Transdermal delivery of levonorgestrel

Improved Topical Drug Delivery: Role of Permeation Enhancers and Advanced Approaches

The delivery of drugs via transdermal routes is an attractive approach due to ease of administration, bypassing of the first-pass metabolism, and the large skin surface area. However, a major drawback is an inability to surmount the skin's stratum corneum (SC) layer. Therefore, techniques reversibly modifying the stratum corneum have been a classical approach. Surmounting the significant barrier properties of the skin in a well-organised, momentary, and harmless approach is still challenging. Chemical permeation enhancers (CPEs) with higher activity are associated with certain side effects restricting their advancement in transdermal drug delivery. Furthermore, complexity in the interaction of CPEs with the skin has led to difficulty in elucidating the mechanism of action. Nevertheless, CPEs-aided transdermal drug delivery will accomplish its full potential due to advancements in analytical techniques, synthetic chemistry, and combinatorial studies. This review focused on techniques such as drug-vehicle interaction, vesicles and their analogues, and novel CPEs such as lipid synthesis inhibitors (LSIs), cell-penetrating peptides (CPPs), and ionic liquids (ILs). In addition, different types of microneedles, including 3D-printed microneedles, have been focused on in this review.

Overcoming the Stratum Corneum: The Modulation of Skin Penetration

It is preferred that topically administered drugs act either dermally or transdermally. For that reason they have to penetrate into the deeper skin layers or permeate the skin. The outermost layer of the human skin, the stratum corneum, is responsible for its barrier function. Most topically administered drugs do not have the ability to penetrate the stratum corneum. In these cases modulations of the skin penetration profiles of these drugs and skin barrier manipulations are necessary. A skin penetration enhancement can be achieved either chemically, physically or by use of appropriate formulations. Numerous chemical compounds have been evaluated for penetration-enhancing activity, and different modes of action have been identified for skin penetration enhancement. In addition to chemical methods, skin penetration of drugs can be improved by physical options such as iontophoresis and phonophoresis, as well as by combinations of both chemical and physical methods or by combinations of several physical methods. There are cases where skin penetration of the drug used in the formulation is not the aim of the topical administration. Penetration reducers can be used to prevent chemicals entering the systemic circulation. This article concentrates on the progress made mainly over the last decade by use of chemical penetration enhancers. The different action modes of these substances are explained, including the basic principles of the physical skin penetration enhancement techniques and examples for their application.

Levonorgestrel and 17beta-estradiol given transdermally for the prevention of postmenopausal osteoporosis

AIM

To evaluate the efficacy and safety of a new transdermal continuous combined hormone replacement therapy (HRT) for the prevention of postmenopausal osteoporosis.

METHODS

212 osteopenic (lumbar spine and/or hip (femoral neck) bone mineral density (BMD) between -1.0 and -2.5 S.D. of the premenopausal mean value) postmenopausal women aged 45-65 years participated in a 2-year prospective study. Treatments were 45 microg 17beta-estradiol combined with 30 (n = 69) or 40 microg (n = 72) levonorgestrel daily or placebo (n = 71) given as a 7-day patch. All received a daily supplement of 500 mg calcium. BMD at lumbar spine (L2-L4), hip and total body, as well as blood and urinary biochemical markers of bone turnover (serum osteocalcin (sOC), serum bone-specific alkaline phosphatase (sBSAP), urinary calcium (uCa) and urinary CrossLaps (uCTX)) were measured regularly.

RESULTS

BMD at the lumbar spine, hip and total body increased by 8, 6 and 3% (P < 0.001), respectively, in the hormone groups versus placebo. The bone markers all decreased accordingly (sOC: 37%, sBSAP: 34% and uCTX: 65% from baseline (all P < 0.001)), except for uCa that did not change significantly. No significant dose-related effect of levonorgestrel was found. Vaginal bleeding/spotting decreased from 48 to 25% of the HRT-treated women during the study period. Skin tolerance was good in 84% of the women with no difference between the study groups. No incidences of endometrial hyperplasia, uterine or mammary cancer occurred.

CONCLUSION

The transdermal combination of 17beta-estradiol and levonorgestrel has a positive effect on BMD in an osteopenic postmenopausal population. Furthermore, a high safety profile was observed.