Timolol pharmacokinetics and effects on heart rate and blood pressure after acute and chronic administration

Short-term Efficacy and Safety of Topical β-Blockers (Timolol Maleate Ophthalmic Solution, 0.5%) in Acute Migraine: A Randomized Crossover Trial

Importance

Oral β-blockers used for the prevention of migraine headache are not effective for the treatment of acute pain. Small case series have suggested that topically applied β-blockers may be useful in the management of acute migraine pain, warranting evaluation with randomized clinical trials.

Objective

To evaluate the short-term efficacy and safety of topically applied timolol maleate ophthalmic solution, 0.5%, compared with topically applied placebo eyedrops in the treatment of acute migraine attacks.

Design, Setting, and Participants

In this randomized, masked placebo-controlled crossover trial conducted from May 27, 2015, to August 28, 2017, 50 patients with migraine were randomized to receive either timolol eyedrops, 0.5%, or a placebo eyedrop (carboxymethyl cellulose, 0.5%). After a 3-month treatment period, patients completed a 1-month washout period and were crossed over to receive the opposite treatment for a final 3 months. Analysis was performed on a modified intent-to-treat basis.

Intervention

After random assignment, patients were instructed to use 1 drop of the assigned medication in each eye at the earliest onset of migraine.

Main Outcomes and Measures

The main outcome measure was reduction in pain score with treatment. The primary end point was reduction of pain score by 4 points, or to zero, 20 minutes after instillation of the eyedrop.

Results

Of the 50 patients, 42 (84%) were females and the mean (SD) age was 27.3 (11.3) years. Of a total of 619 migraine attacks, 284 (46%) were treated with timolol, 271 (44%) were treated with the placebo, and 64 (10%) occurred during the washout period when no study medications were used. Seven patients (14%) withdrew after randomization. A total of 233 of the timolol-treated migraine attacks (82%) were associated with a reduction in pain score by 4 points, or to zero, at 20 minutes compared with 38 of the placebo-treated attacks (14%), with a difference of 68 percentage points (95% CI, 62-74 percentage points). A generalized estimating equation analysis revealed that pain score reduction at 20 minutes was greater in the timolol group compared with the placebo group by a mean (SE) of 4.63 points (0.34) (P < .001).

Conclusions and Relevance

This randomized crossover trial supports consideration of timolol eyedrops in the acute treatment of migraine. Further research is warranted to determine if the improvements observed are sustained for a longer follow-up and with larger groups.

Trial Registration

CTRI/2015/05/005829, UTN: U1111-1167-6439.

Combination product of dermal matrix, human mesenchymal stem cells, and timolol promotes diabetic wound healing in mice

Diabetic foot ulcers are a major health care concern with limited effective therapies. Mesenchymal stem cell (MSC)-based therapies are promising treatment options due to their beneficial effects of immunomodulation, angiogenesis, and other paracrine effects. We investigated whether a bioengineered scaffold device containing hypoxia-preconditioned, allogeneic human MSCs combined with the beta-adrenergic antagonist timolol could improve impaired wound healing in diabetic mice. Different iterations were tested to optimize the primary wound outcome, which was percent of wound epithelialization. MSC preconditioned in 1 μM timolol at 1% oxygen (hypoxia) seeded at a density of 2.5 × 10⁵  cells/cm² on Integra Matrix Wound Scaffold (MSC/T/H/S) applied to wounds and combined with daily topical timolol applications at 2.9 mM resulted in optimal wound epithelialization 65.6% (24.9% ± 13.0% with MSC/T/H/S vs 41.2% ± 20.1%, in control). Systemic absorption of timolol was below the HPLC limit of quantification, suggesting that with the 7-day treatment, accumulative steady-state timolol concentration is minimal. In the early inflammation stage of healing, the MSC/T/H/S treatment increased CCL2 expression, lowered the pro-inflammatory cytokines IL-1B and IL6 levels, decreased neutrophils by 44.8%, and shifted the macrophage ratio of M2/M1 to 1.9 in the wound, demonstrating an anti-inflammatory benefit. Importantly, expression of the endothelial marker CD31 was increased by 2.5-fold with this treatment. Overall, the combination device successfully improved wound healing and reduced the wound inflammatory response in the diabetic mouse model, suggesting that it could be translated to a therapy for patients with diabetic chronic wounds.

Absorption and Safety of Topically Applied Timolol for Treatment of Chronic Cutaneous Wounds

Objective: There are no safety or absorption studies to guide topical timolol therapy for treatment of chronic wounds. This study was undertaken to address this gap. Approach: A prospective, observational, cross-sectional comparative study of timolol plasma levels in patients after topical administration to a chronic wound, compared with levels in patients after timolol ocular administration for the indication of glaucoma. Results: There was no statistically significant difference in the average plasma level of timolol in wound as compared with glaucoma patients. No bradycardia or wheezing was observed after administration. Innovation: We determined the single time point concentration of timolol in plasma 1 h after application of timolol 0.5% gel-forming solution to debrided chronic wounds, providing insight as to the safety of this emerging off-label treatment. Conclusion: The topical application of timolol for chronic wounds shares the same safety profile as the widely used application of ocular administration for glaucoma.

Multi-functional scaling methodology for translational pharmacokinetic and pharmacodynamic applications using integrated microphysiological systems (MPS)

Microphysiological systems (MPS) provide relevant physiological environments in vitro for studies of pharmacokinetics, pharmacodynamics and biological mechanisms for translational research. Designing multi-MPS platforms is essential to study multi-organ systems. Typical design approaches, including direct and allometric scaling, scale each MPS individually and are based on relative sizes not function. This study's aim was to develop a new multi-functional scaling approach for integrated multi-MPS platform design for specific applications. We developed an optimization approach using mechanistic modeling and specification of an objective that considered multiple MPS functions, e.g., drug absorption and metabolism, simultaneously to identify system design parameters. This approach informed the design of two hypothetical multi-MPS platforms consisting of gut and liver (multi-MPS platform I) and gut, liver and kidney (multi-MPS platform II) to recapitulate in vivo drug exposures in vitro. This allows establishment of clinically relevant drug exposure-response relationships, a prerequisite for efficacy and toxicology assessment. Design parameters resulting from multi-functional scaling were compared to designs based on direct and allometric scaling. Human plasma time-concentration profiles of eight drugs were used to inform the designs, and profiles of an additional five drugs were calculated to test the designed platforms on an independent set. Multi-functional scaling yielded exposure times in good agreement with in vivo data, while direct and allometric scaling approaches resulted in short exposure durations. Multi-functional scaling allows appropriate scaling from in vivo to in vitro of multi-MPS platforms, and in the cases studied provides designs that better mimic in vivo exposures than standard MPS scaling methods.

Semi-automated protein binding methodology using equilibrium dialysis and a novel mixed-matrix cassette approach

A semi-automated protein binding assay using equilibrium dialysis (ED) and a novel mixed-matrix methodology has been developed. This method decreases mass spectrometer run time and reduces the likelihood of experimental artifacts. In this cassette-based approach, a single matrix is prepared following dialysis by mixing dialyzed plasma and buffer containing different test compounds from the same dialysis plate. This approach differs from the traditional mixed-matrix method where fresh plasma and fresh buffer are mixed with opposing dialyzed samples. This new mixed-matrix methodology is compatible with various high-throughput ED and ultrafiltration devices, many liquid handling systems, and can be used for plasma, serum, albumin, alpha-1 acid glycoprotein, microsomal, and fine tissue homogenate binding studies. The utility of the method can be further enhanced by varying the number of replicates, concentrations, and matrices with simple modifications. Using 29 structurally diverse marketed drugs with a wide range of protein binding values reported in the literature, we have shown the new procedure reduces the total number of samples by nearly half compared to traditional methods, eliminates the need for standard curves, and increases the uniformity of the sample matrix for LC/MS/MS analysis.

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.

Timolol LA: a double-masked, active-controlled, randomized, crossover, comfort, ocular safety, and systemic bioavailability study in healthy volunteers

PURPOSE

A new formulation of timolol with sorbic acid, timolol-LA (TLA) (Istaloldagger), has been developed which increases its ocular bioavailability. In the present study, we desired to evaluate the ocular comfort and systemic bioavailability of TLA in healthy volunteers in comparison to standard timolol maleate ophthalmic solution (TIM).

METHODS

This study was a randomized, double-masked, active-controlled, crossover evaluation of 0.5% TLA and 0.5% TIM, bid, in 12 normal healthy volunteers. Visits were at Days 0, 1, 2, 4 and 8 in each period, and there was a minimum 7 day interperiod washout.

RESULTS

At all three post-dosing evaluation times (Day 1: Peak, Day 8: Trough, and Day 8: Peak), the 95% confidence interval for the difference between TLA and TIM was not more than 0.37 ng/mL. After administration of TLA, there was a greater incidence of burning/stinging and tearing, but not foreign body sensation, relative to TIM. In general, most symptoms were mild in intensity, and no subject discontinued treatment due to ocular discomfort. Both treatments decreased IOP to a similar level.

CONCLUSION

TLA was relatively comfortable, with a safety profile consistent with further clinical development, and, with bid dosing (exaggerated [2X] that anticipated for clinical use), had a systemic bioavailability similar to that of TIM 0.5%, bid. The incidence of burning and stinging was higher with TLA than with TIM, although reports were mild in severity and did not result in any patient discontin uations. Although the results are of interest, further evaluation in a larger trial may be warranted.

Systemic adverse effects of beta-adrenergic blockers: an evidence-based assessment

PURPOSE

To present an evidence-based review of the systemic adverse effects of beta-adrenergic blockers and recommend safety guidelines for use of ophthalmic beta-adrenergic blockers.

DESIGN

Literature review of published articles in peer-reviewed journals and medical texts.

METHODS

Pre-MEDLINE and MEDLINE search of relevant English language articles from 1966 to the present. Cardiovascular, pulmonary, endocrine/metabolic, central nervous system, sexual, exercise, and neuromuscular effects of systemic or ophthalmic beta-adrenergic blockers were reviewed.

RESULTS

Systemic beta-adrenergic antagonists unequivocally reduce mortality in patients with mild, moderate, and even severe congestive heart failure. Development of symptomatic bradycardia on systemic or ophthalmic beta-adrenergic blockers alone likely indicates underlying cardiac conduction disturbances. Beta 2-adrenergic blockade, regardless of route of administration, may exacerbate or trigger bronchospasm in patients with asthma or pulmonary disease associated with hyper-reactive airways. This review identifies no scientific studies supporting the development of worsening claudication, depression, hypoglycemic unawareness, or prolonged hypoglycemia in non-insulin-dependent diabetes, sexual dysfunction, or impaired neuromuscular transmission with systemic or ophthalmic beta-adrenergic blockers.

CONCLUSIONS

Many commonly presumed adverse beta-adrenergic blocker effects observed via systemic or ocular administration are not supported by published randomized clinical trials. Wide acceptance of such traditionally purported side effects has been largely due to propagation of isolated case reports and short series as well as personal communication felt to reflect expert opinion. Many more patients may be eligible to use these drugs. Obtaining a careful medical history and checking pulse rate and rhythm in the office should identify the vast majority of patients with potential cardiopulmonary contraindications.

Glucose kinetics during exercise in trained men

Six trained men were studied to examine the relative increases in hepatic glucose output and peripheral glucose uptake during 40 min of exercise at 75% VO2max. Rates of appearance (Ra) and disappearance (Rd) were measured using a primed, continuous intravenous infusion of D-[3-3H]glucose. Plasma glucose increased (P < 0.05) from 4.8 +/- 0.2 mmol l-1 at rest to 6.2 +/- 0.5 mmol l-1 after 40 min of exercise. Both Ra and Rd increased (P < 0.05) during exercise, however, during the early phase of exercise, Ra exceeded Rd (P < 0.05). Ra peaked at 42.0 +/- 3.2 mumol kg-1 min-1 after approximately 15 min of exercise. In contrast, the highest Rd of 33.9 +/- 4.3 mumol kg-1 min-1 was measured at the end of exercise. In additional experiments, five men were studied during 40 min of exercise at 70-75% VO2max, 2 h after ingestion of the non-selective beta-adrenergic antagonist timolol or a placebo capsule. Subjects were unable to complete the exercise bout following timolol, fatiguing after 28.0 +/- 4.0 min (P < 0.05). The increase in blood glucose from 4.3 +/- 0.1 to 4.7 +/- 0.3 mmol l-1 (P < 0.05) following 20 min of exercise under control conditions was completely abolished by prior timolol ingestion (4.2 +/- 0.2 to 4.1 +/- 0.2 mmol l-1). These results demonstrate that during exercise at 75% VO2max in trained men, hepatic glucose output is not always closely matched to peripheral muscle glucose uptake and may be subject to feed-forward regulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ocular carteolol and timolol on plasma high-density lipoprotein cholesterol level

Fifty-eight healthy, normolipidemic adult men participated in a prospective, masked, randomized crossover study designed to compare the effects of two topical nonselective beta-adrenergic antagonists, carteolol and timolol, on plasma high-density lipoprotein cholesterol levels. Two eight-week treatment periods were separated by an eight-week drug-free period. Carteolol 1.0% or timolol 0.5% was used, one drop twice daily, in both eyes without nasolacrimal occlusion. Fresh plasma was assayed for levels of total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, and apolipoproteins A-I and B-100. With indistinguishable effects on intraocular pressure, carteolol and timolol induced different (P = .013) decrements in high-density lipoprotein cholesterol levels. Carteolol treatment decreased high-density lipoprotein cholesterol levels by 3.3% (-0.04 mmol/l) and raised the ratio of total to high-density lipoprotein cholesterol levels by 4.0% (0.15 unit); timolol treatment decreased high-density lipoprotein cholesterol levels by 8.0% (-0.10 mmol/l) and raised the ratio of total to high-density lipoprotein cholesterol levels by 10.0% (0.37 unit). There was no differential drug effect on the other lipid variables measured. Ocular nonselective beta-adrenergic antagonist therapy can produce clinically relevant decrements in high-density lipoprotein cholesterol levels in healthy men.

Clinical significance of genetic influences on cardiovascular drug metabolism

Inherited differences in metabolism may be responsible for individual variability in the efficacy of drugs and the occurrence of adverse drug reactions. Among the cardiovascular drugs reported to exhibit genetic polymorphism are debrisoquine, sparteine, some beta-adrenoceptor antagonists, flecainide, encainide, propafenone, nifedipine, procainamide, and hydralazine. The implications of genetic differences in the metabolism of these drugs for cardiovascular therapeutics is the subject of this review.

Assay of timolol in human plasma using gas chromatography with electron-capture detection

A simple and sensitive gas chromatographic method has been developed for the determination of timolol in plasma using electron-capture detection and propranolol as internal standard. Timolol was extracted using butyl chloride and derivatized using trifluoroacetic anhydride in butyl acetate. The lower detection limit for the assay was found to be 1 ng/ml from 1 ml of plasma. Extracted standards gave within-day precision of 12.55, 9.68 and 3.78% for 1, 20 and 100 ng/ml plasma samples, respectively. A recovery of at least 80% of timolol was found using the extraction method described. The assay was used in a randomized cross-over bioequivalence trial using an oral administration of 20 mg of timolol. Pharmacokinetic parameters compare favourably with other literature values.

A sensitive radioligand binding assay for timolol in plasma

A sensitive and reproducible radioreceptor assay (RRA) is described for the determination of low picogram levels of timolol in plasma. The plasma or serum samples (1 mL) are prepared by selectively extracting timolol with lipophilic solvents or, alternatively, only plasma (serum) proteins are precipitated prior to binding assay. The recovery of timolol is at least 90% during the sample preparation. In the radioligand binding assay, timolol and the nonselective beta-antagonist [3H](-)-CGP-12177 compete for the binding sites present in the rat reticulocyte membranes. The detection limit for timolol (30 pg/mL) exceeds 50 times the sensitivity of the GC-MS techniques for timolol. The RRA results and GC results obtained from the same clinical samples correlate excellently (r = 0.99). There was no evidence for interference caused by timolol metabolites in the RRA. Timolol concentrations in plasma following its oral and even ocular administration were possible to monitor using the RRA. The method can be modified to also measure several other beta-antagonist drugs in picogram per milliliter quantities.

Ophthalmic beta-blockers since timolol

In the twenty years since beta-blockers were proposed for treatment of glaucoma, use of topical timolol has increased to account for 70% of all glaucoma medications used. The objective of this article is to review the "newer" beta-blockers, and to address the generalization that "all ophthalmic beta-blockers are the same." The review concentrates on agents that have been studied as topical treatments for patients with elevated intraocular pressure. Sections on pharmacology and design of clinical trials are included to aid the ophthalmologist in evaluating the new drugs and published clinical reports. The major questions to consider in evaluating the therapeutic potential of a new beta-blocker for the treatment of glaucoma involve efficacy and safety: Is the drug as effective as timolol? Does it have a duration of action at least as long as timolol? Does it have ocular toxicity? Is it comfortable? What are its systemic effects?

The disposition of bunolol in the rabbit eye

Following topical administration to albino rabbits, bunolol hydrochloride, a beta 1- and beta 2-adrenoceptor antagonist, was rapidly absorbed and distributed in ocular tissues, and transformed intraocularly to a single metabolite, dihydrobunolol. The half-life of bunolol was approximately 1.26 hours in the aqueous humor and 1.63 hours in the ciliary body. There was no significant accumulation of bunolol during a four-day period of twice-daily dosing. Most of the drug was excreted in the urine following ocular or intravenous administration.

Debrisoquine polymorphism and the metabolism and action of metoprolol, timolol, propranolol and atenolol

The contribution of debrisoquine polymorphism to the metabolism and action of beta-adrenoceptor antagonists (beta-blockers) varies widely between drugs. Oxidation phenotype is a major determinant of the metabolism, pharmacokinetics and some of the pharmacological actions of metoprolol, bufuralol and timolol. The poor metabolizer phenotype is associated with an increased area under the plasma drug concentration vs. time curve, a prolongation of elimination half-life and a more intense and sustained beta-blockade. The stereoselective metabolism of metoprolol also displays phenotypic differences, which should be taken into account when interpreting plasma concentration vs. response relationships. Studies in vivo and in vitro have identified some of the metabolic pathways which are subject to this defect, namely the alpha-hydroxylation and the O-demethylation of metoprolol and the 1'-hydroxylation of bufuralol. In contrast, the pharmacokinetics and pharmacodynamics of propranolol, which is also extensively oxidized, are not related to debrisoquine polymorphism, although 4'-hydroxypropranolol formation is deficient in the poor metabolizer phenotype. The disposition of atenolol, which is almost completely eliminated unchanged by renal and faecal excretion, is independent of oxidation phenotype. If standard doses of some beta-blockers are used in poor metabolizers, these patients may be susceptible to concentration-related adverse reactions and they may also require lower and less frequent dosing for control of angina pectoris.

Glaucoma treatment with once-daily levobunolol

Although twice-daily instillation of topical beta-blockers is the standard regimen for treatment of increased intraocular pressure, once-daily therapy might improve patient compliance and provide greater safety. In a three-month, double-masked clinical trial, 92 patients with open-angle glaucoma or ocular hypertension received levobunolol 0.5% or 1% or timolol 0.5% once daily, in both eyes. Overall mean decreases in intraocular pressure were significantly greater in the groups treated with levobunolol than in the group treated with timolol. Intraocular pressure decreases averaged 7.0 mm Hg with levobunolol 0.5%, 6.5 mm Hg with levobunolol 1%, and 4.5 mm Hg with timolol. The intraocular pressures of 72% (18 of 25 patients) of those treated with levobunolol 0.5%, 79% (22 of 28 patients) of those treated with levobunolol 1%, and 64% (16 of 25 patients) of those treated with timolol were successfully controlled during the study. Heart rate and blood pressure decreases were minimal with both levobunolol and timolol. Study results indicated that once-daily treatment with levobunolol and, to a lesser extent, timolol is sufficient to control intraocular pressure successfully and safely.

Levobunolol for the long-term treatment of glaucoma

Systemically, levobunolol is as effective as propranolol for cardiovascular indications, with a greater potency and greater duration of action. Ocularly, levobunolol is as effective and as safe as topical timolol for the long-term treatment of elevated IOP. The utility of topical levobunolol as an additional, effective beta-blocker for the treatment of glaucoma will be determined by additional research and use by ophthalmologists in countries where levobunolol is approved.

Once daily timolol in the prophylaxis of angina pectoris

The clinical efficacy of timolol given once and twice daily was compared in the management of angina pectoris. Following a 2-week entry period, 16 normotensive male subjects with stable angina and proven myocardial ischaemia received timolol 10 mg twice daily, or 20 mg every morning for 1 month followed by 1 month on crossover therapy. All were exercised on separate days in random order 1 hr after administration of 10 mg, 1 hr after administration of 20 mg, 13 hr after administration of 10 mg and 25 hr after administration of 20 mg. In spite of significant differences in the maximum heart rates, rate pressure products and maximum lateral ST segment depression between the once and twice daily regimes, the maximal walking times were not significantly different (P greater than 0.10) and attack rates for angina and trinitrin consumption were similar (P greater than 0.45; P greater than 0.05). This evidence suggests that timolol is as effective in dosage of 20 mg taken once daily as half the dose taken twice daily in the symptom management of angina pectoris.

Timolol and atenolol: relationships between oxidation phenotype, pharmacokinetics and pharmacodynamics

The pharmacokinetics and pharmacodynamics of atenolol and timolol were studied in six extensive and four poor metabolisers of debrisoquine. There was a significant correlation between the debrisoquine to 4-hydroxydebrisoquine ratio and the area under the plasma concentration time curve (AUC) for timolol (rs = 0.75, P less than 0.02). The mean of the AUC values for timolol was significantly greater in the poor metabolisers than in the extensive metabolisers (P less than 0.05). There was a significant correlation between the debrisoquine to 4-hydroxydebrisoquine ratio and beta-adrenoceptor blockade 24 h after dosing with timolol (rs = 0.66, P less than 0.05). The mean degree of beta-adrenoceptor blockade was significantly greater in the poor metabolisers than in the extensive metabolisers 24 h after dosing with timolol (P less than 0.01). There was no relation between the debrisoquine to 4-hydroxydebrisoquine ratio and the pharmacokinetics or pharmacodynamics of atenolol.

Effect of ophthalmic administration of S-596 (Arotinolol) on intraocular pressure and haemodynamics in health volunteers: comparison with timolol

The effects on intraocular pressure (IOP) and haemodynamics of two beta-blockers, arotinolol and timolol, administered topically to the eye, were studied in 6 healthy volunteers in a cross-over trial. 0.5% timolol or 0.5% arotinolol ophthalmic solutions drop was instilled in both eyes of the volunteers at an interval of 48 hours. Timolol lowered IOP by about 31.9% 1 hour after administration and the effect continued until 3 h, whilst arotinolol lowered it significantly 2 h after instillation and the same maximum effect as that of timolol was obtained after 3 h. Arotinolol was detected in blood in all subject and timolol in blood in one subject, although it was found in all subjects in urine. Both drugs lowered heart rate at rest and attenuated the increase in the double product (products of blood pressure and heart rate) at exercise. The effect of timolol on the double products was larger. Thus, arotinolol and timolol decreased IOP to similar extent, although the maximal effect of arotinolol was delayed. Arotinolol as well as timolol affected haemodynamics through absorption into circulation, but the former had less effect on haemodynamics during exercise.

Relationships among timolol doses, plasma concentrations and beta-adrenoceptor blocking activity

1 We investigated the relationships among dose, plasma concentration and beta-adrenoceptor blockade after single and repeated doses (0.5-20 mg) of timolol and placebo in six normal men. 2 Maximal suppression of exercise-induced tachycardia (bicycle ergometry) was dose-dependent and greater at 2 than at 6 h after dosing; activity up to 12 h was evident on the last dosing day. 3 Attenuation of exercise-induced tachycardia was strongly correlated with the timolol dosage over the 0.5 to 5-10 mg range. 4 A plasma timolol concentration of 27 ng/ml was associated with maximal suppression of exercise-induced tachycardia. 5 Suppression of exercise-induced tachycardia and areas under the plasma concentration-time curves did not differ significantly on the first and last dosing days.

Pindolol--a beta-adrenoceptor blocking drug with partial agonist activity: clinical pharmacological considerations

1 Pindolol is a beta-adrenoceptor antagonist equally effective on beta 1- and beta 2-adrenoceptors which has a relatively long duration of action. It is practically completely absorbed and, unlike most other beta-adrenoceptor blockers, is only metabolized to a small extent during the first passage through the liver. 2 Pindolol possesses partial agonist activity (intrinsic sympathomimetic activity, ISA). This means that apart from blocking beta-adrenoceptors it produces some stimulation. Pindolol therefore only slightly influences normal sympathetic drive at rest but effectively reduces the effects of elevated sympathetic activity. 3 Various therapeutic advantages have been attributed to the partial agonist activity of pindolol: no or only slight alterations in normal cardiac output, heart rate and peripheral blood flow occur. Peripheral resistance is reduced during chronic oral therapy. No alteration of HDL/LDL cholesterol ratio has been observed. Rebound phenomena on sudden withdrawal of therapy and bronchoconstriction in susceptible patients are less likely than with drugs devoid of ISA.

Pharmacokinetics, mechanisms of action, indications, and adverse effects of timolol maleate, a nonselective beta-adrenoreceptor blocking agent

Timolol, a nonselective beta-adrenoreceptor blocking agent without intrinsic sympathomimetic or membrane stabilizing activity, has been shown effective in the treatment of angina and hypertension. It is particularly useful in patients with stable angina pectoris and patients with mild to moderate hypertension. In both of these conditions, timolol appears to be comparable to propranolol. A recent study has suggested that timolol reduces mortality and reinfarction rate in patients who have recently had a myocardial infarction. When given topically timolol reduces intraocular pressure in patients with open-angle glaucoma; the drug may be used as the primary agent or as an adjunct to standard therapy. Careful selection of patients will reduce the frequency of adverse effects due to beta-receptor inhibition. Thus, timolol should not be used in patients who are predisposed to asthmatic bronchitis or cardiac failure, and it should be used with caution in patients with peripheral vascular disease or diabetes mellitus.

Influence of intrinsic sympathomimetic activity of beta-adrenoceptor blockers on the heart rate and blood pressure responses to graded exercise

1 The relationship between plasma concentration and effect on heart rate and blood pressure at rest and at three levels of exercise were examined for four β-adrenoceptor blocking drugs having differing pharmacological properties.

2 Four doses of each drug were administered, the highest doses producing maximum effects of the work-heart rate and work-blood pressure relationships.

3 Pindolol and oxprenolol, which have intrinsic sympathomimetic activity (ISA) differed from timolol and metoprolol (which do not) in having a smaller effect on resting heart rate at each dose.

4 During exercise the four drugs had similar maximum effects on slope of the work-heart rate relationship suggesting similar suppression of reflex enhancement of sympathetic activity during exercise by each drug. The higher heart rate after drugs with ISA at rest was therefore still present at each level of exercise, e.g. maximum reduction of heart rate at 0.5 maximum work capacity was 20.5, 20.8. 24 and 28% for pindolol, oxprenolol, metoprolol and timolol respectively (P < 0.01 for difference between drugs with and without ISA).

5 The relationship between plasma concentration and reduction of heart rate at 0.5 maximum work capacity was qualitatively similar for each drug and was adequately described by a sigmoidal relationship wtih half-maximal effects at 4.4, 22, 35 and 5 ng/ml for pindolol, oxprenolol, metoprolol and timolol respectively whilst maximal effects occurred at approximately 30, 150, 100 and 30 ng/ml.

6 The results suggest that differences with exercise heart rate due to ISA are mainly due to effects on resting heart rate. The dose-response relationship of β-adrenoceptor blockers reaches a plateau at higher doses, irrespective of whether or not they possess ISA.

Comparison of effectiveness of timolol administered once a day and twice a day in the control of blood pressure in essential hypertension

The effects of a single dose and of two equally divided doses of timolol were compared in a double-blind trial in 15 patients with essential hypertension. The amount of timolol per day remained constant for each patient, but individual patients received different amounts (from 10 mg to 30 mg/day). Timolol combined with a diuretic produced similar lowering of blood pressure in patients who required 10 mg, 20 mg or 30 mg of timolol per day when given either as one dose or in two equal doses. Plasma concentrations of timolol were high enough to be a major contributing factor to the long duration of the hypotensive response.