Iontophoretic in vivo transdermal delivery of beta-blockers in hairless rats and reduced skin irritation by liposomal formulation

PURPOSE

To demonstrate the in vivo transdermal delivery and establish the comparative pharmacokinetics of five beta-blockers in hairless rat.

METHODS

Intravenous dosing was initially done via jugular cannula. For iontophoretic delivery, current (0.1 mA/cm2) was applied for 2 h through a drug reservoir patch containing the beta-blocker (10 mg/ml). Blood samples were collected and analyzed by stereoselective HPLC assays. Any irritation resulting from patch application was quantified by a chromameter. Multilamellar liposomal formulation was prepared by the thin-film hydration method and converted to unilamellar liposomes by extrusion.

RESULTS

With transdermal iontophoresis, therapeutically relevant amounts of propranolol (83.78 +/- 7.4 ng/ml) were delivered within an hour and lasted for up to 4 h. Cmax (185.1 +/- 56.8 ng/ml) was reached at hour 3. A significantly higher amount (p < 0.05) of sotalol HCl was delivered compared to other beta-blockers. There was no significant difference in the S/R ratio of AUC0-t for enantiomers after both intravenous and transdermal delivery. Skin irritation was significantly reduced (p < 0.05) when a liposomal formulation of the propranolol base was used rather than the base itself.

CONCLUSIONS

The comparative pharmacokinetics of intravenous and transdermal iontophoretic delivery of five beta-blockers in hairless rats was established. It was shown that there is no stereoselective permeation.

Oxprenolol-loaded bioadhesive microspheres: preparation and in vitro/in vivo characterization

Biologically adhesive delivery systems offer important advantages over conventional drug-delivery systems. In this paper, microspheres intended as a sustained release carrier for oral or nasal administration have been prepared by associating a known bioadhesive polymer, poly(acrylic acid), in gelatin microspheres. A model drug oxprenolol hydrochloride was chosen. It was found that some of the formulation variables can influence the characteristics of the beads in a controlled manner. The internal structure of the microspheres studied by X-ray diffraction, thermal analysis and optical microscopy showed the absence of drug crystals in microspheres and a lowering in the glass transition temperature. The dynamic swelling of the beads obeyed the square root of time and a shift from the diffusional to the relaxational process dependent on the content of poly(acrylic acid) in gelatin microspheres was observed. As expected, drug release from gelatin/poly(acrylic acid) microspheres was influenced by the poly(acrylic acid) content in beads, by the particle size of microspheres and by the pH of the medium. The mechanism of release was analysed by applying the empirical exponential equation and by calculation of the approximate contribution of the diffusional and relaxational mechanisms to the anomalous release process by fitting the data to the coupled Fickian/Case II equation. In vitro and in vivo experiments in rats showed good adhesive characteristics of the gelatin/poly(acrylic acid) microspheres, which were greater if the poly(acrylic acid) content was greater. A significant retardation in gastric and intestinal emptying time of the beads was observed. This was also suggested by the bioavailability of the model drug after intragastric and intranasal administration of the microspheres. The pharmacokinetic parameters after microsphere administration were more appropriate to a slow release drug-delivery system. The work suggests the potential of this pharmaceutical delivery system as an alternative controlled-release dosage form, either for oral or nasal administration.

Dynamic swelling behaviour of gelatin/poly(acrylic acid) bioadhesive microspheres loaded with oxprenolol

The dynamic swelling of gelatin/poly(acrylic acid) microspheres loaded with oxprenolol has been evaluated. The movement of two distinct and characteristic swelling boundaries was measured directly using an optical microscope. Swelling rate constants associated with the inner moving front and the outer swelling boundary were determined. A polynomial equation incorporating both Fickian diffusion and case II relaxational models was used to fit the kinetics of liquid uptake. The influence of the concentration of the cross-linking agent, the poly(acrylic acid) load, the pH of the swelling medium and the particle size of the microspheres, on the swelling kinetics, was evaluated and discussed.

Oxprenolol release from bioadhesive gelatin/poly(acrylic acid) microspheres

Drug release from gelatin/poly(acrylic acid) oxprenolol-loaded microspheres has been evaluated using an in situ sink immersion method and a wetting method. The kinetics of drug release were analysed by applying the empirical exponential equation and by the calculation of the approximate contribution of the diffusional and relaxational mechanism to the anomalous release process by fitting the data to the coupled Fickian/Case II equation. The influence of glutaraldehyde cross-linking agent concentration, the poly(acrylic acid) content, the pH of the release medium and the particle size of the beads on the drug release kinetics were evaluated and discussed.

Relationship between amount of beta-blockers permeating through the stratum corneum and skin irritation after application of beta-blocker adhesive patches to guinea pig skin

We evaluated the relationship between the cumulative amounts of 5 kinds of beta-blockers (alprenolol, oxprenolol, timolol, acebutolol and atenolol) permeating through the stratum corneum and a* values obtained by measuring the formation of erythema, a skin irritation reaction, with a chromameter after transdermal application of adhesive patches containing 2 beta-blocker to the skin of guinea pigs. The cumulative amount of beta-blocker released from each adhesive patch to the skin increased with the increase in application time. The contents of alprenolol, oxprenolol and timolol in the stratum corneum and in the stripped skin increased markedly up to 4 h after application and thereafter were maintained at high levels up to 24 h. The contents of acebutolol and atenolol, on the other hand, increased up to 24 h, but these values were low. a* values of all adhesive patches 24 h after application were higher than those before application. The correlation coefficients between the cumulative amounts of alprenolol, oxprenolol, timolol, acebutolol or atenolol permeating through the stratum corneum and (delta a* -delta a*Placebo) values were 0.739, 0.717, 0.722, 0.551 and 0.633, respectively. The correlation coefficient calculated by averaging the cumulative amounts of 6 kinds of beta-blockers permeating through the stratum corneum [including propranolol which was reported previously (Kobayashi I., et al., Biol. Pharm. Bull., 19, 839-844 (1996))] was 0.731, higher than the correlation coefficient between contents of these beta-blockers in the stripped skin and (delta a* -delta a*Placebo) values (r = 0.552). This suggests that there was a high correlation between the cumulative amounts of beta-blockers permeating through the stratum corneum and (delta a* -delta a*Placebo) values.

Disposition of human drug preparations in the horse. V. Orally administered oxprenolol

Urinary concentrations of the beta-antagonist oxprenolol and some of its major human metabolites were determined following oral administration of a dose of 160 mg to five fasted horses. Quantitation was performed by gas chromatography-mass spectrometry (GC-MS) in the selected ion mode (SIM) by monitoring ion m/z 466 of the heptafluorobutyric derivatives. As early as 2 h after dosage oxprenolol could be detected in hydrolysed urine and remained detectable up to 24 h. Maximum urinary concentrations and excretion rates were obtained between 2 and 12 h. After 12 h only 2.8% of the administered dose was excreted as conjugates of oxprenolol and major human metabolites including 4-OH-oxprenolol and 5-OH-oxprenolol. These metabolites were detectable up to 48 h.

[Chronology of regression of hypertensive ventricular hypertrophy during antihypertensive therapy with beta blockers]

To define the time course of regression of left ventricular hypertrophy (LVH) during antihypertensive therapy with beta-blocking agents, 73 hypertensive patients were serially studied by echocardiography during 12-months therapy with beta-blockers. Blood pressure decreased significantly after 1 month and further on after 12 months (from 164 +/- 18/110 +/- 9 to 139 +/- 14/94 +/- 7 mmHg, p < 0.001). Left ventricular (LV) end-diastolic dimension increased significantly after 1 month (from 51.2 +/- 3.9 to 52.2 +/- 4.7 mm, p < 0.01) and decreased after 12 months (50.4 +/- 4.0 mm, p < 0.05). Septal and posterior wall thickness decreased progressively after 1 month and 3 months, respectively. LV mass index decreased significantly after 3 months, and further on after 12 months (from 164 +/- 42 to 145 +/- 33 g/m2, p < 0.001). LV fractional shortening did not significantly change throughout the study. Thus, a reduction of hypertensive LVH occurred after 3 months of therapy with beta-blocking agents and went on during the subsequent months without impairment of LV systolic function.

Constant-rate drug release from novel anionic gel beads with transient composite structure

A new anionic composite bead system with a transient membrane-matrix structure, capable of prolonged constant-rate drug release, has been developed from suspension-polymerized poly(methyl methacrylate-co-methacrylic acid) (PMMA/MAA). These composite beads have a thin PMMA/MAA surface layer and a core consisting of the sodium salt form of the polymer (PMMA/MANa). The high loading (> 20%) of a model drug (oxprenolol HCl) that is achievable in this system from a loading solution concentration as low as 0.5% suggests the formation of a drug-polymer complex in the form of an ionic salt in the core. The release of oxprenolol from such composite beads shows an initial burst effect followed by an extended constant-rate region before leveling off. Apparently, the surface PMMA/MAA layer functions as a transient rate-controlling membrane before it is completely ionized. Because the ionization process is slow, the rate-controlling characteristics of the surface layer and the resulting constant rate of drug release are both sustained for an extended period. The unique feature of the present system is not only its high drug loading capability, but also the transient nature of the rate-controlling surface layer, which is completely ionized towards the latter part of the drug release, thus avoiding prolonged tailing of drug release that is normally associated with permanent membrane-matrix systems.

The effect of oxprenolol dosage time on its pharmacokinetics and haemodynamic effects during exercise in man

We have studied the effect of dosage time of oxprenolol (Trasicor) on its pharmacokinetics and pharmacodynamics in six healthy volunteers. The drug effects measured were heart rate and systolic blood pressure during exercise. Oxprenolol was taken orally at 08.00 h, 14.00 h, 20.00 h, and 02.00 h in randomized order, with 1 week between successive doses. There were differences in the pharmacokinetics of oxprenolol for the ratio between the apparent volume of distribution and systemic availability (P = 0.04) and for elimination half-life (P = 0.006). Both were lowest after administration at 14.00 h (163 (77) l and 1.2 (0.6) h; mean (SD)) and highest after administration at 02.00 h (229 (100) l, and 1.7 (0.6) h). The systolic blood pressure during exercise before oxprenolol did not vary with dosage time, but heart rate during exercise before intake was lowest before dosage time 08.00 h and highest before dosage time 20.00 h (P = 0.03). The time-course of heart rate during exercise after oxprenolol was described by a model that incorporated the factors drug concentration and spontaneous diurnal variation. EC50 and Emax did not vary between dosage times. The spontaneous diurnal variation in heart rate during exercise was unaffected by oxprenolol, leading to an apparently greater effect of oxprenolol during the night than during the day.

Effect of loading on swelling-controlled drug release from hydrophobic polyelectrolyte gel beads

The effect of oxprenolol HCl loading on the kinetics of polymer swelling and drug release from suspension-polymerized poly(methyl methacrylate-co-methacrylic acid) (PMMA/MAA) beads has been studied in detail. Within the range of variables studied, the polymer swelling rate increases with buffer pH and concentration. And an ionization-controlled swelling mechanism (analogous to the relaxation-controlled mechanism) mechanism) seems to become more rate-limiting at higher buffer concentrations. At oxprenolol HCL loading levels below 17.8%, the drug release and associated dimensional changes (in pH 7.4) exhibit an extended quasi-linear region despite the inherent limitation of spherical geometry. At higher loading levels, the drug release becomes faster and first-order in nature. This is apparently a result of the transition from a dissolved to a dispersed system above a percolation threshold (15-18% loading in the present study). As a result of competition from processes such as the reduction of bead dimension due to drug release and the dimensional increase due to polymer swelling and osmotic contributions from the drug, the transient bead diameter increases monotonically during drug release at loading levels up to 25.6%, whereas upon further increasing the drug loading, the bead diameter goes through a maximum during the early drug release, which eventually increases again as a result of the slow but continuous increase in polymer swelling due to further ionization. In all cases, both the drug release and the dimensional changes approach completion as the penetrating ionization fronts meet at the center, indicating a true swelling-controlled behavior.

Hydrophobic anionic gel beads for swelling-controlled drug delivery

Using oxprenolol HCl as a model drug, the effects of pH and buffer concentration on the swelling and drug release properties in cross-linked poly(methyl methacrylate-co-methacrylic acid) (PMMA/MAA) beads have been investigated. The kinetics of swelling of such hydrophobic anionic gel beads from the dehydrated state appear to be governed primarily by a diffusion-ionization process which becomes more ionization-controlled at higher buffer concentrations. Within the range of ionic compositions studied, the swelling rate increases and the initial swelling/ionization front penetration becomes increasingly linear in time with increasing pH or buffer concentration of the swelling medium. The corresponding swelling bead diameter appears to reach an equilibrium value as soon as the penetrating ionization fronts meet at the center, suggesting a swelling equilibrium in the ionized shell due to rapid mechanical readjustment in the gel phase. At oxprenolol loading levels up to 15%, both the transient drug release and swelling bead diameter exhibit extended quasi-linear regions despite the inherent limitation of decreasing surface area at the penetrating front in the spherical geometry. In addition, both the drug release and the dimensional changes reach completion when the penetrating ionization fronts meet at the center, suggesting a true swelling-controlled drug release behavior.

Relative bioavailability of oral sustained-release and regular-release oxprenolol tablets at steady-state

The relative bioavailability of a test sustained-release (SR) oxprenolol tablet against an approved regular-release (RR) tablet has been investigated at steady-state. In a randomized two-way crossover study, one tablet of 160 mg SR oxprenolol once every 24 h and one tablet of 80 mg RR oxprenolol once every 12 h were given to 12 healthy volunteers for 5 days. Blood samples were collected from each subject just prior to each dose-administration on days 1 through 4, and at scheduled time points on day 5 and analysed for oxprenolol concentration using HPLC. The SR tablet resulted in 42 per cent reduction in mean peak drug levels (p = 0.0341) and a statistically non-significant 14 per cent increase in mean trough levels (p = 0.8357) than the RR tablet. However it required 160 per cent longer time to reach average steady-state concentrations (Css) on day 5 (1.38 h for SR versus 0.53 h for RR; p = 0.0205). The mean area under the plasma drug concentration-time curve at steady state (AUC96-120) with the SR tablet was approximately 18 per cent lower than that observed with the RR tablet, and the degree of fluctuation (DF) was reduced by 30 per cent (2.81 for SR versus 4.11 for RR; p = 0.0069). On average, a single dose of SR tablet and two doses of RR tablets maintained the drug levels above a constant Css of 204.6 ng ml-1 for 7.88 and 7.65 h, respectively (p = 0.3513).

Efficacy and tolerability of long term oxprenolol and chlorthalidone singly and in combination in hypertensive blacks

Sixty two black patients who had confirmed but untreated hypertension participated in a double blind clinical trial of the efficacy and tolerability of slow-release oxprenolol in a daily dose of 160 mg initially and 320 mg subsequently versus chlorthalidone 50 mg daily. Thereafter, a combination of oxprenolol with chlorthalidone in an initial dose of 160 mg and 25 mg and a subsequent dose of 320 mg and 50 mg, respectively, was administered and the effects compared with those of the same drugs given singly. The trial lasted for 3 years, but each participant took active medication for 1 year. Oxprenolol as monotherapy had no effect on the blood pressure, irrespective of the dose. Chlorthalidone as monotherapy produced a significant fall in blood pressure (p less than 0.01). Combining the 2 drugs enhanced their blood pressure lowering effects (p less than 0.001). Oxprenolol as monotherapy and as part of combination therapy was well tolerated by all patients. Chlorthalidone as monotherapy was well tolerated by most patients while a fraction of the patients developed biochemical derangements. These results confirm the findings that a beta-blocker alone may be ineffective in lowering blood pressure in hypertensive blacks. The results also show that the efficacy and tolerability of a beta-blocker and a diuretic are enhanced by their combined administration. Finally, the results show that increasing the dose of a beta-blocker or a diuretic does not produce a further increase in its blood pressure lowering effect.

[A comparative study of the ocular hypotonic action of collyria with oxprenolol and timolol maleate]

Comparison of the decrease in intraocular tension in a group of 25 patients show that the collyria of oxprenolol, 0.25%, led to an average decrease of 6.36 mmHg, whereas that of thymolol maleate, 0.25%, to a decrease of 8.76 mmHg. Both decreases were statistically significant versus the initial intraocular tension.

Zero-order release formulation of oxprenolol hydrochloride with swelling and erosion control

Zero-order release of oxprenolol hydrochloride was obtained by controlling the swelling and erosion of the matrix. This formulation involves only mixing of drug, hydroxypropylmethylcellulose (HPMC), and sodium carboxymethylcellulose (Na CMC) at the ratio of 1:0.4:1.6, respectively, and compressing the mixture directly into tablets. The in vitro release pattern from this optimized matrix tablet was reproducible. Accelerated stability studies revealed that the optimized formulation remains stable for an approximately 2-year shelf life. This sustained-release (SR) tablet was evaluated in dogs, and for comparison a conventional (CV) formulation was also given at the same dose level. Plasma oxprenolol levels were monitored by a sensitive and specific high-performance liquid chromatographic (HPLC) method. Significant differences in the pharmacokinetic parameters, i.e., lower Cmax, higher values of tmax, MRT, AUC, and plasma concentration at 24 hr, and nearly constant plasma levels over 12 hr, indicated that the SR matrix tablet is superior to the CV rapid-releasing formulation. The in vitro release parameters and in vivo pharmacokinetics correlated well.

Effects of chlorthalidone, oxprenolol, and their combination in hypertensive blacks: a randomized double-blind crossover study

One hundred twenty black patients with mild to moderate essential hypertension participated in a double-blind placebo-controlled crossover study of the efficacy and tolerability of slow release oxprenolol versus chlorthalidone singly and in combination. Oxprenolol as monotherapy produced no effect on blood pressure as compared with placebo even after doubling the dose. Chlorthalidone as monotherapy produced a significant decrease in blood pressure (p less than 0.01). Combining oxprenolol with chlorthalidone yielded hypotensive effects in excess of those of either of the components given singly. Oxprenolol produced a significant decrease in plasma renin activity (PRA) whereas chlorthalidone produced a significant increase in PRA. These results indicate that a beta-blocking agent alone is ineffective in lowering blood pressure in hypertensive blacks, even when the dose is high. Oxprenolol may increase the hypotensive effect of chlorthalidone by counteracting the hypokalemic effect of the diuretic and by attenuating the diuretic-induced increase in plasma renin activity.

Relationship between the rate of appearance of oxprenolol in the systemic circulation and the location of an oxprenolol Oros 16/260 drug delivery system within the gastrointestinal tract as determined by scintigraphy

1. The position in the gastrointestinal tract of an orally administered oxprenolol Oros drug delivery system labelled with technetium-99m DTPA was followed by gamma scintigraphy, and the corresponding plasma drug concentration-time profiles after oral and i.v. administration were used to relate pharmacokinetic and transit data. 2. Gastric emptying time (0.8 +/- 0.4 h, mean +/- s.d.), and the time to arrival in the colon (3.8 +/- 0.7 h) were reasonably consistent after administration of the Oros system to fasted subjects, as were the calculated small intestine transit times (3.0 +/- 0.7 h). As expected there were wide individual variations in colonic transit, so that recorded values for total transit ranged from 6 to 32 h (median, 24.7 h). 3. Absorption of oxprenolol occurred throughout the GI tract including the colon. Plasma drug concentration-time profiles and input functions (calculated by deconvolution) could be related to transit behaviour and in vitro release. Inflexions in the calculated rate of drug input when the Oros system was located in the colon corresponded with periods of stagnation at the hepatic and splenic flexures in two subjects and the ileocaecal junction in two others. The mechanism of these changes is unclear.

Relationships between verapamil plasma concentrations and its antihypertensive action

Twenty-seven hypertensive outpatients were studied to evaluate the efficacy of verapamil after a single oral dose as well as following a short-term treatment and also in combination with oxprenolol. Blood pressure was significantly reduced (p 0.01) after verapamil monotherapy and the combined treatment. PR interval was lengthened from 30 min to 4 h during acute testing, and also after short-term treatment. QT was only prolonged after the verapamil monotherapy. Systolic time intervals (STIs) were not modified, except left ventricular ejection time (LVETc). Direct correlations were found among verapamil plasma concentrations and changes provoked on blood pressure and PR interval. The mean side effects found were disturbance of atrioventricular conduction in two patients without ulterior complications. The results suggest that verapamil monotherapy or in combination with oxprenolol could be useful in the treatment of essential hypertension.

Myocardial ischemia in untreated hypertensive patients: effect of a single small oral dose of a beta-adrenergic blocking agent

In a non-double-blind, prospective, randomized study, the intra-operative electrocardiograms of 128 mildly hypertensive surgical patients were examined in order to determine the incidence of myocardial ischemia during anesthesia. No patient had been receiving chronic antihypertensive therapy prior to the study, but a single small oral dose of a beta-adrenergic blocking agent (labetalol, atenolol, or oxprenolol) was given to 89 of them along with premedication. Forty-four per cent of the untreated control patients and 61% of the patients pretreated with a beta-adrenergic blocking agent had normal preoperative electrocardiograms and no risk factors for coronary artery disease other than hypertension (this difference between groups was not statistically significant). During tracheal intubation and/or emergence from anesthesia, a brief, self-limited episode of myocardial ischemia was detected in 11 of 39 untreated control patients, and in two of 89 patients pretreated with a beta-adrenergic blocking agent (P less than 0.001). Tachycardia always accompanied the ischemic events, but a conspicuous increase in blood pressure did not. The authors conclude that mild hypertension, when untreated prior to the induction of anesthesia, is associated with a high incidence of myocardial ischemia; and that a single small oral dose of a beta-adrenergic blocking agent, given with pre-medication, can significantly reduce that risk.

Evaluation of two oxprenolol oral osmotic (OROS) delivery systems in patients with essential hypertension

The effects of two oxprenolol oral osmotic (OROS) delivery systems on heart rate and blood pressure before and during recovery from exercise at a predetermined load were examined in twelve patients with hypertension previously responding to beta-blocker monotherapy. Haemodynamic responses were attenuated during the 24 h after single and repeated (15 days') once daily administrations of 10/170 and 16/260 oxprenolol OROS. At 24 h after repeated doses, compared to placebo there were significant reductions in resting blood pressure and in heart rate immediately following exercise. Attenuation of heart rate after exercise was dose related but differences between the systems with respect to resting heart rate and blood pressure were inconsistent. Antihypertensive responses after repeated doses were greater than those after single doses. However, reductions in resting and exercise heart rates were consistently less on chronic therapy. This may reflect enhanced expression of the partial agonist activity of oxprenolol due to altered receptor sensitivity after prolonged beta-blockade. The plasma oxprenolol profiles after both systems indicated slow absorption and substantial concentrations were apparent 24 h after drug administration. These observations suggest that both oxprenolol OROS systems display sustained drug release and on once daily dosing provide 24 h beta-blockade and control of blood pressure at rest and following exercise.

Antihypertensive effect of a new formulation of slow release oxprenolol in essential hypertension

To test whether a new formulation of a slow release oxprenolol (SLOx) can produce a steady 24-h antihypertensive effect, we recorded 24-h intraarterial blood pressure (Oxford technique) in eight ambulant inpatients (age 44.5 +/- 3.0 years, mean +/- SE) with a mild or moderate hypertension who were untreated since three weeks. The study was started seven days after hospitalization and was conducted according to a randomized doubleblind cross-over design. Blood pressure recordings were made after (a) a 7-day administration of SLOx in a single evening dose, and (b) a 7-day administration of placebo. This design allowed to determine the effect of SLOx without interference from nonspecific blood pressure lowering factors. Blood pressure effects of handgrip, submaximal cyclette exercise, and cold pressor test 20-24 h after the administration of SLOx and placebo were also evaluated. The blood pressure tracing was analyzed beat-to-beat by a computer which provided also the analysis of the heart rate data. The 24-h mean systolic and diastolic blood pressure measured during placebo were 144.6 +/- 6.4 and 81.1 +/- 3.9 mm Hg, the corresponding heart rate being 76.9 +/- 3.5 beats/min. SLOx reduced these values by 6.2, 10.6, and 4.8%, respectively, all effects being similarly evident throughout the blood pressure recording. The pressor responses to handgrip, cyclette exercise, and cold pressor test were not affected by SLOx. By contrast, the small tachycardic response to handgrip and the large tachycardic response to submaximal cyclette exercise were significantly reduced by the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

The pharmacokinetics of oxprenolol following oral and rectal dosing--a comparison of delivery systems and routes of administration

Plasma oxprenolol concentrations were measured in eight healthy volunteers who received equivalent oral doses of the drug in the form of an aqueous solution and a 10/170 oxprenolol Oros drug delivery system. Absorption from the lower gastrointestinal tract was assessed by measurement of plasma concentrations after rectal administration of the pre-equilibrated Oros systems. Because three of the first four volunteers suffered local irritation, however, the other four volunteers received Slow Trasicor 160 mg orally as a comparative preparation. The rate of in vivo absorption after oral administration of the Oros system closely mirrored its in vitro release rate. Drug availability from Oros was reduced, however, and was equivalent to 77% of that from the oral solution. Oxprenolol was well absorbed from the rectum while the system was present in this segment of the gut. The reduced systemic availability in three of the volunteers could be accounted for largely by drug loss when the system was expelled. Slow Trasicor produced higher peaks but lower 24 h plasma concentrations than the orally administered Oros system. As judged from the relative areas under the plasma concentration-time curve, however, the availability of the drug from the two dosage forms was comparable.

Evaluation of oxprenolol slow release and osmotic release by exercise testing and ambulatory electrocardiographic monitoring in patients with chronic stable angina pectoris

We have treated eleven patients with chronic stable angina pectoris with slow-release oxprenolol (160 mg and 320 mg) in a double-blind crossover study and evaluated its efficacy objectively by exercise testing between 180 and 240 min after dosing. The mean exercise time increased significantly from 6.2 min on placebo to 7.2 min and 7.3 min on oxprenolol 160 mg and 320 mg respectively. No overall beneficial effects could be demonstrated for the higher dose. A further 20 patients received slow release oxprenolol 160 mg and 10/170 mg "Oros" (osmotic release) oxprenolol in a double-blind crossover study using exercise testing and ambulatory electrocardiographic monitoring at 21-23 h after dosing. The mean exercise time increased significantly from 7.0 min on placebo to 8.3 min on slow-release oxprenolol and to 8.1 min on "Oros" oxprenolol. The effects of the 2 treatments on exercise and ambulatory heart rates were comparable. Two patients were withdrawn during the double-blind treatment period while receiving oxprenolol slow-release, one because of unstable angina and another because of throbbing headache. These findings confirm that slow-release oxprenolol is effective in treating chronic stable angina pectoris at the 160-mg dose. "Oros" oxprenolol 10/170 mg has a profile of action closely similar to but without any additional benefit over slow-release oxprenolol 160 mg.

Comparison of pharmacokinetic profiles of single and multiple doses of a slow release Oros oxprenolol delivery system in young normotensive and elderly hypertensive subjects

Oxprenolol in an Oros 8/130 sustained release osmotic pump system (equivalent to 120 mg oxprenolol hydrochloride in a conventional formulation and releasing 8 mg h-1) was given to eight normal young subjects (mean age 23 years) and eight elderly hypertensive patients (mean age 77 years). The plasma concentration-time profiles of oxprenolol were determined over 32 h using gas liquid chromatography after the initial dose and following seven doses. The elderly patients had a significantly higher AUC and maximum plasma oxprenolol concentration following both the first and final doses studied. It is unlikely that this difference is due to a prolonged absorption phase in the elderly patients. Reduced drug clearance seems the most probable explanation.

[Effect of beta-adrenergic blockaders and their combination with an alpha-adrenergic blockader on physical exertion tolerance in patients with hypertension]

The effect of long-term treatment with propranolol (45 patients), trasicor (15), visken (23) and combinations thereof with phentolamine and labetalol (12) on submaximum exercise tolerance was studied in patients with second-stage essential hypertension. Beta-adrenoblockers had no effect on total systemic oxygen consumption, but reduced significantly its myocardial consumption and brought down systolic and diastolic arterial blood pressure at rest and during exercise. Differences were demonstrated in the hemodynamic mechanism of the decline in resting arterial pressure: under the effect of propranolol and trasicor, peripheral resistance increased insufficiently in response to a fall of the cardiac index; visken and labetalol depressed peripheral resistance without affecting the cardiac index. During exercise, all 4 beta-adrenoblockers reduced the cardiac index, mainly at the expense of a smaller pulse rate. An additional hypotensive effect of phentolamine that owes to reduced peripheral resistance was demonstrated.

Evaluation of L-tryptophan for treatment of insomnia: a review

Sleep laboratory and outpatient studies of the hypnotic efficacy of the amino acid L-tryptophan are reviewed, with particular emphasis on evaluation of therapeutic effectiveness in the treatment of insomnia. In younger situational insomniacs, whose sleep problem consists solely of longer than usual sleep latencies, L-tryptophan is effective in reducing sleep onset time on the first night of administration in doses ranging from 1 to 15 g. In more chronic, well-established sleep-onset insomnia or in more severe insomnias characterized by both sleep onset and sleep maintenance problems, repeated administration of low doses of L-tryptophan over time may be required for therapeutic improvement. In these patients, hypnotic effects appear late in the treatment period or, as shown in some studies, even after discontinuation of treatment. The improvement in sleep measures post-treatment has given rise to use of a treatment regimen known as "interval therapy", in which L-tryptophan treatment alternates with an L-tryptophan-free interval until improvement occurs. The absence of side effects and lack of development of tolerance in long-term use are important factors in the decision to embark upon a trial of L-tryptophan treatment. In addition, L-tryptophan administration is not associated with impairment of visuomotor, cognitive, or memory performance, nor does it elevate threshold for arousal from sleep.

Hydrochlorothiazide and triamterene with sustained-release oxprenolol in the treatment of hypertension

A single-blind, three-way Latin square crossover study without wash-out periods was performed in a general practice. Thirty moderately hypertensive patients were studied to compare the antihypertensive effect of 160 mg sustained-release oxprenolol once daily, 25 mg hydrochlorothiazide/50 mg triamterene once daily or a combination of the two preparations once daily, each treatment being given for 1 month. Blood pressure control was significantly better with the combination than with either agent used separately. Pulse rates, as expected, were lower when sustained-release oxprenolol was taken either alone or in the combination. Adverse events led to withdrawal in 1 patient only. Otherwise, all treatments were well tolerated and compliance was excellent. Renal function tests indicated a slight increase in creatinine, urate and urea levels after the treatments which included hydrochlorothiazide compared with oxprenolol alone, although the results were of no clinical significance.

Interaction of calcium antagonists with beta-adrenoceptor blocking agents

Responsiveness to verapamil, the best studied calcium antagonist, was examined in cardiac preparations of rabbits pretreated with beta-adrenoceptor blockers (propranolol 2 mg/kg or oxprenolol 4 mg/kg s.c.) twice daily for either one or six weeks. Using this dose-regimen, the degree of cardiac beta-adrenoceptor blockade in conscious rabbits was substantial and similar for propranolol and oxprenolol. When administered for one week, neither propranolol nor oxprenolol affected to any marked extent the electrical and mechanical response to verapamil, diltiazem or fendiline in tissues isolated from various parts of the heart. In contrast, pretreatment with propranolol for six weeks resulted in a significant aggravation of the negative inotropic effect of verapamil in both atrial and ventricular muscle, and the verapamil-induced delay in atrio-ventricular and intra-ventricular conduction also became more pronounced. The same long-term administration of oxprenolol, one of the beta-blockers with "intrinsic" sympathomimetic activity, did not alter the atrial or ventricular contractile response to verapamil and did not significantly increase the lengthening of atrio-ventricular conduction time occurring in the presence of verapamil. It is concluded that from the point of view of adverse direct cardiac interactions with verapamil prolonged administration of oxprenolol appears to be less dangerous than chronic treatment with propranolol. It is also assumed that in those cases in which acute administration of verapamil may be necessary, concomitant chronic blockade of cardiac beta-adrenoceptors is less dangerous if drugs known to possess not only beta-adrenoceptor blocking properties, but also some "intrinsic" sympathomimetic activity are applied.

The pharmacokinetics and dynamics of oxprenolol: a simulation study with six subjects

Experimental results of plasma concentration determinations and lowering of exercise heart rate for six subjects taking a conventional tablet and a sustained release preparation of oxprenolol have been analysed by a comprehensive computer simulation model. Individual plasma values were simulated using a lest squares procedure and the results were applied to evaluate individual release patterns following dosage with the sustained release preparation. Application of the model to the lowering of exercise heart rate indicated that the response is in a steady state with the plasma values and that the response-concentration relation is of the saturable, Emax, type. The parameters for this were evaluated for each subject for the results after a dose of a conventional tablet. These parameters were applicable to the results after dosage with a sustained release preparation. The method should be applicable to other sustained release preparations.

Angiotensin converting enzyme inhibitors and quality of life: the European trial

Two prospective multi-centre randomized trials were initiated to compare the relative efficacy and influence on quality of life of captopril, alone or in combination with hydrochlorothiazide, against either methyldopa, alone or in combination with hydrochlorothiazide, or oxprenolol in combination with chlorothalidone. The complaint rate, activity index and psychiatric morbidity were evaluated as indices of quality of life. Captopril was associated with a significantly (P less than 0.05) greater reduction in complaint rate compared with methyldopa and a tendency for less symptoms of depression compared with oxprenolol (P = 0.06), the latter drug being associated with an increase in depression scores. The trends in quality of life indices in the captopril-treated patients would suggest the need for double-blind placebo-controlled trials to investigate these apparent benefits.

Evaluation of oxprenolol and metoprolol Oros systems in the dog: comparison of in vivo and in vitro drug release, and of drug absorption from duodenal and colonic infusion sites

The performance of oxprenolol and metoprolol Oros systems has been evaluated in the dog. One study compared in vivo and in vitro release from both systems over 2-14 h. The other compared the systemic availabilities of both drugs after 3 h infusion at a constant rate into the cephalic and hepatic portal veins, and into the lumen of the duodenum and colon. In the in vivo release studies, Oros systems were recovered throughout the gut from the stomach to the colon. The amounts of drug remaining in the systems corresponded closely to those measured in a parallel in vitro release experiment. In vitro testing is thus a reliable indicator of in vivo system performance. In the absorption studies, both metoprolol and oxprenolol were shown to be subject to substantial first-pass metabolism. Additionally, for metoprolol the data indicated a significant loss during transport from the gut lumen into the portal circulation. For both drugs the availability from the colon was equal to that from the duodenum. These results provide some justification for the development of oral dosage forms with extended durations of release even for drugs which undergo significant first-pass metabolism.

A multiple dose comparative study of the pharmacodynamic and pharmacokinetic behaviour of polymer-matrix and Oros dosage forms of oxprenolol in healthy volunteers

A new osmotic drug delivery system (Oros) has been evaluated in multiple-dose studies in young healthy volunteers as a sustained-release vehicle for once-daily administration of oxprenolol. Two Oros systems were examined in two separate studies, one containing 170 mg oxprenolol succinate with an initial zero-order release rate of 10 mg/h, and the other containing 260 mg oxprenolol succinate with an initial release rate of 16 mg/h. These were compared respectively with conventional oxprenolol hydrochloride (Trasicor) 80 mg twice daily and polymer-matrix oxprenolol hydrochloride (Slow Trasicor) 160 mg once daily. Variations in mean plasma levels and beta-adrenoceptor blockade (measured by inhibition of exercise tachycardia) were considerably reduced on the 10/170 Oros once-daily compared with the Trasicor 80 mg twice-daily regimen. With both formulations there was no significant change in mean plasma concentrations or areas under the curve after 8 days' treatment, and similar pre-dose plasma concentrations were obtained. There was significant inhibition of exercise tachycardia throughout 24 h after the 10/170 Oros on the eighth day. The 16/260 Oros system gave smoother pharmacokinetic and pharmacodynamic profiles, and on repeated dosing a higher mean pre-dose plasma oxprenolol concentration than Slow Trasicor. Drug availability was similar for the two dose forms, suggesting an acceptable level of absorption of oxprenolol from most of the gastrointestinal tract. On the eighth day exercise heart rate was significantly reduced throughout 24 h with 16/260 oxprenolol Oros, but only between 1 and 15 h with Slow Trasicor.

Gastrointestinal transit of Oros drug delivery systems in healthy volunteers: a short report

Transit times for oxprenolol and metoprolol Oros drug delivery systems through the gastrointestinal tract have been measured in 35 individuals in six separate studies. A total of 45 systems were recovered in a median time of 27.4 h; individual transit times varied from 5.1 to 58.3 h. The residual amount of drug in recovered systems was inversely related to transit time and corresponded closely with the amount estimated from in vitro dissolution profiles.

Exercise and resting blood pressure and heart rate changes 24 h after dosing in patients with essential hypertension receiving 16/260 oxprenolol Oros once daily

Nineteen patients receiving oxprenolol slow-release (SR) 160 mg (three patients) or 320 mg (16 patients) once daily for mild to moderate hypertension were treated with oxprenolol Oros 16/260 once daily for 3 weeks following a 2 week placebo wash-out period. Repeated dosing with both Oros and SR oxprenolol preparations, in comparison with placebo, significantly reduced supine systolic and diastolic blood pressures, and pulse rate at 24 h after dosing. Single Oros doses also significantly reduced pulse rate and diastolic, but not systolic, blood pressure at 24 h. The reduction in supine systolic blood pressure was greater during repeated dosing with oxprenolol SR than after a single dose of the Oros preparation. Control of supine diastolic blood pressure (less than or equal to 90 mm Hg) at 24 h after dosing was achieved in 13 out of 18 patients with oxprenolol SR (two out of three patients given 160 mg, and 11 out of 15 given 320 mg). Similar control was achieved in 11 out of 18 patients after a single dose of oxprenolol Oros, and in 13 out of 17 patients treated for 3 weeks. The mean percentage reduction in exercise heart rate (EHR) compared to placebo, at 24 h after dosing, was 16% following Oros treatment for 3 weeks, and 12% following SR administration. After a single dose of oxprenolol Oros EHR, was reduced by 9% at 24 h compared to placebo. At 3 weeks the Oros formulation was significantly better than the SR tablet at reducing EHR. Oxprenolol Oros 16/260 was effective over 24 h and well tolerated.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxprenolol absorption in man after single bolus dosing into two segments of the colon compared with that after oral dosing

The systemic availability of oxprenolol after colonic and oral administration has been compared in a crossover study involving six healthy male volunteers. Drug administration into two regions of the colon (caecum and left flexure) was achieved by means of a colonoscopic technique. There were no obvious differences in plasma concentrations after drug administration to the caecum and left flexure, although in one subject it was necessary to repeat colonic administration because of unexpectedly high plasma drug levels on the first occasion. The possible reasons for this abnormal response are discussed. The mean systemic availability of oxprenolol was 82% after colonic compared with oral dosing, although marked differences were observed in individual plasma levels following drug administration by the two routes. The results of this study support the concept of extending the duration of oxprenolol release from a rate-controlled dosage form to permit once-daily administration with this short elimination half-life drug.

In vitro and in vivo deconvolution assessment of drug release kinetics from oxprenolol Oros preparations

The relationship between in vitro and in vivo drug release from Oros systems has been examined by analysing plasma concentration data from two pharmacokinetic studies, using a numerical deconvolution technique. This method generates an input profile by comparing the response with that achieved following an instantaneous reference unit dose. The approach is conceptually simple and does not require compartmental pharmacokinetic modelling or curve fitting. In the analysis of the first study, the plasma profile following intravenous dosing was used as the reference function, allowing the combined release/absorption process to be calculated; for the second, an oral bolus was used, the result of the deconvolution therefore indicating the in vivo dissolution rate of the Oros systems. The in vivo release from Oros in most volunteers followed the same pattern as that measured in vitro; only after 6-8 h was the decline in the in vivo release rate somewhat greater than expected. In a few individuals the cumulative absorption profile reached an early plateau level which coincided, on some but not all occasions, with the premature excretion of the Oros system from the body. The amount of drug in recovered systems agreed reasonably with the prediction of the deconvolution analysis.

Osmotic delivery systems for the beta-adrenoceptor antagonists metoprolol and oxprenolol: design and evaluation of systems for once-daily administration

The essential features and mode of action of oral osmotic drug delivery systems (Oros) for metoprolol fumarate and oxprenolol succinate are described. Critical aspects in the development of systems for once-daily administration of both drugs are discussed, and methods for evaluating in vitro release characteristics are presented. In vitro testing confirmed that drug delivery corresponded closely to the theoretical release behaviour predicted from the physicochemical and membrane permeability characteristics for both oxprenolol and metoprolol systems. In vitro release rates were also shown to be unaffected by pH, in vitro test procedures, dissolution media and long-term storage at different temperatures.

Serial measurements of systolic time intervals during treatment with hydrochlorothiazide alone and combined with other antihypertensive agents

As part of the Veterans Administration cooperative studies on antihypertensive agents, systolic time intervals (STIs) were recorded before and after 2 or 4 weeks of treatment with hydrochlorothiazide (HCTZ) alone in 320 asymptomatic patients with mild to moderate hypertension. After treatment with HCTZ, left ventricular ejection time corrected for heart rate (delta LVET) was significantly reduced. This decrease is consistent with other hemodynamic observations indicating a reduced preload and stroke volume after administration of thiazides. Electromechanical systole corrected for heart rate (delta QS2) decreased, while the ratio of preejection period to LVET (PEP/LVET) increased, reflecting reduced left ventricular function. PEP did not change. Four step 2 drugs--hydralazine, prazosin, oxprenolol and propranolol--were then added randomly to HCTZ and further recordings of STIs were taken at 1 and 6 months after administration of these drugs. The delta LVET and delta QS2 increased and PEP/LVET decreased, suggesting improved left ventricular function after administration of all 4 agents. These changes may have been due to the added agents or to the recovery of cardiac output that occurs independently during long-term treatment with thiazide diuretic drugs alone. PEP decreased slightly after hydralazine and prazosin and increased slightly after treatment with the beta-blocking drugs, although none of these changes were significant except those during hydralazine treatment. Processing of the STIs was greatly facilitated by the automated system for recording and analyzing the measurements.

Single-dose pharmacokinetic and pharmacodynamic comparison of polymer-matrix (Slow Trasicor) and Oros dosage forms of oxprenolol in healthy volunteers

Oxprenolol was administered in single doses by mouth to healthy volunteers either in a polymer-matrix slow-release formulation (Slow Trasicor) or in osmotic drug-delivery systems (oxprenolol Oros). Plasma oxprenolol concentrations and heart rates after exercise were measured. Plasma concentrations of the drug were maximal at 3 h but negligible at 24 h after administration of Slow Trasicor. Following ingestion of the Oros systems measurable concentrations were maintained throughout 24 h. Significant reduction of exercise-induced tachycardia persisted for 24 h after administration of oxprenolol Oros. With Slow Trasicor heart rate responses had returned to baseline values by this time. The osmotic drug-delivery systems appear to sustain significant beta-adrenoceptor blockade for 24 h after a single oral dose.

Concentration-effect relationship of oxprenolol in healthy volunteers: a retrospective analysis

A mathematical model describing the relationship between plasma concentrations of oxprenolol and submaximal-exercise heart rates has been developed on the basis of data available from 34 healthy volunteers. This relationship, which is exponential in type, is consistent with the 'law of diminishing returns', and is independent of the pharmaceutical formulations used; it appears to be established instantaneously, and is not modified by repeated drug administration over 8 days. At oxprenolol concentrations of 190-250 ng/ml, between half and three-quarters of the subjects investigated reached 90% of their estimated maximum levels of beta-adrenoceptor blockade.

Reproducibility of oxprenolol plasma concentrations in young female volunteers following oral administration of an oxprenolol Oros dosage form

Plasma oxprenolol concentrations were measured in six young healthy female volunteers after single oral dosing with a 16/260 oxprenolol Oros system on three separate occasions. Reproducibility was assessed by comparing individual plasma profiles, areas under the curve, peak concentrations and times to peak. Plasma concentration-time profiles were consistent with an extended duration of drug release from the Oros system. Individual and mean profiles on the three occasions were similar, and no significant differences in mean plasma levels, or derived pharmacokinetic parameters, were detected. The mean amount of drug in eight systems recovered from faeces corresponded to 11% of the dose. Individual amounts were related to the total transit time of the system through the body. The 16/260 Oros system functioned reproducibly within the gastrointestinal tract, and in vivo absorption mirrored in vitro drug release.

Pre-dosing plasma concentrations and beta-adrenoceptor blocking effects during repeated once daily dosing with 160 mg sustained-release propranolol (Inderal LA) and 16/260 oxprenolol Oros to healthy volunteers

Plasma drug concentrations and attenuations in sub-maximal exercise tachycardia were measured in six healthy subjects 24 h after the third and fourth doses of Inderal LA and 16/260 oxprenolol Oros administered once daily. Both drugs significantly reduced exercise heart rates relative to the placebo response, at both observation times. The mean percentage reductions on the third and fourth days were, respectively, 15.7 and 11.6% for Inderal LA compared with 18.1 and 12.2% for 16/260 oxprenolol Oros. The differences between formulations were not statistically significant. The mean plasma concentrations at 24 h on the third and fourth day were 119 and 101 ng/g for oxprenolol and 16.2 and 15.8 ng/g for propranolol.

Pharmacokinetic investigation of the absorption of oxprenolol from Oros delivery systems in healthy volunteers: comparison of in vivo and in vitro drug release

The absorption kinetics of oxprenolol have been investigated in eight healthy volunteers after single dosing with 16/260 Oros drug delivery systems. Oxprenolol disposition kinetics in individual subjects were estimated from intravenous dose data. Loo-Riegelman analysis of the plasma concentration data indicated an extended duration of drug absorption for the Oros system. Initially, the in vivo absorption rate was similar to the in vitro release rate but after 5-6 h it slowed perceptibly. However, at later times similar in vivo and in vitro rates were again observed. The absolute bioavailabilities for prototype and clinical trial systems were shown to be similar, at approximately 42%, and no significant differences in plasma profiles or pharmacokinetic constants were detected between the two Oros forms. A comparison of plasma concentration data in seven subjects who received the prototype system on two occasions in separate studies indicated a consistent level of drug absorption from this preparation. Approximately 10-15% of the administered dose was found in Oros systems recovered from faeces. The quantity of drug remaining was poorly correlated with the observed areas under the plasma concentration-time curve.

Influence of food intake on plasma oxprenolol concentrations following oral administration of conventional and Oros preparations

Plasma concentrations of oxprenolol have been measured in six healthy volunteers following single-dose oral administration of the drug in conventional and Oros dosage forms in fasting and postprandial states. After the Oros system, plasma concentrations reached peaks in most subjects at 3-8 h after dosing and were approximately 25% of those achieved with the conventional tablet. Plasma concentrations were well sustained for at least 24 h. A secondary peak occurred consistently at 12 h, possibly reflecting a transient change in clearance and/or distribution of the drug following the evening meal. With each formulation, plasma drug concentration profiles following administration in the fasting state did not differ significantly from those obtained when the drug was given postprandially. Drug absorption in vivo corresponded reasonably closely with in vitro drug release from the Oros system.

A double-blind randomized evaluation of converting enzyme inhibition as the first-step treatment of mild to moderate hypertension

The new angiotensin converting enzyme inhibitor, enalapril (MK-421), was tested by a double-blind trial. Patients with uncomplicated essential hypertension were randomly allocated to one of two stepped-care treatment groups: enalapril 20 mg once-a-day, or placebo as the first step, followed when necessary by the successive addition of hydrochlorothiazide (25 and 50 mg), oxprenolol (160 and 320 mg) and dihydralazine (50 and 100 mg). Blood pressure was normalized in both groups, although the enalapril group showed lower systolic and diastolic blood pressures than the placebo group (systolic 130.5 +/- 12 versus 136.6 +/- 9 mmHg, P less than 0.01; diastolic 82.8 +/- 6 versus 87.0 +/- 5 mmHg, P less than 0.001). These results were obtained with a smaller number of tablets per day (2.6 +/- 1.8 versus 4.2 +/- 2.4 mmHg, P less than 0.0001). Plasma potassium was identical for both groups at the start of treatment. At the end of the study, it was significantly higher in the enalapril group than in the placebo group (4.1 +/- 0.3 versus 3.9 +/- 0.5 mmol/l; P less than 0.05). Spontaneous complaints were noted during the bi-weekly or monthly visit and were also expressed by patients completing a self-administered questionnaire. Differences in spontaneous complaints or in the symptoms evaluated by the questionnaire were not significant. The increase in the number of symptoms at the end of the study was greater in the placebo group than in the enalapril group, but the difference was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)