotic -1- DNA gyrase. Dose 400 mg/d PO X w/ renal insuff, avoid antacids Caution [C, —] Interactions w/ cation-containing products Contra Quinolone all gy, children <18 y,T QT interval, X Disp Tabs SE NA/ /D, abd pain, photosens, Szs, HA, dizziness, tendon rupture, periph al neuropathy, pseudomembranous cohtis, anaphylaxis Interactions t Effects W/ cimetidine, probenecid T effects OF cyclosporine, warfarin, caffeine X effects W/ antacids EMS Monitor ECG for TqT int val, esp in pts taking class lA/III antiarrhythmics monitor ECG and BP for signs of h5 povolemia and electrol5rte disturbances (hypokalemia) d/t D T risk of photosensitivity Rxns OD May cause NA /D, confusion and Szs symptomatic and supportive... 

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