Comparative bioequivalence studies with Estradot® and Menorest® transdermal systems

Estradiol matrix patches for pubertal induction: stability of cut pieces at different temperatures

OBJECTIVE

Transdermal estradiol patches are primarily designed for adult women. No low-dose patches are licensed for pubertal induction in hypogonadal girls. Low doses can be achieved by cutting a matrix patch into smaller pieces. However, the manufacturers do not guarantee stability or utility of cut estradiol patches. The aim of the study was to assess 1-month stability of cut estradiol patches from four different manufacturers in the laboratory at room temperature (+21°C) and at an elevated temperature (+35°C).

DESIGN AND METHODS

Estraderm MX 50 µg, Systen 50 µg and Oesclim 25 µg matrix patches were cut into eight pieces while Estradot 50 µg small patches were cut in half. The cut patches were stored in their respective pouches at +21°C or at +35°C for up to 1 month. The estradiol drug was extracted from the patch by ethyl acetate n-hexane and determined by radioimmunoassay.

RESULTS

Storage at +21°C or +35°C up to 1 month did not reduce the estradiol concentration in Estraderm MX, Systen and Oesclim patches. However, although the estradiol in Estradot patches was not affected by storage at +21°C, at +35°C, estradiol decreased by 57% (±1%) in cut pieces.

CONCLUSIONS

Unused Estraderm MX, Systen and Oesclim patch pieces may be stored for at least 1 month at ≤+35°C. Where estradiol patches for children are not available, cut pieces of these or similar patches can be used for pubertal induction. The Estradot patch was too small to properly cut into low doses and not stable in elevated temperatures.

Interindividual variation in transdermal and oral drug deliveries

It is generally assumed that the topical absorption of drugs is subject to more interindividual variation than the oral absorption of drugs. To date, we are unaware of any clinical studies or meta-analyses that compare the interindividual variation of transdermal and oral drug deliveries for a large number of medications. In this research article, the absorption data for 10 medications that can be used as an oral medication or a transdermal patch were compiled, and from the collected data, the interindividual variance was calculated for topical and oral absorption as an overall average and by drug. This research article also briefly reviews the pharmacokinetics and pharmacodynamics of transdermal and oral drug absorption. Our results indicate that there is considerable interindividual variation in topical and oral absorption for the 10 medications investigated. Yet, surprisingly, the calculated overall mean and median coefficient of variation (CV) for topical and oral absorption were comparable (within 10% of each other). Therefore, the interindividual variation in topical and oral absorption may not be as divergent as assumed previously. In a drug-by-drug comparison, certain medications demonstrated considerably more variation when absorbed orally versus topically and vice versa. It is unclear why certain drugs had less variation in absorption when delivered topically versus orally (or vice versa). However, patterns in drug molecular weight (MW) or octanol partition coefficient (log K(OCT) ) could not totally explain these findings. In our analysis, the previously reported correlation between MW or log K(OCT) and interindividual variation in absorption could only be replicated when plotting the topical absorption CV and MW. What became clear from our analysis is that the drug itself is an important variable when considering which route of delivery (oral or topical) will provide the least amount of interindividual variation. Our study had many limitations because of study design, which may have affected our calculations and conclusions. Further experimentation is needed to support and reveal the basic science of skin or drug chemistry that can further explain these findings.

New hormonal therapies and regimens in the postmenopause: routes of administration and timing of initiation

Since the publication of the Women's Health Initiative (WHI) study followed by the results of the Million Women Study (MWS), the role of hormonal therapy in postmenopausal women has been further challenged. The risks attributed to hormone therapy have been overestimated and the data has been wrongly extrapolated to the whole class of therapies. The trends in postmenopausal hormonal therapy seem now to favor the non-oral delivery routes for both the estrogen and the progestin for women with an intact uterus, based on the assumption that a lesser stimulation of the liver proteins and a neutral metabolic profile would be more favorable in terms of cardiovascular and venous risk. The combination of non-oral administration of estradiol and local delivery of progesterone or a progestin such as levonorgestrel by means of gels, sprays, vaginal rings or intrauterine systems would represent new methods of replacement therapy for the menopausal woman, improving compliance and minimizing the risks of hormone replacement. Several of these systems are either available or in development. Long-term studies on the risk/benefit of various non-oral formulations are certainly warranted.

Transdermal drug pharmacokinetics in man: Interindividual variability and partial prediction

A database of human dermatopharmacokinetic parameters of 12 transdermal patches is established. The effect of system design, application site, and metabolism on pharmacokinetic data is discussed, and interindividual variability of data and its possible sources evaluated. Using multiple regression analysis, two equations based on drugs physicochemical characteristics are suggested for partial prediction of peak plasma concentration (C(max)) after patch application. Patch application presumably decreases variance as rub-off, wash and exfoliation steps are diminished. The results showed that interindividual variation, in terms of coefficient of variation (CV) of C(max), is inversely correlated with drugs molecular weight and lipophilicity in the range of 200<MW<400 and 1.6<logK(oct)<4.3. Multiple regression analysis of C(max) against physichochemical parameters demonstrated the prominent contribution of hydrogen bonding acceptability of the molecules on their maximal plasma concentration after patch administration. The findings suggest that the serum concentration profile for transdermal therapeutic systems (TTS) is a net result of the system performance, drug absorption and elimination. Thus, the variability in serum concentration is a function of variability of each process involved. This should be noted in explanation of effect of molecular features of drugs on their plasma concentration profile.