Drug interactions I: detection of inorganic nitrite in organic nitrate esters under acidic conditions simulating the human stomach.

Both unformulated (bulk) and formulated (drugs) organic nitrate esters (isosorbide dinitrate, nitroglycerin, and pentaerythritol tetranitrate) were studied in the presence and absence of hydrochloric acid to determine if they could be sources of nitrite (and therefore lead to nitrosamine formation) under acidic conditions similar to those found in the stomach. The presence and generation of nitrite ion was detected by a modification of the Griess reaction. Bulk isosorbide dinitrate and nitroglycerin were found to be contaminated with 13.8-121.4 mumoles of inorganic nitrite per mole of nitrate ester. In addition, in the presence of hydrochloric acid, these preparations generated 0.52-1.18 mumoles of inorganic nitrite/mole of nitrate ester/min. Unformulated nitroglycerin generated nitrite at a rate roughly twice that of isosorbide dinitrate. In contrast, no evidence for nitrite contamination or generation by pentaerythritol tetranitrate was found. Tablets and capsules of isosorbide dinitrate contained approximately 27-216 mumoles of nitrite/mole of nitrate ester and, in the presence of hydrochloric acid, generated an average of 0.55 mumole nitrite/min. For isosorbide dinitrate, this rate was similar for bulk and formulated drug. In comparison to isosorbide dinitrate, the amount of nitrite initially present in tablets and capsules of nitroglycerin varied more widely (approximately 25-2290 mumoles nitrite/mole of nitrate ester), and in this case nitrite was generated at higher rates than unformulated drug averaging approximately 4.7 mumoles nitrite/mole of nitrate ester/min. Contrary to a literature report, we found that nitrate ion is not reduced to nitrite by hydrochloric acid (pH 1-3).(ABSTRACT TRUNCATED AT 250 WORDS)

Drug interactions. III. Formation of nitrosamines from therapeutic drugs. Formation, mutagenic properties and safety assessment of propranolol hydrochloride with respect to the intragastric formation of N-nitrosopropranolol under conditions found in patients.

In the preceding report, the kinetics of formation of N-nitrosopropranolol (NNP) from propranolol and inorganic nitrite were determined in solutions of hydrochloric acid over the range of pH similar to that found in the human stomach. In this communication, NNP formation was examined in human gastric juice and in the presence of organic nitrate ester vasodilator drugs. In comparison to HCl solutions, equivalent concentrations of propranolol and nitrite produced similar amounts of NNP in gastric juice; however, the yield increased as the pH was lowered and the kinetics of nitrosamine formation were different. Endogenous nitrite concentrations in 22 samples of human gastric juice were below the minimum concentration (10(-5) M) required for production of detectable levels of NNP. Maximal therapeutic dosages of propranolol (10(-2) M) incubated with isosorbide dinitrate (3,4-6.8 X 10(-3) M) or nitroglycerin (8.6 X 10(-4) M) also failed to produce NNP. However, NNP formed adventitiously during the concentration of aqueous and methylene chloride solutions that contained propranolol and organic nitrates, underscoring the importance of avoiding artifactual formation of nitrosamines. Furthermore, synthetic NNP was not mutagenic in either the Ames tester strains (TA92, TA98, TA100, TA1535, TA1537 and TA1538) or the hepatocyte-mediated mammalian cell mutagenesis assay. We conclude that NNP is unlikely to form in the stomach under conditions normally present in patients. Moreover, even if NNP formed under exceptional circumstances, this compound is unlikely to be a carcinogen. With respect to the potential formation of nitrosamines during drug dissolution in the stomach, long-term therapy with propranolol hydrochloride appears to be safe.

Drug interactions. II. Formation of nitrosamines from therapeutic drugs. Properties and kinetics of the formation of N-nitrosopropranolol from nitrite and the secondary amine propranolol hydrochloride.

In the presence of hydrochloric acid, nitrosamines may be generated from amines and nitrite. Most nitrosamines are carcinogens and many commonly used drugs contain potentially nitrosatable amine groups. Beta-adrenergic blockers, which have such amine groups, are widely prescribed and are often ingested for the lifetime of the patients, but their safety with respect to the intragastric formation of nitrosamines has not been established. The studies in this and the following report were designed to assess the potential risk posed by the endogenous formation of a nitrosamine in the stomach to individuals receiving longterm treatment with propranolol hydrochloride. The putative nitrosamine, N-nitrosopropranolol (NNP), was synthesized and its stability was examined under various experimental conditions. A high-pressure liquid chromatographic method was developed which detects a minimum of 7 X 10(-11) mol of NNP in the presence of large quantities of unreacted drug. Preparations of propranolol hydrochloride were found to contain several non-nitrosamine contaminants, which were removed before kinetic studies. At 37 degrees C, in solutions of HCl within the pH range found in the stomach, the optimum pH for the formation of NNP was 3. The yield of NNP increased linearly as incubation time and concentration of propranolol increased and exponentially as the concentration of nitrite was raised. Under optimal conditions in hydrochloric acid, the minimum concentration of nitrite required for the production of detectable amounts of NNP was 10(-5) M.

Studies of the effects of alpha-difluoromethylornithine and ethanol on the pathogenesis of bleomycin-induced pulmonary fibrosis in mice.

Both DL-alpha-difluoromethylornithine (DFMO) and ethanol have been reported to inhibit the growth of fibroblasts in cell culture. The objectives of the present study were to determine whether these compounds could be used to inhibit the growth of fibroblasts in vivo, with a bleomycin-induced mouse model of pulmonary fibrosis. DBA/2J mice were given a single endotracheal injection of bleomycin, 10 nmol. In addition to bleomycin (BLM), groups of animals received 2% DFMO in drinking water for 4 days prior to BLM and 18 days after (BLM DFMO), 6% ethanol in drinking water for 7 days prior to BLM and 21 days after (BLM E7), 6% ethanol in drinking water for 21 days initiated on the day of BLM intubation (BLM E), or DFMO, E7, and BLM in combination (BLM DFMO E7). Animals died or were killed 21 days after bleomycin treatment and lungs were evaluated by histopathologic criteria. DFMO failed to alter the incidence or severity of fibrotic lesions, increased the severity of epithelial metaplasia (p less than 0.05), and reduced the lung disease index (from 56.3 to 42.1%, p less than 0.05) and mortality from 83.3 to 41.7% (p less than 0.025). In contrast to the unsatisfactory response to DFMO, pretreatment with ethanol (BLM E7) reduced the incidence of interstitial fibrosis from 91.3 to 71.4% (p less than 0.05) and confluent fibrosis from 73.9 to 20.0% (p less than 0.005). The severity of lesions was also reduced by ethanol, resulting in an 18.5% decrease in interstitial fibrosis, a 25.9% decrease in epithelial metaplasia, and a 55.4% reduction in the lung disease index (all p less than 0.01). However, when ethanol and DFMO were administered in combination, the beneficial effects of ethanol alone were not observed, and only the lung disease index was decreased.

Bleomycin for the cure of Trypanosoma brucei brucei infections in mice: lack of pulmonary toxicity.

Although bleomycin is a known pulmonary toxin, results presented herein indicate its relative safety for treatment of trypanosomiasis. More than 4 times the curative dose in this acute model of infection does not induce significant alterations of lung hydroxyproline levels, which are known to directly correlate with histopathological criteria of pulmonary fibrosis.