Assessment of topical bioequivalence using dermal microdialysis and tape stripping methods.

PURPOSE: To assess the bioequivalence of two commercial topical formulations of oxytetracycline HCl by tape stripping and microdialysis in healthy volunteers. METHODS: Tape stripping study was conducted on 12 healthy volunteers. After a 30-minute application of the formulations, adhesive tapes were used to sample stratum corneum at 0.25, 0.5, 1, 1.5, 2, 3, 4 hr. Ten of these volunteers were included in the microdialysis study with a period of 4 weeks between the experiments. Microdialysis probes were inserted into the dermis of the forearm. Following the application of the test and reference simultaneously, dialysates were collected in 30-minute sampling intervals up to 4 hr. RESULTS: Pharmacokinetic evaluation by microdialysis yielded that the test could not be said to be bioequivalent to the reference at 90% CI. The intersubject variability of oxytetracycline content in stratum corneum was moderate when it was compared to the dermal levels. The test was found to be bioequivalent to reference according to the dermatopharmacokinetic evaluation by tape stripping. CONCLUSIONS: No significant correlations were found between microdialysis and tape stripping methods as regarding the topical bioequivalence of oxytetracycline HCl formulations.

Comparison of plasma and saliva concentrations of lamotrigine in healthy volunteers.

The relationship between lamotrigine (CAS 84057-84-1) concentrations in saliva and plasma in healthy volunteers were examined, as well as the possibility of using saliva to monitor levels for effective therapy. The study was performed with 14 healthy volunteers, mean age 23 +/- 2 (SD) years. After single oral doses of 200 mg, plasma and stimulated saliva samples were collected simultaneously at 0, 0.25, 0.5, 1, 2, 4, 6, 8, 10, 12, 24, 48, 72 and 96 h. The pH values of saliva samples were recorded. Lamotrigine concentrations were determined by a validated HPLC method. Fraction of drug bound to plasma proteins was calculated mathematically by the modified Henderson-Hasselbalch equation. Linear regression was used to evaluate the correlations. The remnant of orally administered drug contaminated the saliva samples and gave spuriously high values for up to 2 h, which were omitted. There was significant correlation (r2 = 0.677, p < 0.0001) between plasma and saliva concentrations from 2-96 h after administration. The mean ratio of saliva to plasma concentration was 0.426 +/- 0.153 (mean +/- SD). Protein binding, calculated from the concentrations in saliva was 57.5 +/-15.1% (mean +/- SD). Noncompartmental analysis was conducted with the program Kinetica. Plasma t1/2 and MRT were not significantly different from those found from saliva. The mean values of lamotrigine peak saliva concentrations (C(max)), areas under the curve of concentration versus time from zero to infinity (AUC(0-->infinity)), and areas under the curves of the product of time and concentration versus time from zero to infinity (AUMC(0-->infinity) were proportionally lower than in plasma. The results support the use of saliva concentration as a convenient, painless and noninvasive alternative to plasma for monitoring lamotrigine therapy.

Nonisothermal stability tests of famotidine and nizatidine.

Nonisothermal stability tests have been proposed as an attractive and alternative method to the conventional isothermal stability tests. The stability and the degradation properties of famotidine and nizatidine were investigated using both isothermal and nonisothermal stability test techniques. Linear and logarithmic temperature programs were used and the degradation rate constant and activation energies were calculated using a computer program, which was written in BASIC. Also the advantages and disadvantages of these temperature programs are compared. The method to estimate parameters is based on nonlinear curve fitting the nonisothermal concentration-time-temperature curve equation. The nonisothermal stability test results were compared with the results of isothermal stability tests and similar results were obtained.