Systemic beta-blockade with once daily Betimol or Timoptic-XE

Association between Ophthalmic Timolol and Hospitalisation for Bradycardia

Introduction. Ophthalmic timolol, a topical nonselective beta-blocker, has the potential to be absorbed systemically which may cause adverse cardiovascular effects. This study was conducted to determine whether initiation of ophthalmic timolol was associated with an increased risk of hospitalisation for bradycardia. Materials and Methods. A self-controlled case-series study was undertaken in patients who were hospitalised for bradycardia and were exposed to timolol. Person-time after timolol initiation was partitioned into risk periods: 1–30 days, 31–180 days, and >180 days. A 30-day risk period prior to initiating timolol was also included. All remaining time was considered unexposed. Results. There were 6,373 patients with at least one hospitalisation for bradycardia during the study period; 267 were exposed to timolol. Risk of bradycardia was significantly increased in the 31–180 days after timolol initiation (incidence rate ratio (IRR) = 1.93; 95% confidence interval (CI) 1.00–1.87). No increased risk was observed in the first 30 days or beyond 180 days of continuous exposure (IRR = 1.40; 95% CI 0.87–2.26 and IRR = 1.21; 95% CI 0.64–2.31, resp.). Conclusion. Bradycardia is a potential adverse event following timolol initiation. Practitioners should consider patient history before choosing a glaucoma regime and closely monitor patients after treatment initiation with topical nonselective beta-blocker eye drops.

Evaluation of aqueous humor concentrations of Istalol and Betimol following a single ocular instillation in rabbit eyes

PURPOSE

The aim of this study was to evaluate the pharmacokinetic absorption profiles of two commercially available ophthalmic solutions following a single instillation into each eye of New Zealand white rabbit eyes.

METHODS

A single dose of either timolol maleate with potassium sorbate (TLA) or timolol hemihydrate (THH) was instilled into each eye of New Zealand white rabbits (15 rabbits/drug preparation, 50-microL dose). Animals were euthanized 15, 30, 60, 120, and 180 min after instillation, with 3 animals/drug/time intervals. Aqueous humor from both eyes of each animal was pooled and analyzed for timolol concentration, using the high-performance liquid chromatography method.

RESULTS

TLA reached a mean peak concentration of 3.705 +/- 0.3012 microg/mL at 15 min, tapering to 0.539 +/- 0.1431 microg/mL by 180 min. THH reached a mean peak concentration of 2.239 +/- 0.1430 microg/mL at 15 min postinstillation, tapering to 0.148 +/- 0.0282 microg/mL by 180 min.

CONCLUSIONS

TLA containing potassium sorbate demonstrated an absorption profile of more rapid absorption (1.7 fold greater at 15 minutes) and longer residences time (3.6 fold greater at 180 minutes) than the THH. At every time point throughout the study, TLA demonstrated greater drug concentration than THH.

Ophthalmic timolol: plasma concentration and systemic cardiopulmonary effects

Timolol maleate is a non-selective beta-adrenoceptor antagonist currently used mainly as an ocular preparation for the treatment of glaucoma and ocular hypertension. Despite the topical administration, ophthalmic timolol causes systemic adrenergic beta-blocking because of absorption from the eye into the systemic circulation. Gel formulations of ophthalmic timolol have been developed to reduce systemic absorption and adverse effects in comparison with conventional aqueous solution formulations. Timolol is metabolized by the polymorphic cytochrome P450 2D6 enzyme (CYP2D6). The changes in heart rate (HR) are the most striking effects of the systematically absorbed fraction of ophthalmic timolol, with 0.5 % aqueous formulations presenting larger effects than 0.1 % hydrogel formulations, especially during exercise. Plasma levels of ophthalmic timolol correlate with the changes in HR. Neither 0.5 % aqueous nor 0.1 % hydrogel formulations of timolol have exerted noteworthy effects on systolic (SAP) or diastolic (DAP) arterial pressures, probably because of a compensatory increase in systemic vascular resistance due to the attenuation of HR. Ophthalmic timolol does not exert remarkable effects on pulmonary parameter peak expiratory flow (PEF) and forced expiratory volume in 1 s (FEV1) in non-asthmatic patients. CYP2D6 activity is clearly associated with the pharmacokinetic parameters, particularly when 0.5 % aqueous solution of timolol is used: peak plasma concentration, elimination half-life and area-under-the-curve are highest in CYP2D6 poor metabolizers. Finally, since there is a correlation between the plasma level of timolol and several haemodynamic effects - especially HR in the state of elevated beta-adrenergic tonus - the CYP2D6 poor metabolizers may be more prone to bradycardia during treatment with (aqueous) ophthalmic timolol.

Cardiovascular effects of timolol maleate, brimonidine or brimonidine/timolol maleate in concomitant therapy

PURPOSE

To examine the influence on maximal exercise performance in young healthy volunteers of timolol 0.5%, brimonidine 0.2% or placebo versus brimonidine 0.2% and timolol 0.5% used concomitantly.

METHODS

The subjects in this prospective, double-masked, crossover comparison were dosed 15 min prior to treadmill testing. A period of 1 week was allowed between tests.

RESULTS

The 20 subjects who completed the trials (average age 24.5 +/- 7.4) had a mean maximum exercise heart rate of 196 +/- 12 bpm for placebo, 182 +/- 13 bpm for timolol, 187 +/- 10 bpm for brimonidine, and 186 +/- 11 bpm for timolol/brimonidine concomitant therapy (p < 0.005). During recovery, the placebo group demonstrated a statistically higher systolic blood pressure (min 6) and pulse (mins 2 and 4) (p < 0.01). In addition, subjects treated with timolol/brimonidine demonstrated more premature contractions (atrial or ventricular) overall during exercise and recovery (p = 0.01). The brimonidine and concomitant treatment groups showed the greatest number of adverse events per subject, the most common of which were dizziness and fatigue (p = 0.031).

CONCLUSION

This study suggests that both timolol and brimonidine, used alone and concomitantly, cause cardiovascular effects consistent with their pharmacology.

Comparison of the cardiovascular effects of unoprostone 0.15%, timolol 0.5% and placebo in healthy adults during exercise using a treadmill test

PURPOSE

To compare the cardiovascular effects of unoprostone 0.15%, timolol 0.5% and placebo in healthy adults during exercise using a treadmill test.

METHODS

Thirty subjects aged 18-37 years (mean age = 24.1 years) were randomized to one of six treatment sequences in a three-treatment, three-period crossover study (William's design). Study medication was instilled b.i.d. for 5 days before visits 2, 3, and 4. Between treatments, study medication was washed out for 9-10 days. Each subject underwent a submaximal treadmill test at visits 2 through 4, 15 min after dosing.

RESULTS

After 15 min of exercise, average heart rates were 143.1 +/- 21.2, 134.5 +/- 20.0 and 145.4 +/- 20.8 bpm for the unoprostone, timolol and placebo treatments, respectively. At no timepoint was there a statistically significant difference between the unoprostone and placebo treatments (p > 0.05). Beginning with the second minute of exercise, timolol produced a greater decrease in heart rate at all timepoints from placebo than unoprostone (p < 0.05). No consistent differences in systolic or diastolic blood pressure were observed between drug treatments (p > 0.05).

CONCLUSIONS

Unlike timolol, unoprostone 0.15% does not reduce exercise-induced heart rate, indicating a lack of clinical effect on systemic beta-adrenergic receptors in young and healthy subjects.

Beta-adrenergic antagonists in the treatment of glaucoma

PURPOSE

Beta-blockers have been used since the late 1970's as 'first-choice' in the treatment for glaucoma. Since the introduction of new molecules in clinical routine, the current role of beta-blockers in glaucoma therapy has been rediscussed. In particular, concerns have been raised regarding their actual safety profile.

METHODS

This review will focus on the latest advances on the efficacy and safety profiles of non-selective beta-blockers.

CONCLUSIONS

The data provided will help to trace a more appropriate role for beta-blockers in glaucoma therapy.