Biotransformation of bromhexine by Cunninghamella elegans, C. echinulata and C. blakesleeana

Abstract Fungi is a well-known model used to study drug metabolism and its production in in vitro condition. We aim to screen the most efficient strain of Cunninghamella sp. among C. elegans, C. echinulata and C. blakesleeana for bromhexine metabolites production. We characterized the metabolites produced using various analytical tools and compared them with mammalian metabolites in Rat liver microsomes (RLM). The metabolites were collected by two-stage fermentation of bromhexine with different strains of Cunninghamella sp. followed by extraction. Analysis was done by thin layer chromatography, high performance thin layer chromatography, Fourier transform infrared spectroscopy, high performance liquid chromatography and Liquid chromatography–mass spectrometry. The role of Cytochrome P3A4 (CYP3A4) enzymes in bromhexine metabolism was studied. Fungal incubates were spiked with reference standard – clarithromycin to confirm the role of CYP3A4 enzyme in bromhexine metabolism. Three metabolites appeared at 4.7, 5.5 and 6.4 min retention time in HPLC. Metabolites produced by C. elegans and RLM were concluded to be similar based on their retention time, peak area and peak response of 30.05%, 21.06%, 1.34%, and 47.66% of three metabolites and bromhexine in HPLC. The role of CYP3A4 enzyme in metabolism of bromhexine and the presence of these enzymes in Cunninghamella species was confirmed due to absence of peaks at 4.7, 5.4 and 6.7 min when RLM were incubated with a CYP3A4 enzyme inhibitor – clarithromycin.

Biotransformation of bromhexine by Cunninghamella elegans, C. echinulata and C. blakesleeana.

Fungi is a well-known model used to study drug metabolism and its production in in vitro condition. We aim to screen the most efficient strain of Cunninghamella sp. among C. elegans, C. echinulata and C. blakesleeana for bromhexine metabolites production. We characterized the metabolites produced using various analytical tools and compared them with mammalian metabolites in Rat liver microsomes (RLM). The metabolites were collected by two-stage fermentation of bromhexine with different strains of Cunninghamella sp. followed by extraction. Analysis was done by thin layer chromatography, high performance thin layer chromatography, Fourier transform infrared spectroscopy, high performance liquid chromatography and Liquid chromatography-mass spectrometry. The role of Cytochrome P3A4 (CYP3A4) enzymes in bromhexine metabolism was studied. Fungal incubates were spiked with reference standard - clarithromycin to confirm the role of CYP3A4 enzyme in bromhexine metabolism. Three metabolites appeared at 4.7, 5.5 and 6.4min retention time in HPLC. Metabolites produced by C. elegans and RLM were concluded to be similar based on their retention time, peak area and peak response of 30.05%, 21.06%, 1.34%, and 47.66% of three metabolites and bromhexine in HPLC. The role of CYP3A4 enzyme in metabolism of bromhexine and the presence of these enzymes in Cunninghamella species was confirmed due to absence of peaks at 4.7, 5.4 and 6.7min when RLM were incubated with a CYP3A4 enzyme inhibitor - clarithromycin.

Metabolism of bromhexine in pig hepatocyte cultures.

The metabolism of bromhexine [N-cyclohexyl-N-methyl-2-(2-amino-3,5-di-bromo-benzyl)-amine] was studied using pig hepatocyte cultures and LC/MS/MS techniques. Phase I 'single-step' reactions, i.e. hydroxylation and demethylation occurred the fastest whereas the formation of hydroxylated/demethylated and aminal hydroxylated metabolites, which can be considered as multiple-step reactions, occurred more slowly. Phase II conjugates were detected for all hydroxylated metabolites. The glucuronides of the hydroxylated/demethylated components tended to accumulate. In addition to metabolites known to be formed in vivo, three unknown components related to bromhexine were detected. Two of these metabolites accumulated during incubation. Based on the fragmentation patterns, a possible molecular structure is proposed for these components.

High-performance liquid chromatographic determination of ambroxol in human plasma.

Ambroxol has been determined in biological fluids using a rapid and sensitive high-performance liquid chromatographic method. The samples prepared from plasma by liquid-liquid extraction were analysed on reversed-phase silica gel by competing-ion chromatography with ultraviolet detection. The method was applied to the determination of ambroxol levels in twelve healthy volunteers after oral administration of 90 mg of ambroxol in tablets of Mucosolvan and Ambrosan.

Pharmacokinetics and first-pass effect of bromhexine in rats.

The pharmacokinetics and first-pass effect of bromhexine (BH) were studied in rats. Upon i.v. administration of 0.3 and 1 mg/kg of BH hydrochloride to normal rats, the plasma concentrations followed a biexponential curve, with slower terminal elimination (t1/2 beta = 8.9-11 h). In bile duct cannulated rats, the plasma concentration-time profile was similar to that of normal rats and the bile excreted within 30 h contained only 1.5 +/- 1.2% of the dose as intact and conjugated BH. These results suggest that a slower terminal elimination of BH after i.v. injection is due to a relatively small plasma clearance and large distribution volume rather than the enterohepatic recycling of the drug. Renal clearance of BH was negligible since urinary excretion of intact BH for 24 h after i.v. injection did not exceed 1% of the dose. After oral administration of BH, the systemic availability ranged only 1.8-3.9% based on i.v. and oral data, showing the poor bioavailability of oral BH. The first-pass effect of BH was measured by comparing the area under plasma concentration-time curve (AUC) after i.v., oral or hepatic portal (h.p.v.) administration of the drug. The AUC following h.p.v. dosing was only one-tenth of that obtained following i.v. administration and the AUC after oral dose was a quarter of that after h.p.v. administration. The hepatic extraction ratio was estimated to be 0.92. A low bioavailability after oral BH was explained by both hepatic and intestinal first-pass clearance, but mainly due to hepatic extraction.

Lack of detectable DNA alkylation for bromhexine in man.

It is known that in vitro incubation of the expectorant drug bromhexine (N-methyl-N-cyclohexyl-(2-amino-3,5-dibromobenzyl)-ammonium hydrochloride) with nitrite yields methylcyclohexyl nitrosamine (NMCA). NMCA is capable of methylating DNA when administered to rats. In vivo tests with bromhexine have also demonstrated that the drug methylates DNA when it is orally administered in the presence of sodium nitrite, presumably due to the intragastric formation of NMCA. In this study the potential of bromhexine to methylate nucleic acids in man, under physiological conditions, has been investigated. 20 volunteers were orally administered on each of three successive days 48 mg of bromhexine hydrochloride, labelled with three deuterium atoms in the N-methyl group. Urine was collected before treatment and subsequent to the last dose, and analysed by GC-MS for d0- and d3-7-methylguanine. 7-Methylguanine is naturally occurring in urine owing to the turnover of t-RNA of which it is a minor constituent. It is also a repair product from nucleic acids methylated by carcinogens, which is known to be excreted unmetabolised largely within 24 h of the methylation process. Unlabelled 7-methylguanine was present at levels of 7.36 +/- 2.43 mg/d in control urine and 6.12 +/- 2.36 mg/d in treated urine, in accord with previously published values. The excretion of isotopically labelled 7-methylguanine averaged 0.43 +/- 0.077% of the unlabelled concentration for control urines and 0.44 +/- 0.066% for treated urines, i.e. no d3-7-methylguanine could be detected following the drug treatment. The observed signals were largely accounted for by the naturally occurring isotopes 13C and 15N.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of detectable N-nitroso-N-methyl-N-cyclohexylamine in humans after administration of bromhexine.

The possible formation of N-nitroso-N-methyl-N-cyclohexylamine (NMCA) from the drug bromhexine (N-methyl-N-cyclohexyl-(2-amino-3,5-dibromobenzyl)-ammonium hydrochloride) and nitrite was investigated in humans using three different approaches: 1. analysis on metabolites of NMCA in human urine; 2. analysis on NMCA in human gastric juice; 3. in vitro incubation of human gastric juice with therapeutic bromhexine doses. Diet given to volunteers was varied during these investigations with respect to nitrate content. Experiments with a maximum load of 200 mg nitrate to stimulate nitrite formation were performed. Results of in vivo experiments did not indicate any formation of NMCA. In one out of 39 ex-vivo/in-vitro experiments (with a load of 100 mg nitrate in drinking water) 0.5 ng NMCA/ml gastric juice could be detected which is near the detection limit. Finally, this study showed that bromhexine is not secreted by saliva. This allows to conclude that nitrite and bromhexine do not reach the stomach simultaneously over a longer period of time. In consequence, medication with bromhexine is not regarded to represent a risk due to nitrosamine formation.

Nitrosation of bromhexine and aminophenazone in gastric juice after high nitrate loading in the diet. An ex-vivo/in-vitro study in humans.

In an ex-vivo study, nitrosation of bromhexine (N-methyl-N-cyclohexyl-(2-amino-3,5-dibromobenzyl)-ammonium hydrochloride) in human gastric fluid under conditions of high dietary nitrate intake was investigated. 26 healthy volunteers received 200 mg of nitrate in a vegetable during a standard breakfast. Nitrite values in saliva were significantly increased 2 to 3 h after nitrate intake. In contrast, nitrite levels in gastric fluid sampled 3 h after nitrate intake remained in the low concentration range of less than or equal to 1.7 micrograms/No2-/ml. Incubation of gastric fluid samples at 37 degrees C with the recommended maximum single oral dose of bromhexine (16 mg/100 ml) or an equimolar concentration of aminophenazone revealed in 4/26 cases formation of N-nitrosomethylcyclohexylamine from bromhexine at barely detectable levels. In contrast, aminophenazone generated N-nitrosodimethylamine at a very high rate, resulting in yields of greater than 50% in several samples. In view of the average daily background exposure to preformed nitrosamines in foods (0.5-1 microgram/capita), according to these results the possible contribution of in-vivo nitrosation of bromhexine corresponds at best to 10% in addition to the daily background exposure and therefore can be regarded as negligible.

Bioavailability of bromhexine tablets and preliminary pharmacokinetics in humans.

The absorption of bromhexine from Bromhexin tablets 8 mg, DAK has been compared with that from Bisolvon tablets 8 mg, Boehringer Ingelheim, in a two-way complete crossover study. Four tablets of each of the two bromhexine products, corresponding to a single dose of 32 mg of bromhexine hydrochloride (77.6 mumol), was administered to each of the 10 volunteers. The plasma concentration was followed over the 4-hour period following each administration. By means of Pratt's test for paired data no statistically significant difference (p greater than 0.10) between the two products was found with respect to maximum plasma concentration (89 and 84 nmol.1(-1), respectively), the times for their occurrence (1.3 and 1.0 h, respectively), and the area under the plasma concentration-time curves (140 and 132 nmol.1(-1).h, respectively). It is concluded that Bromhexin, DAK and Bisolvon are bioequivalent. Provisional pharmacokinetic data for bromhexine, after oral administration, in man were obtained. The first-pass effect and the biological half-life were estimated by combining plasma and 30 h urine data from four of the volunteers. The first-pass effect was estimated to be c. 75 per cent, the biological half-life to be c. 6 h, and c. 0.1 per cent of the dose was found as unmetabolized bromhexine in the urine. The data indicate that the pharmacokinetics of bromhexine may be described as a two-compartment open model.

Erythromycin and bromhexine in acute exacerbations of chronic bronchitis. A study on sputum penetration and clinical effectiveness.

A group of 22 patients with acute purulent exacerbations of chronic bronchitis were treated with 1 g erythromycin ethyl succinate granules twice daily orally for 10 days. Half the patients were given bromhexine additionally and the other half received placebo instead. Serum and sputum erythromycin concentrations were measured microbiologically at intervals after the first dose. The clinical results in both treated groups were rather poor, with many patients becoming infected again immediately after the chemotherapy. Blood and sputum concentrations of erythromycin did not greatly differ in the two patient groups. The sputum concentration of erythromycin was often higher than the blood concentration at the same time. The MIC's of erythromycin (in particular, those for the Haemophilus influenzae strains) were often higher than the drug concentrations attained in the sputum.

Pharmacokinetics of bromhexine in the dog.

Bromhexine hydrochloride was administered to dogs i.v. and p.o. Plasma determinations of the unchanged drug were carried out by gas-liquid chromatography with electron-capture detection. The plasma levels obtained after i.v. administration were consistent with a two-compartment open model. Comparison of the results of i.v. and oral administration show a low bioavailability, probably due to a first pass effect.

Studies on the formation of cyclohexylamine and N-methylcyclohexylamine from bromhexine in animals and man, and simultaneous determination of cyclohexylamine and N-methylcyclohexylamine by gas chromatography.

In order to detect cyclohexylamine and N-methylcyclohexylamine simultaneously in urine, a gas chromatographic method was developed in which Chromosorb 103 (porous polymer) was found to be suitable as the column packing. The detection limits were 0.1 mug/ml of cyclohexylamine and 0.4 mug/ml of N-methylcyclohexylamine in urine. In tests on animals administered bromhexine, which contains N-methylcyclohexylamine as part of its side-chain, neither cyclohexylamine nor N-methylcyclohexylamine was detected in the urine.

The absorption, excretion and metabolic pattern of bromhexine in man after oral and i.v. administration.

The fate of 14C-labelled bromhexine (Bisolvon¿) in man following intravenous and oral administration was studied by investigation of the blood and plasma levels and the excretion profiles. Slight variations observed between the two administration routes are explained by the somewhat different distribution patterns resulting from the different "first path" after oral application (liver) and intravenous injection (tissues).