Linezolid: Pharmacokinetic and Pharmacodynamic Evaluation of Coadministration with Pseudoephedrine HCl, Phenylpropanolamine HCl, and Dextromethorphan HBr

Concomitant Administration of Ozanimod and Serotonergic Antidepressants in Patients With Ulcerative Colitis or Relapsing Multiple Sclerosis

BACKGROUND

Ozanimod, approved for the treatment of moderately to severely active ulcerative colitis (UC) and relapsing multiple sclerosis (RMS), is a weak in vitro monoamine oxidase B (MAO-B) inhibitor. MAO-B inhibitors can cause serotonin accumulation with concomitant use of selective serotonin reuptake inhibitors (SSRIs) or serotonin and norepinephrine reuptake inhibitors (SNRIs). We evaluated the incidence of treatment-emergent adverse events (TEAEs) potentially associated with serotonin accumulation during ozanimod and concomitant SSRI/SNRI use in this post hoc analysis of pooled UC studies and the open-label extension RMS DAYBREAK.

METHODS

Data for ozanimod 0.92 mg from pooled UC studies (n = 1158; cutoff: January 10, 2022) and RMS DAYBREAK (n = 2257; cutoff: February 1, 2022) were analyzed. Concomitant SSRI/SNRI use was allowed in the UC (n = 67) and RMS (n = 274) studies. A narrow Medical Dictionary for Regulatory Activities search ("serotonin syndrome," "neuroleptic malignant syndrome," and "malignant hyperthermia") and a broad search including terms potentially associated with serotonin accumulation were conducted. The percentages of patients with TEAEs in both searches were analyzed by concomitant SSRI/SNRI use when the TEAE occurred.

RESULTS

No patients had TEAEs matching the narrow search criteria. No differences were observed in the percentages of patients with ≥1 TEAE matching the broad search regardless of SSRI/SNRI use in UC (with: 25.4% [n = 17 of 67]; without: 15.0% [n = 164 of 1091]) and RMS (with: 12.4% [n = 34 of 274]; without: 15.6% [n = 310 of 1982]) studies.

CONCLUSIONS

No evidence of increased TEAEs potentially associated with serotonin accumulation was observed with concurrent use of ozanimod and SSRIs/SNRIs.

CLINICAL TRIAL REGISTRATION

NCT01647516, NCT02531126, NCT02435992, NCT02576717.

Evaluation of the rational prescription of linezolid, the prevalence of thrombocytopenia and major drug interactions in patients with cardiovascular diseases: are there any cautions?

The present study evaluated the rational prescription of linezolid, the prevalence of thrombocytopenia, and major drug interactions in patients with cardiovascular diseases. We conducted a retrospective cross-sectional study on linezolid-treated patients at Shahid Chamran Heart Hospital in Isfahan from March 21, 2021, to March 20, 2022. Our research involved 132 patients who received linezolid. We reported 43.18% of linezolid prescriptions as irrational. Linezolid-induced thrombocytopenia is more common than previous studies, with a prevalence of 47.9%. We found a significant relationship between thrombocytopenia and the concomitant use of aspirin. The duration of treatment was identified as predicting factor for linezolid-induced thrombocytopenia. Moreover, the prevalence of interactions in the X and D categories was determined. Serotonergic and catecholamine medications were associated with 56.1% and 47.7% medication interactions, respectively. Our study found a high prevalence of linezolid-induced thrombocytopenia among patients with cardiovascular diseases. Based on this study, physicians should focus more closely on prescribing linezolid to patients with cardiovascular diseases. In addition to following rational antibiotic use, this susceptible group is also at an elevated risk of side effects (thrombocytopenia) and medication interactions.

The effects of drug-drug interaction on linezolid pharmacokinetics: A systematic review

OBJECTIVES

Linezolid is a commonly used antibiotic in the clinical treatment of gram-positive bacterial infections. The impacts of drug interactions on the pharmacokinetics of linezolid are often overlooked. This manuscript aims to review the medications that affect the pharmacokinetics of linezolid.

METHODS

In accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we queried the PubMed, Embase, and Cochrane Library for publications from database establishment to November 3, 2023, using the search terms: "Linezolid" and "interaction," or "interact," or "drug-drug interaction," or "co-treatment," or "cotreatment," or "combined," or "combination."

RESULTS

A total of 24 articles were included. Among the reported medication interactions, rifampicin, levothyroxine, venlafaxine, and phenobarbital could reduce the concentration of linezolid; clarithromycin, digoxin, cyclosporine, proton pump inhibitors, and amiodarone could increase the concentration of linezolid, while aztreonam, phenylpropanolamine, dextromethorphan, antioxidant vitamins, and magnesium-containing antacids had no significant effects on linezolid pharmacokinetics. The ratio of mean (ROM) of linezolid AUC in co-treatment with rifampicin to monotherapy was 0.67 (95%CI 0.58-0.77) and 0.63 (95%CI 0.43-0.91), respectively, in 2 studies, and co-treatment with 500 mg clarithromycin to monotherapy was 1.81 (95%CI 1.49-2.13).

CONCLUSIONS

This systematic review found that numerous drugs have an impact on the pharmacokinetics of linezolid, and the purported main mechanism may be that linezolid is the substrate of P-glycoprotein. In clinical practice, it is prudent to pay attention to the changes in linezolid pharmacokinetics caused by interactions. Conducting therapeutic drug monitoring (TDM) is beneficial to improve efficacy and reduce adverse reactions of linezolid.

The Association of Serotonin Toxicity with Combination Linezolid-Serotonergic Agent Therapy: A Systematic Review and Meta-Analysis

Linezolid (LZD) has a longstanding reported association with the onset of serotonin toxicity (ST), secondary to drug-drug interactions with serotoninergic agents. There have been no conclusive data supporting the incidence or contributing risk factors to date. The study evaluated the incidence of ST in patients treated with LZD and serotonergic agents concomitantly versus LZD alone. The secondary objectives included a comparison of ST incidence in patients treated with one serotonergic agent + LZD versus two or more serotonergic agents + LZD. The studies used for this meta-analysis were retrieved from PubMed, Scopus, and Google Scholar. All studies including a comparison between LZD alone and LZD + a serotonergic agent published between 1 January 2000 and 1 October 2023 and meeting the quality standards were considered for inclusion. Fourteen studies were identified, with five meeting all inclusion and exclusion criteria with no significant heterogeneity. For the analysis of LZD monotherapy vs. SA combination therapy, four studies with 6025 patients total were analyzed and yielded an odds ratio of 1.78 (CI [1.04, 3.02]; I2 = 49%; GRADE certainty: low). Four studies and 2501 patients were included in the analysis of one versus more than one SA with an odds ratio of 5.18 (CI [1.05, 25.49]; I2 = 44.87; GRADE certainty: moderate). The Newcastle-Ottawa score, visual inspection of the funnel plot, and Egger's statistic were used to evaluate quality and heterogeneity. The Peto method was used to calculate the summary odds ratios. All analyses were performed using Comprehensive Meta-Analysis version 3.0 and R, while GRADE was used to evaluate the quality of the final recommendation. The number of concomitant serotonergic agents may play a role in the development of serotonin toxicity in patients prescribed linezolid. In patients requiring linezolid therapy and serotonergic agents, risk versus benefit analysis should pay attention to the number of interacting drugs.

Contemporary pharmacologic treatments of MRSA for hospitalized adults: rationale for vancomycin versus non-vancomycin therapies as first line agents

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) remains an important pathogen in the hospital setting and causes significant morbidity and mortality each year. Since the initial discovery over 60 years ago, vancomycin has remained a first-line treatment for many different types of MRSA infections. However, significant concerns related to target attainment and nephrotoxicity have spurred efforts to develop more effective agents in the last two decades.

AREAS COVERED

Newer anti-MRSA antibiotics that have been approved since 2000 include linezolid, daptomycin, and ceftaroline. As clinical evidence has accumulated, these newer agents have become more frequently used, and some are now recommended as co-first-line options (along with vancomycin) in clinical practice guidelines. For this review, a scoping review of the literature was conducted to support our findings and recommendations.

EXPERT OPINION

Vancomycin remains an important standard of care for MRSA infections but is limited with respect to nephrotoxicity and rapid target attainment. Newer agents such as linezolid, daptomycin, and ceftaroline have specific indications for treating different types of MRSA infections; however, newer agents also have unique attributes which require consideration during therapy.

Current and emerging drug treatment strategies to tackle invasive community-associated methicillin-resistant Staphylococcus aureus (MRSA) infection: what are the challenges?

INTRODUCTION

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections represent a leading cause of purulent skin and soft tissue infections in some geographical regions. Traditionally, 'old antibiotics' such as trimethoprim-sulfamethoxazole, tetracyclines, clindamycin, chloramphenicol,vancomycin, and teicoplanin have been used to treat these infections, but these were often associated with low efficacy and excessive side effects and toxicity, especially nephrotoxicity. Along with the development of new compounds, the last decade has seen substantial improvements in the management of CA-MRSA infections.

AREAS COVERED

In this review, the authors discuss the current and emerging drug treatment strategies to tackle invasive CA-MRSA infections. Articles reported in this review were selected from through literature searches using the PubMed database.

EXPERT OPINION

The availability of new drugs showing a potent in vitro activity against CA-MRSA represents a unique opportunity to face the threat of resistance while potentially reducing toxicity. All these compounds represent promising options to enhance our antibiotic armamentarium. However, data regarding the use of these new drugs in real-life studies are limited and their best placement in therapy and in terms of optimization of medical resources and balance of cost-effectiveness requires further investigation.

Recent advances in oxazolidinones as antituberculosis agents

Tuberculosis (TB) is an infectious and fatal disease caused by Mycobacterium tuberculosis (Mtb) and remains a serious public health threat; therefore, the development of new antitubercular agents is a priority for the World Health Organization's End TB strategy and the United Nations' Sustainable Development Goals to eradicate TB. Oxazolidinones are a class of synthetic antibacterial agents with a distinct mode of action developed for the treatment of Gram-positive bacterial infections. Many oxazolidinones exhibit good activity against Mtb, and some are currently in clinical trials for multidrug-resistant TB and extensively drug-resistant TB therapy. In this review, the mechanism of action, activity and toxicity of oxazolidinones and recent progress in the research and development of oxazolidinones as anti-TB agents are summarized.

Drug-Drug Interactions With Over-The-Counter Medicines: Mind the Unprescribed

BACKGROUND

This review provides a summary of the currently available clinical data on drug-drug interactions (DDIs) involving over-the-counter (OTC) medicines. It aims to educate and increase awareness among health care providers and to support decisions in daily practice.

METHODS

An extensive literature search was performed using bibliographic databases available through PubMed.gov. An initial structured search was performed using the keywords "drug-drug-interaction AND (over-the-counter OR OTC)," without further restrictions except for the language. The initial results were screened for all described DDIs involving OTC drugs, and further information was gathered specifically on these drugs using dedicated database searches and references found in the bibliography from the initial hits.

RESULTS

From more than 1200 initial hits (1972-June 2021), 408 relevant publications were screened for DDIs involving OTC drugs, leading to 2 major findings: first, certain types of drug regimens are more prone to DDIs or have more serious DDI-related consequences, such as antiretroviral, anti-infective, and oral anticancer therapies. Second, although most DDIs involve OTC drugs as the perpetrators, some prescription drugs (statins or phosphodiesterase-5 inhibitors) that currently have OTC status can be identified as the victims in DDIs. The following groups were identified to be frequently involved in DDIs: nonsteroidal anti-inflammatory drugs, food supplements, antacids, proton-pump inhibitors, H2 antihistamines, laxatives, antidiarrheal drugs, and herbal drugs.

CONCLUSIONS

The most significant finding was the lack of high-quality evidence for commonly acknowledged interactions. High-quality interaction studies involving different phenotypes in drug metabolism (cytochrome P450) and distribution (transporters) are urgently needed. This should include modern and critical drugs, such as oral anticancer medications and direct oral anticoagulants.

Multiple-Dose Pharmacokinetics of Ozanimod and its Major Active Metabolites and the Pharmacodynamic and Pharmacokinetic Interactions with Pseudoephedrine, a Sympathomimetic Agent, in Healthy Subjects

INTRODUCTION

The aims of this study were to characterize the multiple-dose pharmacokinetics (PK) of ozanimod's major active metabolites (CC112273 and CC1084037) and to evaluate the pharmacodynamic and PK interactions with pseudoephedrine (PSE).

METHODS

In this phase 1, single-center, randomized, double-blind, placebo-controlled study, 56 healthy adult subjects were randomized to receive either placebo or ozanimod once daily for 30 days (0.23 mg on days 1-4, 0.46 mg on days 5-7, 0.92 mg on days 8-10, and 1.84 mg on days 11-30). On day 30, a single oral dose of PSE 60 mg was co-administered with placebo or ozanimod. Maximum time-matched change in systolic blood pressure (SBP) from baseline (day 29) following PSE administration on day 30 was calculated. Plasma PK parameters for ozanimod, CC112273, CC1084037, and PSE were estimated using noncompartmental methods.

RESULTS

Fifty-two subjects (92.9%) completed the study. Following multiple dosing, approximately 94% of circulating total active drug exposure was represented by ozanimod (6%), CC112273 (73%), and CC1084037 (15%). Exposures of CC112273 and CC1084037 were highly correlated. Mean maximum time-matched change from baseline for SBP was not significantly different between ozanimod + PSE and placebo + PSE. Ozanimod also had no effect on the PK of PSE. Co-administration of ozanimod with a single dose of PSE in healthy subjects was generally well tolerated. While CC112273 and CC1084037 selectively inhibited monoamine oxidase (MAO)-B in vitro, both active metabolites do not inhibit platelet MAO-B activity in vivo.

CONCLUSION

Concomitant administration of ozanimod with PSE, a sympathomimetic agent, did not potentiate the effects on blood pressure.

TRIAL REGISTRATION

NCT03644576.

The safety of treatment options for acute bacterial skin and skin structure infections

INTRODUCTION

Acute bacterial skin and skin-structure infections (ABSSSI) may develop in both in-patients and out-patients, possibly with a severe clinical presentation. Since most phase 3 randomized clinical trials have shown non-inferiority in efficacy across different agents, considerations regarding their different safety profiles inevitably play a crucial role in the everyday choice about which of them should be employed for the treatment of ABSSSI.

AREAS COVERED

In this review, the authors discuss the safety profile of different treatment options for ABSSSI.

EXPERT OPINION

The spread of methicillin-resistant Staphylococcus aureus (MRSA) in the last decades has inevitably influenced the therapeutic approach to ABSSSI. Adequate knowledge of the peculiar toxicity profile of each drug active against MRSA is essential for guiding, monitoring and managing adverse events, in turn reducing any unfavorable impact of toxicity on patients' outcomes. In the next five years, potential toxicity will play a critical role in establishing the best available therapy for each specific patient, together with consideration regarding the possibility of avoiding hospitalization or allowing a switch from intravenous to oral therapy and early discharge.

Pharmacokinetics of Tedizolid and Pseudoephedrine Administered Alone or in Combination in Healthy Volunteers

Therapeutic doses of tedizolid phosphate, an oxazolidinone antibiotic, lack monoamine oxidase inhibition in vivo, potentially resulting in an improved safety profile versus other oxazolidinones. This randomized, double-blind, placebo-controlled, 2-period, 2-sequence, crossover, phase 1 study (NCT01577459) assessed the potential for pharmacokinetic (PK) interactions between tedizolid and pseudoephedrine. Eighteen healthy volunteers (age: 18⁻45 years) were block-randomized to 1 of 2 treatment sequences containing 2 treatment periods (tedizolid phosphate or placebo once daily for 4 days; single dose of pseudoephedrine 60 mg on day 5) separated by a 2-day washout. Median time to maximum plasma concentration for tedizolid and pseudoephedrine ranged from 3 to 4 h, regardless of treatment coadministration. Steady-state tedizolid had no effect on the PK of pseudoephedrine; geometric mean ratio and 90% confidence interval remained within the no-effect 0.8 to 1.25 boundaries. The maximum observed concentration of tedizolid decreased by approximately 14% when pseudoephedrine was coadministered; no changes in the area under the plasma concentration-time curve or the minimum observed plasma concentration occurred. All adverse events (AEs) were mild, and there were no serious AEs or study drug discontinuations. No meaningful PK interactions occurred between tedizolid and pseudoephedrine, and tedizolid was well tolerated when administered in conjunction with pseudoephedrine.

Critical role of tedizolid in the treatment of acute bacterial skin and skin structure infections

Tedizolid phosphate has high activity against the Gram-positive microorganisms mainly involved in acute bacterial skin and skin structure infections, such as strains of Staphylococcus aureus (including methicillin-resistant S. aureus strains and methicillin-sensitive S. aureus strains), Streptococcus pyogenes, Streptococcus agalactiae, the Streptococcus anginosus group, and Enterococcus faecalis, including those with some mechanism of resistance limiting the use of linezolid. The area under the curve for time 0-24 hours/minimum inhibitory concentration (MIC) pharmacodynamic ratio has shown the best correlation with the efficacy of tedizolid, versus the time above MIC ratio and the maximum drug concentration/minimum inhibitory concentration ratio. Administration of this antibiotic for 6 days has shown its noninferiority versus administration of linezolid for 10 days in patients with skin and skin structure infections enrolled in two Phase III studies (ESTABLISH-1 and ESTABLISH-2). Tedizolid's more favorable safety profile and dosage regimen, which allow once-daily administration, versus linezolid, position it as a good therapeutic alternative. However, whether or not the greater economic cost associated with this antibiotic is offset by its shorter treatment duration and possibility of oral administration in routine clinical practice has yet to be clarified.

Applicability of a Single Time Point Strategy for the Prediction of Area Under the Concentration Curve of Linezolid in Patients: Superiority of Ctrough- over Cmax-Derived Linear Regression Models

Background and Objectives

Linezolid, a oxazolidinone, was the first in class to be approved for the treatment of bacterial infections arising from both susceptible and resistant strains of Gram-positive bacteria. Since overt exposure of linezolid may precipitate serious toxicity issues, therapeutic drug monitoring (TDM) may be required in certain situations, especially in patients who are prescribed other co-medications.

Methods

Using appropriate oral pharmacokinetic data (single dose and steady state) for linezolid, both maximum plasma drug concentration (C_max) versus area under the plasma concentration–time curve (AUC) and minimum plasma drug concentration (C_min) versus AUC relationship was established by linear regression models. The predictions of the AUC values were performed using published mean/median C_max or C_min data and appropriate regression lines. The quotient of observed and predicted values rendered fold difference calculation. The mean absolute error (MAE), root mean square error (RMSE), correlation coefficient (r), and the goodness of the AUC fold prediction were used to evaluate the two models.

Results

The C_max versus AUC and trough plasma concentration (C_trough) versus AUC models displayed excellent correlation, with r values of >0.9760. However, linezolid AUC values were predicted to be within the narrower boundary of 0.76 to 1.5-fold by a higher percentage by the C_trough (78.3 %) versus C_max model (48.2 %). The C_trough model showed superior correlation of predicted versus observed values and RMSE (r = 0.9031; 28.54 %, respectively) compared with the C_max model (r = 0.5824; 61.34 %, respectively).

Conclusions

A single time point strategy of using C_trough level is possible as a prospective tool to measure the AUC of linezolid in the patient population.

Therapeutic challenges posed by critical drug-drug interactions in cystic fibrosis

This review seeks to re-introduce cystic fibrosis (CF) clinicians to the pharmacology of drug-drug interactions among medications commonly used in CF and provide a framework for understanding these interactions among medications outside the scope of this discussion. We here focus on drugs impacted by the cytochrome P-450 (CYP450) enzyme system and on interactions involving antimicrobials, psychotropic medications, and cystic fibrosis transmembrane conductance regulator (CFTR) modulators. Particular attention is needed when prescribing rifampin, azole antifungals and the CFTR modulators, ivacaftor, and lumacaftor/ivacaftor, in combination with other medications. The complexities of these interactions provide a strong rationale for case management by pharmacists and pharmacologists as a routine part of CF care. Pediatr Pulmonol. 2016;51:S61-S70. © 2016 Wiley Periodicals, Inc.

Augmentation of the Inotropic Effects of Dopamine Following Linezolid Administration in an Infant

Although generally safe and effective, one of the unique properties of linezolid is its weak inhibitory effect on monoamine oxidase. As such, it may interact with other medications that act through the adrenergic or serotonergic systems, including selective-serotonin reuptake inhibitors and vasoactive agents. We present a 3-month-old infant who was being treated with dopamine to maintain mean arterial pressure during mechanical ventilation following viral-induced respiratory failure. Hypertension and tachycardia developed during the administration of linezolid on two separate occasions. The physiology of catecholamine metabolism is reviewed including the role of the monoamine oxidase system. The potential interaction between linezolid and vasoactive agents such as dopamine is discussed.

Safety profiles of old and new antimicrobials for the treatment of MRSA infections

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) is a frequent cause of severe nosocomial and community-acquired infections. Various adverse effects have been associated with compounds that are commonly used in the treatment of MRSA.

AREAS COVERED

Prolonged use of high-dose vancomycin has been linked with nephrotoxicity. Linezolid use has been associated with lactic acidosis in regimens longer than 14 days and occurrence of thrombocytopenia in patients with renal impairment. Daptomycin use correlates with reversible and often asymptomatic myopathy. Among new compounds, telavancin has shown increased toxicity compared to vancomycin, especially in patients with severe renal impairment, while a low rate of adverse effects was reported others glycolipopeptides such as dalbavancin and oritavancin and for new cephalosporins. Recently studied oxazolidinones (tedizolid and radezolid) also showed mild adverse effects in Phase 2 and 3 clinical trials.

EXPERT OPINION

Due to the constant increase in antimicrobial resistance, the use of higher doses and prolonged regimens of antibiotics employed in the treatment of Gram-positive infections has become more common and linked to increased toxicity. Furthermore, new compounds with MRSA activity have been recently approved and will be regularly employed in clinical practice. The knowledge of the adverse effects and risk factors for the development of toxicity associated with anti-MRSA antimicrobials is paramount for the correct use of old and new compounds, especially in the treatment of severe infections.

Novel antibiotic treatment for skin and soft tissue infection

PURPOSE OF REVIEW

Acute bacterial skin and skin structure infection (ABSSSI) is a common and significant indication for antibiotic treatment. The microbial aetiology is becoming more resistant to available antibiotics and the treatment of patients is additionally challenged by extremes of age, obesity, diabetes and other co-morbidities. This review examines recent antimicrobial developments.

RECENT FINDINGS

In many parts of the world, multidrug-resistant (MDR) staphylococci are the predominant cause of ABSSSI in both the community and in hospital. Increasing resistance in Gram-negative organisms presents problems in the management of surgical-site infections. Most new antibiotics have been developed to treat MDR Gram-positive bacteria and there are few agents to treat infections caused by MDR Gram-negative pathogens.

SUMMARY

A number of novel agents are available clinically, with other agents of related chemical structure under development. There are no entirely new classes of antibiotics. Maintaining the efficacy of antimicrobial treatment require effective antibiotic stewardship, good infection prevention and the development of further new antibiotics.

A review of linezolid: the first oxazolidinone antibiotic

Resistance of Gram-positive bacterial pathogens, such as Staphylococcus aureus and Enterococcus faecium, to existing antibiotics continues to increase, and new antibiotics with activity against these pathogens are in demand. Linezolid (Zyvox, Pharmacia and Upjohn) is the first agent of a new class of antibiotics called the oxazolidinones. Linezolid possesses excellent microbial activity against a wide variety of Gram-positive pathogens including those resistant to methicillin and vancomycin (Vancocin, Eli Lilly). Linezolid is available for intravenous and oral administration and possesses excellent bioavailability. It exhibits good penetration into pulmonary, as well as skin and related structure tissues, and does not require dosage adjustment in hepatic or renal dysfunction. Linezolid is generally well-tolerated, with the predominant adverse effect manifesting as a duration dependent, reversible thrombocytopenia. Linezolid possesses monoamine oxidase inhibitor activity and caution is warranted with coadministration of adrenergic or seritonergic medications. Clinical trials conducted with linezolid in skin and structure infections, lower respiratory tract infections and vancomycin-resistant enterococcal infections demonstrate that linezolid is an effective therapy. Recent data suggest that linezolid may be superior to vancomycin for the treatment of infections caused by methicillin-resistant S. aureus. Linezolid is an excellent and promising new antibiotic for the treatment of resistant Gram-positive pathogens.

In vitro, in vivo, and clinical studies of tedizolid to assess the potential for peripheral or central monoamine oxidase interactions

Tedizolid phosphate is a novel oxazolidinone prodrug whose active moiety, tedizolid, has improved potency against Gram-positive pathogens and pharmacokinetics, allowing once-daily administration. Given linezolid warnings for drug-drug and drug-food interactions mediated by monoamine oxidase (MAO) inhibition, including sporadic serotonergic toxicity, these studies evaluated tedizolid for potential MAO interactions. In vitro, tedizolid and linezolid were reversible inhibitors of human MAO-A and MAO-B; the 50% inhibitory concentration (IC50) for tedizolid was 8.7 μM for MAO-A and 5.7 μM for MAO-B and 46.0 and 2.1 μM, respectively, with linezolid. Tedizolid phosphate was negative in the mouse head twitch model of serotonergic activity. Two randomized placebo-controlled crossover clinical studies assessed the potential of 200 mg/day tedizolid phosphate (at steady state) to enhance pressor responses to coadministered oral tyramine or pseudoephedrine. Sensitivity to tyramine was determined by comparing the concentration of tyramine required to elicit a ≥ 30-mmHg increase in systolic blood pressure (TYR30) when administered with placebo versus tedizolid phosphate. The geometric mean tyramine sensitivity ratio (placebo TYR30/tedizolid phosphate TYR30) was 1.33; a ratio of ≥ 2 is considered clinically relevant. In the pseudoephedrine study, mean maximum systolic blood pressure was not significantly different when pseudoephedrine was coadministered with tedizolid phosphate versus placebo. In summary, tedizolid is a weak, reversible inhibitor of MAO-A and MAO-B in vitro. Provocative testing in humans and animal models failed to uncover significant signals that would suggest potential for hypertensive or serotonergic adverse consequences at the therapeutic dose of tedizolid phosphate. Clinical studies are registered at www.clinicaltrials.gov as NCT01539473 (tyramine interaction study conducted at Covance Clinical Research Center, Evansville, IN) and NCT01577459 (pseudoephedrine interaction study conducted at Vince and Associates Clinical Research, Overland Park, KS).

Spectrofluorimetric determination of terbinafine hydrochloride and linezolid in their dosage forms and human plasma

A highly sensitive, simple and rapid spectrofluorimetric method was developed for the determination of Terbinafine HCl (TRH) and linezolid (LNZ) in their pharmaceutical formulations. The proposed method is based on measuring the native fluorescence of the studied drugs in water at 336 nm after excitation at 275 nm for TRH and 375 nm after excitation at 254 nm for LNZ. The fluorescence-concentration plots were rectilinear over the range of 0.02-0.15 μg/mL for TRH and 0.5-5.0 μg/mL for LNZ. With lower detection limits of 3.0 and 110.0 ng/mL and a lower quantification limit of 9.0 and 320.0 ng/mL for TRH and LNZ, respectively. The method was successfully applied to the analysis of TRH in its commercial tablets, cream, gel and spray formulations and the results were in good agreement with those obtained with the official method. In addition the method was also applied to the analysis of LNZ in its capsule and I.V solution and the results were in good agreement with those obtained with the comparison method. The effect of sensitizers was studied. The method was extended to the determination of the studied drugs in spiked human plasma and the results were satisfactory.

Serotonergic and Adrenergic Drug Interactions Associated with Linezolid: A Critical Review and Practical Management Approach

OBJECTIVE

To describe the evidence for serotonergic and adrenergic drug interactions with linezolid and discuss clinical management strategies.

DATA SOURCES

A literature search of PubMed (1947–November 2012), MEDLINE (1946–November 2012), EMBASE (1974–November 2012), and International Pharmaceutical Abstracts (1970–November 2012) was conducted using the terms linezolid, drug interaction, serotonin syndrome, serotonin toxicity, sympathomimetic, serotonergic agents, and adrenergic agents. Citations of retrieved articles were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

English-language articles describing coadministration of serotonergic or adrenergic agents with linezolid to humans were included. Studies published only in abstract form were excluded.

DATA SYNTHESIS

One prospective study, 6 retrospective studies, and 24 case reports were identified describing a serotonergic or adrenergic drug interaction. Incidence of serotonin syndrome in patients on linezolid and serotonergic agents ranged between 0.24% and 4%. Serotonergic agents determined to have probable (according to the Horn Drug Interaction Probability Scale) linezolid interactions in case reports included meperidine, citalopram, escitalopram, fluoxetine, paroxetine, sertraline, duloxetine, and venlafaxine. Serotonergic agent dose and duration of coadministration with linezolid did not appear to influence the occurrence of serotonin syndrome. Adrenergic medication coadministration was associated with a possible drug interaction as determined by the Horn Drug Interaction Probability Scale but did not appear to result in clinically significant drug interactions with linezolid.

CONCLUSIONS

Linezolid-associated serotonergic drug interactions occur more commonly than adrenergic interactions. Serotonergic interactions considered probable according to the Horn Drug Interaction Probability Scale do not appear to correlate with drug dosage; time of onset ranges from <1 to 20 days, and effect resolves in <1 to 5 days after discontinuation of offending agents. If coadministration of linezolid and a serotonergic agent cannot be avoided, clinicians should be aware of the symptoms and management of serotonergic toxicity; close monitoring is recommended and additional serotonergic agents should not be used. While adrenergic drug interactions with linezolid are less common in clinical practice, monitoring for signs of hypertension remains important.

The Pharmacokinetics of Linezolid Are Not Affected by Concomitant Intake of the Antioxidant Vitamins C and E

In vitro metabolism experiments have suggested a possible role for endogenous reactive oxygen species (ROS) in the in vivo clearance of linezolid, a synthetic antibiotic of the oxazolidinone class. This observation has resulted in the hypothesis that dietary antioxidant supplements might disturb the balance of ROS in vivo and thereby lower the clearance of linezolid. The purpose of this open-label, two-group parallel design study was to investigate whether continuous intake of widely used vitamin C or vitamin E will affect the pharmacokinetics of linezolid. A total of 28 healthy volunteers (27 male and 1 female), including 22 of Chinese origin, were administered a single oral dose of 600 mg linezolid on days 1 and 8. Half of the subjects received daily oral doses of 1000 mg vitamin C on days 2 through 9, whereas the other half were administered daily oral doses of 800 IU vitamin E during the same time period. Serial blood samples for assessment of the pharmacokinetic parameters of linezolid and its two inactive metabolites were collected on days 1 and 8, whereas vitamin concentrations were measured prior to and after the vitamin intake on these days. Urine was collected on days 1 and 8 to assess the fraction of dose excreted as linezolid and its major metabolites. All linezolid samples were analyzed according to validated HPLC/MS/MS methods. Linezolid was well tolerated in both groups with no reported clinically significant adverse events. No significant changes were found between the day 1 and day 8 AUC0- infinity and Cmax values of linezolid in either the vitamin C treatment group (p = 0.55 and p = 0.64, respectively) or the vitamin E treatment group (p = 0.06 and p = 0.49, respectively). Assessment of other pharmacokinetic parameters did not imply any change across the study groups. In conclusion, linezolid pharmacokinetics are not affected by concomitant administration with vitamins C and E. Therefore, no dose adjustment is necessary in patients taking vitamin C or vitamin E. These no-effect drug interaction data are in accord with current literature indicating that antioxidant vitamins have only subtle effects on overall ROS balance in vivo.

Linezolid, a Novel Oxazolidinone Antibiotic: Assessment of Monoamine Oxidase Inhibition Using Pressor Response to Oral Tyramine

The primary objective of this study was to compare the effects of oral linezolid with moclobemide and placebo on the pressor response to oral tyramine. Secondary objectives were to determine possible mechanisms of the effect based on changes in the pharmacokinetics of tyramine and to evaluate alternative methods for quantifying the pressor effect. Subjects received linezolid (625 mg bid orally), moclobemide (150 mg tid orally), or placebo for up to 7 days. Using the oral tyramine dose producing a >30 mmHg increase in systolic blood pressure (SBP) (PD>30), a positive pressor response was defined as a PD>30 index (pretreatment/treatment ratio of PD>30) of > or = 2. There were 8/10, 11/11, and 1/10 responders with linezolid, moclobemide, and placebo, respectively. Responses returned to baseline within 2 days of drug discontinuation. The ratio of mean greatest SBP and heart rate at the time of greatest SBP (GSBP/HR) increased linearly with tyramine dose both pretreatment and during treatment with linezolid and moclobemide. During treatment, responses to tyramine when subjects took linezolid or moclobemide were significantly different from placebo. Both drugs significantly decreased tyramine oral clearance compared with placebo. Urinary excretion of catecholamines and metabolites was consistent with MAOI activity of the drugs, but results were variable. The MAOI activity of linezolid is similar to that of moclobemide, a drug used clinically without food restrictions. Restrictions to normal dietary intake of tyramine-containing foods are not warranted when taking linezolid.

The efficacy and safety of linezolid and glycopeptides in the treatment of Staphylococcus aureus infections

To assess the effectiveness and safety of linezolid in comparison with glycopeptides (vancomycin and teicoplanin) for the treatment of Staphylococcus aureus infections, we conducted a meta-analysis of relevant randomized controlled trials. A thorough search of Pubmed and other databases was performed. Thirteen trials on 3863 clinically assessed patients were included. Linezolid was slightly more effective than glycopeptides in the intent-to-treat population (odds ratio [OR], 1.05; 95% confidence interval [CI], 1.01–1.10), was more effective in clinically assessed patients (OR 95% CI: 1.38, 1.17–1.64) and in all microbiologically assessed patients (OR 95% CI: 1.38, 1.15–1.65). Linezolid was associated with better treatment in skin and soft-tissue infections (SSTIs) patients (OR 95% CI: 1.61, 1.22–2.12), but not in bacteraemia (OR 95% CI: 1.24, 0.78–1.97) or pneumonia (OR 95% CI: 1.25, 0.97–1.60) patients. No difference of mortality between linezolid and glycopeptides was seen in the pooled trials (OR 95% CI: 0.98, 0.83–1.15). While linezolid was associated with more haematological (OR 95% CI: 2.23, 1.07–4.65) and gastrointestinal events (OR 95% CI: 2.34, 1.53–3.59), a significantly fewer events of skin adverse effects (OR 95% CI: 0.27, 0.16–0.46) and nephrotoxicity (OR 95% CI: 0.45, 0.28–0.72) were recorded in linezolid. Based on the analysis of the pooled data of randomized control trials, linezolid should be a better choice for treatment of patients with S. aureus infections, especially in SSTIs patients than glycopeptides. However, when physicians choose to use linezolid, risk of haematological and gastrointestinal events should be taken into account according to the characteristics of the specific patient populations.

Clinical update on linezolid in the treatment of Gram-positive bacterial infections

Gram-positive pathogens are a significant cause of morbidity and mortality in both community and health care settings. Glycopeptides have traditionally been the antibiotics of choice for multiresistant Gram-positive pathogens but there are problems with their use, including the emergence of glycopeptide-resistant strains, tissue penetration, and achieving and monitoring adequate serum levels. Newer antibiotics such as linezolid, a synthetic oxazolidinone, are available for the treatment of resistant Gram-positive bacteria. Linezolid is active against a wide range of Gram-positive bacteria and has been generally available for the treatment of Gram-positive infections since 2000. There are potential problems with linezolid use, including its bacteriostatic action and the relatively high incidence of reported adverse effects, particularly with long-term use. Long-term use may also be complicated by the development of resistance. However, linezolid has been shown to be clinically useful in the treatment of several serious infections where traditionally bacteriocidal agents have been required and many of its adverse effects are reversible on cessation. It has also been shown to be a cost-effective treatment option in several studies, with its high oral bioavailability allowing an early change from intravenous to oral formulations with consequent earlier patient discharge and lower inpatient costs.

Pharmacokinetic drug interactions of antimicrobial drugs: a systematic review on oxazolidinones, rifamycines, macrolides, fluoroquinolones, and Beta-lactams

Like any other drug, antimicrobial drugs are prone to pharmacokinetic drug interactions. These drug interactions are a major concern in clinical practice as they may have an effect on efficacy and toxicity. This article provides an overview of all published pharmacokinetic studies on drug interactions of the commonly prescribed antimicrobial drugs oxazolidinones, rifamycines, macrolides, fluoroquinolones, and beta-lactams, focusing on systematic research. We describe drug-food and drug-drug interaction studies in humans, affecting antimicrobial drugs as well as concomitantly administered drugs. Since knowledge about mechanisms is of paramount importance for adequate management of drug interactions, the most plausible underlying mechanism of the drug interaction is provided when available. This overview can be used in daily practice to support the management of pharmacokinetic drug interactions of antimicrobial drugs.

Linezolid interaction with serotonin reuptake inhibitors: report of two cases and incidence assessment

BACKGROUND

Prompted by the advent of potentially life-threatening neuromuscular symptoms following initiation of linezolid therapy in two patients receiving treatment with a serotonin reuptake inhibitor antidepressant, an evaluation was conducted to determine the incidence and characteristics of symptomatic serotonin toxicity among hospitalized patients receiving combined treatment with these medications.

METHODS

Patients admitted between January 1, 2006 and August 30, 2008 who received linezolid concurrently with citalopram or escitalopram were identified and their medical records were examined. Patients were judged to have serotonin toxicity if their records contained documentation of clinical evidence adequate to fulfill requisites of the Hunter Serotonin Toxicity Criteria. Severity of serotonin-related symptoms was graded according to previously established criteria.

RESULTS

During the period of observation, 24 patients received concurrent treatment with linezolid and citalopram or escitalopram. Of these, one patient (4%) treated with citalopram met evidentiary requirements for diagnosis of serotonin toxicity. The severity of symptoms in this patient was graded as mild. No evidence of serious harm related to a possible drug interaction was identified.

CONCLUSIONS

Severe symptoms associated with serotonin toxicity were shown to be uncommon in patients receiving linezolid and selected serotonin reuptake inhibitors. Nonetheless, serious interaction-related toxicity has been observed at our institution and reported in detail by others. Accordingly, concurrent use of these medications is categorized as contraindicated. Alternative antimicrobial therapy should be instituted in most cases. If no suitable alternative is available, recipient patients should be hospitalized for expectant observation and rigorous monitoring.

Linezolid pharmacokinetics and pharmacodynamics in clinical treatment

Linezolid has been widely used in the treatment of Gram-positive infections for more than a decade. It is unique amongst antibiotics active against most multiply-resistant Gram-positive bacteria in that there is an oral preparation with 100% bioavailability and an extensive volume of distribution. This review examines pharmacokinetic data relating to linezolid use in different patient groups (obesity, enteral feeding, renal failure, neonates, and paediatrics) and in different clinical conditions (sepsis syndrome, skin and soft tissue infection, diabetic foot infection, pneumonia, bone and joint infection, infection of the central nervous system, eye infection, and neutropenic sepsis).

Pharmacological issues of linezolid: an updated critical review

Linezolid is the first oxazolidinone agent introduced into clinical practice for use against Gram-positive bacteria that are resistant to beta-lactams and glycopeptides, including methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). An optimal antibacterial effect is achieved when plasma drug concentrations are above the minimum inhibitory concentration (MIC) [T>MIC] for the entire length of treatment and the ratio between the area under the plasma concentration-time curve (AUC) and the MIC (AUC/MIC) is greater than 100, as is most commonly obtained with administration of the standard dosage of linezolid 600 mg twice daily. A wide tissue distribution, including the CNS and respiratory tract, nearly linear pharmacokinetics and good tolerability are additional characteristics of linezolid. However, variability in the drug pharmacokinetics associated with clinical conditions (e.g. sepsis, burn injuries, end-stage renal disease, cystic fibrosis), haemodialysis and/or young age may lower the T>MIC and the AUC/MIC ratio, thus impairing both antibacterial activity and prevention of mutants. In most cases, changes in the dosage or in the schedule of administration (e.g. an additional [third] daily dose) may improve the effectiveness of linezolid. It is worth noting that linezolid could affect its own metabolism as a result of protein synthesis inhibition in mitochondria, and this could lead to high plasma concentrations and an increased risk of non-negligible toxicities. The latter may be reported during long-term administration of linezolid or in the presence of some pathological conditions (e.g. renal disease or kidney transplantation) associated with high plasma drug concentrations. Therefore, treatment optimization should be considered a requirement for more effective and tolerable use of the drug, particularly in special populations.

Effect of obesity on the pharmacokinetics of drugs in humans

The prevalence of obesity has dramatically increased in recent years and now includes a significant proportion of the world's children, adolescents and adults. Obesity is linked to a number of co-morbidities, the most prominent being type 2 diabetes mellitus. While many agents are available to treat these conditions, the current knowledge regarding their disposition in the obese remains limited. Over the years, both direct and indirect methodologies have been utilized to assess body composition. Commonly used direct measures include underwater weighing, skinfold measurement, bioelectrical impedance analysis and dual-energy x-ray absorptiometry. Unfortunately, these methods are not readily available to the majority of clinicians. As a result, a number of indirect measures to assess body composition have been developed. Indirect measures rely on patient attributes such as height, bodyweight and sex. These size metrics are often utilized clinically and include body mass index (BMI), body surface area (BSA), ideal bodyweight (IBW), percent IBW, adjusted bodyweight, lean bodyweight (LBW) and predicted normal weight (PNWT). An understanding of how the volume of distribution (V(d)) of a drug changes in the obese is critical, as this parameter determines loading-dose selection. The V(d) of a drug is dependent upon its physiochemical properties, the degree of plasma protein binding and tissue blood flow. Obesity does not appear to have an impact on drug binding to albumin; however, data regarding alpha(1)-acid glycoprotein binding have been contradictory. A reduction in tissue blood flow and alterations in cardiac structure and function have been noted in obese individuals. At the present time, a universal size descriptor to describe the V(d) of all drugs in obese and lean individuals does not exist. Drug clearance (CL) is the primary determinant to consider when designing a maintenance dose regimen. CL is largely controlled by hepatic and renal physiology. In the obese, increases in cytochrome P450 2E1 activity and phase II conjugation activity have been observed. The effects of obesity on renal tubular secretion, tubular reabsorption, and glomerular filtration have not been fully elucidated. As with the V(d), a single, well validated size metric to characterize drug CL in the obese does not currently exist. Therefore, clinicians should apply a weight-normalized maintenance dose, using a size descriptor that corrects for differences in absolute CL between obese and non-obese individuals. The elimination half-life (t((1/2))) of a drug depends on both the V(d) and CL. Since the V(d) and CL are biologically independent entities, changes in the t((1/2)) of a drug in obese individuals can reflect changes in the V(d), the CL, or both. This review also examines recent publications that investigated the disposition of several classes of drugs in the obese--antibacterials, anticoagulants, antidiabetics, anticancer agents and neuromuscular blockers. In conclusion, pharmacokinetic data in obese patients do not exist for the majority of drugs. In situations where such information is available, clinicians should design treatment regimens that account for any significant differences in the CL and V(d) in the obese.

Linezolid: a review of safety and tolerability

Linezolid has demonstrated activity against antibiotic-susceptible and antibiotic-resistant aerobic Gram-positive cocci. The availability of intravenous and oral formulations, with near 100% bioavailability of the latter, is hoped to facilitate the management of multiply drug-resistant Gram-positive infections. Linezolid was approved for clinical use in the United States in April 2000 and has subsequently been approved in other countries for the management of community-acquired and nosocomial pneumonia, complicated and uncomplicated skin and soft-tissue infections, and infections caused by methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci, including cases with concurrent bacteremia. Additional studies have demonstrated potential use in febrile cancer patients with neutropenia, and case reports have documented some efficacy in the management of infective endocarditis, tuberculosis, nocardiosis, and in anaerobic infections. Given the potential for significantly increased use of linezolid, a thorough review and update of its tolerability and safety profile is warranted.

Management of nosocomial external ventricular drain-related ventriculomeningitis

INTRODUCTION

Neurocritical care patients requiring external ventricular drainage are at risk for the development of a device-related infection. Infection rate of external ventriculostomy catheters is high with reported incidences ranging from 5% up to more than 20%. Nosocomial ventriculitis or ventriculomeningitis are potential life-threatening conditions which may contribute to a permanent adverse outcome of the patient. Reducing morbidity and mortality is strongly dependent on prompt diagnosis and on the initiation of appropriate antiinfective therapy.

SCIENTIFIC BACKGROUND

Management of nosocomial ventriculitis is challenging and needs to consider the most likely pathogens involved, local resistance patterns, the nature of the underlying disease, patient factors such as age, comorbidity, and immune status. Further, decisions on catheter exchange and the type and duration of systemic or local antimicrobial therapy have to be made. Because so many factors have to be taken into account, it is evident that the diagnostic and therapeutic approach to nosocomial ventriculitis is difficult to standardize. Staphylococci are the pathogens most frequently identified in nosocomial ventriculitis. Therefore, initial treatment with an antistaphylococcal agent with adequate cerebrospinal fluid penetration may be considered as first-line therapy for this infection.

CONCLUSION

In the review of a contemporary case we will discuss important issues in the management of device-related ventriculitis.

Prediction of clinical pharmacokinetic parameters of linezolid using animal data by allometric scaling: applicability for the development of novel oxazolidinones

1. Allometric scaling has previously been used as an effective tool for the prediction of human pharmacokinetic data. The pharmacokinetic data for linezolid, a novel oxazolidinone to treat Gram-positive pathogens, in mice, rats and dogs were subjected to simple allometric scaling. Generated allometric equations for parameters such as clearance (CL), volume of distribution (Vss) and elimination rate constant (K10) were used to predict human pharmacokinetic parameters including elimination half-lives. In addition, the human plasma concentration-time curve was simulated using a one-compartmental model. 2. Application of simple allometry (Y = aWb) for animal parameters such as CL, Vss, and K10 showed excellent allometric fit (r > or = 0.98). The allometric equations for CL, Vss, and K10 were -0.5465W(0.6595), -0.1369W(0.9246), and -0.4117W(-0.3139), respectively. The confidence in predictability of CL and Vss parameters was particularly high since the allometric exponents of CL and Vss almost approached the suggested values of 0.75 and 1.00, respectively. 3. Animal pharmacokinetic parameters generated in the present authors' laboratories for linezolid were in close agreement with reported literature values. The predicted human values for CL (4.68 l h(-1)), Vss (37.07 litres), and K10 (0.10 h(-1)) were within the range observed for linezolid in the literature (CL = 4-10.5 l h(-1); Vss = 21-53 litres; K10 = 0.09-0.3 h(-1)). The human half-life (t(1/2)) predicted using allometry (6.9 h) was similar to reported values in humans of 5 h. In summary, the retrospective analysis for linezolid suggests that allometric scaling can be used as a prospective tool for predicting human pharmacokinetic parameters of novel oxazolidinones.

Linezolid versus glycopeptide or beta-lactam for treatment of Gram-positive bacterial infections: meta-analysis of randomised controlled trials

Linezolid has been approved for the treatment of patients with infections caused by Gram-positive cocci that are resistant to traditionally used antibiotics, including glycopeptides. This oxazolidinone antibiotic has been reported to have excellent pharmacokinetics and effectiveness. We did a meta-analysis of randomised controlled trials (RCTs) to clarify whether linezolid is superior to glycopeptides or beta-lactams for the treatment of Gram-positive infections. 12 RCTs, involving 6093 patients, were included. Overall, with respect to treatment success, linezolid was more effective than glycopeptides or beta-lactams (odds ratio [OR] 1.41 [95% CI 1.11-1.81]). Mortality was similar between the groups (OR 0.97 [0.79-1.19]). Linezolid was more effective than comparators in patients with skin and soft-tissue infections (OR 1.67 [1.31-2.12]) and bacteraemia (OR 2.07 [1.13-3.78]). However, there was no difference in treatment success for patients with pneumonia (OR 1.03 [0.75-1.42]). Treatment with linezolid was not associated with more adverse effects in general (OR 1.40 [0.95-2.06]); however, thrombocytopenia was recorded more commonly in patients receiving linezolid (OR 11.72 [3.66-37.57]). Although linezolid is more effective than its comparators for the empirical treatment of selected patients, several points, such as the use of less potent antistaphylococcal beta-lactams, the same all-cause mortality, and the higher probability of thrombocytopenia, should be taken into account and may limit the use of linezolid to specific patient populations or infections that are difficult to treat with other antibiotics.

Risk of serotonin syndrome with concomitant administration of linezolid and serotonin agonists

Linezolid, an antimicrobial used to treat resistant gram-positive bacteria, can inhibit monoamine oxidase, an enzyme that metabolizes serotonin and other biogenic amines. Inhibition of this enzyme can predispose patients who are concomitantly taking serotonin agonists to serotonin syndrome. Because of the potential of linezolid to inhibit monoamine oxidase, premarketing studies were conducted with drugs such as selective serotonin reuptake inhibitors. No cases of serotonin syndrome were recorded. After linezolid was released to the United States market, several case reports of serotonin syndrome emerged. A literature search revealed 13 cases of serotonin syndrome occurring with the concomitant use of linezolid and drugs possessing serotonergic properties. To direct clinical management of this potential drug interaction, we reviewed reports of serotonin syndrome to determine relevant drug interactions with linezolid and serotonergic drugs and to characterize similarities and differences in the reported cases. Clinicians should obtain complete drug histories to identify patients at risk, strictly monitor drug therapy including concomitant drugs, and receive education about this potential drug interaction and the symptoms of serotonin syndrome.

Role of linezolid in the treatment of orthopedic infections

Gram-positive organisms, particularly staphylococci and streptococci, are responsible for the majority of bone and joint infections. The rising incidence of antimicrobial resistance among Staphylococcus aureus, coagulase-negative staphylococci and enterococci means that novel antibiotics with unique mechanisms of antimicrobial activity are needed, especially in orthopedic infections. Linezolid is the first of the oxazolidinones, a new class of antibacterial agents particularly effective against Gram-positive infections including methicillin- and vancomycin-resistant strains. With an excellent oral bioavailability and acceptable safety profile, linezolid offers a valuable alternative to more traditional therapies, such as glycopeptides. No large randomized trials have been published on its use in patients with orthopedic infections, but early results are encouraging. Reported adverse events, especially bone marrow suppression and optic neuropathy seen with prolonged administration, mean that treatment of such patients must be undertaken with careful follow-up of laboratory tests. Until now, little resistance has been reported.

Antibiotic drug interactions

Drug-drug interactions in the field of infectious diseases continue to expand as new drugs are approved, metabolic enzymes and transporters are identified, and recommendations for co-administration of drugs are revised. This article provides an overview of the principles and mechanisms of drug-drug interactions and describes pharmacokinetic-pharmacodynamic interactions commonly associated with antibacterial therapy, antiviral agents (non-retroviral), and drugs for tuberculosis.

Pharmacokinetics of intravenous linezolid in cerebrospinal fluid and plasma in neurointensive care patients with staphylococcal ventriculitis associated with external ventricular drains

The pharmacokinetic profile of linezolid in cerebrospinal fluid (CSF) in five neurointensive care patients with staphylococcal ventriculitis was studied. The mean area under concentration-time curve (+/- standard deviation) was 63 +/- 18.9 mg x h/liter, with a CSF-to-plasma ratio of 0.8 +/- 0.3. Times above MIC in CSF were 99.8% and 57.2% for pathogens with MICs of 2 mg/liter and 4 mg/liter, respectively.

Serotonin toxicity associated with the use of linezolid: a review of postmarketing data

BACKGROUND

Linezolid is the first oxazolidinone antimicrobial marketed in the United States. It exhibits monoamine oxidase (MAO) type A and MAO type B inhibitory effects. The concomitant administration of nonselective MAO inhibitors or MAO-A inhibitors with drugs that increase serotonin concentrations is associated with serotonin toxicity.

METHODS

We requested from the US Food and Drug Administration all postmarketing adverse event reports regarding linezolid that included serotonin toxicity or any report describing cognitive or behavioral symptoms and autonomic and neuromuscular excitability. We assessed the case summaries obtained from the Adverse Event Reporting System database for serotonin toxicity. A case of serotonin toxicity was defined as having the following: (1) linezolid as the primary suspect drug; (2) concurrent administration of > or =1 secondary suspect drug known to increase serotonin concentrations in the central nervous system; and (3) serotonin toxicity, as defined by the modified Hunter Serotonin Toxicity Criteria or by the reporter.

RESULTS

Twenty-nine cases were classified as serotonin toxicity. Patients' ages ranged from 17-83 years, and the ratio of females to males was 1:1. The most common class of drugs received concurrently with linezolid was selective serotonin reuptake inhibitors (26 of 43 patients). Thirteen patients required an intervention to prevent permanent impairment or required hospitalization for the adverse event.

CONCLUSION

The use of linezolid with medications that increase concentrations of serotonin in the central nervous system may result in serotonin toxicity. Prescribers must weigh risks and benefits of this combination. Patients and prescribers should be cognizant of signs and symptoms of serotonin toxicity and should initiate appropriate measures if such symptoms develop.

The impact of oral phenylpropanolamine on blood pressure: a meta-analysis and review of the literature

Oral phenylpropanolamine is commonly used to treat congestion and obesity. Clinicians often wonder what effect it has on blood pressure and whether they are safe in hypertensive patients. The purpose of our systematic review was to assess whether these drugs cause clinically meaningful elevations in pulse or blood pressure. English-language, randomized, placebo-controlled trials of oral phenylpropanolamine in adults with extractable data on pulse or blood pressure were studied. MEDLINE (1966-2003), Embase, the Cochrane library and reviewed article references were used as sources. Systolic (SBP) and diastolic blood pressure (DBP) and heart rate data were extracted. Additional extracted data included demographics, year, study design, study duration, drug dose and frequency, duration of washout and country. Study quality was assessed using the methods of Jadad and data were synthesized using a random effects model using weighted mean differences. In all, 33 trials reporting 48 treatment arms with 2165 patients were included. Phenylpropanolamine increased SBP 5.5 mmHg (95% CI: 3.1-8.0) and DBP 4.1 mmHg (95% CI: 2.2-6.0) with no effect on pulse. Patients with controlled hypertension were not at greater risk of blood pressure elevation. Immediate release preparations had greater effects on blood pressure than sustained release ones. Higher doses and shorter duration use also caused greater increases. Eighteen studies contained at least one treated subjects having blood pressure elevations > or =140/90 mmHg, an increase in SBP > or =15 mmHg or an increase in DBP > or =10 mmHg. In conclusion, phenylpropanolamine caused a small, but significant increase in systolic blood pressure. The effect was more pronounced with shorter-term administration, higher doses of medication and immediate release formulations.

What's New in Antibiotics?

Antibiotics are important agents in dermatologic practice. New drugs have expanded the therapeutic approach to uncomplicated skin infections and complicated infections involving deeper soft tissue or infections that require surgical intervention. This article reviews new antibiotics of dermatologic importance, including daptomycin (cyclic lipopeptide), linezolid (oxazolidinone), quinupristin-dalfopristin (streptogramins), moxifloxacin and gatifloxacin (fluoroquinolones), and dalbavancin and oritavancin, which are presently under investigation.

Effect of oral linezolid on the pressor response to intravenous tyramine

AIMS

To investigate the effect of monoamine oxidase A inhibition from a single oral dose of linezolid on the pressor response to intravenous (i.v.) tyramine, using positive and negative controls to validate the methodology.

METHODS

This placebo-controlled, three-period crossover study was conducted in 12 healthy male volunteers. Each volunteer received either one oral dose of moclobemide (300 mg), linezolid (600 mg), or placebo tablet followed by an i.v. tyramine pressor test until an increase in systolic blood pressure of at least 30 mmHg above baseline occurred. Each study day was separated by a 7-day washout period. The dose of tyramine required to raise the blood pressure by 30 mmHg (TYR30) was calculated for each oral treatment by linear interpolation between log-transformed doses of i.v. tyramine. The influence of body mass index (BMI) on TYR30 was also investigated.

RESULTS

The tyramine sensitivity factor (ratio of the geometric least square mean TYR30 for placebo and active oral treatment) was 1.8 [90% confidence interval (CI) 1.6, 2.0, P < 0.0001] for linezolid and 2.1 (90% CI 1.8, 2.4, P < 0.0001) for the positive control moclobemide. BMI had a statistically significant effect on TYR30.

CONCLUSIONS

There was a significant difference in the pressor response to i.v. tyramine between linezolid and placebo. Moclobemide (positive control) and linezolid have a similar pressor response to i.v. tyramine. The statistically significant effect of BMI on TYR30 underlines the advantage of within-individual comparisons of treatments in order to reduce variability and provide more accurate treatment estimates.

Nonantimicrobial Effects of Antibacterial Agents

One of the major advances in modern medicine was the development of antimicrobial chemotherapy. However, many antibacterial agents have unexpected or undesirable nonantimicrobial effects on humans. Microbes and man share many essentials of life, including DNA, adenosine triphosphate, and other biochemical pathways. Hence, some of these nonantimicrobial effects may also turn out to be pharmacologically useful. Oral hypoglycemic agents (i.e., sulfonylureas) and a certain diuretic agent (acetazolamide) are derivatives of sulfonamides. Erythromycin has been used clinically for its stimulatory effect on gastrointestinal motility. Macrolides, lincosamides, and tetracyclines have been known for their immunomodulatory effects. A tetracycline has been used to treat the syndrome of inappropriate antidiuretic hormone. Aminoglycosides may influence mucus production in patients with cystic fibrosis. Other antimicrobials may have side effects that are not therapeutically useful, such as osmotic diuresis with high-dose beta -lactam administration, neuromuscular blockade of aminoglycosides, dysglycemia of fluoroquinolones, and serotonin syndrome with oxazolidinones.