The selective beta-1 blocker Metoprolol was tested for a period of one month in a double-blind trial involving 36 patients with open-angle glaucoma or intraocular hypertension in whom the substance was applied twice daily to the eye in concentrations of 1, 2, 4 and 8%. At all these concentrations the intraocular pressure showed a reduction of 23%. The concentrations over 1% were less well tolerated, the difference being statistically significant; the patients concerned complained of an unpleasant burning sensation for 30 seconds after the application. The subjective intolerance shown increased in proportion to the concentration. It is not clear whether the solvent used contributed to the intolerance. The Metoprolol drops had no effect on pupillary diameter, blood pressure or resting pulse. An important finding was that during the one month's treatment there was no fall-off in the effectiveness of the preparation, i.e., the reduction in intraocular pressure and duration of action showed no diminution such as is seen, for example, with Timolol.
In a double-blind cross-over study, the intraocular pressure-lowering action and side effects of a 5% guanethidine/1% adrenaline combination were studied and compared with those of two components alone. The subjects were 63 glaucoma patients divided into three random groups given the three preparations in a different order. The pressure-lowering effect of the combination is significantly better (P less than 1%) than that of either component alone but the side effects were more severe.
The authors summarize findings in a clinical trial of the betablockers Timolol and Metoprolol, as well as the effectiveness of various concentration of the combination preparation Guanethidine-Adrenaline. In the trial Timolol proved to be the almost ideal drug for glaucoma therapy. However, as a pressure-lowering agent the guanethidine-epinephrine combination is more effective. Metroprolol, which is a pure beta 1-blocker, is probably preferable to Timolol in asthmatic patients.
Undesirable side effects have limited the use of adrenaline/guanethidine combinations in the usual concentrations in the treatment of chronic simple glaucoma. Better tolerance to lower concentrations has already been demonstrated in other studies. In the double-blind study described here, three different combinations (adrenaline 1%, 0.5% and 0.2% combined respectively with guanethidine 5%, 3% and 1%) were compared in respect of their depressive action on intraocular pressure and the tolerance shown to them. All three combinations were found to be effective. The combination with the lowest concentration was significantly less hypotensive in its effect than the other two but the number of patients treated was too small to allow a clear distinction to be made between the effects of the other two combinations. Nevertheless, there was a tendency for the effectiveness to fall with decreasing concentration. As far as tolerance was concerned, there was little difference between the middle and lowest concentrations, the latter being that best tolerated. The excellent effect of the strongest concentration was impaired by the poor tolerance shown to it. The comparison between the three combinations was followed by a study of the diurnal pressure changes in patients during the course of the treatment. The slow rise up to midday and the abrupt afternoon fall remain unexplained. The low concentration of the preparation had a better hypotensive action than pilocarpine, while the middle concentration proved even a little better than the beta-blocker Timolol
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