Influence of ranitidine, pirenzepine, and aluminum magnesium hydroxide on the bioavailability of various antibiotics, including amoxicillin, cephalexin, doxycycline, and amoxicillin-clavulanic acid

Do dietary interventions exert clinically important effects on the bioavailability of β-lactam antibiotics? A systematic review with meta-analyses

BACKGROUND

Managing drug-food interactions may help to achieve the optimal action and safety profile of β-lactam antibiotics.

METHODS

We conducted a systematic review with meta-analyses in adherence to PRISMA guidelines for 32 β-lactams. We included 166 studies assessing the impact of food, beverages, antacids or mineral supplements on the pharmacokinetic (PK) parameters or PK/pharmacodynamic (PK/PD) indices.

RESULTS

Eighteen of 25 β-lactams for which data on food impact were available had clinically important interactions. We observed the highest negative influence of food (AUC or Cmax decreased by >40%) for ampicillin, cefaclor (immediate-release formulations), cefroxadine, cefradine, cloxacillin, oxacillin, penicillin V (liquid formulations and tablets) and sultamicillin, whereas the highest positive influence (AUC or Cmax increased by >45%) for cefditoren pivoxil, cefuroxime and tebipenem pivoxil (extended-release tablets). Significantly lower bioavailability in the presence of antacids or mineral supplements occurred for 4 of 13 analysed β-lactams, with the highest negative impact for cefdinir (with iron salts) and moderate for cefpodoxime proxetil (with antacids). Data on beverage impact were limited to 11 antibiotics. With milk, the extent of absorption was decreased by >40% for cefalexin, cefradine, penicillin G and penicillin V, whereas it was moderately increased for cefuroxime. No significant interaction occurred with cranberry juice for two tested drugs (amoxicillin and cefaclor).

CONCLUSIONS

Factors such as physicochemical features of antibiotics, drug formulation, type of intervention, and patient's health state may influence interactions. Due to the poor actuality and diverse methodology of included studies and unproportionate data availability for individual drugs, we judged the quality of evidence as low.

Physiologically based pharmacokinetic modeling to assess the drug-drug interactions of anaprazole with clarithromycin and amoxicillin in patients undergoing eradication therapy of H. pylori infection

OBJECTIVE

This study aimed to assess the pharmacokinetic (PK) interactions of anaprazole, clarithromycin, and amoxicillin using physiologically based pharmacokinetic (PBPK) models.

METHODS

The PBPK models for anaprazole, clarithromycin, and amoxicillin were constructed using the GastroPlus™ software (Version 9.7) based on the physicochemical data and PK parameters obtained from literature, then were optimized and validated in healthy subjects to predict the plasma concentration-time profiles of these three drugs and assess the predictive performance of each model. According to the analysis of the properties of each drug, the developed and validated models were applied to evaluate potential drug-drug interactions (DDIs) of anaprazole, clarithromycin, and amoxicillin.

RESULTS

The developed PBPK models properly described the pharmacokinetics of anaprazole, clarithromycin, and amoxicillin well, and all predicted PK parameters (Cmax,ss, AUC0-τ,ss) ratios were within 2.0-fold of the observed values. Furthermore, the application of these models to predict the anaprazole-clarithromycin and anaprazole-amoxicillin DDIs demonstrates their good performance, with the predicted DDI Cmax,ss ratios and DDI AUC0-τ,ss ratios within 1.25-fold of the observed values, and all predicted DDI Cmax,ss, and AUC0-τ,ss ratios within 2.0-fold. The simulated results show no need to adjust the dosage when co-administered with anaprazole in patients undergoing eradication therapy of H. pylori infection since the dose remained in the therapeutic range.

CONCLUSION

The whole-body PBPK models of anaprazole, clarithromycin, and amoxicillin were built and qualified, which can predict DDIs that are mediated by gastric pH change and inhibition of metabolic enzymes, providing a mechanistic understanding of the DDIs observed in the clinic of clarithromycin, amoxicillin with anaprazole.

An Assessment of Occasional Bio-Inequivalence for BCS1 and BCS3 Drugs: What are the Underlying Reasons?

Despite having adequate solubility properties, bioequivalence (BE) studies performed on immediate release formulations containing BCS1/3 drugs occasionally fail. By systematically evaluating a set of 17 soluble drugs where unexpected BE failures have been reported and comparing to a set of 29 drugs where no such reports have been documented, a broad assessment of the risk factors leading to BE failure was performed. BE failures for BCS1/3 drugs were predominantly related to changes in C_max rather than AUC. C_max changes were typically modest, with minimal clinical significance for most drugs. Overall, drugs with a sharp plasma peak were identified as a key factor in BE failure risk. A new pharmacokinetic term (t½C_max) is proposed to identify drugs at higher risk due to their peak plasma profile shape. In addition, the analysis revealed that weak acids, and drugs with particularly high gastric solubility are potentially more vulnerable to BE failure, particularly when these features are combined with a sharp C_max peak. BCS3 drugs, which are often characterised as being more vulnerable to BE failure due to their potential for permeation and transit to be altered, particularly by excipient change, were not in general at greater risk of BE failures. These findings will help to inform how biowaivers may be optimally applied in the future.

Improving antibacterial prescribing safety in the management of COPD exacerbations: systematic review of observational and clinical studies on potential drug interactions associated with frequently prescribed antibacterials among COPD patients

Background

Guidelines advise the use of antibacterials (ABs) in the management of COPD exacerbations. COPD patients often have multiple comorbidities, such as diabetes mellitus and cardiac diseases, leading to polypharmacy. Consequently, drug–drug interactions (DDIs) may frequently occur, and may cause serious adverse events and treatment failure.

Objectives

(i) To review DDIs related to frequently prescribed ABs among COPD patients from observational and clinical studies. (ii) To improve AB prescribing safety in clinical practice by structuring DDIs according to comorbidities of COPD.

Methods

We conducted a systematic review by searching PubMed and Embase up to 8 February 2018 for clinical trials, cohort and case–control studies reporting DDIs of ABs used for COPD. Study design, subjects, sample size, pharmacological mechanism of DDI and effect of interaction were extracted. We evaluated levels of DDIs and quality of evidence according to established criteria and structured the data by possible comorbidities.

Results

In all, 318 articles were eligible for review, describing a wide range of drugs used for comorbidities and their potential DDIs with ABs. DDIs between ABs and co-administered drugs could be subdivided into: (i) co-administered drugs altering the pharmacokinetics of ABs; and (ii) ABs interfering with the pharmacokinetics of co-administered drugs. The DDIs could lead to therapeutic failures or toxicities.

Conclusions

DDIs related to ABs with clinical significance may involve a wide range of indicated drugs to treat comorbidities in COPD. The evidence presented can support (computer-supported) decision-making by health practitioners when prescribing ABs during COPD exacerbations in the case of co-medication.

Doxycycline in the management of sexually transmitted infections

Doxycycline is a second-generation tetracycline, available worldwide for half a century. It is an inexpensive broad-spectrum antimicrobial agent largely used in the management of several bacterial infections, particularly involving intracellular pathogens, as well as in the treatment of acne or for the prophylaxis of malaria. Physicochemical characteristics of doxycycline (liposolubility) allow a high diffusion in the tissues and organs. It has high bioavailability and a long elimination half-life allowing oral administration of one or two daily doses. Over the last decade, the prevalence of bacterial sexually transmitted infections (STIs) (syphilis, chlamydiosis, gonorrhoea and Mycoplasma genitalium infections) has increased in most countries, mainly in MSM, many of whom are infected with HIV. In light of increasing prevalence of resistance towards first-line regimens of some STI agents and recently updated recommendations for STI management, doxycycline appears to be an attractive option compared with other available antibiotics for the treatment of some STIs due to its efficacy, good tolerability and oral administration. More recently, indications for doxycycline in STI prophylaxis have been evaluated. Considering the renewed interest of doxycycline in STI management, this review aims to update the pharmacology of, efficacy of, safety of and resistance to doxycycline in this context of use.

Effects of medicines used to treat gastrointestinal diseases on the pharmacokinetics of coadministered drugs: a PEARRL Review

Objectives

Drugs used to treat gastrointestinal diseases (GI drugs) are widely used either as prescription or over-the-counter (OTC) medications and belong to both the 10 most prescribed and 10 most sold OTC medications worldwide. The objective of this review article is to discuss the most frequent interactions between GI and other drugs, including identification of the mechanisms behind these interactions, where possible.

Key findings

Current clinical practice shows that in many cases, these drugs are administered concomitantly with other drug products. Due to their metabolic properties and mechanisms of action, the drugs used to treat gastrointestinal diseases can change the pharmacokinetics of some coadministered drugs. In certain cases, these interactions can lead to failure of treatment or to the occurrence of serious adverse events. The mechanism of interaction depends highly on drug properties and differs among therapeutic categories. Understanding these interactions is essential to providing recommendations for optimal drug therapy.

Summary

Interactions with GI drugs are numerous and can be highly significant clinically in some cases. While alterations in bioavailability due to changes in solubility, dissolution rate, GI transit and metabolic interactions can be (for the most part) easily identified, interactions that are mediated through other mechanisms, such as permeability or microbiota, are less well-understood. Future work should focus on characterising these aspects.

Does the placebo effect modulate drug bioavailability? Randomized cross-over studies of three drugs

BACKGROUND

Medication effect is the sum of its drug, placebo, and drug*placebo interaction effects. It is conceivable that the interaction effect involves modulating drug bioavailability; it was previously observed that being aware of caffeine ingestion may prolong caffeine plasma half-life. This study was set to evaluate such concept using different drugs.

METHODS

Balanced single-dose, two-period, two-group, cross-over design was used to compare the pharmacokinetics of oral cephalexin, ibuprofen, and paracetamol, each described by its name (overt) or as placebo (covert). Volunteers and study coordinators were deceived as to study aim. Drug concentrations were determined blindly by in-house, high performance liquid chromatography assays. Terminal-elimination half-life (t_½) (primary outcome), maximum concentration (C_max), C_max first time (T_max), terminal-elimination-rate constant (λ), area-under-the-concentration-time-curve, to last measured concentration (AUC_T), extrapolated to infinity (AUC_I), or to T_max of overt drug (AUC_Overttmax), and C_max/AUC_I were calculated blindly using standard non-compartmental method. Covert-vs-overt effect on drug pharmacokinetics was evaluated by analysis-of-variance (ANOVA, primary analysis), 90% confidence interval (CI) using the 80.00-125.00% bioequivalence range, and percentage of individual pharmacokinetic covert/overt ratios that are outside the +25% range.

RESULTS

Fifty, 30, and 50 healthy volunteers (18%, 10%, and 6% females, mean (SD) age 30.8 (6.2), 31.4 (6.6), and 31.2 (5.4) years) participated in 3 studies on cephalexin, ibuprofen, and paracetamol, respectively. Withdrawal rate was 4%, 0%, and 4%, respectively. Eighteen blood samples were obtained over 6, 10, and 14 h in each study period of the three drugs, respectively. ANOVA showed no significant difference in any pharmacokinetic parameter for any of the drugs. The 90% CIs for AUC_T, AUC_I, C_max, AUC_Overttmax, and C_max/AUC_I were within the bioequivalence range, except for ibuprofen C_max (76.66-98.99), ibuprofen C_max/AUC_I (77.19-98.39), and ibuprofen (45.32-91.62) and paracetamol (51.45-98.96) AUC_Overttmax. Out of the 126 individual covert/overt ratios, 2.0-16.7% were outside the +25% range for AUC_T, 2.0-4.2% for AUC_I, 25.0-44.9% for C_max, 67.3-76.7% for AUC_Overttmax, and 45.8-71.4% for T_max.

CONCLUSIONS

This study couldn't confirm that awareness of drug ingestion modulates its bioavailability. However, it demonstrates the trivial effect of blinding in bioequivalence studies and the extent of bio-variability that would be expected when comparing a drug product to itself.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01501747 (registered Dec 26, 2011).

A limited number of prescribed drugs account for the great majority of drug-drug interactions

PURPOSE

The purpose of this study was to investigate the prevalence of prescribed combinations of interacting drugs in the Swedish population.

METHODS

This study design was retrospective and cross-sectional, based on a national register of dispensed prescription drugs during the period from January 1 to April 30, 2010. Prescription data was linked to the drug-drug interaction database SFINX to yield the prevalence of interacting combinations dispensed in the population. The study focused in particular on C- (clinically relevant interactions that can be handled, e.g. by dose adjustments), and D-interactions (clinically relevant interactions that should be avoided).

RESULTS

Thirty-eight and 3.8 % of the population were dispensed combinations of drugs classified as C- or D- interactions, respectively, i.e. clinically relevant, involving all therapeutic areas. Half of the D-interactions were associated with increased risk of adverse drug reactions whereas the other half were considered interactions with a potential to cause therapeutic failure. We identified a top 15 list of D-interactions that included 80 % of the total number of interacting drug combinations. Regarding individual drugs, a group of only ten drugs was involved in as much as 94 % of all D-interactions.

CONCLUSIONS

This study reveals that the majority of prescribed interacting drug combinations in Sweden involve a limited number of drugs. The findings may increase the awareness among prescribers of these most common drug interactions in clinical practice and highlight an area for pharmacological education. It may also serve as an inventory of potential interactions within different therapeutic areas for further research.

Outcome of intravenous azithromycin therapy in patients with complicated scrub typhus compared with that of doxycycline therapy using propensity-matched analysis

There are no well-matched, controlled studies comparing azithromycin with doxycycline for the treatment of complicated scrub typhus. A retrospective propensity score-matched case-control study was performed for patients who presented with complicated scrub typhus and were treated with doxycycline or azithromycin between 2001 and 2011. Data on comorbidities, clinical manifestations, laboratory studies, treatments, and outcomes were extracted for analysis. The clinical characteristics and outcomes of the azithromycin-treated group (n=73) were compared to those of the doxycycline-treated group (n=108). Of 181 patients, 73 from each group were matched by propensity scores. There were no significant differences in baseline characteristics between the matched groups. The treatment success and survival rates were not significantly different (89% [65/73 patients] versus 96% [70/73 patients] and 96% [70/73 patients] versus 96% [70/73 patients], respectively [P>0.05]). No difference was observed in the time to defervescence or length of hospital stay between the two groups (P>0.05). In complicated scrub typhus patients (n=181), multivariate analysis showed that only APACHE II score was an independent risk factor for mortality (95% confidence interval, 1.11 to 1.56; P<0.001). Our data suggest that outcomes of azithromycin therapy are comparable to those of doxycycline therapy in patients with complicated scrub typhus.

Quantitative PCR and in vivo efficacy of antibiotics in the treatment of Vibrio vulnificus infection in a mouse model

The Centers for Disease Control and Prevention (CDC) recommend oral or intravenous doxycycline plus a third-generation cephalosporin or fluoroquinolone alone for the treatment of Vibrio vulnificus infections. Until now, no study has compared oral with parenteral administered doxycycline with respect to their in vivo efficacy. In the present work, ICR mice infected with a high dose of V. vulnificus were administered ciprofloxacin, ceftriaxone, and doxycycline. The bacterial DNA copy number in surviving and non-surviving mice was determined using quantitative polymerase chain reaction (qPCR). In this setting, ciprofloxacin was the most effective monotherapeutic drug, but a higher survival rate (50%) was achieved using the combination therapy of intraperitoneal doxycycline plus ceftriaxone. The blood of non-surviving mice at 12 h post-infection contained at least 10(4) DNA copies/μL, in contrast to 10(2) to 10(3) DNA copies/μL in surviving mice. Thus, in the treatment of V. vulnificus infections in humans, when the intravenous form of doxycycline is unavailable, ciprofloxacin might be a better option than oral doxycycline to lower mortality. In addition, our results demonstrate that qPCR can be a useful tool for identifying the V. vulnificus load in infected patients, with the DNA copy number providing a marker of either disease severity or mortality.

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.

Suspected side effects of doxycycline use in dogs - a retrospective study of 386 cases

This study investigated doxycycline-related side effects in a large population of dogs. Data from 386 dogs that had received doxycycline for the treatment of various infectious diseases were analysed retrospectively. Potential side effects that developed during treatment were documented, and correlations with signalment, dose, duration of treatment, frequency of application, doxycycline preparation and use of additional drugs were investigated. Vomiting was reported in 18.3 per cent of dogs, 7.0 per cent developed diarrhoea and 2.5 per cent developed anorexia. While being treated with doxycycline, 39.4 per cent of dogs showed an increase in alanine aminotransferase (ALT) activity and 36.4 per cent showed an increase in alkaline phosphatase (ALP) activity. There was a dose-related risk of an increase in ALP activity (P=0.011, odds ratio [OR]=1.27, 95 per cent confidence interval [CI] 1.06 to 1.53), and older dogs treated with doxycycline were more likely to develop an increase in ALT activity (P=0.038, OR=1.23, 95 per cent CI 1.01 to 1.50) and vomiting (P=0.017, OR=1.11, 95 per cent CI 1.02 to 1.21).

Doxycycline for malaria chemoprophylaxis and treatment: report from the CDC expert meeting on malaria chemoprophylaxis

Doxycycline, a synthetically derived tetracycline, is a partially efficacious causal prophylactic (liver stage of Plasmodium) drug and a slow acting blood schizontocidal agent highly effective for the prevention of malaria. When used in conjunction with a fast acting schizontocidal agent, it is also highly effective for malaria treatment. Doxycycline is especially useful as a prophylaxis in areas with chloroquine and multidrug-resistant Plasmodium falciparum malaria. Although not recommended for pregnant women and children < 8 years of age, severe adverse events are rarely reported for doxycycline. This report examines the evidence behind current recommendations for the use of doxycycline for malaria and summarizes the available literature on its safety and tolerability.

Safety and Efficacy Review of Doxycycline

Doxycycline is a member of the tetracycline class of antibiotics and has been used clinically for more than 40 years. It is a well-tolerated drug that is bacteriostatic and acts via the inhibition of bacterial ribosomes. It is generally given at a dose of 100-mg daily or twice daily. It is well absorbed and has generally good tissue penetration. The serum half-life is 18-22 hours and dosage does not need to be adjusted in the presence of renal or hepatic impairment. Major side effects are gastro-intestinal and dermatological and it is generally contra-indicated in pregnancy or childhood because of concerns about discolouration of developing teeth and potential effects on growing bones. Drug interactions are not common although can occur with the concomitant use of methotrexate and the oral contraceptive pill, and its absorption can be reduced by the co-administration with some antacids and iron preparations. It has activity against many organisms, including Gram-positives, Gram-negatives and atypical bacteria. In addition, it appears to have some potentially clinically useful anti-inflammatory properties.

Lack of pharmacokinetic interaction between linezolid and antacid in healthy volunteers

Several antibiotics show significant pharmacokinetic interactions when they are given orally concomitantly with antacids. The objective of this study was to evaluate the effects of antacid (containing magnesium) on the pharmacokinetics of linezolid. A single dose of 600 mg linezolid was given orally alone and 10 min after administration of the antacid Maalox 70mVal, which contains 600 mg magnesium hydroxide and 900 mg aluminum hydroxide, to nine healthy males and nine healthy females in a crossover and randomized study. Linezolid plasma concentrations were determined by high-performance liquid chromatography, and pharmacokinetic parameters were calculated for both treatments. Coadministration with antacids did not change the pharmacokinetics of linezolid. The ratios (90% confidence intervals) of the individual values of the area under the concentration-time curve and the maximum concentration in plasma (C(max)) (linezolid plus antacid versus linezolid alone) were 1.01 (0.99 to 1.02) and 0.99 (0.96 to 1.02), respectively. Likewise, no significant difference in any of the other pharmacokinetic parameters was observed between the treatment groups (the time to C(max), lag time, volume of distribution [V/F], and clearance [CL/F]). However, a significant sex difference was observed for AUC, C(max), V/F, and CL/F; and these differences could be almost completely explained by the differences in body weight between males and females. No clinically relevant adverse effects were detected under either condition. The coadministration of antacids had no effect on the pharmacokinetics of linezolid. This demonstrates that the oral absorption of linezolid was not affected by the presence of antacids containing magnesium hydroxide and aluminum hydroxide. Antacids can be safely administered together with linezolid.

A randomized crossover study investigating the influence of ranitidine or omeprazole on the pharmacokinetics of cephalexin monohydrate

Limited data characterize pharmacokinetic interactions between cephalexin and ranitidine, and no data exist for an interaction with proton pump inhibitors. The purpose of this study was to investigate the effects of ranitidine or omeprazole administration on the pharmacokinetics and pharmacodynamics of cephalexin. A randomized single- and multiple-dose crossover study was conducted in healthy subjects ingesting cephalexin before and after steady-state administration of ranitidine or omeprazole. Time-concentration profiles were determined and pharmacokinetic parameters were characterized using noncompartmental methods. Pharmacokinetic data were analyzed in accordance with the two 1-sided test for bioequivalence. The percentage of time that serum concentrations remain above the MIC(90) during the dosing interval (T > MIC(90)) for Streptococcus pyogenes and Staphylococcus aureus associated with the pharmacokinetic profiles was calculated. The coadministration of cephalexin with ranitidine or omeprazole resulted in relatively minor changes in C(max), AUC(infinity), t(1/2), or CL/F. t(max) was significantly prolonged when cephalexin was administered with ranitidine or omeprazole. Suboptimal T > MIC(90) was observed for cephalexin irrespective of acid suppression. Delay in absorption of cephalexin resulted in a decrease in the percentage of T > MIC(90) for certain acid-suppressive regimens and pathogen combinations. With the exception of an increase in t(max), there were no significant pharmacokinetic interactions between cephalexin and ranitidine or omeprazole. Delayed t(max) associated with acid suppression may result in a diminished T > MIC(90).

[Pharmacokinetic/pharmacodynamic analysis of antibiotic therapy in dentistry and stomatology]

INTRODUCTION

This study evaluates the efficacy of various antimicrobial treatments for orofacial infections on the basis of pharmacokinetic/pharmacodynamic (PK/PD) criteria.

METHODS

A complete a literature search was undertaken to establish the MIC90 values of the five microorganisms most frequently isolated in odontogenic infections and the pharmacokinetic parameters of 13 antibiotics used in these infections. Pharmacokinetic simulations were then carried out with mean population parameters and efficacy indexes were calculated for the 47 treatment regimens analyzed. For drugs showing time-dependent antibacterial killing, the time above MIC (t > MIC) was calculated. For drugs with concentration-dependent bactericidal activity, the AUC/MIC was calculated.

RESULTS

Amoxicillin-clavulanic (500 mg/8 h or 1000 mg/12 h) and clindamycin (300 mg/6 h) in the time-dependent killing group and moxifloxacin (400 mg/24 h) in the concentration-dependent group showed adequate efficacy indexes against the five pathogens considered to be the most commonly implicated in odontogenic infections. The spiramycin plus metronidazole combination, present in the commercial formulation Rhodogyl, did not reach satisfactory PK/PD indexes.

CONCLUSION

PK/PD indexes, which are useful predictors of the potential efficacy of antibacterial therapy, were used with ontogenic infections in the present study. The PK/PD simulations showed that amoxicillin-clavulanic, clindamycin and moxifloxacin were the most suitable antibiotics for this kind of infection. Clinical trials are required to confirm that this methodology is useful in these pathologic processes.

Pharmacokinetic/Pharmacodynamic Evaluation of Antimicrobial Treatments of Orofacial Odontogenic Infections

OBJECTIVE

To evaluate the efficacy of antimicrobial therapy in oral odontogenic infections using estimated pharmacokinetic/pharmacodynamic parameters or efficacy indices, and to compare pharmacokinetic/pharmacodynamic breakpoints with National Committee for Clinical Laboratory Standards' (NCCLS) breakpoints.

STUDY DESIGN

Retrospective literature search to obtain minimum inhibitory concentration (MIC) values, pharmacokinetic parameters of antimicrobials and NCCLS breakpoints. Pharmacokinetic simulations were carried out using WinNonlin software (Pharsight Corporation, Mountain View, CA, USA).

METHODS

For antimicrobials with time-dependent activity, the time that the plasma drug concentration exceeds the MIC as the percentage of dose interval at steady state was calculated. For antimicrobials with concentration-dependent activity, the total area under the plasma concentration-time curve over 24 hours at steady state divided by the MIC was calculated. Pharmacokinetic/pharmacodynamic breakpoints were calculated according to these parameters.

RESULTS

Only amoxicillin/clavulanic acid and clindamycin showed adequate efficacy indices against the most commonly isolated bacteria in odontogenic infections. Metronidazole reached good indices against anaerobes only. Pharmacokinetic/pharmacodynamic susceptibility breakpoints do not coincide exactly with NCCLS breakpoints.

CONCLUSION

Owing to the scarcity of double-blind, clinical trials on the use of antimicrobials in endodontics, this study may be useful in determining the best antimicrobial treatment in these infections. However, as we have not used concentration data in infected tissue to determine pharmacokinetic/pharmacodynamic indices, it would be necessary to design clinical trials in order to confirm these results.

Prevention of the selection of resistant Staphylococcus aureus by moxifloxacin plus doxycycline in an in vitro dynamic model: an additive effect of the combination

Twenty-four hour ratios of area under the curve (AUC(24)) to MIC of 200-240 h providing quinolone concentrations above the mutant prevention concentration (MPC) protected from enrichment of resistant Staphylococcus aureus in our recent study that simulated the pharmacokinetics of moxifloxacin, gatifloxacin, levofloxacin and ciprofloxacin. These protective AUC(24)/MICs might also be achieved by using antibiotic combinations, assuming additive effects of two anti-staphylococcal agents. To test this hypothesis, changes in S. aureus susceptibility were examined in a dynamic model that simulates 5-day treatment with moxifloxacin and doxycycline, alone and in combination at sub-optimal AUC(24)/MICs of each agent. Significant increases in MIC were observed with monotherapy where moxifloxacin or doxycycline concentrations fell into the mutant selection window (MSW) for more than 80% of the dosing interval (AUC(24)/MIC 60 h). Less pronounced changes in MIC occurred when the summed concentrations of moxifloxacin (AUC(24)/MIC 30 and 60 h) and doxycycline (AUC(24)/MIC 30 and 60 h) were inside the MSWs for the individual drugs for 30-50% of the dosing interval. No loss in susceptibility was found at moxifloxacin or doxycycline AUC(24)/MIC 170 h combined with the smaller AUC(24)/MIC (60 h) of the second compound. These data suggest that the total AUC(24)/MIC of 230 h might protect against S. aureus resistance. As this value is very close to that predicted in monotherapy with moxifloxacin (220 h), an additive protective effect of quinolone+doxycycline on the selection of resistant S. aureus is proposed. The use of drug combinations may be useful for restricting the enrichment of resistant mutants with agents whose clinically achievable AUC(24)/MICs do not provide concentrations above the MPC.

Increased therapeutic failure for cephalexin versus comparator antibiotics in the treatment of uncomplicated outpatient cellulitis

We reviewed records of outpatients to determine the therapeutic failure rate of cephalexin in treating uncomplicated cellulitis. Therapeutic failure was defined as an increase in antibiotic dosage, prescription renewal, or addition or substitution of another antibiotic. Demographics, physical characteristics, risk factors, intervention, and outcome data were collected. Twenty-seven percent of patients failed therapy with an oral antibiotic. The failure rate for cephalexin was 40% versus 20% for comparator antibiotics (p=0.02, odds ratio [OR] 2.62, 95% confidence interval [CI] 1.18-5.75). We identified no statistically significant variables related to cephalexin failure. Concomitant acid suppressive therapy was administered with cephalexin in 42% of failures and 20% of nonfailures (p=0.11, OR 2.78, 95% CI 0.77-9.87). These data suggest that cephalexin's efficacy was less than that of other antimicrobials in treating cellulitis, possibly related to concurrent acid suppression.

Drug, meal and formulation interactions influencing drug absorption after oral administration. Clinical implications

Drug-drug, drug-formulation and drug-meal interactions are of clinical concern for orally administered drugs that possess a narrow therapeutic index. This review presents the current status of information regarding interactions which may influence the gastrointestinal (GI) absorption of orally administered drugs. Absorption interactions have been classified on the basis of rate-limiting processes. These processes are put in the context of drug and formulation physicochemical properties and oral input influences on variable GI physiology. Interaction categorisation makes use of a biopharmaceutical classification system based on drug aqueous solubility and membrane permeability and their contributions towards absorption variability. Overlaying this classification it is important to be aware of the effect that the magnitudes of drug dosage and volume of fluid administration can have on interactions involving a solubility rate limits. GI regional differences in membrane permeability are fundamental to the rational development of extended release dosage forms as well as to predicting interaction effects on absorption from immediate release dosage forms. The effect of meals on the regional-dependent intestinal elimination of drugs and their involvement in drug absorption interactions is also discussed. Although the clinical significance of such interactions is certainly dependent on the narrowness of the drug therapeutic index, clinical aspects of absorption delays and therapeutic failures resulting from various interactions are also important.

Pharmacokinetic drug interactions with anti-ulcer drugs

The safety profile of any pharmacological agent is defined on the basis of its toxicity, tolerability and potential for pharmacokinetic and/or pharmacodynamic interactions with other compounds, which may belong to the same or to a different pharmacological class. Drug-drug interactions are important in clinical practice because short and long term therapeutic regimens frequently require coadministration of different drugs. The pharmacological treatment of gastric and duodenal ulcers (and of related syndromes) includes older and newer compounds, which have different mechanisms of action and exert different therapeutic effects. These compounds are widely prescribed in combination with other drugs being given for the treatment of concomitant diseases. This article reviews pharmacokinetic interactions with anti-ulcer drugs, paying particular attention to those which have clinically relevant adverse effects. Drugs mentioned in the literature as causing any pharmacokinetic interaction with anti-ulcer compounds are considered in this article.

Pharmacokinetics and dose proportionality of ceftibuten in men

The pharmacokinetics and dose proportionality of ceftibuten were evaluated in healthy male volunteers receiving single oral doses of 200, 400, and 800 mg of ceftibuten. The drug was absorbed with similar times to the maximum concentration of drug in plasma for all three doses. Concentrations of ceftibuten in plasma increased with increasing dose. Analysis of variance was carried out on the dose-adjusted values for the maximum concentration of drug in plasma and the area under the plasma concentration-time curve; the results indicated that the concentrations in plasma after the 200- and 400-mg doses were dose proportional, and after the 800-mg of dose they were less than dose proportional. The elimination half-life from plasma ranged from 2.0 to 2.3 h and was independent of dose. The total excretion of unchanged ceftibuten in urine accounted for 53 to 68% of the dose, and the renal clearance was estimated to be 53 to 61 ml/min after all doses. The amount of ceftibuten-trans, the major in vitro and in vivo conversion product of ceftibuten, was low in both plasma and urine.

Multiple-dose pharmacokinetics of ceftibuten in healthy volunteers

The pharmacokinetics of ceftibuten, a new cephalosporin antibiotic, and its conversion product, ceftibutentrans, were studied in healthy male volunteers following daily oral administration of a 400-mg capsule for 7 days. Mean concentrations of ceftibuten in plasma obtained on day 5 were similar to those obtained on day 7. Analysis of variance indicated that the concentrations in plasma on days 5 and 7 were at steady state. The mean accumulation factor was 1.14 for day 5 and 1.13 for day 7. The half-life (2.4 h) was independent of the duration of drug administration, and the mean maximum concentration of drug in plasma was 18 to 19 micrograms/ml. Urinary excretion was the major elimination route for ceftibuten, by which 57 to 59% of the drug was excreted unchanged over a 24-h period. The amounts of ceftibuten-trans in plasma and urine were low.

Drug interactions with antacids. Mechanisms and clinical significance

Concomitant use of antacid preparations with other medications is common. The potential for antacid-drug interactions is dependent upon the chemistry and physical properties of the antacid preparation. The intragastric release of free aluminum and magnesium ions has potent effects on gastrointestinal function and on drug pharmacokinetics. Antacid-drug interactions may occur secondary to changes in gastrointestinal motility or alterations in gastric and urinary pH. Direct adsorption also results in decreased drug bioavailability. Human drug interaction studies are usually performed with healthy volunteers; extrapolation of these results to clinical situations may not always be valid. However, the current literature would suggest that significant interactions with antacids do occur with certain members of the quinolone, nonsteroidal anti-inflammatory drug (NSAID) and cephalosporin classes of drugs. Notable interactions also occur with tetracycline, quinidine, ketoconazole and oral glucocorticoids. These interactions are particularly relevant in the patient with sepsis, cardiac disease or inflammatory syndromes.

Fluoroquinolones: interaction profile during enteral absorption

Fluoroquinolones are used worldwide in the treatment of severe infections. These drugs, however, can interact with other agents. This paper is a review of drug interactions with different quinolone derivatives at the absorption phase; the review deals mainly with the prototype quinolones, ciprofloxacin and ofloxacin, and also with some of the newer agents. The concomitant agents considered are food, H2-receptor antagonists, anticholinergic drugs and metallic cation-containing compounds. Food (standard breakfast), H2-receptor antagonists and anticholinergic drugs had no major effect on the bioavailability of the quinolones. However, antacids, ferrous sulfate and other metallic cation-containing compounds impaired the bioavailability of the quinolones. This effect is due to chelation between the functional groups of the quinolone molecule and the metallic cations, resulting in insoluble complexes that can be absorbed. The degree of impairment varied between different quinolone derivatives.

Pharmacokinetics of roxithromycin and influence of H2-blockers and antacids on gastrointestinal absorption

The pharmacokinetics of roxithromycin (300 mg orally) and the influence of the antacid aluminum magnesium hydroxide and the H2-blocker ranitidine on bioavailability of roxithromycin in ten healthy volunteers were studied. Pharmacokinetics after a single dose of roxithromycin were characterized by high peak serum levels (9.1 +/- 2.1 mg/l) and a long elimination half-life (7.2 +/- 2.5 h), resulting in a large area under the curve (116.9 +/- 32.7 mg h/l). High inter- and intraindividual variations were found for both the absorption time and the elimination half-life. The bioavailability of roxithromycin was not affected by coadministration with antacids or ranitidine.

Effect of antacid on the bioavailability of cefprozil

The effect of antacid on the bioavailability of cefprozil was investigated in a two-way crossover study. Eight healthy male subjects received a single 500-mg oral dose of cefprozil with and without coadministration of 30 ml of an antacid suspension containing magnesium hydroxide and aluminum hydroxide (Maalox). Cefprozil consists of cis and trans isomers in an approximate 90:10 ratio. When cefprozil was administered alone (treatment A), the mean maximum concentrations (Cmax) of the cis and trans isomers were 9.2 and 1.2 micrograms/ml, respectively. When cefprozil was coadministered with Maalox (treatment B), the Cmax values of the cis and trans isomers were 8.7 and 1.3 micrograms/ml, respectively. The mean values of the area under the curve from time zero to infinity (AUC0-infinity) were 27.7 and 3.5 micrograms.h/ml for treatment A and 27.5 and 3.5 micrograms.h/ml for treatment B for the cis and trans isomers, respectively. The other pharmacokinetic parameters, time to Cmax, elimination half-life, mean residence time, renal clearance, and percent urinary excretion, were essentially the same for the two isomers. The respective values of the elimination half-life for the cis and trans isomers were 1.36 and 1.32 h for treatment A and 1.36 and 1.42 h for treatment B. Mean urinary excretion was 63 and 60% for treatment A and 58 and 56% for treatment B for the cis and trans isomers, respectively. No significant differences between the two treatments were found for any of the pharmacokinetic parameters for either isomer. For the cis isomer, bioavailability point estimates (90% confidence intervals) of the mean Cmax and AUG0-infinity values for the Maalox treatment relative to those for the reference treatment were 95% (87%, 103%) and 99% (95%, 104%), respectively. For the trans isomer, the value were 109% (92%, 126%) for Cmax and 97% (88%, 106%) for AUC0-infinity. On the basis of the results of this study, it is concluded that the bioavailability of cefprozil is not affected by the coadministration of Maalox.

Pharmacokinetics of cefpodoxime proxetil and interactions with an antacid and an H2 receptor antagonist

Cefpodoxime proxetil is a new oral esterified cephem antibiotic with a broad antibacterial spectrum. The dissolution of cefpodoxime proxetil is pH dependent. The objectives of this study were to characterize the pharmacokinetics of cefpodoxime proxetil in two different oral doses and to examine possible interactions with an antacid, aluminum magnesium hydroxide (Maalox 70), and an H2 receptor antagonist, famotidine. Two studies involving the same 10 healthy volunteers were performed. In the first study, cefpodoxime proxetil was administered in two doses, 0.1 and 0.2 g. In the second study, two interventions were performed in a randomized crossover design. For one intervention, the volunteers were pretreated with 40 mg of famotidine 1 h before 0.2 g of cefpodoxime proxetil was administered. In the second trial, participants were given 10 ml of Maalox 70 2 h and 10 ml of Maalox 70 15 min before they received 0.2 g of cefpodoxime proxetil. Serum and urine concentrations were determined by high-performance liquid chromatography. For the statistical evaluation, these data were tested by using the pharmacokinetics of 0.2 g of cefpodoxime proxetil from the first study. The maximum concentrations were 1.19 +/- 0.32 mg/liter after 0.1 g of cefpodoxime proxetil and 2.54 +/- 0.64 mg/liter after 0.2 g of cefpodoxime proxetil. The elimination half-lives were 149 min for 0.1 g and 172 min for 0.2 g of cefpodoxime proxetil. The total increase in the area under the concentration-time curve (AUC) was dose dependent. Combination with Maalox 70 caused a reduction in the AUC from 14.0 +/- 3.9 to 8.44 +/- 1.85 mg.h/liter. After famotidine, the AUC decreased to 8.36 +/- 2.0 mg . h/liter. Corresponding changes were registered for the maximum concentration of drug in serum, 24-h urine recovery, and the time to maximum concentration of drug serum. Cefpodoxime proxetil was well tolerated without any seriously adverse drug reactions.

The drug interaction potential of ranitidine: an update

Ranitidine is a H2-receptor antagonist widely used in the treatment of a variety of gastrointestinal disorders. Since cimetidine--the predecessor drug of ranitidine--interacts with a variety of other agents and moreover ranitidine is often administered in combination with other drugs the interaction potential of ranitidine has been subject to extensive investigations. This review updates the information available from 1988 to present. Pharmacokinetic interactions of ranitidine with other drugs may occur at the site of absorption, metabolism and renal excretion. Most of the interactions reported at each of the three levels are minor and of low clinical significance. In view of some uncontrolled anecdotal reports, one cannot completely rule out the possibility that ranitidine might have some limited interaction potential in special patient populations under certain clinical conditions. However, it must be emphasized that numerous controlled studies have proven that ranitidine can be safely coadministered with other drugs.