Transdermal Therapeutic Systems for the Treatment of Alzheimer's Disease: A Patent Review

Two classes of medications are used to treat Alzheimer's disease (AD); donepezil, galantamine, and rivastigmine are acetylcholinesterase inhibitors, and memantine is a non-competitive antagonist of the N-methyl-D-aspartate receptor. Although these are typically taken orally, there are transdermal therapeutic systems (TTSs) commercially available for rivastigmine and donepezil. The transdermal route has been preferable for guardians/caregivers due to ease of use, reduced side effects, and improved adherence to therapy.

The study aimed to obtain knowledge of the properties of these drugs and to search for patents relating to the TTS for AD using the Espacenet platform.

The search terms were "rivastigmine AND transdermal AND skin delivery AND Alzheimer's", changing the drugs "memantine", "donepezil", and "galantamine", between January 2015 and January 2022. Title and abstract were used to choose patents.

TTSs present some limit factors in terms of absorption due to skin physiology and the size of the molecules with established limits of percutaneous penetration (molecular mass of 500 g/mol and log P of 5). We found 1, 4, 4, and 2 patents for galantamine, rivastigmine, donepezil, and memantine, respectively. Galantamine TTS seems to be more challenging due to the molecular mass of 287.35 g/mol and logP of 1.8. The permeator of absorption is necessary. Memantine, rivastigmine, and donepezil present logP of 3.28, 2.3, and 4.27 and molecular weights of 179.30, 250.34, and 415.96 g/mol, respectively.

TTSs are primarily effective for delivering small molecules. The use of absorption enhancers and irritation mitigators can be necessary to enhance the performance. The development of these technologies is essential for the convenience of patients and caregivers.