|Spare the needle and save the eye|
|Thursday, 09 September 2010|
Singh RP, Mathews ME, Kaufman M, Riga A. Transscleral delivery of triamcinolone acetonide and ranibizumab to retinal tissues using macroesis. Br J Ophthalmol 2010; 94: 170-3.
In a nutshell
This article appears in the ‘Innovations’ section of the British Journal of Ophthalmology. Two pre-clinical studies are described, using two drugs commonly injected into the eyeball.
The first simply examined tissue conductivity. A full thickness sample of rabbit ocular wall (conjunctiva to retina) was placed on a gold and ceramic single-surface interdigitated electrode and the change in tissue conductivity secondary to the presence of the drug was measured.
In the second, a simulated vitreous cavity was created by placing ocular tissue over a well of saline. The same electrode was then placed on the tissue and the drugs triamcinolone and ranibizumab were placed on the electrode. The drug passed through the interdigitations in the electrode to reach the ocular tissue, and an alternating current electrical field caused the drug molecules to align in such a way that transport across the tissue was facilitated. The concentration of drug in the saline was then measured.
The second study showed that compared with a 0.05ml intraocular injection of ranibizumab, 92.8% of such a dose could be transported into the eye in six minutes and 42 seconds using macroesis.
Look up ‘Macroesis’ in any dictionary or medical text, including PubMed, and you will find that it is a trademark-protected neologism, describing the application of an electromotive force to first align drug molecules or ions and then transport them through the sclera into the eye. The authors of this article are either employees of, or consultants to, Buckeye Ocular LLC, Cleveland, Ohio, where the research was carried out. Macroesis is based on the well-established principle of iontophoresis, in which a weak electrical current is used to stimulate drug-carrying ions to pass through intact skin.
Publicity for a potentially important medical device aside, this article describes a method of drug administration which could revolutionise the use of anti-vascular endothelial growth factor (VEGF) drugs. Intraocular injections of the commonest anti-VEGF, ranibizumab, currently consume huge amounts of funds, and theatre and consultant time, in all health board areas across the UK. Risks of injection include endophthalmitis, haemorrhage, and retinal detachment. Macroesis could be performed in a clinic room or even in the patient’s own home, effectively and with minimal risk.