Soluble forms of isobutylmethylxanthine enhance the ocular hypotension induced by catecholamines.

Isobutylmethylxanthine (IBMX) suspended in 0.5% hydroxypropyl methylcellulose has been shown to enhance the reduction in intraocular pressure (IOP) induced by epinephrine and norepinephrine in rabbits and beagles. In the present study, the effects of two soluble forms of IBMX, i.e. the ethylenediamine salt (IBMX-ED) and IBMX bound to cyclodextrin in saline (IBMX-CD), were studied in rabbits. When used alone, 1% IBMX-ED did not affect the IOP, but the hypotensive response to 0.1% epinephrine was enhanced dose-dependently by combination of the catecholamine with IBMX-ED. Although 1% IBMX-CD applied alone also failed to influence the IOP, the hypotensive response to epinephrine, dipivalyl epinephrine and norepinephrine was enhanced by combination of these substances with IBMX-CD. Soluble IBMX-ED as well as soluble IBMX-CD and the IBMX suspension enhanced, to a similar extent and in a dose-dependent manner, the IOP reduction induced by catecholamines. IBMX-CD, which has a neutral pH, may be a suitable form of IBMX for future long-term experiments.