Reduction of first-pass hepatic clearance of propranolol by food

Analysis of the interplay of physiological response to food intake and drug properties in food-drug interactions

The effect of food on oral drug absorption is determined by the complex interplay among gut physiological factors and drug properties. The currently used dissolution testing and classification systems (biopharmaceutics classification system, BCS or biopharmaceutics drug disposition classification system, BDDCS) do not account for dynamic changes in gastrointestinal physiology caused by food intake. This study aimed to identify key drug properties that influence food effect (FE) using supervised machine learning approaches. The analysis showed that drugs with high logP, dose number, and extraction ratio have a higher probability of positive FE, while drugs with low permeability and high efflux saturation index have a greater likelihood of negative FE. Weakly acidic drugs also showed a greater probability of positive FE, particularly at pKa >4.3. The importance of drug properties in predicting FE was ranked as logP, dose number, extraction ratio, pKa, and permeability. The accuracy of FE prediction using the models was compared with BCS and extended clearance classification system (ECCS). Overall, the likelihood or magnitude of FE depends on physiological changes to food intake such as altered bile acid secretion rate, intestinal metabolism, transport kinetics, and gastric emptying time, which should be considered along with drug properties (e.g., solubility, logP, and ionization) in predicting FE of orally administered drugs.

Fast-Fed Variability: Insights into Drug Delivery, Molecular Manifestations, and Regulatory Aspects

Among various drug administration routes, oral drug delivery is preferred and is considered patient-friendly; hence, most of the marketed drugs are available as conventional tablets or capsules. In such cases, the administration of drugs with or without food has tremendous importance on the bioavailability of the drugs. The presence of food may increase (positive effect) or decrease (negative effect) the bioavailability of the drug. Such a positive or negative effect is undesirable since it makes dosage estimation difficult in several diseases. This may lead to an increased propensity for adverse effects of drugs when a positive food effect is perceived. However, a negative food effect may lead to therapeutic insufficiency for patients suffering from life-threatening disorders. This review emphasizes the causes of food effects, formulation strategies to overcome the fast-fed variability, and the regulatory aspects of drugs with food effects, which may open new avenues for researchers to design products that may help to eliminate fast-fed variability.

Model-Informed Optimization of a Pediatric Clinical Pharmacokinetic Trial of a New Spironolactone Liquid Formulation

Quantitative pharmacology brings important advantages in the design and conduct of pediatric clinical trials. Herein, we demonstrate the application of a model-based approach to select doses and pharmacokinetic sampling scenarios for the clinical evaluation of a novel oral suspension of spironolactone in pediatric patients with edema. A population pharmacokinetic model was developed and qualified for spironolactone and its metabolite, canrenone, using data from adults and bridged to pediatrics (2 to <17 years old) using allometric scaling. The model was then used via simulation to explore different dosing and sampling scenarios. Doses of 0.5 and 1.5 mg/kg led to target exposures (i.e., similar to 25 and 100 mg of the reference product in adults) in all the reference pediatric ages (i.e., 2, 6, 12 and 17 years). Additionally, two different sampling scenarios were delineated to accommodate patients into sparse sampling schemes informative to characterize drug pharmacokinetics while minimizing phlebotomy and burden to participating children.

The mechanisms of pharmacokinetic food-drug interactions - A perspective from the UNGAP group

The simultaneous intake of food and drugs can have a strong impact on drug release, absorption, distribution, metabolism and/or elimination and consequently, on the efficacy and safety of pharmacotherapy. As such, food-drug interactions are one of the main challenges in oral drug administration. Whereas pharmacokinetic (PK) food-drug interactions can have a variety of causes, pharmacodynamic (PD) food-drug interactions occur due to specific pharmacological interactions between a drug and particular drinks or food. In recent years, extensive efforts were made to elucidate the mechanisms that drive pharmacokinetic food-drug interactions. Their occurrence depends mainly on the properties of the drug substance, the formulation and a multitude of physiological factors. Every intake of food or drink changes the physiological conditions in the human gastrointestinal tract. Therefore, a precise understanding of how different foods and drinks affect the processes of drug absorption, distribution, metabolism and/or elimination as well as formulation performance is important in order to be able to predict and avoid such interactions. Furthermore, it must be considered that beverages such as milk, grapefruit juice and alcohol can also lead to specific food-drug interactions. In this regard, the growing use of food supplements and functional food requires urgent attention in oral pharmacotherapy. Recently, a new consortium in Understanding Gastrointestinal Absorption-related Processes (UNGAP) was established through COST, a funding organisation of the European Union supporting translational research across Europe. In this review of the UNGAP Working group "Food-Drug Interface", the different mechanisms that can lead to pharmacokinetic food-drug interactions are discussed and summarised from different expert perspectives.

Incorporation of the Time-Varying Postprandial Increase in Splanchnic Blood Flow into a PBPK Model to Predict the Effect of Food on the Pharmacokinetics of Orally Administered High-Extraction Drugs

Following a meal, a transient increase in splanchnic blood flow occurs that can result in increased exposure to orally administered high-extraction drugs. Typically, physiologically based pharmacokinetic (PBPK) models have incorporated this increase in blood flow as a time-invariant fed/fasted ratio, but this approach is unable to explain the extent of increased drug exposure. A model for the time-varying increase in splanchnic blood flow following a moderate- to high-calorie meal (TV-Q _Splanch) was developed to describe the observed data for healthy individuals. This was integrated within a PBPK model and used to predict the contribution of increased splanchnic blood flow to the observed food effect for two orally administered high-extraction drugs, propranolol and ibrutinib. The model predicted geometric mean fed/fasted AUC and C _max ratios of 1.24 and 1.29 for propranolol, which were within the range of published values (within 1.0-1.8-fold of values from eight clinical studies). For ibrutinib, the predicted geometric mean fed/fasted AUC and C _max ratios were 2.0 and 1.84, respectively, which was within 1.1-fold of the reported fed/fasted AUC ratio but underestimated the reported C _max ratio by up to 1.9-fold. For both drugs, the interindividual variability in fed/fasted AUC and C _max ratios was underpredicted. This suggests that the postprandial change in splanchnic blood flow is a major mechanism of the food effect for propranolol and ibrutinib but is insufficient to fully explain the observations. The proposed model is anticipated to improve the prediction of food effect for high-extraction drugs, but should be considered with other mechanisms.

Bioavailability of propranolol after oral, sublingual, and intranasal administration

The bioavailability of propranolol was compared after oral, sublingual, and intranasal administration in eight healthy male volunteers. Relative to the bioavailability after intranasal (in) administration, which was previously shown to be nearly complete (F relin = 100%), the sublingual (sl) administration of a standard 10-mg tablet gave a bioavailability of F relsl = 63 ± 22%, while the oral (or) administration yielded only F relor = 25 ± 8%. The serum concentration-time curves of propranolol after sublingual administration resembled those of a sustained-release preparation. This sustained-release phenomenon after the sublingual route is reflected in the mean residence times (MRTs) of propranolol in the body (MRTor = 5.7 ± 1.3 hr, MRTsl - 6.4 ± 1.3 hr, MRTin = 4.6 ± 1.0 hr; mean ± SD; N = 8). MRTs after sublingual administration were significantly longer than after the oral and the intranasal doses (P < 0.05 and P < 0.002, respectively).

Predicting pharmacokinetic food effects using biorelevant solubility media and physiologically based modelling

BACKGROUND

Food-induced changes in gastric emptying time, gastric pH and/or intestinal fluid composition may have an impact on the pharmacokinetics of drugs. The aim of this work was to use mathematical models describing physiology in fed and fasted states together with biorelevant solubility and degradation data to simulate food effects for six compounds from recent Roche projects.

METHODS

The solubility of each compound was measured in different biorelevant media: simulated human gastric fluid for the fasted and fed state, simulated human intestinal fluid for the fasted, fed and high-fat state, and simulated human colonic fluid for the upper and the lower colon. A physiologically based absorption model was developed in GastroPlustrade mark for each compound using permeability, solubility, metabolism and distribution data. By incorporating the appropriate physiological parameters and solubility data into the model, the oral pharmacokinetics of each drug was simulated under fasted, fed and/or high-fat conditions. Predicted and observed plasma concentration-time profiles and food effects were compared for a range of doses to assess the accuracy of the simulations.

RESULTS

The models were able to distinguish between minor and significant food effects. The simulation captured well the magnitude of the food effects and for the six compounds correctly predicted the observed plasma exposure in fasted, fed and high-fat conditions.

CONCLUSION

Biorelevant solubility tests can be used together with physiologically based absorption models to predict clinical food effects caused by solubility and/or dissolution rate limitations.

In vitro characterization of some biopharmaceutical properties of praziquantel

In several studies of patients with neurocysticercosis under treatment with praziquantel (PZQ), the pharmacokinetic data were difficult to interpret probably because of the low solubility as well as its variable oral bioavailability. Because there is limited information available regarding the biopharmaceutical properties of PZQ, the aim of this work was to evaluate the absorption characteristics of the drug and its dissolution behaviour in simulated media. Additionally, its in vitro protein binding and displacement by highly bound drugs was evaluated. Permeability evaluation was carried out by using Caco-2 cells. Dissolution release profiles were evaluated using the USP apparatus and the following dissolution media: HCl containing 2mg of sodium laurylsulfate per milliliter, milk, FeSSIF and FaSSIF. Protein binding of PZQ was carried out by equilibrium dialysis. Results showed that praziquantel was absorbed by passive diffusion. The apparent permeability constant value was 4.4x10(-5) cm/s. Binding was not influenced by the addition of highly bound drugs. Dissolution from a tablet formulation showed that the rate of praziquantel was dependent on the components of the media. Although the simulated media could explain the influence of the lipids on praziquantel absorption, they were not able to forecast the influence of carbohydrates. Further refinements are required to explain the in vivo data.

Time effects of food intake on the pharmacokinetics and pharmacodynamics of quazepam

AIMS

There is little information on interaction between food and the hypnotic agent quazepam. We therefore studied the effects of food and its time interval on the pharmacokinetics and pharmacodynamics of quazepam.

METHODS

A randomized three-phase crossover study with 2-week intervals was conducted. Nine healthy male volunteers took a single oral 20 mg dose of quazepam under the following conditions: 1) after fasting overnight; 2) 30 min after eating standard meal; or 3) 3 h after eating the same meal. Plasma concentrations of quazepam and its metabolite, 2-oxoquazepam and psychomotor function using the Digit Symbol Substitute Test (DSST), Stanford Sleepiness Scale (SSS) and Visual Analogue Scale were measured up to 48 h.

RESULTS

During the food treatments at 30 min and 3 h before dosing, the peak concentrations (Cmax) were 300% (95% CI 260, 340%; P < 0.001) and 250% (95% CI 210, 290%; P < 0.01) of the corresponding value during the fasting phase. For quazepam, the area under the plasma concentration-time curve from 0 to 8 h measured at 30 min and 3 h before dosing was significantly increased, with the food treatments by 2.4-fold (95% CI 2.0; 2.8-fold; P < 0.001) and 2.1-fold (95% CI 1.7; 2.4-fold; P < 0.01), respectively. In response to pharmacokinetic changes, some of the pharmacodynamics (DSST, P < 0.05; SSS, P < 0.05) differed significantly between fasted status and fed status. No difference was found in any pharmacokinetic or pharmacodynamic parameters between the two food treatment phases.

CONCLUSIONS

A food effect on quazepam absorption is evident and continues at least until 3 h after food intake. The dosing of quazepam after a long period of ordinary fasting might reduce its efficacy because a 3 h interval between the timing of the evening meal and bedtime administration of hypnotics is regarded as normal in daily life.

Food does not influence the pharmacokinetics of a new extended release formulation of tolterodine for once daily treatment of patients with overactive bladder

OBJECTIVE

To determine whether food intake influences the pharmacokinetics of a new, once daily, extended release (ER) capsule formulation of tolterodine in healthy volunteers, and to compare its bioavailability with that of the existing immediate release (IR) tablet.

DESIGN

Open, randomised, 3-way crossover trial.

PARTICIPANTS

17 healthy volunteers (3 females, 14 males) aged between 19 and 50 years. With the exception of 1 male volunteer, all participants were classified as extensive metabolisers by cytochrome P450 2D6 genotyping.

METHODS

Volunteers received single oral doses of tolterodine L-tartrate ER 8 mg (2 x 4 mg capsules) on an empty stomach or with a standardised high-fat breakfast. Reference therapy comprised tolterodine L-tartrate IR 4 mg (2 x 2 mg tablets), administered in the fasting state. Serum concentrations of tolterodine, its active 5-hydroxymethyl metabolite (5-HM) and the active moiety (sum of unbound tolterodine + 5-HM) were measured for up to 72 hours post-dose. Safety endpoints were also determined.

RESULTS

No effect of food on the bioavailability of tolterodine ER capsules was apparent and there was no sign of dose-dumping with meals. The geometric mean fed:fasting ratio of area under the serum concentration-time curve to infinity (AUCinfinity) of the active moiety, for all volunteers combined, was 0.95 (90% confidence interval 0.88 to 1.03). Equivalence with respect to AUCinfinity (dose-corrected) was also found for the ER capsule compared with the IR tablet, although uncorrected maximum serum concentrations were around 50% lower despite the fact that the capsule dose was twice as high. Seven volunteers reported adverse events, predominantly headache. No volunteer reported dry mouth. Overall, there were no safety concerns.

CONCLUSIONS

The new ER formulation of tolterodine shows no pharmacokinetic interaction with food. On the basis of these results, patients with overactive bladder may, therefore, be advised to take the drug without regard to the timing of meals, maximising convenience during therapy.

Drug, meal and formulation interactions influencing drug absorption after oral administration. Clinical implications

Drug-drug, drug-formulation and drug-meal interactions are of clinical concern for orally administered drugs that possess a narrow therapeutic index. This review presents the current status of information regarding interactions which may influence the gastrointestinal (GI) absorption of orally administered drugs. Absorption interactions have been classified on the basis of rate-limiting processes. These processes are put in the context of drug and formulation physicochemical properties and oral input influences on variable GI physiology. Interaction categorisation makes use of a biopharmaceutical classification system based on drug aqueous solubility and membrane permeability and their contributions towards absorption variability. Overlaying this classification it is important to be aware of the effect that the magnitudes of drug dosage and volume of fluid administration can have on interactions involving a solubility rate limits. GI regional differences in membrane permeability are fundamental to the rational development of extended release dosage forms as well as to predicting interaction effects on absorption from immediate release dosage forms. The effect of meals on the regional-dependent intestinal elimination of drugs and their involvement in drug absorption interactions is also discussed. Although the clinical significance of such interactions is certainly dependent on the narrowness of the drug therapeutic index, clinical aspects of absorption delays and therapeutic failures resulting from various interactions are also important.

No effect of high-protein food on the stereoselective bioavailability and pharmacokinetics of verapamil

The effects of high-protein food on the bioavailability of both the racemate and individual enantiomers of verapamil were investigated in 12 healthy volunteers using a randomized crossover design. Food had no effect on any parameter of bioavailability for both the racemate and the individual enantiomers of verapamil except time to maximum concentration (tmax), which was significantly prolonged after food intake. The pharmacokinetics of the enantiomers of norverapamil were not significantly changed by food intake. These results suggest that high-protein food does not alter the pharmacokinetics and bioavailability of either the racemate or the individual enantiomers of verapamil. Therefore, the clinical efficacy of verapamil is not related to food intake, except for a slight prolongation in the time to onset of the pharmacologic effects. The present data can be applied to the high-protein content meal intake.

Effects of sensory (teasing) exposure to food on oral propranolol bioavailability

In order to further examine the mechanism of the increase in the plasma propranolol concentration versus time curve (AUC) caused by ingestion of propranolol with food, we administered R, S-propranolol tablets (0.5 mg kg-1) orally to healthy human volunteers and dogs in the presence and absence of sensory exposure to food without ingestion (teasing). Six healthy human volunteers were fasted on one occasion and on the other they were presented with an appetising meal, without eating it (teasing protocol). There was a strong trend to a greater propranolol AUC in the teasing protocol (139 +/- 54 mg mL-1 h-1 fasting, 178 +/- 105 mg mL-1 h-1 teasing; p = 0.1), and time of peak concentration (tmax) was significantly prolonged (80 +/- 22 min and 120 +/- 32 min, respectively; p < 0.03). Further studies were carried out in dogs who received R-propranolol (2 mg kg-1) as an oral solution by gavage tube on four different occasions: fasting, following intragastric administration of a high-value liquid meal, following teasing with food in the animal house at normal feeding time (high-intensity teasing). There were no significant differences in pharmacokinetic parameters between the fasting and intragastric food protocols. Low-intensity teasing resulted in significantly lower AUC and peak concentrations (Cmax) compared with fasting (p < 0.05), confirming food effect patterns known to occur in dogs. High-intensity teasing resulted in significantly greater AUC and Cmax compared with fasting (p < 0.05), reproducing in dogs the increase in propranolol AUC known to occur with food ingestion in humans. These findings suggest that the mechanism of the 'food effect' may involve physiological responses to the sight and smell of food additional to mechanisms activated by ingestion.

The hepatic first-pass metabolism of problematic drugs

The first-pass hepatic metabolism of a number of important therapeutic agents is inconsistent with traditional models that assume that the hepatic extraction ratio of a drug is constant in each individual (independent of the concentration of drug in the hepatic sinusoidal blood and also independent of the history of exposure to the drug). In this review, the authors examine the first-pass metabolism of five "problematic drugs" (propranolol, lidocaine, propafenone, verapamil, and nitroglycerin). Each of these compounds has unique facets to its hepatic clearance and pharmacokinetics as well as striking similarities. Selected aspects of first-pass metabolism are reviewed, and a theory that may explain some of the unusual behavior of the four lipophilic bases (propranolol, lidocaine, propafenone, and verapamil) is presented. Finally, the unusual and variable clearance of nitroglycerin is discussed.

Pharmacokinetics of D-propranolol following oral, intra-arterial and intraportal administration: contrasting effects of oral glucose pretreatment

Several research groups have reported that in man the oral administration of propranolol with food leads to a marked increase (about 50 per cent) in the area under the plasma concentration-time curve (AUCpo) of this well absorbed and highly metabolized drug. An acute change in hepatic metabolic enzyme activity has been postulated as one of the mechanisms which could be responsible for this observed 'food effect'. The administration of simple carbohydrates such as glucose and fructose has been documented to influence hepatic drug metabolism. Therefore, in the present study, the effect of oral glucose (4 g kg-1 as a 50 per cent aqueous solution) on the disposition kinetics of d-propranolol was examined in male Sprague-Dawley rats (8 to 9 per group). Oral glucose treatment caused a statistically significant decrease (50.4 +/- 12.3 vs 36.6 +/- 15.2 min micrograms ml-1; p < 0.05) in the AUCpo of propranolol when this drug was given by oral intubation (10 mg kg-1). This glucose treatment also caused the apparent mean residence time of propranolol after an oral dose to increase from 0.70 +/- 0.08 h to 1.79 +/- 0.29 h (p < 0.05), but did not change its rate of elimination (suggesting collectively a decreased apparent intrinsic clearance and prolonged drug absorption). In a second study, the same oral glucose treatment was demonstrated to have little impact on the steady state concentrations of propranolol when this drug was infused intraarterially at a constant rate. This confirms that the systemic clearance of propranolol is influenced minimally by the glucose treatment. In a third study, propranolol was infused at a constant rate into the portal vein (pyloric vein infusion) bypassing the processes of intestinal metabolism and absorption (i.e. to remove these sources of variability associated with oral administration). Under these conditions, no significant changes in AUC or apparent mean residence time were observed for the two propranolol doses studied (10 mg kg-1 and 5 mg kg-1). We conclude that the oral glucose and oral propranolol interaction appears to be due to an alteration in the input process before drug enters the liver. Furthermore, this experimental series suggests that studies combining accurate assessments of systemic clearance (constant rate intra-arterial infusion studies), intrinsic hepatic clearance (pyloric vein infusion studies), and oral administration supplemented with necessary protein binding studies may be used together to characterize the mechanism responsible for drug-nutrient and drug-drug interactions.

Mechanisms and variations in the food effect on propranolol bioavailability

Mechanisms and variations in the food-induced increase in the bioavailability of propranolol were assessed by single-dose (80 mg) studies in healthy volunteers who took the drug on an empty stomach, immediately after a protein-rich breakfast, and together with a carbohydrate-rich, protein-poor breakfast. Concomitant intake of the protein-rich, but not the carbohydrate-rich, protein-poor breakfast, increased the bioavailability of propranolol in most, but not all, subjects. The food (protein) effect displayed much inter-individual variation, from a decrease to a 250% increase, which could be explained, at least in part, by a correlation between the oral clearance of propranolol and the food-induced increase in its bioavailability. The food effect was not associated with decreased total availability, but with delayed appearance, of the oxidative metabolites 4-OHP, NLA and PG. Hence the food (protein) effect does not seem to be caused by enzyme inhibition, but rather it is due to reduced hepatic extraction of propranolol, probably consequent to an increase hepatic entry rate. When taken together with the protein-rich breakfast, propranolol usually appeared in systemic blood at least as early as when taken on an empty stomach, implying that gastric absorption of propranolol may be possible in the presence of protein-rich food. Within the individual the food effect was reproducible, but its magnitude showed an intraindividual variation that may reflect its dependence upon the rates of gastrointestinal absorption and splanchnic-hepatic blood flow, and hence upon the rate of hepatic drug entry.

Influence of food on the bioavailability of diltiazem and two of its metabolites following the administration of conventional tablets and slow-release capsules

The influence of food on the bioavailability of a conventional tablet and of a slow-release capsule of diltiazem was investigated in two separate groups of 24 healthy volunteers in two open crossover studies. Diltiazem, as a conventional tablet (2 x 30 mg, first group) or as a slow-release capsule (120 mg SR, second group), was administered in a fasting condition and 30 min after a breakfast of 784 kcal (23 per cent proteins, 55 per cent lipids, and 22 per cent of carbohydrates). Multiple blood samples were withdrawn during the next 24 h and diltiazem, desmethyldiltiazem, and deacetyldiltiazem were assayed by HPLC. Neither the rate of absorption, assessed by the rate constant of absorption, the peak plasma concentration, and the time required to reach the peak, nor the amount of drug reaching the systemic circulation, assessed by the area under the plasma concentration time curve (AUC infinity) were influenced by food, and that independently of the formulation. Compared to the fasting experiment, food did not affect either the rate of formation or the AUC infinity of desmethyldiltiazem or deacetyldiltiazem. The results of the present study show that the relative bioavailability of the single dose of diltiazem administered as a slow-release capsule is significantly higher (69 per cent) than that estimated after the administration of diltiazem in a conventional tablet. It was concluded that food does not influence the bioavailability of diltiazem administered as a conventional tablet or as a slow-release formulation.

Once-daily propranolol for hypertension: a comparison of regular-release, long-acting, and generic formulations

This randomized, single-blind, crossover study compared three formulations of propranolol, each given once daily for hypertension. After an initial titration phase, subjects randomly received regular-release, long-acting, or a generic propranolol formulation. Each drug was given for 4 weeks and each active treatment was separated by a washout phase to allow blood pressure to return to baseline. Twelve subjects received all three active treatments. Systolic and diastolic blood pressures and pulses were significantly reduced from baseline by all formulations. There was no significant difference among drugs. Examination of diastolic blood pressures suggested some loss of antihypertensive control at the end of the dosing interval. These results indicate that it may be possible to administer propranolol once daily for hypertension and that there is no advantage for using the long-acting form.

Drug interactions in hypertension

Interactions between drugs and antihypertensive agents can result in either increased or decreased antihypertensive effects. These interactions may be pharmacokinetic or pharmacodynamic in type, resulting in either altered plasma drug concentrations or altered drug effects at similar plasma concentrations. Drugs may limit the absorption of antihypertensive agents, alter their metabolism through either enzyme inhibition or induction, or change renal excretion. In addition, by altering cardiovascular and volume homeostasis, changes in antihypertensive response may be produced.

Circadian changes in the pharmacokinetics and cardiovascular effects of oral propranolol in healthy subjects

Four subjects were synchronized with activity from 07 to 23 h and were given a single oral dose of 80 mg racemic propranolol at fixed times (08, 14, 20 and 02 h) at weekly intervals. ANOVA revealed significant circadian changes in the peak propranolol concentration (Cmax), with a maximum at 08 h and a minimum at 02 h after drug intake; tmax was not dependent on the circadian phase. The elimination half-life varied significantly with the time of day, being shortest at 08 h (3.3 h) and longest at 20 h (4.9 h). The stereospecificity of the propranolol pharmacokinetics was not dependent on the time of drug intake. No circadian variation was found in the maximum decrease in heart rate, but the time to peak effect was dependent on the time of drug intake; tmax was 2.3 h at 08 h and 7.0 h at 02 h. Thus, the time to peak drug concentration did not coincide with the time to peak effect on heart rate at different times of day. Circadian changes were also found in the systolic blood pressure and in the double product. The results show a significant daily variation in the pharmacokinetics and cardiovascular effects of propranolol. However, chronokinetics cannot explain the circadian changes in the effects of the drug. It is concluded that circadian variation in sympathetic tone and vascular reactivity is mainly responsible for the circadian changes in the effects of propranolol.

Effect of hydralazine on the elimination of antipyrine in the rat

The concomitant administration of hydralazine with metoprolol or propranolol substantially increases the oral bioavailability of these beta-blockers, presumably via reduction of the first-pass effect. It has been suggested that this effect may be secondary to a decrease in the intrinsic clearance of propranolol, possibly by inhibition of oxidative metabolism. To examine the possibility that hydralazine alters oxidative metabolism in vivo, the effect of hydralazine on the pharmacokinetics of antipyrine was examined in the rat. The oral administration of hydralazine hydrochloride, 7.5 mg/kg, 15 min prior to antipyrine administration reduced antipyrine clearance from 9.66 +/- 1.18 to 8.19 +/- 0.76 ml/min/kg (P less than 0.05). Hydralazine was observed to cause substantial hypothermia. The study was repeated in temperature-regulated animals and no alteration in antipyrine clearance was found. Two doses of hydralazine in temperature-regulated rats also failed to alter antipyrine clearance. Thus, it appears that the effect of hydralazine on antipyrine clearance is secondary to the hypothermic effect of hydralazine and not due to a direct inhibition of cytochrome P-450-mediated enzyme activity.

The influence of nutrition on the systemic availability of drugs. Part II: Drug metabolism and renal excretion

Plasma concentrations of an active compound vary between individuals and within a subject, even if the same drug dosage is used. These differences are related to variations of drug absorption from the gastrointestinal tract, of presystemic drug metabolism in the intestine or the liver, and of drug elimination from the systemic circulation, for instance by hepatic metabolism or renal excretion. All of these processes can be modified by nutrition. However it is necessary to emphasize the significance of the pharmaceutical formulation for variations of both drug absorption and elimination. The role of nutrition should receive adequate attention during therapeutic use of drugs as well as in drug disposition studies. Recent guidelines for the assessment of the systemic availability of drugs therefore do recommend nutrition to be controlled.

Food increases the bioavailability of propafenone

The effect of food intake on the bioavailability of propafenone, a new antiarrhythmic agent, was evaluated by comparing its kinetics in 24 healthy volunteers in a fasted state and after a standard breakfast. With food, the maximum plasma drug concentration was reached earlier and was significantly increased. When data from 'slow' metabolizers were excluded, there was an average increase of 147% in the area under the concentration-time curve (AUCo) following the standard breakfast. There was a significant correlation (r = 0.946) between [(AUCo fed - AUCo fasted)/AUCo fasted] and propafenone intrinsic clearance in the fasted state. Food intake, however, does not appear to affect the bioavailability of propafenone in 'slow' metabolizers. Patients should be advised to take propafenone in a constant relationship to food to assure consistent bioavailability.

The influence of food on the oral absorption of bevantolol

The bioavailability of bevantolol was compared in 12 healthy volunteers given single doses of the drug as the HCl salt after an overnight fast, or 15 minutes before or after a standardized breakfast in a nonblind, randomized crossover design. Bevantolol was rapidly absorbed in all three treatment groups, with maximum concentrations (Cmax) observed at 1.0, 0.9, and 1.8 hours for the fasting, before breakfast, and after breakfast groups, respectively. Time to Cmax was significantly longer than fasting only when bevantolol was given after breakfast. Food ingestion did not significantly affect Cmax, total of absorbed drug, or the drug elimination rate. Since food only slightly decreases the drug absorption rate and has no measurable effect on the extent of drug absorption, the relationship of bevantolol administration to meals is not expected to influence therapeutic efficacy.

Individualization of calcium entry-blocker dosage for systemic hypertension

The calcium entry blockers are used in a wide variety of clinical situations. Coexisting disease states, such as renal or hepatic dysfunction, may require individualized dosing of these agents. The physiologic changes associated with aging may also affect the pharmacokinetic properties of the drugs. If calcium entry blockers are used concurrently with other medications, dosage adjustment or selection of an alternative drug may be needed. Drug interactions between calcium entry blockers and cimetidine, digoxin and quinidine appear to be clinically significant. Individualized dosing in patients who have coexisting disease or who are using other medications is essential to achieve an adequate therapeutic response and avoid adverse effects. Considerations to attain an optimal response in such situations are presented.

Influence of food on the intravenous and oral dose kinetics of propranolol in the dog

The intravenous and oral dose kinetics of propranolol were studied in the dog both in a fasted state and immediately after a meal consisting of 100 g of cooked beef liver. Fifty microCi of 3H-propranolol was administered intravenously simultaneously with a 40-mg oral dose of unlabeled propranolol. Plasma 3H-propranolol was measured by specific extraction and liquid scintillation spectrometry, and unlabeled plasma propranolol was determined by gas chromatography-mass spectrometry. Feeding significantly reduced (25%) the elimination half-life and increased (52%) the systemic clearance of intravenous propranolol. The increase in the systemic clearance of propranolol after feeding was mostly due to an increase (60%) in apparent hepatic blood flow, which appeared to remain elevated for 5-7 hr. The meal had no influence on the apparent volume of distribution or plasma binding. Feeding did not affect the area under the concentration-time curve of oral propranolol, but significantly delayed the rate of oral propranolol absorption, shifting the time to reach peak plasma levels from 60 to 158 min. The results of this study suggest that feeding alters the disposition of propranolol in the dog by producing a sustained increase in hepatic blood flow.

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.

Stable oral availability of sustained release propranolol when co-administered with hydralazine or food: evidence implicating substrate delivery rate as a determinant of presystemic drug interactions

A study was made of the influence of hydralazine on the oral availability of a sustained release formulation of propranolol (Inderal LA). Sustained release propranolol 160 mg was given orally either alone or in combination with oral hydralazine 25 mg on separate occasions to six healthy volunteers. Blood and urine samples were collected post-dosing over 34 h. Peak concentrations of propranolol, time to peak and area under the plasma concentration-time curve (AUC) were not altered by co-administration of hydralazine with sustained release propranolol. Similarly, there was no change in recovery of 11C-labelled propranolol and metabolites in those individuals to whom tracer label was given. These results contrast with previous reports of marked interaction between the conventional formulation of propranolol and hydralazine or food. Interactions were confirmed between hydralazine and conventional propranolol in three subjects who had been studied previously with sustained release propranolol. Analysis of metabolite profiles in one of these subjects established that the major metabolites do change under hydralazine stimulus. These results indicate that substrate delivery rates may determine presystemic drug interactions, suggesting capacity limitations of hydroxylation processes or short-term flow redistribution following hydralazine, resulting in functional shunting past the hydroxylation enzymes. These results exclude global or lasting enzyme inhibition by hydralazine or simple flow-sensitivity of presystemic clearance.

Influence of food intake on presystemic clearance of drugs

Many drugs have a low degree of oral bioavailability even though their gastrointestinal absorption is complete. This is because they undergo extensive presystemic metabolic transformation during the first passage of the drug through the gastrointestinal mucosa and the liver. In addition to effects on the absorption of some drugs, food intake has been found to influence the bioavailability of drugs with extensive presystemic metabolic clearance. Extensive presystemic clearance occurs commonly with compounds that are lipophilic bases, e.g. propranolol and amitriptyline, but rarely if ever with lipophilic acids, e.g. salicylic acid and penicillin, except for esters of such acids, e.g. acetylsalicylic acid (aspirin) and pivampicillin. While presystemic clearance of (esterified) acidic drugs is unaffected by food, concurrent food intake markedly reduces presystemic clearance, and thus enhances bioavailability, of several lipophilic bases. Among these are propranolol, metoprolol, labetalol, dixyrazine and hydralazine, which are presystemically metabolised by hydroxylation, glucuronidation and acetylation enzymes systems. In contrast, the bioavailability of lipophilic bases which undergo presystemic dealkylation (amitriptyline, codeine, dextropropoxyphene, prazosin, zimelidine) is unaffected by concurrent food intake. Food intake reduces presystemic clearance of hydralazine and propranolol when these drugs are administered in conventional rapid-release tablets but not when they are given in slow-release formulations. Likewise, coadministration of hydralazine reduces presystemic clearance of rapid-release but not slow-release propranolol. These and other observations favour the view that food may reduce presystemic clearance of (certain) lipophilic basic drugs via transient, complex effects on splanchnic-hepatic blood flow and/or shunt processes, and that the extent of this effect is influenced by the rate of drug delivery to the liver. In addition, these findings refute the notion that the reduced presystemic clearance results from (long-lasting) hepatic enzyme inhibition by some nutrient. On the other hand, repeated intake of specific nutrients (protein) and food contaminants (benzpyrene) can enhance presystemic drug clearance by enzyme induction. Thus, food may exert a dual effect on presystemic drug clearance. A complete evaluation of the influence of food on presystemic drug clearance necessitates bioavailability studies carried out following both single and repeated meals, including different kinds of food prepared by various cooking methods. The influence of food on the presystemic clearance of drugs is most likely to be clinically relevant with drugs having narrow therapeutic margins and/or steep dose-response curves.