Reduction in oral penicillamine absorption by food, antacid, and ferrous sulfate

A magnesium transporter is involved in the cesium ion resistance of the high-concentration cesium ion-resistant bacterium Microbacterium sp. TS-1

Cesium ion (Cs⁺) resistance has been reported in bacteria but is poorly understood as reports on Cs⁺-resistant bacteria have been limited. We previously reported a novel Cs⁺/H⁺ antiporter CshA implicated in Cs⁺-resistance in Microbacterium sp. TS-1. The present study used the same screening method to isolate novel Cs⁺-sensitive mutants and their revertants from TS-1. A comparative mutation site analysis using whole-genome sequencing revealed that MTS1_03028 encodes the Mg²⁺ transporter MgtE and is a candidate Cs⁺ resistance-related gene. We performed a bioinformatic analysis of MTS1_03028 and complementation experiments on Cs⁺ resistance in the TS-1 MTS1_03028 mutants Mut5 and Mut7 as well as Escherichia coli expressing MTS1_03028 in the presence of Mg²⁺. We established the role of MgtE in Cs⁺ resistance through a functional analysis of TS-1. Enhancing Mg²⁺ transport by expression of MTS_03028 conferred increased Cs⁺ resistance. When this strain was exposed to Cs⁺ concentrations exceeding 200 mM, CshA consistently lowered the intracellular Cs⁺ concentration. To our knowledge, the present study is the first to clarify the mechanism of Cs⁺ resistance in certain bacteria. The study findings offer important insights into the mechanism of bacterial resistance to excess Cs⁺ in the environment, suggesting the potential for bioremediation in high Cs-contaminated areas.

Flavonoids and stilbenoids as a promising arsenal for the management of chronic arsenic toxicity

Rapid industrial and technological development has impacted ecosystem homeostasis strongly. Arsenic is one of the most detrimental environmental toxins and its management with chelating agents remains a matter of concern due to associated adverse effects. Thus, safer and more effective alternative therapy is required to manage arsenic toxicity. Based on existing evidence, native and indigenous plant-based active biomolecules appear as a promising strategy to mitigate arsenic-induced toxicity with an acceptable safety profile. In this regard, various phytochemicals (flavonoids and stilbenoids) are considered important classes of polyphenolic compounds with antioxidant and chelation effects, which may facilitate the removal of arsenic from the body more effectively and safely with regard to conventional approaches. This review presents an overview of conventional chelating agents and the potential role of flavonoids and stilbenoids in ameliorating arsenic toxicity. This report may provide a roadmap for identifying novel prophylactic/therapeutic strategies for managing arsenic toxicity.

Review on Preclinical and Clinical Evidence of Food (Beverages, Fruits and Vegetables) and Drug Interactions: Mechanism and Safety

Background:

The therapeutic potency and efficacy of drugs can be affected by a patient’s dietary habit. The food composition and their nutritional value interact with drugs that lead to alteration of the therapeutic response of drugs in patients.

Objective:

This present review is an attempt to illustrate clinical reports of food-drug interaction. Further, it also highlights specific interaction mechanism(s) and the safety thereof.

Methods:

Through the search engine “Scopus”; literature on recent advances in food and drug interactions includes almost all therapeutic categories such as antimicrobials, antiviral, antifungal, antihistamines, anticoagulants, non-steroidal anti-inflammatory drugs, and drugs acting on the central nervous system and cardiovascular system.

Results:

Preclinical and clinical studies that have been conducted by various researchers affirm significant drug-food interactions across the various therapeutic categories of drugs. Preclinical studies have documented the effects of food, milk products, alcohols, fruit and vegetables on the drug absorption, metabolizing enzymes and drug transporters. The clinical studies on fruits/vegetables and drugs interactions report significant alteration in therapeutic response.

Conclusion:

Based on the preclinical and clinical reports, it can be concluded that the interaction of food with drug(s) significantly alters their therapeutic potential. The inputs from clinical practitioners to elucidate potential risk of food-drug interaction need to be intensified in order to prevent adverse clinical consequences.

Drug Interactions with Antiulcer Agents: Considerations in the Treatment of Acid-Peptic Disease

All of the antiulcer agents have been implicated in drug interactions. These agents generally influence the absorption, metabolism, or elimination of other medications. However, these interactions can lead to alterations in pharmacodynamic response. The mechanisms by which antiulcer agents produce drug interactions differ among the agents. It is beyond the scope of this article to review all of the drug interactions that have been reported with antiulcer agents. However, it is the intent to provide the reader with a detailed understanding of the mechanisms by which antiulcer agents may interact with other medications and to provide insight into factors that may influence the potential magnitude or clinical consequences of these interactions. An understanding of antiulcer drug interactions will aid pharmacists in assisting clinicians with drug selection and/or monitoring of drug interactions. Specifically, pharmacists can assist with the identification of potential antiulcer drug interactions and develop strategies designed to minimize adverse consequences of these interactions.

Disposition of d-penicillamine, a promising drug for preventing alcohol-relapse. Influence of dose, chronic alcohol consumption and age: studies in rats

Pharmacokinetic studies concerning d-penicillamine (an acetaldehyde sequestering agent) are scarce and have not evaluated the influence of chronic ethanol consumption and age on its disposition. Since recent preclinical studies propose d-penicillamine as a promising treatment for alcohol relapse, the main aim of the present work was to evaluate the influence of these two factors on d-penicillamine disposition in order to guide future clinical studies on the anti-relapse efficacy of this drug in alcoholism. Additionally, the effect of the administered dose was also evaluated. To this end, three studies were carried out. Study 1 assessed the influence of dose on d-penicillamine disposition, whereas studies 2 and 3 evaluated, respectively, the influence of chronic alcohol consumption and age. Rapid intravenous administrations of 2, 10 and 30 mg/kg of d-penicillamine were performed using young or adult ethanol-naïve rats or adult ethanol-experienced (subjected to a long-term ethanol self-administration protocol) rats. Pharmacokinetic parameters were derived from the biexponential model. Statistical analysis of CL, normalized AUC0 (∞) , V1 and k10 revealed that disposition, in the range plasma concentrations assayed, is non-linear both in young ethanol-naïve and in adult ethanol-experienced rats. Notably, no significant changes in t1/2 were detected. Chronic ethanol consumption significantly reduced CL values by 35% without affecting t1/2 . d-Penicillamine disposition was equivalent in young and adult animals. In conclusion, although DP pharmacokinetics is non-linear, the lack of significant alterations of the t1/2 would potentially simplify the clinical use of this drug. Chronic consumption of ethanol also alters d-penicillamine disposition but, again, does not modify t1/2.

Beneficial effect of sesame oil on heavy metal toxicity

Heavy metals become toxic when they are not metabolized by the body and accumulate in the soft tissue. Chelation therapy is mainly for the management of heavy metal-induced toxicity; however, it usually causes adverse effects or completely blocks the vital function of the particular metal chelated. Much attention has been paid to the development of chelating agents from natural sources to counteract lead- and iron-induced hepatic and renal damage. Sesame oil (a natural edible oil) and sesamol (an active antioxidant) are potently beneficial for treating lead- and iron-induced hepatic and renal toxicity and have no adverse effects. Sesame oil and sesamol significantly inhibit iron-induced lipid peroxidation by inhibiting the xanthine oxidase, nitric oxide, superoxide anion, and hydroxyl radical generation. In addition, sesame oil is a potent inhibitor of proinflammatory mediators, and it attenuates lead-induced hepatic damage by inhibiting nitric oxide, tumor necrosis factor-α, and interleukin-1β levels. Because metal chelating therapy is associated with adverse effects, treating heavy metal toxicity in addition with sesame oil and sesamol may be better alternatives. This review deals with the possible use and beneficial effects of sesame oil and sesamol during heavy metal toxicity treatment.

Stimulation of human TRPA1 channels by clinical concentrations of the antirheumatic drug auranofin

Gold compounds, which were widely used to treat rheumatoid arthritis, have been recently used as experimental agents for tumor treatment. Transient receptor potential (TRP) ankyrin repeat 1 (TRPA1) is a Ca2+-permeable ion channel that senses acute and inflammatory pain signals. Electrophilic compounds such as mustard oil and cinnamaldehyde activate TRPA1 by interacting with TRPA1 cysteine residues. Here we investigate the effects of the gold compound auranofin (AUR) on TRPA1 channels. Intracellular Ca2+ and whole cell patch-clamp recordings were performed on human embryonic kidney cells transiently expressed with TRPA1, TRP melastatin 8 (TRPM8), and vanilloid type TRP (TRPV1–4) channels. AUR stimulated TRPA1 in a concentration-dependent manner with a half-maximum potency of around 1.0 μM. The AUR-induced response was effectively blocked by HC030031, a TRPA1 antagonist. On the other hand, AUR failed to activate TRPM8 and TRPV1–4 channels, which are highly expressed in sensory neurons as nociceptors. The stimulatory effect on TRPA1 channels depended on the C414, C421, C621, and C633 cysteine residues and not on the inhibition of thioredoxin reductase by AUR. Moreover, AUR effectively activated TRPA1 channels expressed in human differentiated neuroblastoma cell lines. The study shows that AUR is a potent stimulator of TRPA1 channels.

Clinically significant drug interactions with antacids: an update

One may consider that drug-drug interactions (DDIs) associated with antacids is an obsolete topic because they are prescribed less frequently by medical professionals due to the advent of drugs that more effectively suppress gastric acidity (i.e. histamine H(2)-receptor antagonists [H2RAs] and proton pump inhibitors [PPIs]). Nevertheless, the use of antacids by ambulant patients may be ever increasing, because they are freely available as over-the-counter (OTC) drugs. Antacids consisting of weak basic substances coupled with polyvalent cations may alter the rate and/or the extent of absorption of concomitantly administered drugs via different mechanisms. Polyvalent cations in antacid formulations may form insoluble chelate complexes with drugs and substantially reduce their bioavailability. Clinical studies demonstrated that two classes of antibacterials (tetracyclines and fluoroquinolones) are susceptible to clinically relevant DDIs with antacids through this mechanism. Countermeasures against this type of DDI include spacing out the dosing interval - taking antacid either 4 hours before or 2 hours after administration of these antibacterials. Bisphosphonates may be susceptible to DDIs with antacids by the same mechanism, as described in the prescription information of most bisphosphonates, but no quantitative data about the DDIs are available. For drugs with solubility critically dependent on pH, neutralization of gastric fluid by antacids may alter the dissolution of these drugs and the rate and/or extent of their absorption. However, the magnitude of DDIs elicited by antacids through this mechanism is less than that produced by H2RAs or PPIs; therefore, the clinical relevance of such DDIs is often obscure. Magnesium ions contained in some antacid formulas may increase gastric emptying, thereby accelerating the rate of absorption of some drugs. However, the clinical relevance of this is unclear in most cases because the difference in plasma drug concentration observed after dosing shortly disappears. Recent reports have indicated that some of the molecular-targeting agents such as the tyrosine kinase inhibitors dasatinib and imatinib, and the thrombopoietin receptor agonist eltrombopag may be susceptible to DDIs with antacids. Finally, the recent trend of developing OTC drugs as combination formulations of an antacid and an H2RA is a concern because these drugs will increase the risk of DDIs by dual mechanisms, i.e. a gastric pH-dependent mechanism by H2RAs and a cation-mediated chelation mechanism by antacids.

Important drug–nutrient interactions

Drugs have the potential to interact with nutrients potentially leading to reduced therapeutic efficacy of the drug, nutritional risk or increased adverse effects of the drug. Despite significant interest in such interactions going back to over more than 40 years, the occurrence and clinical significance of many drug–nutrient interactions remains unclear. However, interactions involving drugs with a narrow therapeutic margin such as theophylline and digoxin and those that require careful blood monitoring such as warfarin are likely to be those of clinical significance. Drugs can affect nutrition as a result of changes in appetite and taste as well as having an influence on absorption or metabolism of nutrients. Moreover, foods and supplements can also interact with drugs, of which grapefruit juice and St John's wort are key examples. Significant numbers of people take both supplements and medication and are potentially at risk from interactions. Professionals, such as pharmacists, dietitians, nurses and doctors, responsible for the care of patients should therefore check whether supplements are being taken, while for researchers this is an area worthy of significant further study, particularly in the context of increasingly complex drug regimens and the plethora of new drugs.

An evidence-based assessment of the clinical significance of drug-drug interactions between disease-modifying antirheumatic drugs and non-antirheumatic drugs according to rheumatologists and pharmacists

BACKGROUND

Clinically relevant drug-drug interactions (DDIs) must be recognized in a timely manner and managed appropriately to prevent adverse drug reactions or therapeutic failure. Because the evidence for most DDIs is based on case reports or poorly documented clinical information, there is a need for better assessment of their clinical relevance.

OBJECTIVE

This study evaluates the interdisciplinary agreement between rheumatologists and clinical (hospital) pharmacists in assessing the clinical relevance of DDIs with disease-modifying antirheumatic drugs (DMARDs) and non-DMARD medications.

METHODS

Potential DDIs were identified from the medical literature using MEDLINE and EMBASE for the years 1968-2009. The following search terms were used for the key word, title, and abstract sections of the publications: interaction(s), DMARD, disease-modifying antirheumatic drug(s), antirheumatic, rheumatology, rheumatoid arthritis, and the names of the individual DMARDs of interest (abatacept, adalimumab, anakinra, auranofin, aurothioglucose, aurothiomalate, d-penicillamine, etanercept, gold, [hydroxy]-chloroquine, interleukin-1 receptor antagonist, IL1-RA, infliximab, leflunomide, methotrexate, rituximab, and sulfasalazine/sulphasalazine). Reference lists of the retrieved publications were searched for further information on potential DDIs. All pharmacodynamic or pharmacokinetic DDIs between a DMARD and a non-DMARD identified were included in the study, with the exception of evidence regarding DMARD doses higher than used in the treatment of rheumatoid arthritis and interactions with phytotherapeutic or homeopathic preparations. Using a standard information set for each DDI (eg, from product labeling, textbooks, and the medical literature), a group of rheumatologists and a group of clinical pharmacists independently assessed whether the individual drug-DMARD combinations interacted and whether they required immediate intervention. Both groups consisted of 3 members (2 men and 1 woman), aged 40 to 60 years, who had >5 years of clinical experience and were currently involved in clinical practice in large, nonacademic teaching hospitals in the Netherlands.

RESULTS

Forty potential DDIs with DMARDs were retrieved and assessed by the 2 groups. For 30 (75%) of these, rheumatologists and clinical pharmacists agreed about the requirement for immediate intervention. Specifically, 17 drug combinations (43%) were judged to interact and to require immediate intervention, and 13 combinations (33%) were judged either not to interact or to interact but not to require immediate intervention. For 10 combinations (25%), rheumatologists and clinical pharmacists were not in agreement. Overall, agreement between the groups was good (kappa = 0.80) for judging whether the drug combinations were interactions, and agreement was fair (kappa = 0.39) for judging whether immediate intervention was required. Prospective analysis of the data showed that rheumatologists tended to recommend immediate intervention more often when the adverse reaction to the DDI involved an increased risk of toxicity of the DMARD. In contrast, clinical pharmacists more often advocated immediate intervention when the adverse reaction involved decreased effectiveness of the DMARD.

CONCLUSION

For a subset of DMARD-drug combinations, rheumatologists and clinical pharmacists differed in their assessments of clinical relevance.

Effect of zobo drink (Hibiscus sabdariffa water extract) on the pharmacokinetics of acetaminophen in human volunteers

Acetaminophen, a common antipyretic-analgesic OTC drug is often administered orally anytime of the day with water or beverages irrespective of possible interactions. Zobo drink, is a sweetened water extract of the dried calyx of Hibiscus Sabdariffa. This work is designed to investigate the effect of zobo drink on an oral dose of acetaminophen. Six healthy male volunteers, ages 28.50 +/- 1.76 years, weighing 62.67 +/- 1.67kg participated in the study. The study was carried out in two phases. In the first phases an oral dose of acetaminophen (1g) was administered to the volunteers and in the second phases, zobo drink was ingested by the volunteers 1.30 h prior the administration of acetaminophen (1g). Acetaminophen concentration in plasma was determined using a validated spectrophotometric method. Pharmacokinetic values obtained were found to be in similar ranges as those previously reported. The absorption parameters t1/2a, Ka, Tmax, Cmax and AUC0-alpha showed no statistically significant changes (p>0.05) after the administration of zobo. There were however statistically significant changes (p<0.05) in Kbeta and t1/2beta of acetaminophen when administered after the zobo drink. This also resulted in 11.69% increase in ClT.

Food-drug interactions

Interactions between food and drugs may inadvertently reduce or increase the drug effect. The majority of clinically relevant food-drug interactions are caused by food-induced changes in the bioavailability of the drug. Since the bioavailability and clinical effect of most drugs are correlated, the bioavailability is an important pharmacokinetic effect parameter. However, in order to evaluate the clinical relevance of a food-drug interaction, the impact of food intake on the clinical effect of the drug has to be quantified as well. As a result of quality review in healthcare systems, healthcare providers are increasingly required to develop methods for identifying and preventing adverse food-drug interactions. In this review of original literature, we have tried to provide both pharmacokinetic and clinical effect parameters of clinically relevant food-drug interactions. The most important interactions are those associated with a high risk of treatment failure arising from a significantly reduced bioavailability in the fed state. Such interactions are frequently caused by chelation with components in food (as occurs with alendronic acid, clodronic acid, didanosine, etidronic acid, penicillamine and tetracycline) or dairy products (ciprofloxacin and norfloxacin), or by other direct interactions between the drug and certain food components (avitriptan, indinavir, itraconazole solution, levodopa, melphalan, mercaptopurine and perindopril). In addition, the physiological response to food intake, in particular gastric acid secretion, may reduce the bioavailability of certain drugs (ampicillin, azithromycin capsules, didanosine, erythromycin stearate or enteric coated, and isoniazid). For other drugs, concomitant food intake may result in an increase in drug bioavailability either because of a food-induced increase in drug solubility (albendazole, atovaquone, griseofulvin, isotretinoin, lovastatin, mefloquine, saquinavir and tacrolimus) or because of the secretion of gastric acid (itraconazole capsules) or bile (griseofulvin and halofantrine) in response to food intake. For most drugs, such an increase results in a desired increase in drug effect, but in others it may result in serious toxicity (halofantrine).

[Appropriate administration schedule of D-penicillamine for pediatric Wilson's disease patients based on urinary copper excretion]

The purpose of this study was to increase the amount of copper excreted resulting from the administration of D-penicillamine(DP) in pediatric Wilson's disease(WD) patients. By measuring the urinary copper excretion after adjusting the administration schedules, the appropriate timing for DP administration was investigated. The subjects were three brothers with pediatric WD. The initial daily dose of DP was 5 mg/kg/day, and gradually increased to the maintenance dose of 20 mg/kg/day. Until the maintenance daily dose was reached, DP was administered 2 h after the morning and evening meal. After reaching the maintenance daily dose of DP, the appropriate timing for taking DP was investigated in both the morning and evening. Three schedules of DP administration were compared: 2 h after meals; 30 min before meals (with fasting); and 1 h before the morning and 1.5 before the evening meal (direction 1). The resulting urinary copper excretion on each dosing schedule was compared. Little difference was found in urinary copper excretion on the first two schedules, i.e., 2 h after meals and 30 min before meals. When DP was administered 30 min before meals, urinary copper excretion [microgram/day] was 1173 in the first brother, 918 in the second, and 875 in the third. When DP was administered according to direction 1, however, urinary copper excretion was increased significantly to 1701 in the first brother, 2701 in the second, and 3808 in the third. It is known that the efficiency of urinary copper excretion with DP administration depends on the maintenance of chelating ability after absorption from the gastrointestinal tract. Our results indicate that the excretion was lower when DP was administered 2 h after or 30 min before meals (with fasting), as recommended in the package insert. Thus to achieve better copper excretion efficiency, direction 1 is recommended for WD patients.

Effects of D-penicillamine on urinary copper excretion in high-copper supplemented sheep

The effects of a single oral application of D-penicillamine (DPA, mean dosage 28 mg/kg body weight) on urinary copper (Cu) excretion and general renal function in six high-Cu supplemented sheep (Cu intake of 3.7 mg/day per kg body weight for 84 days) and four controls (Cu intake of 0.16 mg/day per kg body weight) were investigated to quantify induced cupruresis and the therapeutic effect of DPA as a decoppering agent. Changes in liver Cu concentration were examined before and after DPA treatment by liver biopsies. The influence of DPA treatment on general renal function was low. A 10-fold increase in renal Cu excretion was induced in both groups of sheep. Maximal Cu excretion was observed 4 h after DPA treatment, with mean values of 280 pmol/min per kg body weight in the high Cu group and 145 pmol/min per kg body weight in the controls. In the high Cu sheep, urinary Cu excretion within 24 h after DPA application was equivalent to only 0.42 +/- 0.26% of liver Cu content (mean concentration 347 +/- 124 mg/kg wet weight). Moreover, no effect of DPA on liver Cu concentration was evident. These findings demonstrate that a single application of DPA is not effective in inducing sufficient Cu loss from the bodies of Cu-loaded sheep.

Can antioxidants be beneficial in the treatment of lead poisoning?

Recent studies have shown that lead causes oxidative stress by inducing the generation of reactive oxygen species, reducing the antioxidant defense system of cells via depleting glutathione, inhibiting sulfhydryl-dependent enzymes, interfering with some essential metals needed for antioxidant enzyme activities, and/or increasing susceptibility of cells to oxidative attack by altering the membrane integrity and fatty acid composition. Consequently, it is plausible that impaired oxidant/antioxidant balance can be partially responsible for the toxic effects of lead. Where enhanced oxidative stress contributes to lead-induced toxicity, restoration of a cell's antioxidant capacity appears to provide a partial remedy. Several studies are underway to determine the effect of antioxidant supplementation following lead exposure. Data suggest that antioxidants may play an important role in abating some hazards of lead. To explain the importance of using antioxidants in treating lead poisoning the following topics are addressed: (i) Oxidative damage caused by lead poisoning; (ii) conventional treatment of lead poisoning and its side effects; and (iii) possible protective effects of antioxidants in lead toxicity.

Ferrous sulphate interacts with captopril

AIMS

To determine if iron binds strongly to captopril and reduces captopril absorption.

METHODS

A variety of in vitro experiments was conducted to examine iron binding to captopril and a randomized, double-blind, placebo controlled, cross-over study design was used to assess the in vivo interaction. Captopril (25 mg) was coingested with either ferrous sulphate (300 mg) or placebo by seven healthy adult volunteers. Subjects were phlebotomized and had blood pressure measured at 0, 0.25, 0.5, 1, 2, 4, 6, 8, and 12 h post ingestion. A 1 week washout period was used.

RESULTS

The coingestion of ferrous sulphate and captopril was associated with a 37% (134 ng ml(-1) h, 95% CI 41-228 ng ml(-1) h, P = 0.03) decrease in area under the curve (AUC) for unconjugated plasma captopril. There were no substantial changes in Cmax (mean difference; -32; 95% CI -124-62 ng ml(-1) (P = 0.57)) or in tmax (mean difference; 0; 95% CI -18-18 min (P = 0.65)) for unconjugated captopril when captopril was ingested with iron. There was a statistically insignificant increase in AUC for total plasma captopril of 43% (1312 ng ml(-1) h, 95% CI -827-3451 ng ml(-1) h P = 0.27) when captopril was ingested with iron. The addition of ferric chloride to captopril resulted in the initial rapid formation of a soluble blue complex which rapidly disappeared to be replaced by a white precipitant. The white precipitate was identified as captopril disulphide dimer. There were no significant differences in systolic and diastolic blood pressures between the treatment and placebo groups.

CONCLUSIONS

Co-administration of ferrous sulphate and iron results in decreased unconjugated captopril levels likely due to a chemical interaction between ferric ion and captopril in the gastrointestinal tract. Care is required when coprescribing captopril and iron salts.

Interaction of norfloxacin with divalent and trivalent pharmaceutical cations. In vitro complexation and in vivo pharmacokinetic studies in the dog

The formation constants of the fluoroquinolones norfloxacin and ciprofloxacin with Mg2+ (log beta 1 = 2.97(4), log beta 2 = 5.6(2)), Zn2+ (log beta 1 = 3.77(2), log beta 2 = 7.59(3)), and Fe2+ (log beta 1 = 3.99(5), log beta 2 = 7.2(5)) were determined by potentiometric titration. The pH at which precipitation occurred in the titration solutions was compared for the metal ions Ca2+, Mg2+, Zn2+, Fe2+, Cu2+, and Al3+. The formation constants were used to predict a rank order of metals that may be expected to hinder the gastrointestinal absorption of the fluoroquinolones, in vivo. The effects of metal ions on the pharmacokinetics of orally-administered norfloxacin in the dog were investigated. Norfloxacin (12 mg/kg) was administered alone or with equimolar doses of each of the chloride salts of Ca2+, Mg2+, Zn2+, Fe2+, and Al3+. Statistically significant reductions in serum norfloxacin concentrations were observed after analysis by HPLC. The Cmax was reduced 29-85%, while the area under the norfloxacin serum concentration-time curve (AUC0-infinity) was reduced by 29-79%. The extent of the reduction in AUC0-infinity was correlated with the magnitude of the formation constant of the 1:1 norfloxacin:metal chelate complex for the divalent metal ions. On coadministration of 12 mg/kg norfloxacin with various doses of Mg2+ (chloride) the AUC0-infinity and Cmax decreased with increasing Mg2+ dose. The interaction peaked at a Mg2+:norfloxacin ratio of 1:2 suggesting the formation of a 1:2 Mg:norfloxacin complex. Formation constant data were used to simulate the percentage of norfloxacin complexed at pH 6.5. Combinations of metal ion and norfloxacin which result in only a small extent (< 20%) of norfloxacin complex formation can result in relatively large decreases in oral bioavailability of this antimicrobial agent.

Ferrous sulfate does not reduce serum levels of famotidine or cimetidine after concurrent ingestion

A series of randomized crossover studies were performed to determine whether there was a reduction in serum levels of cimetidine and famotidine when coingested with ferrous sulfate (300 mg). Coingestion of a ferrous sulfate tablet with cimetidine (300 mg) was associated with little reduction in serum cimetidine area under the curve (AUC) (mean versus mean, 20.8 versus 23.4 mumol.hr/L; mean percentage difference, -11%; 95% confidence interval [CI] of percentage difference, -26% to 4.2%) or peak concentration (Cmax) (mean versus mean, 5.1 versus 6.1 mumol/L; mean percentage difference, -16%; CI of percentage difference, -36% to 4%). Similarly, ferrous sulfate solution coingested with cimetidine caused little change in cimetidine AUC (mean versus mean, 19.9 versus 23.0 mumol.hr/L; mean percentage difference, -13%; CI of percentage difference, -34% to 7%) or Cmax (mean versus mean, 5.0 versus 5.0 mumol/L; mean percentage difference, 1%; CI of percentage difference, -18% to 20%). Concurrent ingestion of famotidine (40 mg) with a ferrous sulfate tablet did not result in significant reductions in serum famotidine AUC (mean versus mean, 1.78 versus 1.99 mumol.hr/L; mean percentage difference, -10%; CI of percentage difference, -34% to 13%) or Cmax (mean versus mean, 0.31 versus 0.32 mumol/L; mean percentage difference, -3%; CI of percentage difference, -27% to 22%). The formation of famotidine:iron(III) complexes was shown in methanol but was not observed in an aqueous buffer at pH 6.5. Ranitidine did not bind iron in an aqueous buffer and only weakly bound iron in methanol. Coingestion of ferrous sulfate with either cimetidine or famotidine does not cause a clinically relevant reduction in serum histamine H2-receptor blocker levels and, on the basis of in vitro binding experiments, iron is unlikely to interact with ranitidine.

Iron-ovotransferrin preparation does not interfere with ciprofloxacin absorption

Iron supplements can interfere with the bioavailability of a number of drugs, including thyroxine, tetracycline derivatives, penicillamine, methyldopa, levodopa, carbidopa, ciprofloxacin, and the newer fluoroquinolones. A new iron formulation was tested in which iron ions are bound to ovotransferrin, a protein that shares more than an 80% similarity with the sequence of human transferrin and apparently is less likely than the commonly used iron salts to reduce drug absorption. Ciprofloxacin was taken as a model drug, of wide use and restricted range of therapeutic levels, and its absorption was evaluated after the administration of the iron-ovotransferrin complex versus an iron-gluconate formulation in healthy volunteers. At variance with the iron gluconate formulation, which led to a reduction of about 50% of peak serum ciprofloxacin levels (Cmax; 1.0 +/- 0.2 versus 2.4 +/- 0.3 micrograms/ml; p < 0.01) and of the area under the serum concentration-time curve from time 0 to infinity [AUC(0 - infinity); 10.1 +/- 1.1 versus 18.3 +/- 1.0 mg.L-1.hr; p < 0.01], the iron-ovotransferrin complex caused only modest, non significant changes in absorption with a minimal reduction of the AUC[0 - infinity) (17.3 +/- 1.0 versus 18.3 +/- 1.0 mg.L-1.hr; difference not significant) and a nonsignificant decrease in the Cmax (2.2 +/- 0.3 versus 2.4 +/- 0.3 microgram/ml; difference not significant). Iron was also well absorbed from the formulation in the presence of a fatty meal. The very common drug interactions with oral iron preparations can be effectively prevented by the use of the iron-ovotransferrin complex interacting to a minimal extent with a sensitive drug with a reduced margin of efficacy, such as ciprofloxacin.

Ferrous sulfate reduces cimetidine absorption

A variety of drugs that bind to iron have significant reductions in absorption when coadministered with iron compounds. Cimetidine has a structure that would suggest strong binding to iron ions. In vitro experiments were performed to examine a variety of characteristics of the binding of iron to cimetidine. Further studies were conducted to determine the effect of concurrent administration of ferrous sulfate on cimetidine absorption in an in vivo isolated perfused rat jejunal model of drug absorption. The dose of cimetidine was chosen to represent a human dose of 300 mg, while the ferrous sulfate doses were chosen to represent 150- and 300-mg doses. The higher ferrous sulfate dose completely inhibited cimetidine absorption (P < 0.01), while the lower dose of ferrous sulfate caused a 63% reduction in cimetidine absorption (P < 0.05). In vitro iron in its ferrous from rapidly oxidizes to the ferric form. The ferric form of iron binds to cimetidine and may be the cause of the decreased cimetidine absorption. Care should be taken in prescribing iron supplements with cimetidine.

Urinary excretion of metals during treatment with D-penicillamine and 2-mercaptopropionylglycine in normal and cystinuric dogs

Urinary excretion of metals during treatment with 2-mercaptopropionylglycine (2-MPG) was studied in 11 normal and 20 cystinuric male dogs. The results were compared with those obtained during D-penicillamine treatment. Twenty-four-h urine and morning samples of urine were taken for determination of 13 metals before and during treatment. After single intravenous and oral D-penicillamine treatment of the normal dogs, significant increases were found in the 24-h urinary excretion of Ca, Cu and Zn. Oral intake of D-penicillamine increased the excretion of Co, Cr, Fe and Mg as well. No effect on renal metal excretion was observed after single intravenous and up to 2 months of daily oral treatment with 2-MPG. In 14 cystinuric dogs no effect was found after single intravenous and oral administrations of 2-MPG. However, after oral treatment of six cystinuric dogs with 2-MPG for 2-4 months, significantly increased excretions of Ca and Mg were found. Fourteen of the cystinuric dogs were also investigated after 2-6 years of continuous 2-MPG treatment, and after this period no significant elevation in the urinary excretion of metals was found. The present study shows that in contrast to D-penicillamine, 2-MPG does not increase the urinary excretion of metals to any appreciable extent. Observed increases in the excretion of Ca and Mg seemed to be a temporary effect only.

Iron supplements: a common cause of drug interactions

Iron-drug interactions of clinical significance may occur in many patients and involve a large number of therapies. Concurrent ingestion of iron causes marked decreases in the bioavailability of a number of drugs. The affected drugs, tetracycline, tetracycline derivatives (doxycycline, methacycline and oxytetracycline), penicillamine, methyldopa, levodopa, carbidopa and ciprofloxacin have diverse chemical structures and clinical effects. The major mechanism of these drug interactions is the formation of iron-drug complexes (chelation or binding of iron by the involved drug). A large number of other important and commonly used drugs such as thyroxine, captopril and folic acid have been demonstrated to form stable complexes with iron. There is little known about the effects of concurrent therapy with iron supplements for most of the drugs.

D-penicillamine

D-Pen represents an effective treatment for a proportion of patients with RA and PSS. Its status in the treatment of juvenile RA is uncertain. The best results will be obtained by a skillful, careful physician maintaining careful surveillance for toxicity. Neither the mode of action nor the mechanisms of toxicity are well understood in RA. Consequently, safer and more effective analogues of D-pen have not been produced.

Antirheumatic drugs in pregnancy and lactation

The natural inclination of patients with rheumatic diseases wishing to become pregnant or to breast feed will be to take as few medications as possible. The guidelines outlined above can be used to balance the risk of drug effect on the fetus or neonate with the risk of inducing a flare in disease activity by stopping the drug. Although there are situations where no information on drug behaviour during pregnancy or lactation exists, some guidelines can be developed from a knowledge of the drug's inherent metabolism. In the majority of the rheumatic diseases, disease activity can be reduced to a minimum using the smallest possible dose of drugs known to be safe in pregnancy and lactation, thus providing minimum risk to mother, fetus and neonate.

Effects of concurrent sucralfate administration on pharmacokinetics of naproxen

Sucralfate has been reported to protect the gastroduodenal mucosa against a variety of agents and is known to adsorb bile salts. Since gastrointestinal side effects can seriously compromise the efficacy of nonsteroidal anti-inflammatory drug therapy, and since it seems reasonable to assume that sucralfate may adsorb nonsteroidal anti-inflammatory drugs, the influence of sucralfate on the pharmacokinetic parameters of naproxen was assessed in 12 healthy volunteers. To do so, the pharmacokinetic profile of naproxen, administered alone or with sucralfate, singly or repeatedly (twice daily for five days), was compared. No significant difference was observed with any pharmacokinetic parameter between the single administration of naproxen alone or with sucralfate. However, a significantly lower maximum plasma concentration was attained with the repeated administration of naproxen in combination with sucralfate, compared with the repeated administration of naproxen alone. When single- and multiple-dose administration were compared, significant differences were observed in the maximum plasma concentration and the cumulative area under the curve. These results suggest an accumulation of naproxen after five days' administration. This accumulation, however, is not altered by the administration of sucralfate. The results of this study suggest that when naproxen is administered with sucralfate, only a delay in naproxen's absorption may occur, confirmed by a lower maximum plasma concentration, a longer time to reach the maximum plasma concentration, a similar elimination half-life, and equivalence in bioavailability. The clinical importance of such a delay has yet to be proved; however, it is unlikely that the clinical efficacy of naproxen will be altered, since the amount of drug absorbed remains the same.

Drug-antacid interactions: assessment of clinical importance

Antacids and adsorbents are commonly used preparations that are generally considered to be pharmacologically inert and free from adverse effects. They may, however, interact with a diverse range of primary drugs and the sequelae can be disadvantageous to the efficacy of the primary medication. Many such reports in the literature are based on animal experiments, or on single-dose studies in healthy subjects. Some reports are anecdotal and are unconfirmed; others are based solely on in vitro evidence. Potentially important interactions have been suggested for a relatively small group of drugs: tetracyclines, phenytoin, digoxin, chloroquine, cimetidine, quinidine, nonsteroidal antiinflammatory drugs, and beta-blocking agents. The evidence for these has been critically evaluated, as well as for antacid-anticoagulant and antacid-nitrofurantoin interactions that have been wrongly emphasized in the literature. The majority of literature reports on interactions with antacids have been overemphasized; only ferrous sulfate-, isoniazid-, and tetracycline-antacid interactions fall into a category I importance (scale I-III of descending importance). This category is for those interactions with good evidence of actual or potential importance in patients or in relevant studies on normal subjects.

Single dose pharmacokinetics of ketoprofen, indomethacin, and naproxen taken alone or with sucralfate

The effects of sucralfate on the rate and extent of absorption of ketoprofen, indomethacin, and naproxen were investigated in healthy volunteers. Six volunteers each received sucralfate (2 g) half an hour before a ketoprofen (50 mg) capsule, and, on another occasion, a ketoprofen (50 mg) capsule alone according to a 2 X 2 Latin square pattern of administration. The same design was used for studies with indomethacin (50 mg) capsules and naproxen (500 mg) tablets. Sucralfate decreased significantly (p less than 0.05) the maximum plasma concentrations (Cmax) of ketoprofen, indomethacin, and naproxen. Although the time necessary to attain Cmax (tmax) for the three drugs tended to increase, only for indomethacin was this increase significant. Sucralfate decreased significantly the rate of absorption (ka) of naproxen and indomethacin, but not that of ketoprofen; it had no significant effect on the elimination half-life and area under the plasma concentration as a function of time curves (AUC0----infinity) of the three drugs. Sucralfate thus decreases the Cmax and increases the tmax of ketoprofen, indomethacin, and naproxen without affecting their bioavailabilities.

Determination and metabolism of dithiol-chelating agents: electrolytic and chemical reduction of oxidized dithiols in urine

The presence of oxidized species of the dithiol-chelating agents, meso-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercaptopropane-1-sulfonic acid (DMPS), in human urine was determined by chemical and electrolytic reduction methods. Urine from a human given either DMSA or DMPS was treated with electrolysis, dithiothreitol, or sodium tetrahydridoborate (NaBH4). The SH groups were derivatized with monobromobimane for the determination of unaltered dithiols. Total dithiol (unaltered and oxidized) was determined by reduction followed by derivatization with monobromobimane. The bimane derivatives were identified and quantified by HPLC and fluorescence. Although all three reduction methods gave similar results, electrolytic reduction of oxidized DMSA and chemical reduction with NaBH4 of oxidized DMPS are recommended based upon both day to day reproducibility and recovery of standards. After reduction a 4-fold increase in DMSA and a 20-fold increase in DMPS were found in urine by 12 h after an oral dose of DMSA or DMPS. These new methods for the determination of dithiols and their oxidized forms should lead to a better understanding of the metabolic properties of these increasingly important orally effective chelating agents.

Bioavailability of D-penicillamine in relation to gastrointestinal involvement of generalized scleroderma

The bioavailability of D-penicillamine was measured in 24 patients with generalized scleroderma (Progressive Systemic Sclerosis, PSS). Esophageal changes characteristic of generalized scleroderma were present in 15 of the patients, and 3 of those patients had duodenal involvements as well. The plasma concentrations of D-penicillamine were measured at 0 h, 1 h, 2 h, and 4 h after an oral dose of 300 mg D-penicillamine. Patients with duodenal and/or esophageal changes specific for scleroderma had significantly lower bioavailability of D-penicillamine than scleroderma patients without gastrointestinal manifestations. The decreased plasma D-penicillamine in scleroderma patients with involvement of the gastrointestinal tract may be due to an increased degradation of D-penicillamine in the gastrointestinal tract and/or an impaired absorption of the drug. Since the plasma level of D-penicillamine is so sensitive to pathological changes of the gastrointestinal tract, it may be advisable to adjust the dose of D-penicillamine on the basis of measurements of the plasma concentration of D-penicillamine.

Effects of magnesium oxide on trichlormethiazide bioavailability

The effect of an antacid, magnesium oxide (MgO), on the bioavailability of a thiazide diuretic, trichlormethiazide, was studied in 10 healthy subjects who fasted overnight. A single oral dose of 4 mg of 1 alone or in combination with 0.5 g of MgO was given in a two-way Latin-square crossover design. Urine concentrations of 1 during the 24 h after each dose were determined by an HPLC method. There were no significant differences for drug alone versus drug with MgO in the mean percentage recovery (60 versus 62%) and the cumulative amount excreted unchanged in urine over 24 h (2408 versus 2463 micrograms). However, coadministration of MgO increased the mean excretion rate of 1 at 0.75 h and 1.5 h (p less than 0.05), the cumulative amount excreted unchanged in urine over 2 h (p less than 0.05), and the absorption rate constant (p less than 0.05). Therefore, the extent of bioavailability was not influenced by MgO, but the rate of absorption was enhanced. The solubility of 1 increased remarkably by changing from pH 1.2 to 8.0 (141 to 1365 micrograms/mL). The dissolution rate of 4 mg of 1 in 500 mL of medium was not affected by an increase in pH. However, a 1.5-fold increase of the dissolution rate in 20 mL of medium was observed by changing from pH 1.2 to 7.3.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of food on the bioavailability of enalapril

In a randomized, two-period crossover study in 12 normal volunteers, serum and urine concentrations of the angiotensin-converting enzyme inhibitor enalapril and its active metabolite enalaprilat were determined following administration of a single 40-mg tablet of enalapril maleate administered both in the fasting state and with a standard breakfast. A 7-d interval separated the two treatment periods. Area under the serum concentration-time curves for enalaprilat and urinary recoveries for enalaprilat and total drug did not differ significantly between the fed and fasted conditions. The mean observed maximum serum concentration of enalaprilat was slightly higher for the fasting treatment, but the time to peak concentration was almost identical for the two treatments. Enalapril maleate is unlike the prototype angiotensin-converting enzyme inhibitor captopril in that a standard meal does not appear to influence absorption of this new drug.

Factors contributing to variability in drug pharmacokinetics. I. Absorption

Apart from the physical and chemical properties of a drug, and also the dosage form in which it is presented, many other factors may affect the absorption of orally administered compounds and give rise to variable systemic availability. Three such factors, gastrointestinal (GI) disease, drug-drug interactions, and drug-food interactions are considered here. Although information regarding these factors, particularly GI disease, is scarce and sometimes conflicting, it is clear that they may give rise to variable drug absorption. The wide spectrum of effects on different drugs precludes the application of general rules and guidelines in drug therapy in most cases. Drugs, dosage forms, and various interactions should be considered individually. Also the types of interactions described in this review must be combined with other factors to be discussed later in this series when considering the influence of variable absorption, distribution, metabolism, and excretion on drug pharmacokinetics and clinical efficacy.