Dose-dependent disposition of oral propranolol in normal subjects

Systemic administration of propranolol reduces bone resorption and inflammation in apical periodontitis of chronically stressed rats

AIM

To evaluate the effect of systemic administration of propranolol on the severity of apical periodontitis (AP) in chronically stressed rats.

METHODOLOGY

Twenty-four 70-day-old male Wistar rats (Rattus norvegicus, albinus) were distributed into three groups (n = 8): rats with AP without stressful conditions (AP-Control), rats with AP and submitted to a chronic unpredictable stress (CUS) protocol (AP + S) and rats with AP and submitted to a CUS protocol treated with propranolol (AP + S + PRO). Stress procedures were applied daily until the end of the experiment. After 3 weeks of CUS, AP was induced in all groups by exposing the pulpal tissue of mandibular and maxillary first molars to the oral environment. Propranolol treatment was administered orally once a day for the entire period of the experiment. Rats were sacrificed at 42 days, and the blood was collected for stress biomarkers serum dosage by multiplex assay. Mandibles were removed and submitted to microtomography and histopathological analyses. Periapical tissue surrounding the upper first molar was homogenized and subjected to RT-PCR analysis to evaluate the mRNA expression of RANKL, TRAP and OPG. Parametric data were assessed using one-way ANOVA followed by Tukey's test while the nonparametric data were analysed by the Kruskal-Wallis followed by Dunn's test. Significance level was set at 5% (p < .05) for all assessed parameters.

RESULTS

Micro-CT revealed statistically significant differences in bone resorption which was greater in the AP + S group (p < .05), but no differences were observed between the Control and AP + S + PRO groups (p > .05). The AP + S + PRO group had a lower intensity and extent of inflammatory infiltrate compared to the AP + S group with smaller areas of bone loss (p < 0.05). The gene expression of RANKL and TRAP was significantly higher in the stressed group AP + S compared to the control group (p < .05), and a significantly higher OPG expression was observed in AP + S + PRO compared to the AP + S group (p < .05).

CONCLUSIONS

Oral administration of propranolol had a significant effect on the AP severity in stressed rats, suggesting an anti-inflammatory effect and a protective role on bone resorption of AP in stressed animals. Further research is necessary to fully comprehend the underlying mechanisms.

Propranolol pharmacokinetics in infants treated for Infantile Hemangiomas requiring systemic therapy: Modeling and dosing regimen recommendations

Propranolol has become the first choice therapy for complicated Infantile Hemangiomas (IH). The pharmacokinetics of propranolol were evaluated after repeated oral administration of a new pediatric solution of propranolol at 3 mg kg⁻¹ day⁻¹ given twice daily (BID) in infants (77‐243 days) with IH. A population model was built to describe the pharmacokinetics of propranolol in infants and to simulate different dosing regimens. One hundred and sixty‐seven plasma concentrations from 22 infants were used in the population analysis. Weight effect was tested on apparent clearance and volume of distribution. Monte‐Carlo simulations were performed for 4 dosing regimens: BID dosing with irregular or strict 12‐hour intervals and 2 different 3 time daily dosing (TID) regimens. The best model was a one‐compartment model with first‐order absorption and elimination rates. The weight affected the clearance but not the volume. Typical oral clearance was estimated at 3.06 L hour⁻¹ kg⁻¹ (95% CI: 1.14‐8.61 L hour⁻¹ kg⁻¹), close to adult clearance data. When regular BID dosing was compared to TID or irregular BID regimens, simulated median Cmin and Cmax were <20% different. To conclude, a model using a weight allometric function on clearance was established and confirmed that the dose in mg/kg should be used without adaptation by range of age in treatment of complicated IH. The simulations support the use of a BID dosing preferably to a TID dosing thanks to close Cmin and Cmax at steady state between both regimen and showed the possibility of irregular BID dosing, allowing early administration in the evening when needed.

Bioavailability of diclofenac potassium at low doses

AIM

Diclofenac-K has been recently launched at low oral doses in different countries for over-the-counter use. However, given the considerable first-pass metabolism of diclofenac, the degree of absorption of diclofenac-K at low doses remained to be determined. The aim of this study was to determine the bioavailability of low-dose diclofenac-K.

METHODS

A randomized, three-way, cross-over study was performed in 10 subjects. Each received diclofenac-K, 22.5 mg via short-term i.v. infusion and orally at single doses of 12.5 mg and 25 mg.

RESULTS

Mean (+/- SD) times to maximal plasma concentration (t(max)) of diclofenac were 0.48 +/- 0.28 h (12.5 mg) and 0.93 +/- 0.96 h (25 mg). The absolute bioavailability of diclofenac-K after oral administration did not differ significantly in the 12.5-mg and 25-mg dose group (63.1 +/- 12.6%vs. 65.1 +/- 19.4%, respectively). The 90% confidence intervals for the AUC(infinity) and AUC(t) ratios for the two oral regimes were 82.6, 103.4% (point estimate 92.4%) and 86.2, 112.9% (point estimate 98.6%), respectively. These values were within the acceptance criteria for bioequivalence (80-125%).

CONCLUSIONS

Our data indicate that diclofenac-K is rapidly and well absorbed at low dose, and are consistent with a rapid onset of action of the drug. Abbreviations AUC, area under plasma concentration-time curve; C(max), peak plasma concentration; CI, confidence interval; COX, cyclooxygenase; D, dose; F, absolute bioavailability; t(max), time to reach C(max).

(S)-4'-hydroxypropranolol causes product inhibition and dose-dependent bioavailability of propranolol enantiomers in the isolated perfused rat liver and in rat liver microsomes

1. Previous evidence suggests that the dose-dependent bioavailability of racemic propranolol may be partly due to product inhibition. We have examined this further by studying the individual enantiomers of propranolol in the perfused rat liver (IPRL) and in rat liver microsomes. 2. In recirculating IPRL experiments, (R)-propranolol (n = 7) or (S)-propranolol (n = 4) were infused at rates of 75, 150 and 231 nmol/min for three sequential 36-min phases. In single-pass experiments, (R)-propranolol (n = 4) or (S)-propranolol (n = 4) were administered at rates of 80, 136 and 239 nmol/min for three sequential 30-min phases. Steady-state bioavailability increased 10-20-fold over this dose range with both enantiomers in both recirculating and single-pass experiments. At the higher administration rates of (S)-propranolol, bioavailability in recirculating experiments was significantly greater than that in single-pass experiments, whereas there was no significant difference for (R)-propranolol. This suggests product inhibition of (S)- but not (R)-propranolol metabolism. 3. Of the metabolites examined, racemic 4'-hydroxypropranolol (4-OHP) inhibited the formation of 4-OHP, 5'-hydroxypropranolol (5-OHP) and desisopropylpropranolol (DIP) from (S)-propranolol and (R)-propranolol in microsomal studies (IC50 20 microM). Tissue levels of (S)-4-OHP in recirculating experiments (28.0 microM) at the highest dose (239 nmol/ min) of (S)-propranolol were greater than its IC50 of 20 microM, suggesting that 4-OHP is the inhibiting metabolite in the intact liver. The absence of evidence for product inhibition with (R)-propranolol in perfused livers suggests that (S)-4-OHP inhibits 4-hydroxylation of each isomer but (R)-4-OHP does not. 4. We conclude that in the recirculating IPRL, product inhibition of propranolol metabolism is evident with the (S)-isomer, but not he (R)-isomer, and that the inhibiting metabolite is (S)-4-OHP.

Pharmacokinetic and pharmacodynamic evaluation during coadministration of nefazodone and propranolol in healthy men

Potential interactions between nefazodone (200 mg every 12 hours) and propranolol (40 mg every 12 hours) were assessed in 18 healthy male volunteers in an open-label, randomized, three-way crossover study. The nature, frequency, and severity of adverse events during coadministration of nefazodone and propranolol were similar to those observed with either treatment alone. There were no clinically significant effects on vital signs, electrocardiographic results, or laboratory parameters. With coadministration, the maximum peak concentration (Cmax) and area under the concentration-time curve over the dosing interval (AUC tau) of propranolol decreased 29% and 14%, respectively; Cmax and AUC tau of 4-hydroxy-propranolol decreased 15% and 21%, respectively. Despite decreased plasma concentrations of the beta-antagonists, the reduction in exercise-induced tachycardia and post-exercise double product was slightly greater with coadministration than with propranolol alone. Administration of nefazodone alone did not significantly affect either pharmacologic parameter. The pharmacokinetics of nefazodone and its metabolites were largely unaffected during coadministration. Coadministration of propranolol and nefazodone results in modest pharmacokinetic inequivalencies, but no clinically significant alterations of the pharmacodynamics of propranolol.

Effect of oral activated charcoal on propranolol pharmacokinetics following intravenous administration to rabbits

The pharmacokinetics of propranolol following intravenous administration (1 mg/kg), with and without treatment with oral activated charcoal, was investigated in rabbits. In charcoal-treated rabbits a significant reduction in propranolol serum concentrations was observed compared to control animals. Charcoal treatment significantly reduced the half-life of elimination (16.6%) and the mean residence time (19%) of propranolol. A 17% increase in the systemic clearance and a 14% decrease in AUC were also noted. Charcoal administration did not significantly alter the volume of distribution (Vc' V(area) and Vss) or the apparent distribution half-life. A two-compartment model adequately described propranolol in control and treated rabbits. The results indicate that administration of oral activated charcoal enhances the systemic elimination of propranolol. This is presumably mediated by interruption of the enterohepatic circulation of propranolol by activated charcoal.

Prediction of steady state bioequivalence relationships using single dose data II-nonlinear kinetics

Two nonlinear pharmacokinetic models were simulated to investigate the relationship between single and multiple dose bioequivalency parameters for drugs such as phenytoin and propranolol which exhibit either saturable elimination kinetics or a capacity limited first pass effect. Mean Tmax, Cmax and area under the plasma-concentration time curve values from 0 to infinity (AUC 0-infinity) were compared after a single and multiple dose(s) of a test or reference drug. The aim was to determine if there were systematic changes in the limits of the single dose confidence interval at steady state that would limit the usefulness of confidence intervals following a single dose in accurately predicting bioavailability following multiple dosing. The 90 per cent confidence interval expressed as a percentage of the reference mean for Tmax, Cmax, and AUC 0-infinity showed model dependent changes from single to multiple dosing in response to the level of data error and changes in absorption. Changes in clearance also seemed to have a marked effect on the observed limits of the single and multiple dose confidence intervals especially for Cmax which showed a characteristic change in the intervals as a function of the clearance ratio. The model used to describe phenytoin had confidence intervals for Cmax and AUC 0-infinity from single to multiple dosing that were similar to that seen for the experimental data. However, the model predictions for Tmax confidence intervals following single and multiple dosing was at variance with the experimental data for formulations A and B.

Influence of smoking and gender on the disposition kinetics of metoprolol

The purpose of this study was to examine the influence of cigarette smoking and gender on the pharmacokinetics of metoprolol. Eighteen volunteers with no evidence of clinical disease each randomly received the following doses of metoprolol tartrate: 100 mg orally, 200 mg orally and 20 mg as a constant-rate intravenous infusion over 20 min. The only significant difference between smokers (S) and nonsmokers (NS) was that S had a larger steady-state volume of distribution (3.3 vs 2.5 l/kg). There were no differences in half-life, systemic clearance or bioavailability (f). No differences were observed between males (M) and females (FM) for any of the kinetic parameters examined. Systemic bioavailability varied markedly between subjects (range: 15 to 92%). In fifteen of the eighteen subjects, f was higher after the 200-mg dose compared to the 100-mg dose. These results suggest that metoprolol may be subject to saturable presystemic elimination and extend the previous observations of Johnsson et al. [1] who showed that f increased from 31% to 46% when doses were increased from 20 to 100 mg. However, the difference in f as the dose is increased is unlikely to be clinically significant since the mean difference is smaller than the variation in f among subjects.

Plasma concentrations and bioavailability of propranolol by oral, rectal, and intravenous administration in man

Eight normal male volunteers received 80 mg doses of propranolol by the oral and rectal routes and 2.2 mg by intravenous administration in a crossover fashion. Plasma concentrations of propranolol were measured by a gas chromatographic method using an electron capture detector. Individual subject concentration-time data were analysed and results indicated that the data fit a two compartment model with first order absorption. An approximately two-fold higher plasma propranolol concentration was observed after rectal administration as compared with oral dosing. Statistical analysis of the difference in the total AUCs indicates a significantly higher bioavailability of propranolol administered by the rectal route. The reduced bioavailability after oral administration indicates a substantial first pass effect but that it is possible to bypass the liver, at least partially, by giving the drug rectally to man.

Nonlinear bioavailability of metoclopramide in the rat: evidence for saturable first-pass metabolism

In vivo and in vitro experiments were conducted in rats to examine the possibility of either extrahepatic metabolism or saturable first-pass effect as an explanation for the unusual presystemic clearance of metoclopramide (I) previously reported. In vivo studies involved two-thirds hepatectomized rats and animals pretreated with carbon tetrachloride to induce hepatic necrosis, whereas in vitro studies involved incubation of equal amounts of I (5.0 mumol/mL) with various tissue homogenates (viz., liver, kidney, and lung) or their 9000 X g supernatant fractions. Results suggest that the metabolism of I principally occurs in the rat liver, and there was no evidence suggesting the involvement of kidney or lung tissue in the metabolism of I. Forty-eight-hour cumulative urinary excretion studies following oral and intravenous administration of less than or equal to 5.0 mg/kg of metoclopramide hydrochloride were conducted. The bioavailability (F) values of I at dosage levels 0.1, 0.5, 1.0, and 5.0 mg/kg were 0.49, 0.75, 0.77, and 0.83, respectively. It is concluded that the liver is the primary organ for the metabolism of I in the rat and that the drug exhibits dose-dependent hepatic first-pass metabolism.

Pharmacokinetics of glucuronidation of propranolol following oral administration in humans

Pharmacokinetic and bioavailability parameters of propranolol were estimated in 10 healthy adult subjects after single oral doses of two commercial tablet formulations of propranolol hydrochloride (2 X 40 mg). Plasma concentrations of propranolol were determined by a high-performance liquid-chromatographic (HPLC) assay. Peak plasma concentrations of propranolol glucuronide were 6-8 times those of the corresponding peak propranolol plasma concentrations. The mean resident time (MRT) of propranolol and of propranolol glucuronide was determined for each subject for both formulations. The MRT of the parent drug was found to be longer than the MRT of the glucuronide metabolite for each of the subjects examined. Statistical moment analysis indicated that this phenomenon is attributable to extensive presystemic glucuronidation of the parent drug.

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.

The relative bioavailability of a commercial propranolol hydrochloride tablet in man

A relative bioavailability study of conventional tablet of propranolol hydrochloride was conducted in a group of 18 healthy volunteers employing the innovator's product as the reference tablet formation. Based on plasma levels of propranolol for the 24 h following administration of 2 x 40 mg oral propranolol hydrochloride tablets, the relative extent of availability was shown to be 100.8 per cent for the test tablet formulation; no significant differences were detected between formulations with respect to any of the pharmacokinetic parameters examined. Large intersubject variations in plasma propranolol concentrations and the subsequently calculated areas under the plasma concentration/time curves were attributed to substantial presystemic biotransformation differences.

Effects of age and smoking on the pharmacokinetics of pindolol and propranolol

1 Pharmacokinetic investigations were carried out in a group of 32 ambulant normal male volunteers in order to determine the effect of age and smoking on steady-state plasma levels of pindolol and propranolol. There were four groups of 8: young non-smokers (YNS), young smokers (YS), old non-smokers (ONS) and old smokers (OS). Each subject received, in a randomized cross-over sequence, 5 mg pindolol and 80 mg propranolol three times daily for 2 days with an interval of at least 14 days between the two treatment periods. 2 Neither age nor smoking was shown to have any influence on the time to reach a peak plasma level after pindolol or propranolol. Age, on the other hand, significantly increased the peak plasma levels and the areas under the plasma concentration time curves, and decreased the elimination rate constants, the differences between the age groups being more pronounced for propranolol than for pindolol. No effect of smoking on these parameters was observed. 3 Differences were found between pindolol and propranolol in respect of time to reach a peak plasma level, peak plasma levels and area under the plasma concentration time curves in the groups ONS and YS when related to the YNS control group. Changes observed (with the exception of the time to reach a peak level) tended to be less for pindolol and were considered to be of little clinical relevance.