Pharmacokinetics of bismuth and ranitidine following multiple doses of ranitidine bismuth citrate

Derivation of biomonitoring equivalents (BE values) for bismuth

Bismuth (Bi) is a natural element present in the environmental media. Bismuth has been used medicinally for centuries, specifically for the treatment of gastrointestinal (GI) disorders. Although bismuth toxicity is rare in humans, an outbreak of bismuth-induced neurotoxicity was reported in France and Australia in the mid-1970s. The primary source of bismuth exposure in the general population is via food. US FDA (2019) estimated recommended daily intake (RDI) for bismuth as 848 mg bismuth/day (12.1 mg Bi/kg-d assuming a body weight of 70 kg) for GI tract disorders. Exposures to bismuth can be quantified by measuring concentrations in blood and urine. Biomonitoring equivalents (BEs) were derived based on US FDA's RDI as a tool for interpretation of population-level biomonitoring data. A regression between steady state plasma concentrations and oral intakes was used to derive plasma BEs. A whole blood: plasma partitioning coefficient of 0.6 was used to convert plasma BE into whole blood BE. A mass balance equation with a urinary excretion fraction of 0.0003 was used to derive urinary BE. The BE values associated with US FDA's RDI for plasma, whole blood and urine were 8.0, 4.8 and 0.18 μg/L, respectively. These BE values together with bismuth biomonitoring data may be used in screening and prioritization of health risk assessment of bismuth in the general population.

Role of Bismuth in the Eradication of Helicobacter pylori

Bismuth salts exert their activity within the upper gastrointestinal tract through action of luminal bismuth. Bismuth exerts direct bactericidal effect on Helicobacter pylori by different ways: forms complexes in the bacterial wall and periplasmic space, inhibits different enzymes, ATP synthesis, and adherence of the bacteria to the gastric mucosa. Bismuth also helps ulcer healing by acting as a barrier to the aggressive factors and increasing mucosal protective factors such as prostaglandin, epidermal growth factor, and bicarbonate secretion. To date, no resistance to bismuth has been reported. Also synergism between bismuth salts and antibiotics was present. It was shown that metronidazole and clarithromycin resistant H. pylori strains become susceptible if they are administered together with bismuth. Bismuth-containing quadruple therapy was recommended both by the Second Asia-Pacific Consensus Guidelines and by the Maastricht IV/Florence Consensus Report as an alternative first choice regimen to standard triple therapy, in areas with low clarithromycin resistance, and it is recommended as the first-line therapeutic option in areas with a high prevalence of clarithromycin resistance. Greater than 90% eradication success can be obtained by bismuth-containing quadruple therapy. Choosing bismuth as an indispensable part of first-line therapy is logical as both metronidazole and clarithromycin resistances can be overcome by adding bismuth to the regimen.

The protective roles of some lichen species on colloidal bismuth subcitrate genotoxicity

Medicinal plants are increasingly being projected as suitable alternative source for the treatment of various diseases. However, toxic effects resulting from therapeutic bismuth compounds are still documented in animals and humans. This study described the genetic effects of five common lichen species and compared their activities on the genotoxicity induced by the colloidal bismuth subcitrate. After the application of colloidal bismuth subcitrate and lichen extracts, separate and together, human whole blood cultures were assessed by sister-chromatid exchange (SCE) and micronucleus tests. According to our results, the frequencies of SCE and micronucleus rate in peripheral lymphocytes were significantly increased by colloidal bismuth subcitrate (at dose 5 μg/mL) compared with controls. However, lichen extracts had no genotoxic effect. The order of anti-genotoxicity efficacy against colloidal bismuth subcitrate was Pseudevernia furfuracea, Dermotocarpon intestiniforme, Ramalina capitata, Parmelia pulla, respectively. However, Rhizoplaca melanophthalma did not show any effect against colloidal bismuth subcitrate genotoxicity. Present findings showed that the protective roles of lichens studied were dose related. In conclusion, this is the first study report describing the therapeutic potential of lichens against drug genotoxicity in human blood.

Effects of Trimethoprim on the Clearance of Apricitabine, a Deoxycytidine Analog Reverse Transcriptase Inhibitor, and Lamivudine in the Isolated Perfused Rat Kidney

Apricitabine (ATC) is a novel deoxycytidine analog reverse transcriptase inhibitor in development for the treatment of human immunodeficiency virus infection. Studies were performed to characterize the excretion of ATC and its metabolite, BCH-335 (-1-(2-hydroxymethyl-[1,3]oxathiolan-4-yl)-1H-pyrimidine-2,4-dione), in the isolated perfused rat kidney (IPK). A second objective was to investigate the effect of trimethoprim on ATC excretion because trimethoprim inhibits the excretion of lamivudine, structurally similar to ATC, in the IPK. ATC excretion was nonlinear at doses of 80 to 1600 microg. The excretion ratio (ratio of clearance to glomerular filtration rate, assuming negligible protein binding) was greater than 1.0, indicating net tubular secretion. In contrast, the excretion of BCH-335 was independent of the dose of BCH-335. Concomitant administration of ATC and BCH-335 did not affect the excretion of either compound. Trimethoprim significantly inhibited the excretion of both ATC and BCH-335, with IC(50) values of 0.45 and 0.54 microg/ml, respectively. In the presence of trimethoprim, the excretion ratios for both compounds were less than 1.0, indicating tubular reabsorption. Trimethoprim inhibited the excretion of ATC and lamivudine to similar extents. Following concomitant administration of ATC, lamivudine, and trimethoprim, there was no evidence of an interaction between ATC and lamivudine. These results suggest that ATC undergoes active tubular secretion in the kidney. Because the renal excretion of both ATC and lamivudine is inhibited by trimethoprim to similar extents, in clinical practice exposure to ATC, it would be expected to be increased in the presence of therapeutic concentrations of trimethoprim to a similar extent as has been shown previously for lamivudine.

Pharmacokinetics and bioequivalence of ranitidine and bismuth derived from two compound preparations

AIM: To evaluate the bioequivalence of ranitidine and bismuth derived from two compound preparations.

METHODS: The bioavailability was measured in 20 healthy male Chinese volunteers following a single oral dose (equivalent to 200 mg of ranitidine and 220 mg of bismuth) of the test or reference products in the fasting state. Then blood samples were collected for 24 h. Plasma concentrations of ranitidine and bismuth were analyzed by high-performance liquid chromatography and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. The non-compartmental method was used for pharmacokinetic analysis. Log-transformed C_max, AUC_(0-t) and AUC_(0-∞) were tested for bioequivalence using ANOVA and Schuirmann two-one sided t-test. T_max was analyzed by Wilcoxon’s test.

RESULTS: Various pharmacokinetic parameters of ranitidine derived from the two compound preparations, including C_max, AUC_(0-t), AUC_(0-∞), T_max and T_1/2, were nearly consistent with previous observations. These parameters derived from test and reference drug were as follows: C_max (0.67 ± 0.21 vs 0.68 ± 0.22 mg/L), AUC_(0-t) (3.1 ± 0.6 vs 3.0 ± 0.7 mg/L per hour), AUC_(0-∞) (3.3 ± 0.6 vs 3.2 ± 0.8 mg/L per hour), T_max (2.3 ± 0.9 vs 2.1 ± 0.9 h) and T_1/2 (2.8 ± 0.3 vs 3.1 ± 0.4 h). In addition, double-peak absorption profiles of ranitidine were found in some Chinese volunteers. For bismuth, those parameters derived from test and reference drug were as follows: C_max (11.80 ± 7.36 vs 11.40 ± 6.55 μg/L), AUC_(0-t) (46.65 ± 16.97 vs 47.03 ± 21.49 μg/L per hour), T_max (0.50 ± 0.20 vs 0.50 ± 0.20 h) and T_1/2 (10.2 ± 2.3 vs 13.0 ± 6.9 h). Ninety percent of confidence intervals for the test/reference ratio of C_max, AUC_(0-t) and AUC_(0-) derived from both ranitidine and bismuth were found within the bioequivalence acceptable range of 80%-125%. No significant difference was found in T_max derived from both ranitidine and bismuth.

CONCLUSION: The two compound preparations are bioequivalent and may be prescribed interchangeably.

Human biokinetics of injected bismuth-207

A healthy male volunteer received an intravenous injection of 207Bi as citrate. Levels of the tracer in blood and in excretion samples, and its retention and distribution within the body, were investigated by appropriate radioactivity measurements. Levels in blood fell very rapidly, with only 1% of the injection remaining at 7 h and only ca. 0.1% at 18 days. There was rapid initial excretion, with 55% lost during the first 47 h, principally in urine; however, longer-term losses were much slower and 0.6% remained in the body at 924 days, when the contemporary rate of loss implied a half-life of 1.9 years. Integration of the retention pattern suggested that steady exposure to bismuth compounds could lead ultimately to a body content of approximately 24 times the daily systemic uptake. The largest organ deposit was in the liver, which after 3 days contained ca. 60% of the contemporary whole body content, consistent with reports of hepatotoxicity. These findings differ markedly from the metabolic model for bismuth proposed by the International Commission on Radiological Protection, which envisages a terminal half-life in the body of only 5 days and kidney as the site of highest deposition.

Vanadium pharmacokinetics and oral bioavailability upon single-dose administration of vanadyl sulfate to rats

Vanadium pharmacokinetic parameters and oral bioavailability were determined after administration of vanadyl sulfate, an antidiabetic agent, to male Wistar rats. An optimal sampling design was used over a 21-day period; vanadium was measured in blood by atomic absorption spectrophotometry (AAS). After i.v. bolus injection (3.025 mg V/kg body weight), a three-compartment model was fitted to the data. Mean (+/- SD) half-lives were 0.90 +/- 0.56 hours, 24.8 +/- 14.5 h and 201 +/- 74 h, respectively, for the three phases observed. Vanadium clearance averaged 37.6 +/- 15.8 mL/h. Initial volume of distribution was 2.43 +/- 1.22 L/kg whereas total volume of distribution was 25.4 +/- 3.9 L/kg; these values largely exceeded body weight (i.e. 300 g), in agreement with a great uptake and retention of vanadium in tissues. After oral gavage administration (15.12 and 7.56 mg V/kg body weight), vanadium disposition was best described by a three-compartment model, with absorption appearing to occur by a zero-order rate. This process lasted 10.3 +/- 1.3 h and 10.9 +/- 1.1 h for the two dosage levels, respectively. Half-lives corresponding to the terminal log-linear part of the curve were 173.5 +/- 1.6 h and 172 +/- 6 h (Bayesian estimates). No dose-dependency was observed for any of the parameters determined. Absolute bioavailabilities, with reference to the i.v. administration, were 12.5% and 16.8% when determined from AUCmod. Bioavailability appeared to be higher than generally stated in the literature.

Uptake of bismuth in motor neurons of mice after single oral doses of bismuth compounds

Bismuth, a component of many gastrointestinal medications, is a heavy metal little studied as regards nervous system uptake. We were interested to see if low doses of intragastric bismuth entered the nervous system, and if dietary selenium influenced the amount of bismuth detected. Mice were given 40 to 1200 mg/kg of bismuth subnitrate (BSN), bismuth subsalicylate (BSS), colloidal bismuth subcitrate (CBS), or ranitidine bismuth citrate (RBC) intragastrically. Mice on low- or high-selenium diets were given 4 to 32 mg/kg of bismuth from RBC. One week later, sections of nervous tissue were stained with autometallography to detect bismuth grains (Bi(AMG)). Bismuth was found in neurons with axons outside of the nervous system, in particular motor neurons, and in cells outside the blood-brain barrier. The lowest bismuth dose which resulted in Bi(AMG) in motor neurons was 696 mg/kg from BSN, 57 mg/kg from BSS, 29 mg/kg from CBS, and 26 mg/kg from RBC. No bismuth was seen in motor neurons of mice on the low-selenium diet. Intragastric doses of bismuth therefore enter mouse motor neurons, and the amount detectable varies with dietary selenium.

Eradication of H. pylori with pantoprazole, clarithromycin, and metronidazole in duodenal ulcer patients: a head-to-head comparison between two regimens of different duration

BACKGROUND

The study was conducted to compare the efficacy and tolerability of two pantoprazole-based triple therapies of different length in the eradication of H. pylori.

METHODS

In this double-blind, multicenter parallel group comparison, H. pylori-positive patients were randomly assigned to either the PCM-7 group (7 days of pantoprazole 40 mg bid, clarithromycin 500 mg bid, metronidazole 500 mg bid) or the PCM-14 m group (modified 14 day therapy of the same regimen with metronidazole only given for 10 days due to labeling reasons). H. pylori status was determined by urease test, histology, culture, and 13C-urea breath test. Treatment outcome was assessed 6 weeks after intake of the last study medication.

RESULTS

The following eradication rates were achieved: for PCM-7 in the MITT population 83% (89/107), in the PP population 84% (81/97); for PCM-14 m in MITT 87% (92/106), in PP 88% (91/104). Ulcer healing rates were: for PCM-7 in MITT population 99% (106/107), in the PP population 99% (96/97); for PCM-14 m in MITT 99% (105/106), in PP 99% (103/104). Gastrointestinal symptoms and gastritis scores decreased in both treatment groups. Equivalence of treatment regimens could be proven for all populations. In total, 64 patients reported adverse events. Five serious adverse events occurred, all unrelated to the study medication.

CONCLUSION

The two pantoprazole-based triple therapies tested in this study are equally effective in H. pylori eradication, ulcer healing and relief from ulcer pain. It is concluded that 7 days of triple therapy are generally sufficient.

Pharmacokinetic considerations in the eradication of Helicobacter pylori

As Helicobacter pylori plays an important role in the aetiopathogenesis of peptic ulcer, therapeutic strategies aimed at maintaining long term remission have shifted from the control of intragastric pH to targeting H. pylori. According to recent international guidelines the clinical goals--rapid ulcer healing and prevention of relapse--can be best accomplished by combination therapy consisting of an antisecretory drug (proton pump inhibitor or ranitidine) and 2 antimicrobial agents (preferable amoxicillin, clarithromycin or metronidazole). When applying such multidrug regimens, possible synergy between the agents suggests that pharmacokinetic considerations might help to improve H. pylori eradication rates, which should be above 85 to 90% on an intention-to-treat basis. The present review summarises the pharmacokinetic properties and interaction potential of all drugs presently used in the various H. pylori eradication regimens, with emphasis on particular patient populations such as the elderly and those with renal impairment. The drugs considered are omeprazole, lansoprazole, pantoprazole, rabeprazole, ranitidine and ranitidine bismutrex, bismuth salts, amoxicillin, clarithromycin, azithromycin, roxithromycin, metronidazole, tinidazole and tetracycline. When addressing the clinically important questions of the efficacy, safety and costs of the recommended regimens, the impact of drug disposition on H. pylori eradication should not be neglected.

Distribution of bismuth in the rat after oral dosing with ranitidine bismuth citrate and bismuth subcitrate

Bismuth preparations are used world-wide for the management of peptic ulcer disease, for eradication of Helicobacter pylori, and in the prevention and treatment of diarrhoea. However neurological toxicity of bismuth has always been a major concern and evidence has been found of the absorption of bismuth. Recent studies have suggested that the absorption of bismuth increases when bismuth salts are used with ranitidine hydrochloride. The absorption and deposition of bismuth as a result of the use of the new drug ranitidine bismuth citrate have not been yet clarified. After 15 days of twice daily oral gavage with bismuth subcitrate, 13.7 mg kg(-1) day(-1) to eight rats, deposition of bismuth was found in all the tissues studied, especially the kidney (30.81 +/- 8.59 microg g(-1) dry weight). A similar pattern of distribution and tissue concentrations was found when bismuth subcitrate was given with ranitidine hydrochloride 8.6 mg kg(-1) day(-1) to another eight rats, although this combination resulted in lower brain levels (3.12 + 1.31 microg g(-1) dry weight) than after administration of bismuth subcitrate alone (4.77 +/- 0.97 microg g(-1) dry weight). When six rats were given ranitidine bismuth citrate by gavage at 22.8 mg kg(-1) day(-1) for 15 days, kidney levels were lower (4.24 +/- 1.75 microg g(-1) dry weight) and brain levels were below detection limits; the bismuth concentrations in the faeces from this group were also significantly lower (1603 +/- 104.0 microg g(-1) dry weight) than for the two other groups. After dosing with bismuth alone or in association with ranitidine hydrochloride, bismuth was detected in several organs and deposition was not influenced by gastric pH. Blood levels correlate poorly with organ deposition and brain deposition was not always associated with encephalopathy. After administration of ranitidine bismuth citrate, significantly lower concentrations of bismuth were found in the kidney and bismuth was not detectable in the brain, suggesting lower bismuth absorption. This was confirmed by higher levels in the faeces after dosing with ranitidine bismuth citrate. Thirty days after dosing with ranitidine bismuth citrate or bismuth subcitrate, bismuth could not be detected in any of the organs examined but could be found in the urine. In conclusion, bismuth was deposited in the kidney, brain, lung and liver of rats after oral dosing with bismuth subcitrate. After oral dosing with an equivalent amount of bismuth in the form of ranitidine bismuth citrate, significantly lower concentrations of bismuth were deposited in the kidney; in the brain bismuth was not detectable.