Sonophoresis
Sonophoresis also known as phonophoresis, is a method that utilizes ultrasound to enhance the delivery of topical medications through the stratum corneum, to the epidermis and dermis.
Sonophoresis allows for the enhancement of the permeability of the skin along with other modalities, such as iontophoresis, to deliver drugs with lesser side effects.
[1] This report showcased that a hydrocodone injection yielded better outcomes for bursitis when combined with an ultrasound massage.
[2] Following this, a series of publications from several investigators showed the increased therapeutic effect when combining ultrasound with hydrocortisone injections for various other disease states, further demonstrating the novelty of sonophoresis.
[2] These early studies mainly investigated the combination of therapeutics with high-frequency sonophoresis (HFS), which can be categorized into frequencies greater than 0.7 MHz.
[1] Cavitational effects are inversely proportional to the frequency of the ultrasound applied, which led to further studies of low-frequency sonophoresis (LFS) for use in transdermal drug delivery due to studies showing greater efficacy in enhancing skin permeability in comparison to HFS.
The primary purpose of phonophoresis is to assist in transdermal drug delivery, usually with the help of a coupling agent or medium.
Similarly, the gas bubble will dramatically decay in size when encountering the other positive half of the pressure cycle.
[1] Two factors are increased kinetic energy and diffusivity of drugs, which allow for compounds to pass through the stratum corneum.
The enhanced circulation of blood that comes as a result of increased temperature from ultrasound parameters also allows for better diffusion of compounds.
Thermal effects need to be minimized at higher amplitudes, as burns and necrosis of tissues can occur due to exposure to high, sustained temperatures.
[1] A simple solution to counteract sustained exposure to high temperatures is to periodically replace the coupling agent every so often.
[2] Iontophoresis is similar to sonophoresis as it is a method for transdermal drug delivery but does so by applying a voltage gradient across the skin.
By applying short, high voltage pulses to the stratum corneum, the lipid structure will become disorganized and allow enhancement of drug delivery.
[9] In a 2019 study, they used the drug diclofenac in coordination with thiocolchioside gel to treat patients who suffer from acute lower back pain.
[1] With its credible safety and useful ability in penetrating the stratum corneum, HFS remains an incredibly versatile option for delivering drugs topically.
Since LFS is not restricted by its ability to deliver molecules of varying sizes, drugs such as proteins, nanoparticles, and vaccines are all possible targets.
[22] In previous literature, it has been demonstrated that ocular delivery of drugs can be achieved with high efficacy and minimal invasion.
With 20 kHz ultrasound waves at an average temporal intensity of 2 W/cm^2applied every second, the permeability of drugs with varying lipophilicity were investigated, such as atenolol and carteolol, increased by 2.6 and 2.8-fold respectively.
Since there exists a need to enhance gene transfer into cells, sonophoresis has the ability to achieve higher transfection rate through acoustic cavitation.
