Effect of albumin substitution on pharmacokinetics of piperacillin/tazobactam in patients with severe burn injury admitted to the ICU.

BACKGROUND: Pathophysiological changes in severely burned patients alter the pharmacokinetics (PK) of anti-infective agents, potentially leading to subtherapeutic concentrations at the target site. Albumin supplementation, to support fluid resuscitation, may affect pharmacokinetic properties by binding drugs. This study aimed to investigate the PK of piperacillin/tazobactam in burn patients admitted to the ICU before and after albumin substitution as total and unbound concentrations in plasma. PATIENTS AND METHODS: Patients admitted to the ICU and scheduled for 4.5 g piperacillin/tazobactam administration and 200 mL of 20% albumin substitution as part of clinical routine were included. Patients underwent IV microdialysis, and simultaneous arterial plasma sampling, at baseline and multiple timepoints after drug administration. PK analysis of total and unbound drug concentrations under steady-state conditions was performed before and after albumin supplementation. RESULTS: A total of seven patients with second- to third-degree burns involving 20%-60% of the total body surface were enrolled. Mean (SD) AUC0-8 (h·mg/L) of total piperacillin/tazobactam before and after albumin substitution were 402.1 (242)/53.2 (27) and 521.8 (363)/59.7 (32), respectively. Unbound mean AUC0-8 before and after albumin supplementation were 398.9 (204)/54.5 (25) and 456.4 (439)/64.5 (82), respectively. CONCLUSIONS: Albumin supplementation had little impact on the PK of piperacillin/tazobactam. After albumin supplementation, there was a numerical increase in mean AUC0-8 of total and unbound piperacillin/tazobactam, whereas similar Cmax values were observed. Future studies may investigate the effect of albumin supplementation on drugs with a higher plasma protein binding.

Comparison of ultrafiltration and microdialysis for ceftriaxone protein-binding determination.

BACKGROUND: High protein binding (PB) of antibiotics has an impact on their antimicrobial activity. It has been questioned whether in vitro PB determination can capture the dynamic and concentration-dependent PB of highly bound antibiotics. OBJECTIVES: This clinical study compared in vitro ultrafiltration (UF) and in vivo IV microdialysis (MD) methods to determine ceftriaxone PB. METHODS: Six healthy male volunteers received a single IV 2 g dose of ceftriaxone. Unbound ceftriaxone plasma concentrations were measured with MD and venous plasma sampling with subsequent UF. Pharmacokinetic parameters were determined using non-compartmental pharmacokinetic analysis. Non-linear mixed-effects modelling was used to quantify the PB. The PTA was estimated. RESULTS: The Cmax of ceftriaxone total plasma concentration (297.42 ±â€Š21.0 mg/L) was approximately 5.5-fold higher than for free concentrations obtained with UF (52.83 ±â€Š5.07 mg/L), and only 3.5-fold higher than for free concentrations obtained with MD (81.37 ±â€Š26.93 mg/L). Non-linear, saturable PB binding was confirmed for both UF and MD. Significantly different dissociation constants (Kd) for the albumin/ceftriaxone complex were quantified: in UF it was 23.7 mg/L (95% CI 21.3-26.2) versus 15.9 mg/L (95% CI 13.6-18.6) in MD. Moreover, the estimated number of binding sites (95% CI) per albumin molecule was 0.916 (0.86-0.97) in UF versus 0.548 in MD (0.51-0.59). The PTA obtained with MD was at most 27% higher than with UF. CONCLUSIONS: In vitro UF versus in vivo intravasal MD revealed significantly different PB, especially during the distribution phase. The method of PB determination could have an impact on the breakpoint determination and dose optimisation of antibiotics.

Effect of the human endotoxin challenge on tedizolid tissue penetration.

The effects of the human endotoxin challenge on tissue pharmacokinetics are unknown. In the present study, we aimed to assess the effect of the endotoxin challenge on interstitial fluid pharmacokinetics of tedizolid in healthy volunteers using intramuscular microdialysis. Eight healthy male subjects were treated with 200 mg of tedizolid phosphate for 6 days. On Day 6, an intravenous bolus of lipopolysaccharide (LPS) (2 ng/kg body weight) was administered. LPS infusion did not affect plasma pharmacokinetics of tedizolid. In contrast, following LPS infusion, median muscle tissue fAUC (0.83 [0.75-1.15] vs. 1.14 [1.11-1.43] mg × h/L, P = .0078) and muscle tissue fCmax (0.15 [0.14-0.19] vs. 0.19 [0.18-0.24] mg/L, P = .0078) were significantly increased by 38% and 24%, respectively. The human endotoxin challenge was associated with increased tissue concentrations of tedizolid, without affecting its plasma concentration-time profile. The human endotoxin challenge combined with microdialysis may be used to investigate the influence of systemic inflammation on tissue pharmacokinetics.

Accelerator mass spectrometry for quantification of micro- and therapeutic-dose diclofenac in microdialysis samples.

Background: Microdialysis sampling after drug microdosing may provide tissue pharmacokinetic data early in clinical drug development. However, low administered doses and small sample volumes pose an analytical challenge, particularly for highly protein-bound drugs. Materials & methods: Carbon-14 [14C]diclofenac was used as a model drug to assess the technical and analytical feasibility of in vivo microdialysis after microdose administration in an in vitro setup. Results: [14C]diclofenac dialysate concentrations were accurately quantified with accelerator MS. [14C]diclofenac dialysate recoveries were similar in the presence and absence of therapeutic diclofenac concentrations but were considerably decreased when albumin was added to the immersion solution, suggesting high protein binding. Conclusion: These results demonstrate the feasibility of combining microdosing and microdialysis to assess tissue pharmacokinetics.

Comparison of pharmacokinetics and stability of generics of cefepime, linezolid and piperacillin/tazobactam with their respective originator drugs: an intravenous bioequivalence study in healthy volunteers.

OBJECTIVES: The efficacy and quality of generic antibacterial drug formulations are often questioned by both healthcare specialists and patients. Therefore, the present study investigated the interchangeability of generic drugs with their originators by comparing bioequivalence parameters and stability data of generic cefepime, linezolid and piperacillin/tazobactam with their respective originator drugs. METHODS: In this open-label, randomized, crossover bioequivalence study, three groups of 12 healthy volunteers each received a single intravenous infusion of either 2 g of cefepime or 4.5 g of piperacillin/tazobactam and two generic formulations, or 600 mg of linezolid and one generic formulation. Plasma sampling was performed, with a 5 day washout period between study days. Stability was tested by storing reconstituted generic and originator products according to their own storage specifications and those of the comparator products. All concentrations were measured by LC-MS. RESULTS: Similar ratios of generic/originator (90% CI) Cmax were observed for Cefepime-MIP/Maxipime [93.7 (88.4-99.4)], Cefepime Sandoz/Maxipime [95.9 (89.1-103.2)], Linezolid Kabi/Zyvoxid [104.5 (91.1-119.9)], Piperacillin Kabi/Tazobac [95.9 (90.4-101.7)], Piperacillin Aurobindo/Tazobac [99.7 (84.9-104.7)], Tazobactam Kabi/Tazobac [93.4 (87.4-99.8)] and Tazobactam Aurobindo/Tazobac [97.4 (89.7-105.8)]. Accordingly, similar ratios of AUC0-t were observed for Cefepime-MIP/Maxipime [91.1 (87.6-94.8)], Cefepime Sandoz/Maxipime [97.9 (92.5-103.5)], Linezolid Kabi/Zyvoxid [99.7 (93.3-106.6)], Piperacillin Kabi/Tazobac [92.2 (88.3-96.3)], Piperacillin Aurobindo/Tazobac [99.9 (97.0-102.8)], Tazobactam Kabi/Tazobac [91.4 (86.4-96.7)] and Tazobactam Aurobindo/Tazobac [98.8 (94.3-103.6)]. Stable and similar concentrations were measured for all contiguous substances, regardless of storage conditions. CONCLUSIONS: Compared with their respective originator drugs, generic cefepime, linezolid and piperacillin/tazobactam met the predetermined bioequivalence criteria. All formulations were stable under the storage conditions of their respective comparators.

Influence of tedizolid on the cytokine response to the endotoxin challenge in healthy volunteers: a cross-over trial.

BACKGROUND: Preclinical data suggested anti-inflammatory properties of tedizolid. OBJECTIVES: To investigate the influence of tedizolid on the cytokine response to the human endotoxin challenge and the effect of endotoxaemia on the pharmacokinetics and protein binding of tedizolid. METHODS: In this cross-over trial, 14 male healthy volunteers underwent two treatment periods: (A) 200 mg of tedizolid phosphate once daily for 6 days (3 days orally and 3 days intravenously), followed by an intravenous bolus of 2 ng/kg body weight of LPS on the last treatment day; and (B) intravenous bolus of LPS (2 ng/kg body weight) without concomitant tedizolid treatment. Participants underwent first period A or B, separated by at least 6 weeks. Plasma was sampled to assess cytokines and the pharmacokinetics of tedizolid. RESULTS: Following the endotoxin challenge, the peak plasma concentration (median [IQR]; 280 [155-502] versus 287 [132-541]  pg/mL; P = 0.875) and AUC0-24 (979 [676-1319] versus 1000 [647-1632]  pg·h/mL; P = 0.638) of interleukin-6 remained unchanged with and without concomitant tedizolid treatment. The peak concentration and AUC0-24 of TNF-α remained also unchanged with and without tedizolid (47 [31-61] versus 54 [27-69]  pg/mL; P = 0.73 and 197 [163-268] versus 234 [146-280]  pg·h/mL; P = 0.875, respectively). The total maximum concentration (mean ± SD; 2.94 ± 0.69 versus 2.96 ± 0.62 mg/L), total AUC0-24 (22.3 ± 3.8 versus 21.1 ± 3.6 mg·h/L) and protein binding (21.4% ± 1.7% versus 21.6% ± 1.9%) of tedizolid were similar with and without the endotoxin challenge. CONCLUSIONS: Tedizolid did not attenuate the LPS-induced cytokine response in healthy volunteers. Furthermore, endotoxaemia did not influence the plasma pharmacokinetics of tedizolid.

Diclofenac in vitro microdialysis study comparing different experimental set-ups to improve quantitative recovery.

Several studies investigated diclofenac tissue concentrations using microdialysis (MD). However, thorough evaluations of the optimal MD set-up for diclofenac are unavailable. Thus, this in vitro MD study aimed to compare different set-ups to improve quantitative recovery of diclofenac. In forward and reverse in vitro MD experiments with diclofenac at two concentrations (1 and 100 ng/ml), the perfusion solutions physiological saline 0.9% (PS) and human albumin 1% (HSA) were compared using tissue probes (10-mm membrane) and customized intravenous (iv) probes (30-mm membrane). Using PS, the mean relative recovery of diclofenac at 1 ng/ml was 1.6% ± 0.04% and 3.12% ± 0.00% with the tissue probe and the iv probe, respectively. The respective mean relative recovery for diclofenac at 100 ng/ml was 0.02% ± 0.01% and 0.21% ± 0.11%. Using HSA, the mean relative recovery was 314% ± 25% (tissue probe) and 1064% ± 97% (iv probe) for diclofenac at 1 ng/ml and 444% ± 91% and 1415% ± 217% for diclofenac at 100 ng/ml. In reverse dialysis using PS, the mean relative loss of diclofenac was 99.2% ± 0.5% (tissue probe) and 95.8% ± 1.7% (iv probe). Using HSA, the mean relative loss was -4.4% ± 7.2% and 0.2% ± 7.5%, respectively. PS and HSA were not suitable perfusion solutions for quantification of absolute diclofenac concentrations. Despite methodological challenges, HSA may be used for comparative experiments or bioequivalence studies.

Phase I Study to Assess Safety of Laser-Assisted Topical Administration of an Anti-TNF Biologic in Patients With Chronic Plaque-Type Psoriasis.

Ablative fractional laser treatment facilitates epidermal drug delivery, which might be an interesting option to increase the topical efficacy of biological drugs in a variety of dermatological diseases. This work aims at investigating safety and tolerability of this new treatment approach in patients with plaque-type psoriasis. Eight patients with plaque-type psoriasis were enrolled in this study. All patients received (i) ablative fractional laser microporation (AFL) of a psoriatic lesion with an Er:YAG laser + etanercept (ETA; Enbrel® solution for injection) (AFL-ETA), (ii) ETA alone on another lesion, and, if feasible, (iii) AFL alone on an additional lesion. Overall, all treatment arms showed a favorable safety profile. AFL-ETA improved the lesion-specific TPSS score by 1.75 vs. baseline, whereas ETA or AFL alone showed a TPSS score improvement of 0.75 points, a difference that was not statistically significant and might be attributable to differences in baseline scores. Topical administration of ETA to psoriatic plaques via AFL-generated micropores was generally well-tolerated. No special precautions seem necessary in future studies. Clinical benefit will need assessment in sufficiently powered follow-up studies.

Protein binding of clindamycin in vivo by means of intravascular microdialysis in healthy volunteers.

OBJECTIVES: The efficacy of an anti-infective drug is influenced by its protein binding (PB), since only the free fraction is active. We hypothesized that PB may vary in vitro and in vivo, and used clindamycin, a drug with high and concentration-dependent PB to investigate this hypothesis. METHODS: Six healthy volunteers received a single intravenous infusion of clindamycin 900 mg. Antibiotic plasma concentrations were obtained by blood sampling and unbound drug concentrations were determined by means of in vivo intravascular microdialysis (MD) or in vitro ultrafiltration (UF) for up to 8 h post dosing. Clindamycin was assayed in plasma and MD fluid using a validated HPLC-UV (ultraviolet) method. Non-linear mixed effects modelling in NONMEM® was used to quantify the PB in vivo and in vitro. RESULTS: C max was 14.95, 3.39 and 2.32 mg/L and AUC0-8h was 41.78, 5.80 and 6.14 mg·h/L for plasma, ultrafiltrate and microdialysate, respectively. Calculated ratio of AUCunbound/AUCtotal showed values of 13.9%±1.8% and 14.7%±3.1% for UF and microdialysate, respectively. Modelling confirmed non-linear, saturable PB for clindamycin with slightly different median (95% CI) dissociation constants (Kd) for the alpha-1 acid glycoprotein (AAG)-clindamycin complex of 1.16 mg/L (0.91-1.37) in vitro versus 0.85 mg/L (0.58-1.01) in vivo. Moreover, the estimated number of binding sites per AAG molecule was 2.07 (1.79-2.25) in vitro versus 1.66 in vivo (1.41-1.79). CONCLUSIONS: Concentration-dependent PB was observed for both investigated methods with slightly lower levels of unbound drug fractions in vitro as compared with in vivo.

Single-dose pharmacokinetics of temocillin in plasma and soft tissues of healthy volunteers after intravenous and subcutaneous administration: a randomized crossover microdialysis trial.

BACKGROUND: The antibiotic temocillin has recently been rediscovered as a promising therapeutic option against MDR Gram-negative bacteria. However, some aspects of the pharmacokinetic (PK) profile of the drug are still to be elucidated: subcutaneous administration of temocillin might be of interest as an alternative to the intravenous route in selected patients. Similarly, information on the penetration of temocillin into human soft tissues is lacking. OBJECTIVES: To investigate the feasibility and plasma PK of subcutaneous dosing as well as soft tissue PK of temocillin after intravenous administration to healthy volunteers. METHODS: Eight healthy volunteers received 2 g of temocillin both as intravenous and subcutaneous infusion in a randomized two-period crossover study. Concentration-time profiles of total temocillin in plasma (after both routes) and of unbound temocillin in plasma, muscle and subcutis (only after intravenous dosing) were determined up to 12 h post-dose. RESULTS: Subcutaneous dosing caused some infusion site discomfort but resulted in sustained drug concentrations over time with only slightly decreased overall exposure compared with intravenous dosing. Plasma protein binding of temocillin showed concentration-dependent behaviour and was higher than previously reported. Still, unbound drug concentrations in muscle and subcutis determined by microdialysis markedly exceeded those in plasma, suggesting good tissue penetration of temocillin. CONCLUSIONS: The subcutaneous administration of temocillin is a valid and feasible alternative to intravenous dosing. With the description of plasma protein binding and soft tissue PK of temocillin in healthy volunteers, this study provides important information that adds to the ongoing characterization of the PK profile of temocillin and might serve as input for PK/PD considerations.

High voriconazole target-site exposure after approved sequence dosing due to nonlinear pharmacokinetics assessed by long-term microdialysis.

Voriconazole, a broad-spectrum antifungal drug used to prevent and treat invasive fungal infections, shows complex pharmacokinetics and is primarily metabolised by various CYP enzymes. An adequate unbound antibiotic concentration-time profile at the target-site of an infection is crucial for effective prophylaxis or therapy success. Therefore, the aim was to evaluate the pharmacokinetics of voriconazole after the approved sequence dosing in healthy volunteers in interstitial space fluid, assessed by microdialysis, and in plasma. Moreover, potential pharmacogenetic influences of CYP2C19 polymorphisms on pharmacokinetics were investigated. The prospective, open-labelled, uncontrolled long-term microdialysis study included 9 healthy male individuals receiving the approved sequence dosing regimen for voriconazole. Unbound voriconazole concentrations were sampled over 84 h in interstitial space fluid of subcutaneous adipose tissue and in plasma and subsequently quantified via high-performance liquid chromatography. For pharmacokinetic data analysis, non-compartmental analysis was used. High interindividual variability in voriconazole concentration-time profiles was detected although dosing was adapted to body weight for the first intravenous administrations. Due to nonlinear pharmacokinetics, target-site exposure of voriconazole in healthy volunteers was found to be highly comparable to plasma exposure, particularly after multiple dosing. Regarding the CYP2C19 genotype-predicted phenotype, the individuals revealed a broad spectrum, ranging from poor to rapid metaboliser status. A strong relation between CYP2C19 genotype-predicted phenotype and voriconazole clearance was identified.

Lack of dermal penetration of topically applied gentamicin as pharmacokinetic evidence indicating insufficient efficacy.

Background: Treatment of skin and superficial soft tissue infections with topically applied antibiotics is a controversial topic, because only few clinical studies exist and target site concentrations after topical treatment are widely unknown. Objectives: This study aimed to investigate the target site concentration of topically applied gentamicin as a potential cause of therapeutic failure and to explore if microporation by laser might be used to improve penetration of gentamicin through the skin barrier. Methods: Six healthy volunteers were included in this cross-over Phase 1 study. On two study days, separated by a washout period, microdialysate and plasma sampling was performed for 6 h after administration of 500 mg of gentamicin cream on a predefined area. On one of the study days the skin was microporated before drug application using the P.L.E.A.S.E. Professional laser system. Results: In intact skin, Cmax and AUC values were 3.3 ±âŸ5.64 ng/mL and 5.4 ±âŸ10.4 ng·h/mL, respectively; thereby far under the threshold needed to treat common pathogens. With a Cmax of 474.2 ±âŸ555.3 ng/mL laser application showed a significant increase in tissue penetration and decrease in pharmacokinetic variability; however, even after microporation no therapeutically active concentrations were achieved as indicated by Cmax/epidemiological cut-off ratios of 0.237 and 0.059 for Staphylococcus aureus and Pseudomonas aeruginosa, respectively. Solely after administration on microporated skin, plasma concentrations of gentamicin were quantifiable (lower limit of quantification 10 pg/mL). Conclusions: This study confirmed that after topical administration gentamicin penetration through the dermal barrier is insufficient, providing pharmacokinetic evidence that topical gentamicin in its current form might be inappropriate to treat skin infections.

Pharmacokinetics of doripenem in plasma and epithelial lining fluid (ELF): comparison of two dosage regimens.

PURPOSE: In 2014, FDA released a warning for prescription of doripenem for ventilator-associated bacterial pneumonia due to unsatisfactory clinical cure rates. The present study explores if the observed lack of efficacy might be explained by insufficient target site pharmacokinetics in intensive care patients after two different infusion schemes. METHODS: Plasma and bronchoalveolar lavage sampling was performed in 16 intubated patients with pneumonia receiving doripenem either as 1-h or as 4-h infusion. Doripenem concentrations were measured at steady state in plasma over 8 h, bronchoalvoelar lavage was performed in each patient once either after 0 h, 2 h, 4 h or 6 h. RESULTS: In plasma, mean values of Cmax, Tmax and AUC0-8 were 16.87 mg/L, 0.69 h and 52.98 mg/L×h after 1 h of infusion, and 12.94 mg/L, 3.21 h and 70.64 mg/L×h after 4 h of infusion, respectively. While the later tmax in plasma was with delay mirrored in the lung, for ELF, much lower concentrations were observed (Cmax, Tmax and AUC0-8 after 1-h infusion of 4.6 mg/L, 2 h and 15.3 mg/L×h and after 4-h infusion 6.9 mg/L, 4 h and 14.8 mg/L×h). CONCLUSION: The difference in plasma pharmacokinetics after 1-h and 4-h infusion reflects in the concentration versus time profile in the lung, but concentration at the target site was not only considerably lower but also subject to high inter-individual variability. We hypothesise that insufficient concentrations at the target site might have contributed to the previously described lack of clinical efficacy and confirmed the demand for assessment of target site pharmacokinetics in larger patient collectives.

Tissue pharmacokinetics of telavancin in healthy volunteers: a microdialysis study.

BACKGROUND: Telavancin is a novel lipoglycoprotein antibiotic with MRSA activity. To date, tissue pharmacokinetics (PK) and plasma protein binding of the drug are insufficiently described. OBJECTIVES: To investigate tissue PK and plasma protein binding of telavancin in healthy volunteers. METHODS: Eight male healthy subjects received a single dose of 10 mg/kg of body weight of telavancin as an intravenous infusion over 1 h. At defined timepoints before and up to 24 h after treatment, total telavancin concentrations were measured in plasma. Additionally, unbound telavancin levels were determined in plasma, muscle and subcutis by means of microdialysis. RESULTS: Key PK parameters of total telavancin in plasma were in good agreement with previously described values. Mean ±â€ŠSD Cmax and calculated AUC0-24 of free telavancin in plasma were 13.8 ±â€Š7.8 mg/L and 82.9 ±â€Š34.3 mg·h/L, respectively. Unbound drug levels in plasma ranged from 13.2% to 24.8% of corresponding total telavancin. Mean ±â€ŠSD Cmax and AUC0-24 of unbound telavancin were 4.3 ±â€Š1.5 mg/L and 61.5 ±â€Š27.1 mg·h/L for muscle and 3.4 ±â€Š1.8 and 50.0 ±â€Š29.8 mg·h/L for subcutis, respectively. Relevant PK/pharmacodynamic indices were calculated for total and unbound drug. CONCLUSIONS: This study provides important information on soft tissue PK and plasma protein binding of telavancin in healthy volunteers. Unbound plasma concentrations above levels assumed from previously available data and sustained free drug exposure in soft tissues support the current mode of administration.

Single- and Repeated-Dose Pharmacokinetics of Ceftaroline in Plasma and Soft Tissues of Healthy Volunteers for Two Different Dosing Regimens of Ceftaroline Fosamil.

Ceftaroline fosamil (CPT-F) is currently approved for use for the treatment of complicated skin and soft tissue infections and community-acquired pneumonia at 600 mg twice daily (q12h), but other dosing regimens are under evaluation. To date, very limited data on the soft tissue pharmacokinetics (PK) of the active compound, ceftaroline (CPT), are available. CPT concentrations in the plasma, muscle, and subcutis of 12 male healthy volunteers were measured by microdialysis after single and repeated intravenous administration of 600 mg CPT-F q12h or three times daily (q8h) in two groups of 6 subjects each. Relevant PK and PK/pharmacodynamic (PD) parameters were calculated and compared between groups. In plasma, the area under the concentration-time curve (AUC) from 0 to 24 h for total CPT and the cumulative percentage of the dosing interval during which the free drug concentrations exceeded the MIC (fTMIC) for unbound CPT for the currently established threshold of 1 mg/liter were significantly higher in the group receiving CPT-F q8h. Exposure to free drug in soft tissues was higher in the group receiving CPT-F q8h, but high interindividual variability in relevant PK parameters was observed. The mean ratios of the AUC from time zero to the end of the dosing interval (AUC0-τ) for free CPT in soft tissues and the AUC0-τ for the calculated free fraction in plasma at steady state ranged from 0.66 to 0.75. Administration of CPT-F q8h led to higher levels of drug exposure in all investigated compartments. When MIC values above 1 mg/liter were assumed, the calculated fTMIC after dosing q12h was markedly lower than that after dosing q8h. The clinical implications of these differences are discussed in light of recently completed clinical phase III and PK/PD studies.

Iontophoresis driven concentrations of topically administered diclofenac in skeletal muscle and blood of healthy subjects.

PURPOSE: The present open single-centre, descriptive and comparative pharmacokinetic study aimed to investigate the efficacy of iontophoresis to enhance transdermal delivery by measuring concentration vs. time profiles of diclofenac in local tissue and in plasma in two separate study periods. METHODS: Period 1 determined diclofenac concentrations in both calf muscles simultaneously by using microdialysis after applying diclofenac gel topically as a single dose of 5 g with or without iontophoresis in eight healthy volunteers. In period 2, the same dose was applied to another 8 volunteers to determine plasma concentrations of diclofenac either with or without iontophoresis in a cross over design. RESULTS: In period 1, tissue concentrations were found to be under the limit of detection of 0.5 ng/ml both with and without iontophoresis in all subjects. In period 2, after iontophoresis in 75% of study participants, plasma concentrations of diclofenac could be determined, but only in 25% without iontophoresis. Although area under the concentration-time-curve (AUC, 187.97 ± 315.92 vs. 22.92 ± 42.44 ng*min/ml) and maximum concentration (Cmax, 2.06 ± 3.79 vs. 0.22 ± 0.41 ng/ml) values showed a numerically clear trend for higher values with iontophoresis compared to passive diffusion, no significant difference could be found due to high inter-individual variability. In total, 18.75% of all subjects presented adverse events. CONCLUSIONS: Despite a higher percentage of subjects showed detectable plasma levels of diclofenac after iontophoresis, iontophoresis failed to achieve potentially more effective topical concentrations. The typical mechanism of iontophoresis like electromigration, electroosmosis and increased subcutaneous circulation could be responsible for the results of the present observation. Additional clinical studies are needed to justify the transdermal delivery of diclofenac by using iontophoresis.

Feasibility of microdialysis for determination of protein binding and target site pharmacokinetics of colistin in vivo.

Tissue pharmacokinetics and plasma protein binding of colistin have not been described in humans in vivo. Colistin concentrations in plasma, muscle, and subcutis of healthy volunteers were measured by microdialysis after a single dose of 2.5 million IU of colistin methanesulfonate. In vitro microdialysis experiments and an in vivo pilot study were performed prior to the in vivo main study. Concentration-time profiles of total colistin in plasma were comparable with previously described values. The unbound fraction of colistin in plasma (f(u)) ranged from 2.8% to 14.1%. Low plasma f(u) correlated with low unbound colistin concentrations in muscle and subcutis. In vitro, mean relative recovery of microdialysis probes was higher in the reverse dialysis setting compared to the forward dialysis mode (71 ± 9% vs. 45 ± 14%, respectively); mean overall recovery in the main study in vivo was 49 ± 5%. Present data suggest that colistin is extensively protein bound in plasma and poorly distributed into soft tissue. However, differences in relative recovery between forward and reverse dialysis in vitro indicate that results might have been influenced by adhesion of colistin to microdialysis equipment. Microdialysis should be considered as a semiquantitative method for the estimation of unbound colistin levels in soft tissue.

Magnetic resonance imaging analysis of the spread of local anesthetic solution after ultrasound-guided lateral thoracic paravertebral blockade: a volunteer study.

BACKGROUND: This study was designed to examine the spread of local anesthetic (LA) via magnetic resonance imaging after a standardized ultrasound-guided thoracic paravertebral blockade. METHODS: Ten volunteers were enrolled in the study. We performed ultrasound-guided single-shot paravertebral blocks with 20 ml mepivacaine 1% at the thoracic six level at both sides on two consecutive days. After each paravertebral blockade, a magnetic resonance imaging investigation was performed to investigate the three-dimensional spread of the LA. In addition, sensory spread of blockade was evaluated via pinprick testing. RESULTS: The median (interquartile range) cranial and caudal distribution of the LA relative to the thoracic six puncture level was 1.0 (2.5) and 3.0 (0.75) [=4.0 vertebral levels] for the left and 0.5 (1.0) and 3.0 (0.75) [=3.5 vertebral levels] for the right side. Accordingly, the LA distributed more caudally than cranially. The median (interquartile range) number of sensory dermatomes which were affected by the thoracic paravertebral blockade was 9.8 (6.5) for the left and 10.7 (8.8) for the right side. The sensory distribution of thoracic paravertebral blockade was significantly larger compared with the spread of LA. CONCLUSIONS: Although the spread of LA was reproducible, the anesthetic effect was unpredictable, even with a standardized ultrasound-guided technique in volunteers. While it can be assumed that approximately 4 vertebral levels are covered by 20 ml LA, the somatic distribution of the thoracic paravertebral blockade remains unpredictable. In a significant percentage, the LA distributes into the epidural space, prevertebral, or to the contralateral side.

Pilot investigation on long-term subcutaneous microdialysis: proof of principle in humans.

Reliable drug concentration measurements at the target site are increasingly demanded and can be achieved by microdialysis. The aim of this pilot study was to demonstrate the proof of principle of long-term subcutaneous microdialysis in humans. For long-term microdialysis, a special setting implementing both concentric and linear catheters has been developed ensuring good clinical practice compliance, tolerability, and convenience for participants and personnel. As a model compound, moderately lipophilic voriconazole was selected as a well-characterized drug in in vitro microdialysis experiments. Multiple in vivo relative recovery (RR) determinations for microdialysis were performed by retrodialysis during the entire study (n = 48 samples). Continuous microdialysis was successfully applied and well tolerated over 87 h in three adults for the first time. RR revealed low intra-individual (coefficient of variation (CV) = 4.4-12.5%) and inter-individual variability (CV = 4.3-12.5%) across all samples and catheters. Lower RR values were consistently determined for linear catheters. One catheter leakage was managed without an impact on the reliability of the RR values. Overall, RR values were calculated to be 73.3% (linear: CV = 18.5%, n = 23) and 84.9% (concentric: CV = 5.6%, n = 23). Long-term microdialysis application over almost 4 days was feasible by reliable multiple RR (proof of principle), well tolerated, and reduced the burden in humans avoiding several catheter insertions, thereby allowing to monitor concentration-time courses continuously. Moreover, a moderately lipophilic drug has been proven suitable for in vivo microdialysis, as previously suggested by in vitro microdialysis.