Ocular penetration of hetrazan in rabbits

Ocular findings in a double-blind study of ivermectin versus diethylcarbamazine versus placebo in the treatment of onchocerciasis

The effect of ivermectin, a new microfilaricide, was assessed in a double blind trial against diethylcarbamazine citrate (DEC) and placebo. Fifty-nine adult males with moderate to heavy infection with Onchocerca volvulus and with eye involvement were recruited from an area under Onchocerciasis Control Programme (OCP) vector control in Northern Ghana. They were randomly assigned to an eight-day treatment with ivermectin as a single dose of 12 mg on day 1 followed by placebo for the remaining seven days, or DEC, total dose 1.3 g, or placebo, and ophthalmological review was undertaken over a period of one year. DEC acted quickly to eliminate microfilariae from the eye and was associated with reactive ocular changes and in a few cases functional deficit. Ivermectin eliminated microfilariae slowly from the anterior chamber of the eye over a period of six months. The ocular inflammatory reaction was minimal and no functional deficit occurred. It is postulated that the observed slow action of ivermectin on the eye may be attributed in part to its instability to cross the blood-aqueous humour barrier because of its molecular size as a macrocyclic lactone causing microfilariae to leave the eye gradually along a newly created gradient. Ivermectin is an effective microfilaricide with minimal ocular adverse effect and could therefore be suitable for widespread application without strict supervision.

Effects of various concentrations of diethylcarbamazine citrate applied as eye drops in ocular onchocerciasis, and the possibilities of improved therapy from continuous non-pulsed delivery

Diethylcarbamazine was given as eye drops in varying concentrations in a half-log dilution series from 1.0 to 0.0001% to patients with ocular onchocerciasis. Migration of microfilariae into the cornea, followed by their straightening and disintegration, was observed with delivery rates as low as 0.1 microgram/hour. Dose-related adverse inflammatory reactions, including the development of globular limbal infiltrates with itching and redness, were seen with delivery rates as low as 0.6 microgram/hour, but substantial inflammatory reactions, including severe vasculitis, were seen only with delivery rates of or above 1.0 microgram/hour. This suggests that it should be possible to achieve beneficial clearing of the microfilarial load, without adverse reactions, by continuous non-pulsed delivery of the drug. Technology exists for such delivery, either directly into the eye or systemically by a transdermal system that could give 3 to 7 days' treatment from each application. The observations reported suggest that after preliminary clearing of the microfilarial load by carefully controlled delivery of DEC it may be possible to maintain therapy by less strictly controlled delivery in DEC-medicated salt, or to use treatment with suramin, without incurring substantial adverse reactions, such as a deterioration in vision in cases in which the optic nerve is already compromised. Continuous non-pulsed DEC delivery systems could have a place in the management of onchocercal sclerosing keratitis. The unique opportunities for using the ocular model to define the requirements for beneficial non-damaging therapy with DEC should be explored in further field trials.