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

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.

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 ± 5.64 ng/mL and 5.4 ± 10.4 ng·h/mL, respectively; thereby far under the threshold needed to treat common pathogens. With a Cmax of 474.2 ± 555.3 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.

Selected Medicines Used in Iontophoresis

Iontophoresis is a non-invasive method of systemic and local drug delivery using an electric field. Iontophoresis enables diffusion of the selected drug via skin, mucosa, enamel, dentin, and other tissues. The amount of delivered therapeutic molecules is about 10⁻2000 times greater than conventional forms of delivery. Among other fields, this method is used in dentistry, ophthalmology, otorhinolaryngology, and dermatology. According to related literature, the most important drugs studied or administered by iontophoresis are: Local anesthetics, opioids, steroids, non-steroidal anti-inflammatory drugs, antibacterial drugs, antifungal drugs, antiviral drugs, anticancer drugs, fluorides, and vitamins. The present review covers current available data regarding the selected medicines used in iontophoresis. Furthermore, indications and conditions of iontophoresis application are reviewed.