Quantification of dermal and transdermal delivery of meloxicam gels in rabbits.

BACKGROUND: This study was designed to quantify the effects of penetration enhancers on systemic bioavailability of 0.3% meloxicam (MLX) hydroxypropylcellulose gels. Cutaneous microdialysis was also performed to assess dermis availability and to better understand the penetration process. The gels tested were a 1% oleic acid gel, a 5% menthol gel, and a control gel without penetration enhancers. METHODS: To assess systemic bioavailability, three female rabbits received according to a crossover design 0.135 g/cm(2) of gel applied to a 7.5 × 7.5 cm area of their shaved back and a short (5 min) infusion of 1 mg. In each experiment, blood samples were collected serially for 36 h and analyzed by a validated HPLC method. For skin bioavailability studies, 0.135 g/cm(2) of the same gels were applied to a 1 × 2 cm area on top of a microdialysis probe previously inserted in the dermis. Dialysate samples were collected for 6 h every 30 min. RESULTS: Systemically, the 5% menthol gel delivered 3.93 ± 0.85 mg of MLX versus the 1.41 ± 0.24 mg of the oleic acid gel. Only traces of MLX were detectable from the control gel. In dermis, substantial concentrations of MLX were detected only after the application of the menthol gel, whereas skin concentration from the control gel and the 1% oleic acid gel were always below the lowest limit of quantification (LLOQ). CONCLUSIONS: The 5% menthol gel can possibly deliver therapeutically relevant amount of MLX in vivo. Dermis concentrations can be predictive of systemic plasma levels.

Quantification and prediction of skin pharmacokinetics of amoxicillin and cefuroxime.

The purpose of this project was to develop and validate a pharmacokinetic model and to quantify the rate and extent of distribution between plasma and skin of two beta-lactam antibiotics, amoxicillin (AMX) and cefuroxime (CFX), which are frequently administered systemically to treat skin and skin structure infections. Dosing regimens are usually based on plasma concentration, however, concentrations at the target site are better correlated with the effect. For each antibiotic, three different i.v. bolus doses were administered to three female rabbits according to a randomized cross-over design and plasma samples were collected serially. Skin concentrations were obtained by continuous microdialysis. Skin and unbound plasma concentrations were fitted simultaneously using a semi-physiological model and the transfer constants plasma/skin (K(in)) and skin/plasma (K(out)) were estimated. K(in) and K(out) were then used to predict skin concentrations from the plasma levels obtained from an oral administration of AMX or from an i.v. bolus of CFX. The predicted skin profiles were similar to those measured by microdialysis during the actual experiments. In conclusion, this study shows that it is possible to generate a reasonable prediction of skin pharmacokinetics from any plasma level once a careful characterization of the transfer process between plasma and skin has been made.

Skin microdialysis-based estimation of systemic bioavailability fraction.

Systemic bioavailability is usually determined from plasma data. However, when plasma is difficult to access, as in young children, alternative methods would be particularly beneficial. The present study investigates the possibility of calculating systemic bioavailability fraction (F) from skin concentrations measured by two microdialysis (MD) sampling methods: continuous microdialysis and intermittent microdialysis. When the drug concentration in skin is a linear and time-invariant function of plasma concentration, the area under the drug concentration curve in skin is directly proportional to the drug absorbed systemically. To verify this theory, we compared the F estimated from MD concentrations in the skin with that obtained from the plasma data in the same experiment. Two model drugs were selected for the study: amoxicillin and ketoprofen. Drugs were administered to rabbits as intravenous infusion or oral suspension according to a randomized crossover design. F estimated by either MD method was not significantly different from that obtained from the plasma for both drugs tested. However, the skin data exhibited a larger variability. These results confirm that skin MD could be an alternative way to obtain data for the calculation of systemic fraction of drug absorbed.

In vivo quantification of acyclovir exposure in the dermis following iontophoresis of semisolid formulations.

The objective was to quantify acyclovir (ACV) exposure in the dermis following iontophoresis of nontraditional (pH-11 gels) and traditional (neutral cream) topical formulations of ACV. Given that the application time of a formulation on the skin can be significantly reduced with iontophoresis, the use of formulations optimized for iontophoretic delivery was explored to maximize the delivery of ACV to the site of action for the treatment of Herpes-labialis. Microdialysis probes were inserted into the shaved skin of tranquilized rabbits. Iontophoresis was performed at a constant current density of 200 microA/cm(2) for 60 min using a single-use drug cartridge filled with the following formulations: neutral cream, soluble fraction of the same cream (anodal and cathodal-current), or two formulations of pH-11 gels, one without and one with stabilizers and preservatives (cathodal-current). Results showed that only the ACV in the water phase of the cream is available for transport. All of the pH-11 gels exhibited a statistically significant (p < 0.001) increase in ACV dermis exposure compared to the neutral cream formulations without any additional sign of skin irritation. In conclusion, iontophoresis of ACV pH-11 gels provides higher ACV concentrations in the dermis than iontophoresis of neutral cream formulations, which could result in a better clinical outcome.