Famotidine Theophylline

Diphenoxylate in high doses may produce dependence if coadministered with atropine. Diphenoxylate combined with thioridazine is associated with opioid withdrawal. Famotidine should be taken with care when coadministered with antacids, theophylline, and probenecid. Kaolin should not be administered with any other oral drug. Loperamide overdose should be treated with naloxone hydrochloride.174,175... 

CIMETIDINE FAMOTIDINE NIZATIDINE, RANITIDINE BRONCHODILATORS -THEOPHYLLINE t efficacy and adverse effects, including seizures. There is conflicting information associated with ranitidine, famotidine and nizatidine Inhibition of metabolism via CYP1A2, cimetidine being the best known inhibitor Use alternative acid suppression, e.g. a proton pump inhibitor (not omeprazole or lansoprazole) or monitor closely considerable patient variation. Check levels on day 3 and then at 1 week. A 30-50% i dose of theophylline may be required. For doses <400 mg/day, the interaction may not be clinically significant... 

Drug interactions Cimetidine is a CYP450 inhibitor and can inhibit the metabolism of phenytoin, warfarin, and theophylline. Famotidine, nizatidine, and ranitidine are unlikely to cause clinically significant drug interactions. All antagonists have the potential to interact with other drugs that require gastric acid for absorption (e.g., ketoconazole, itraconazole). 

Bullock, L. Fitzgerald, J.F. Glick, M.R. Parks, R.B. Schnabel, J.G. Hancock, B.G. Stability of famotidine 20 and 40 mg/L and amino acids in total parenteral nutrient solutions. Am.J.Hosp.Pharm., 1989, 46, 2321-2325 [stability-mdicating theophylline (IS)]... 

Cimetidine reduces theophylline Cl by CYP1A2 inhibition dose-dependently up to 1200 mg/day2 Theophylline metabolism is hardly influenced by ranitidine at therapeutic doses, including high doses up to 4200 mg/day2° "< Similarly, famotidine and nizatidine do not alter theophylline... 

Verdiani, R, Di Carlo, S., and Baronti, A., Famotidine effects on theophylline pharmacokinetics in snbjects affected by COPD — comparison with cimetidine and placebo. Chest, 94(4) 807-810, 1988. 

Cimetidine raises theophylline serum levels and toxicity may develop. However, the extent of the interaction is unlikely to be clinically relevant in most patients with low-dose cimetidine. Famotidine, nizatidine, ranitidine and roxatidine appear not to interact. 

Famotidine 40 mg twice daily for 5 days had no effect on the pharmacokinetics of theophylline (given as intravenous aminophylline) in 10 healthy subjects. In another study, 16 patients with bronchial asthma or chronic obstructive pulmonary disease (COPD) found that famotidine 20 mg twice daily for at least 3 days did not affect the clearance of theophylline. Two further studies also found no interaction between intravenous theophylline and famotidine 20 or 40 mg twice daily for 4 or 9 days in COPD... 

Cimetidine is an enzyme inhibitor that reduces the metabolism (predominantly A-demethylation) of theophylline by the cytochrome P450 isoenzyme CYP1A2 in the liver, thereby raising its serum levels. Famotidine, nizatidine and ranitidine do not have enzyme-inhibiting eifects so that it is not clear why they sometimes appear to behave like eimetidine. 

Lin JH, Chremos AN, Chiou R, Yeh KC, Williams R. Comparative effect of famotidine and cimetidine on the pharmacokinetics of theophylline in normal volunteers. BrJ Clin Pharmacol (1987) 24, 669-72. 

Bachmann K, Sullivan TJ, Reese JH, Jauregui L, Miller K, Scott M, Yeh KC, Stepanavage M, King JD, Schwartz J. Controlled study of the putative interaction between famotidine and theophylline in patients with chronic obstructive pulmonary disease. J Clin Pharmacol (1995) 35, 529-35. 

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