Effect of different ointment bases on ocular disposition of ethylphenylephrine in rabbit eyes

Abstract

The influence of vehicle composition on the ocular disposition of ethylphenylephrine, a mydriatic drug used for the treatment of wide-angle glaucoma, has been studied. The vehicles investigated consisted of a hydrocarbon base, an absorption base (10% lanolin in a paraffin base) and a water-soluble base (polyvinyl alcohol, PVA, 15% in water). The albino rabbit was chosen as the animal model. The disposition of the drug in conjunctiva, cornea, iris-ciliary body and aqueous humor of the rabbit was monitored at 1, 2 and 4 h post-installation using extraction technique. At the early time period (1 h post-administration) both oleaginous and water-soluble bases were judged to perform adequately in that they provided approximately the same drug concentrations in various ocular tissues at the aqueous vehicle. However, after 4 h, the oleaginous base provided the highest concentrations of drug in the conjunctiva. The water-soluble PVA formulation gave significantly lower levels in the conjunctiva and the cornea. At this same point, the absorption base containing lanolin produced the highest drug concentration in the cornea, iris-ciliary body and aqueous humor. Collectively, these data suggest that of the 3 bases studied, the oleaginous base and the absorption base show most promise as vehicles to extend the residence time of ethylphenylephrine in the eye. Obviously the final choice of vehicle will also be influenced by factors such as the physical and chemical stability of the drug in the formulation chosen and patient acceptance.