The effects of dopamine, haloperidol and bromocriptine on intraocular pressure

Natural Ergot Alkaloids in Ocular Pharmacotherapy: Known Molecules for Novel Nanoparticle-Based Delivery Systems

Several pharmacological properties are attributed to ergot alkaloids as a result of their antibacterial, antiproliferative, and antioxidant effects. Although known for their biomedical applications (e.g., for the treatment of glaucoma), most ergot alkaloids exhibit high toxicological risk and may even be lethal to humans and animals. Their pharmacological profile results from the structural similarity between lysergic acid-derived compounds and noradrenalin, dopamine, and serotonin neurotransmitters. To reduce their toxicological risk, while increasing their bioavailability, improved delivery systems were proposed. This review discusses the safety aspects of using ergot alkaloids in ocular pharmacology and proposes the development of lipid and polymeric nanoparticles for the topical administration of these drugs to enhance their therapeutic efficacy for the treatment of glaucoma.

A comparative study of topical natural ergot alkaloids on the intraocular pressure and aqueous humor dynamics in oclular normotensive and alpha-chymotrypsin-induced ocular hypertensive rabbits

BACKGROUND

Although it has been suggested that ergot derivatives may play a role in antiglaucoma therapy, little attention has been paid to the ocular hypotensive action of these drugs. Having previously reported that topical natural ergot alkaloids ergocristine alpha-ergocryptine and ergocornine dose-dependently reduce intraocular pressure in ocular normotensive and alpha-chymotrypsin-induced ocular hypertensive rabbits, the aim of the present work was to compare the effect of ergocristine, alpha-ergocryptine and ergocornine on the intraocular pressure and aqueous humor dynamics in ocular normotensive and alpha-chymotrypsin-induced ocular hypertensive rabbits, in order to further explore the ocular actions of these compounds.

METHODS

Experiments were conducted in albino ocular normotensive and hypertensive rabbits by intracameral injection of alpha-chymotrypsin. Intraocular pressure responses to drug vehicle and seven different doses of topical natural ergot alkaloids were examined, in order to obtain dose-response relationships for comparing the intraocular pressure-lowering effect and potency of these drugs. Tonographies were also performed to ascertain the actions of natural ergot alkaloids on aqueous humor dynamics.

RESULTS

All natural ergot alkaloids tested reduced intraocular pressure in a dose-related fashion. The ocular hypotensive effect was greater in alpha-chymotrypsin-induced ocular hypertensive rabbits for the three compounds tested. All natural ergot alkaloids tested decreased both tonographic outflow facility and, to a greater extent, aqueous humor inflow in ocular normotensive and in alpha-chymotrypsin-induced ocular hypertensive rabbits.

CONCLUSION

Taken together, our data suggest that these compounds decrease both tonographic outflow facility and, to a greater extent, aqueous humor inflow, which explains their final effect in ocular normotensive and in alpha-chymotrypsin-induced ocular hypertensive rabbits. Reductions in aqueous humor inflow observed after topical application of natural ergot alkaloids in alpha-chymotrypsin-induced ocular hypertensive rabbits can only be explained by a marked inhibition of active secretion of aqueous humor, since processes involved in aqueous humor formation may probably be altered after alpha-chymotrypsin injection.

Safety and ocular hypotensive efficacy of a single dose of metoclopramide or droperidol in healthy subjects

The purpose of this study was to evaluate the IOP lowering effect of two topical dopamine antagonists, metoclopramide or droperidol, in healthy subjects. Forty healthy volunteers were randomly assigned to receive, in double-masked fashion, topical administration of a single drop of 0.5% metoclopramide or 0.25% droperidol, with the fellow eye receiving isotonic saline as placebo. IOP was measured before and 1, 3, 5, and 7 hours after instillation of drugs. Ocular irritation and conjunctival congestion were also recorded at the time of each measurement. In the metoclopramide group, the maximal mean percentage change in IOP was -14.4% in tested eyes as compared with -10.8% in placebo-treated eyes 3 hours after instillation. All the changes were not significantly different between the metoclopramide-treated and the placebo-treated eyes at all time points. In the droperidol group, the maximal mean percentage change in IOP was -19.6% in tested eyes as compared with -17.7% in placebo-treated eyes at 3 hours after instillation. There was also no significant difference between the droperidol-treated and the placebo-treated eyes. None of the volunteers reported ocular irritation or conjunctival congestion after instillation of the drugs. In conclusion, while topical droperidol or metoclopramide tended to lower IOP in healthy subjects, the decrease in IOP did not differ significantly from that in placebo-treated eyes. Both drugs appear to be safe. Further studies with larger numbers of subjects at higher doses in glaucomatous subjects are needed before definite conclusions on drug efficacy can be drawn.

Fenoldopam, a selective dopamine-1 receptor agonist, raises intraocular pressure in males with normal intraocular pressure

Recent studies have suggested that intravenous infusion of fenoldopam, a selective dopamine-1 receptor agonist, elevates intraocular pressure (IOP) in man. This study evaluated the effect of intravenous fenoldopam on IOP, aqueous humor outflow facility and gonioscopy in 12 healthy human subjects. Three doses (0.2, 0.5 and 1.0 microg/kg/min) were infused for 120 minutes in a double masked, placebo controlled, four-way crossover design. IOP was measured every 20 minutes in the supine position and every 40 minutes while sitting during the drug and placebo infusions. Tonography and gonioscopy were performed at baseline and after 120 minutes of infusion. Compared to placebo, IOP increased by 3.5 mm Hg (32%) for the lowest dose, 5.8 mm Hg (46%) for the intermediate dose, and 6.9 mm Hg (55%) for the highest dose (p<0.05 for all three doses). IOP returned to baseline within 30 minutes of stopping the infusion. The outflow facility decreased from baseline by 26% after 120 minutes of infusion for all drug doses. In contrast, outflow facility increased from baseline by 11% during placebo infusion. Compared to placebo, the fenoldopam induced changes in outflow were statistically significant (p<0.05). There was no change in the gonioscopic appearance of the anterior chamber angle during the infusion. This study shows that systemic administration of a selective dopamine-1 receptor agonist causes a significant dose-dependent increase in IOP that can be explained in part by diminished outflow facility. These results support a role for the dopamine-1 receptor in the modulation of IOP in general and suggest modulation of aqueous humor outflow by dopaminergic receptors.

Effect of intravenous fenoldopam on intraocular pressure in ocular hypertension

Intravenous fenoldopam, a selective dopamine-1 receptor agonist, was compared with placebo in this randomized, double-blind, two-period crossover study to evaluate its effects on intraocular pressure, aqueous dynamics, and macular blood flow in patients with elevated intraocular pressure or primary open-angle glaucoma. Doses of fenoldopam were titrated up to a maximum of 0.5 microgram/kg/min. Intraocular pressure, measured by pneumotonometry, was the primary outcome variable. Other outcomes included macular blood flow assessed by blue field examination, visual field examined by automated perimetry, aqueous outflow facility measured by tonography, and aqueous humor production determined by fluorophotometry. During infusions of fenoldopam, intraocular pressure increased from a mean baseline level of 29.2 mmHg to a mean maximum level of 35.7 mmHg. During the placebo infusions, pressure increased from a mean baseline of 28.4 mmHg to a mean of 29.0 mmHg at the time point that corresponded to the mean maximum intraocular pressure on the day intravenous fenoldopam was administered, to yield a mean difference in pressure between study days of 6.7 mmHg (P < 0.05). There were no apparent changes in macular blood flow, visual fields, or production or outflow of aqueous humor associated with fenoldopam infusion. The increase in intraocular pressure seen in this population of patients with ocular hypertension during infusions of fenoldopam is consistent with fenoldopam-associated increases in intraocular pressure reported in previous studies of healthy volunteers and of patients with accelerated systemic hypertension. These results further suggest that dopamine-1 receptors play a role in the regulation of intraocular pressure.

The determination of additive effect and intraocular pressure lowering effects of 0.05% bromocriptine and 0.25% timolol

It has been confirmed that topically applied bromocriptine has a satisfactory intraocular pressure (IOP) lowering effect without serious ocular or systemic side effects. We compared the IOP lowering effects of 0.05% bromocriptine and 0.25% timolol and determined whether they have an additive effect in lowering IOP in normal volunteers. In a double-blind, randomised, prospective, single-dose study, we measured IOP in 24 ocular normotensive subjects before (baseline) and 2, 4 and 6 hours after topical instillation of the following drugs: timolol and bromocriptine alone (n: 14), timolol+bromocriptine, timolol+placebo, bromocriptine+placebo (n: 10). Both bromocriptine and timolol have a significant IOP lowering effect (p < 0.01) compared with the baseline value during the study period. There were no significant differences in IOP lowering effect between timolol and bromocriptine at 2 and 4 hours (p > 0.05), but timolol was more efficacious than bromocriptine at 6 hours (p < 0.05). An additive effect in lowering IOP was not found. Although timolol and bromocriptine have no additive effect in lowering IOP, topically applied bromocriptine may be used in the treatment of glaucoma.

The novel dopamine D-1 antagonist and D-2 agonist, SDZ GLC-756, lowers intraocular pressure in healthy human volunteers and in patients with glaucoma

PURPOSE

To investigate the intraocular pressure (IOP)-reducing effect and side effects of SDZ GLC-756, a novel dopamine D-1 antagonist and D-2 agonist, in control subjects and patients with open-angle glaucoma or ocular hypertension.

METHODS

A single-application, randomized, placebo-controlled, double-masked study was performed. SDZ GLC-756 eye drops at a concentration of 0.01% (n = 6) or 0.1% (n = 6) were administered to one eye in control subjects, vehicle alone (control) to the contralateral eye. In glaucoma patients the trial was designed as a crossover study administering SDZ GLC-756 (0.1%) eye drops and vehicle alone (control) to one eye in 12 patients with open-angle glaucoma or ocular hypertension.

RESULTS

In control subjects, IOP decreased significantly by 2.0 +/- 0.4 mmHg (P < 0.01) after treatment with 0.01% SDZ GLC-756 and by 4.7 +/- 0.5 mmHg (P < 0.001) after treatment with 0.1% SDZ GLC-756. In the glaucoma group, IOP decreased by 6.8 +/- 0.6 mmHg (P < 0.001) (range, 4-11 mmHg). In both groups, treatment with 0.1% eye drops resulted in a significant IOP-lowering effect for 6 hours, and for 3 hours with treatment with 0.01% eye drops. A significant IOP-lowering effect (P < 0.05) also was found in the contralateral eye. Except for slight conjunctival hyperemia lasting up to 30 minutes after drug application, no ocular or systemic side effects were observed.

CONCLUSION

SDZ GLC-756 reduced IOP significantly for approximately 6 hours. However, due to the study design with repeated IOP measurements before drug administration, the clinical efficacy of the preparation used remains unclear. The only systemic or local side effect observed was slight conjunctival hyperemia. The simultaneous D-1 antagonistic and D-2 agonistic properties of SDZ GLC-756 may provide a new pharmacologic approach to treating glaucoma and ocular hypertension, which deserves further investigation.

Ocular hypotension induced by topical dopaminergic drugs and phosphodiesterase inhibitors

The aim of this work was to investigate the ocular hypotensive activity of some topically administered cAMP-phosphodiesterase inhibitors alone and in combination with dopaminergic compounds. Experiments were performed with ocular normotensive rabbits and during transitory induced ocular hyper- or hypotension. An ocular hypotensive effect was observed after instillation of aminophylline, dyphylline, pentoxifylline, caffeine, and iso-caffeine, but not following topical hydroxypropyl-1,3-dimethylxanthine. Dopaminergic compounds were also studied in order to be combined with phosphodiesterase inhibitors as ocular anti-hypertensive treatment. Significant ocular hypotensive activity was observed after topical application of trifluperidol, fluphenazine, thiothixene, and the S(-) enantiomer of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP). Of the cAMP-phosphodiesterase inhibitors that were tested, pentoxifylline was the most interesting compound, with good ocular tolerance, significant reduction in intra-ocular pressure, and potential retinal microvascular benefits. After allowing adequate time for pentoxifylline to reach its maximal activity, trifluperidol or S(-)-3-PPP was also instilled. A more pronounced ocular hypotensive effect was then observed. The findings of this study may suggest that administration of eye-drops combining drugs acting by separate ways on second messengers involved in the regulation of intra-ocular pressure (e.g. cyclic AMP) could be used to reduce intra-ocular pressure during glaucoma.