Dipyridamole bioavailability in subjects with reduced gastric acidity

New Drug Delivery Systems for Stable Oral Absorption: Theory, Strategies, and Applications

The oral dosage route still remains the most common and preferred route for drug administration due to convenient handling, high patient compliance, and cost-effectiveness. However, the oral absorption of drugs can be a complex process depending upon: (i) physicochemical properties of the drug (e.g., pKa, lipophilicity, solubility), (ii) pharmaceutical factors (e.g., dosage form), and (iii) physiological factors (e.g., gastrointestinal pH values, gastric emptying rate, gastric and intestinal pH, metabolism). Oral administration of drugs sometimes leads to poor and/or variable oral bioavailability, possible leading to unstable clinical outcomes. To offer stable and improved pharmacokinetic behavior of drugs, a number of formulation approaches have been developed with a focus on enhancement of the solubility, dissolution rate, and oral bioavailability of drugs. To provide new formulation platforms for better and safe medication, it is considered essential to understand the physicochemical, biochemical, metabolic, and biological barriers which limit overall drug bioavailability in more detail. The review article considers several crucial factors affecting oral absorption of drug substances. This article also describes the recent progress in formulation approaches to achieve stable and improved biopharmaceutical properties of orally-taken drugs.

Contribution of the Dynamic Intestinal Absorption Model (Diamod) to the Development of a Patient-Centric Drug Formulation

Compound X is a weak basic drug targeting the early stages of Parkinson's disease, for which a theoretical risk assessment has indicated that elevated gastric pH conditions could potentially result in reduced plasma concentrations. Different in vitro dissolution methodologies varying in level of complexity and a physiologically based pharmacokinetic (PBPK) absorption model demonstrated that the dissolution, solubility, and intestinal absorption of compound X was indeed reduced under elevated gastric pH conditions. These observations were confirmed in a crossover pharmacokinetic study in Beagle dogs. As a result, the development of a formulation resulting in robust performance that is not sensitive to the exposed gastric pH levels is of crucial importance. The dynamic intestinal absorption MODel (Diamod), an advanced in vitro gastrointestinal transfer tool that allows to study the gastrointestinal dissolution and interconnected permeation of drugs, was selected as an in vitro tool for the formulation optimization activities given its promising predictive capacity and its capability to generate insights into the mechanisms driving formulation performance. Different pH-modifiers were screened for their potential to mitigate the pH-effect by decreasing the microenvironmental pH at the dissolution surface. Finally, an optimized formulation containing a clinically relevant dose of the drug and a functional amount of the selected pH-modifier was evaluated for its performance in the Diamod. This monolayer tablet formulation resulted in rapid gastric dissolution and supersaturation, inducing adequate intestinal supersaturation and permeation of compound X, irrespective of the gastric acidity level in the stomach. In conclusion, this study describes the holistic biopharmaceutics approach driving the development of a patient-centric formulation of compound X.

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.

pH-Dependent supersaturation from amorphous solid dispersions of weakly basic drugs

PURPOSE

In amorphous solid dispersions (ASDs), the chemical potential of a drug can be reduced due to mixing with the polymer in the solid matrix, and this can lead to reduced drug release when the polymer is insoluble in the dissolution media. If both the drug and the polymer composing an ASD are ionizable, drug release from the ASD becomes pH-dependent. The goal of this study was to gain insights into the pH-dependent solubility suppression from ASD formulations.

METHODS

The maximum release of clotrimazole, a weakly basic drug, from ASDs formulated with insoluble and pH-responsive polymers, was determined as a function of solution pH. Drug-polymer interactions in ASDs were probed using melting point depression, moisture sorption, and solid-state Nuclear Magnetic Resonance spectroscopy (SSNMR) measurements.

RESULTS

The extent of solubility suppression was dependent on polymer type and drug loading. The strength of drug-polymer interactions was found to correlate well with the degree of solubility suppression. For the same ASD, the degree of solubility suppression was nearly constant across the solution pH range studied, suggesting that polymer-drug interactions in residual ASD solids was independent of solution pH. The total drug release agrees with the Henderson-Hasselbalch relationship if the suppressed amorphous solubility of the free drug is independent of solution pH.

CONCLUSIONS

The mechanism of solubility suppression at different solution pHs appeared to be drug-polymer interactions in the solid-state, where the concentration of the free drug remains the same at variable pHs and the total drug concentration follows the Henderson-Hasselbalch relationship.

Improving Dissolution Behavior and Oral Absorption of Drugs with pH-Dependent Solubility Using pH Modifiers: A Physiologically Realistic Mass Transport Analysis

Orally dosed drugs must dissolve in the gastrointestinal (GI) tract before being absorbed through the epithelial cell membrane. In vivo drug dissolution depends on the GI tract's physiological conditions such as pH, residence time, luminal buffers, intestinal motility, and transit and drug properties under fed and fasting conditions (Paixão, P. et al. Mol. Pharm. 2018 and Bermejo, et al. M. Mol. Pharm. 2018). The dissolution of an ionizable drug may benefit from manipulating in vivo variables such as the environmental pH using pH-modifying agents incorporated into the dosage form. A successful example is the use of such agents for dissolution enhancement of BCS class IIb (high-permeability, low-solubility, and weak base) drugs under high gastric pH due to the disease conditions or by co-administration of acid-reducing agents (i.e., proton pump inhibitors, H2-antagonists, and antacids). This study provides a rational approach for selecting pH modifiers to improve monobasic and dibasic drug compounds' dissolution rate and extent under high-gastric pH dissolution conditions, since the oral absorption of BCS class II drugs can be limited by either the solubility or the dissolution rate depending on the initial dose number. Betaine chloride, fumaric acid, and tartaric acid are examples of promising pH modifiers that can be included in oral dosage forms to enhance the rate and extent of monobasic and dibasic drug formulations. However, selection of a suitable pH modifier is dependent on the drug properties (e.g., solubility and pK_a) and its interplay with the pH modifier pK_a or pK_as. As an example of this complex interaction, for basic drugs with high pK_a and intrinsic solubility values and large doses, a polyprotic pH modifier can be expected to outperform a monoacid pH modifier. We have developed a hierarchical mass transport model to predict drug dissolution of formulations under varying pH conditions including high gastric pH. This model considers the effect of physical and chemical properties of the drug and pH modifiers such as pK_a, solubility, and particle size distribution. This model also considers the impact of physiological conditions such as stomach emptying rate, stomach acid and buffer secretion, residence time in the GI tract, and aqueous luminal volume on drug dissolution. The predictions from this model are directly applicable to in vitro multi-compartment dissolution vessels and are validated by in vitro experiments in the gastrointestinal simulator. This model's predictions can serve as a potential data source to predict plasma concentrations for formulations containing pH modifiers administered under the high-gastric pH conditions. This analysis provides an improved formulation design procedure using pH modifiers by minimizing the experimental iterations under both in vitro and in vivo conditions.

Evaluating the impact of acid-reducing agents on drug absorption using biorelevant in vitro tools and PBPK modeling - case example dipyridamole

BACKGROUND

In vitro and in silico methods have become an essential tool in assessing metabolic drug-drug interactions (DDI) and avoiding reduced efficacy and increased side-effects. Another important type of DDI is the impact of acid-reducing agent (ARA) co-therapy on drug pharmacokinetics due to changes in gastric pH, especially for poorly soluble weakly basic drugs.

METHODS

One-stage, two-stage and transfer dissolution experiments with dipyridamole tablets using novel biorelevant media representing the ARA effect were conducted and the results were coupled with a PBPK model. Clinical pharmacokinetic data were compared with the simulations from the PBPK model and with output from TIM-1 experiments, an evolved in vitro system which aims to simulate the physiology in the upper GI tract.

RESULTS

Two-stage and transfer experiments confirmed that these in vitro set-ups tend to overestimate the extent of dipyridamole precipitation occurring in the intestines in vivo. Consequently, data from one-stage dissolution testing under elevated gastric pH conditions were used as an input for PBPK modeling of the ARA/dipyridamole interaction. Using media representing the ARA effect in conjunction with the PBPK model, the ARA effect observed in vivo was successfully bracketed. As an alternative, the TIM-1 system with gastric pH values adjusted to simulate ARA pre-treatment can be used to forecast the ARA effect on dipyridamole pharmacokinetics.

CONCLUSION

Drug-drug interactions of dipyridamole with ARA were simulated well with a combination of dissolution experiments using biorelevant media representing the gastric environment after an ARA treatment together with the PBPK model. Adjustment of the TIM-1 model to reflect ARA-related changes in gastric pH was also successful in forecasting the interaction. Further testing of both approaches for predicting ARA-related DDIs using a wider range of drugs should be conducted to verify their utility for this purpose.

Micelles entrapped microparticles technology: a novel approach to resolve dissolution and bioavailability problems of poorly water soluble drugs

Aim: Aim of this study was to design a solid oral delivery system for a weakly basic drug such as dasatinib (DAS), so as to achieve pH-independent dissolution and improved oral bioavailability.Methods: DAS was solubilised using sodium lauryl sulphate as an aqueous micellar system and such a system containing lactose monohydrate as carrier was spray-dried to obtain a solid mass. Subsequently, the DAS-solid was converted into a tablet using conventional tableting methods.Results: The dissolution study revealed pH-independent dissolution over a wide range of pH conditions. An in vivo bioavailability testing on rats revealed an improved C_max and AUC_0-24. Similarly, viability assay showed a better inhibitory effect of spray-dried dasatinib over the DAS.Conclusions: Micellar solubilisation and spray-drying technology can be approached to resolve poor dissolution and bioavailability of drugs belonging to biopharmaceutical classification system II and III. This technology is amenable to scale-up and has commercial potential.

The Clinician's Guide to Proton Pump Inhibitor Related Adverse Events

A substantial volume of literature exists linking proton pump inhibitor (PPI) use with a multitude of serious adverse events. There is uncertainty, however, over whether these associations are clinically important. Excessive concern about PPI-related adverse events may leave patients at risk of harm by leaving acid-related upper gastrointestinal disease untreated. Conversely, the risk of treatments may outweigh the benefits if any of the purported adverse events are directly caused by PPI use; this is of particular concern where indications for PPI use are not present. In this paper, we review the studies which have reported associations between adverse events and PPI use, discuss the proposed mechanisms of action, grade the confidence in whether these associations are truly causal, and provide advice regarding balancing the benefits of PPI use against their possible harms.

Amorphous solid dispersions of weak bases with pH-dependent soluble polymers to overcome limited bioavailability due to gastric pH variability - An in-vitro approach

Several drugs are pH-dependent soluble weak bases with a poor solubility in the intestinal pH range. Additionally a variable gastric pH, which is a common issue in the population, potentially reduces the in-vivo performance due to reduced solubility at elevated pH. Aiming to avoid the influence of variable gastric pH on the dissolution performance, enteric polymers - hydroxypropylmethylcellulose acetate succinate (HPMCAS), hydroxypropylmethylcellulose phthalate (HP-55, HP-50) and methacrylic acid ethylacrylate copolymer (Eudragit L100-55) together with nevirapine as model drug were used for the preparation of solid dispersions by hot-melt extrusion. We were able to generate solid dispersions without crystalline residuals. The resulting solid dispersions were further tested for stability and dissolution performance applying two different pH-shift experiments (non-sink conditions), to simulate standard and altered gastric conditions. Solid dispersions made of enteric polymers were independent to gastric pH variability and exhibited superior dissolution performances compared to their respective physical mixtures and neat nevirapine.

Prediction Accuracy of Mechanism-Based Oral Absorption Model for Dogs

The purpose of the present study was to evaluate the prediction accuracy of a mechanism-based oral absorption model for the fraction of a dose absorbed (Fa) in dogs, focusing on poorly soluble drugs. As an open mechanism-based model, the gastrointestinal unified theoretical framework was used in this study. The prediction accuracy of the gastrointestinal unified theoretical framework was evaluated using Fa data in dogs (63 data sets for marketed drugs and proprietary compounds). For neutral compounds, Fa was accurately predicted, suggesting that the physiological parameters of dogs were appropriate except for gastrointestinal pH. An extensive literature survey on the small intestinal pH of dogs was then conducted. The result suggested that the pH value ranged between 6.5 and 7.5, with the midst value of 7.0, but there was a great variation among the literature. To confirm the appropriateness of this pH value, the Fa of free acid compounds was predicted by setting the small intestinal pH to 6.5, 7.0, and 7.5. The proportions of compounds with <2-fold error were 57%, 90%, and 76%, respectively. The results of the present study would enable an appropriate use of a mechanism-based model for drug discovery and development.

Gastric-acid-mediated drug-drug interactions with direct-acting antiviral medications for hepatitis C virus infection: clinical relevance and mitigation strategies

Drug-drug interactions (DDIs) between direct-acting antiviral (DAA) medications and acid-reducing agents mediated by gastric acid represent an important issue in drug development and treatment, which could lead to impaired bioavailability and subtherapeutic plasma concentrations of DAA drugs and subsequently compromised treatment outcomes. However, identification of clinically relevant drug interactions associated with elevated gastric pH is not well characterized. Here, we present the first comprehensive analysis of the gastric-acid-mediated drug interactions with all novel DAA medications by analyzing and revisiting in vitro data, prospective DDI trials and retrospective assessments based upon Phase II and III studies, aiming toward an in-depth understanding of the clinical implications and mitigation strategies to circumvent such interactions.

Electrophysiology-Based Assays to Detect Subtype-Selective Modulation of Human Nicotinic Acetylcholine Receptors

The Family Smoking Prevention and Tobacco Control Act of 2009 (Public Law 111-31) gave the US Food and Drug Administration (FDA) the responsibility for regulating tobacco products. Nicotine is the primary addictive component of tobacco and its effects can be modulated by additional ingredients in manufactured products. Nicotine acts by mimicking the neurotransmitter acetylcholine on neuronal nicotinic acetylcholine receptors (nAChRs), which function as ion channels in cholinergic modulation of neurotransmission. Subtypes within the family of neuronal nAChRs are defined by their α- and β-subunit composition. The subtype-selective profiles of tobacco constituents are largely unknown, but could be essential for understanding the physiological effects of tobacco products. In this report, we report the development and validation of electrophysiology-based high-throughput screens (e-HTS)for human nicotinic subtypes, α3β4, α3β4α5, α4β2, and α7 stably expressed in Chinese Hamster Ovary cells. Assessment of agonist sensitivity and acute desensitization gave results comparable to those obtained by conventional manual patch clamp electrophysiology assays. The potency of reference antagonists for inhibition of the receptor channels and selectivity of positive allosteric modulators also were very similar between e-HTS and conventional manual patch voltage clamp data. Further validation was obtained in pilot screening of a library of FDA-approved drugs that identified α7 subtype-selective positive allosteric modulation by novel compounds. These assays provide new tools for profiling of nicotinic receptor selectivity.

The effect of dipyridamole on the pharmacokinetics of metformin: a randomized crossover study in healthy volunteers

PURPOSE

Concomitant treatment with the glucose-lowering drug metformin and the platelet aggregation inhibitor dipyridamole often occurs in patients with type 2 diabetes mellitus who have suffered a cerebrovascular event. The gastrointestinal uptake of metformin is mediated by the human equilibrative nucleoside transporter 4 (ENT4), which is inhibited by dipyridamole in preclinical studies. We hypothesized that dipyridamole lowers the plasma exposure to metformin.

METHODS

Eighteen healthy volunteers (mean age 23 years; 9 male) were randomized in an open-label crossover study. Subjects were allocated to treatment with metformin 500 mg twice daily in combination with dipyridamole slow-release 200 mg twice daily or to metformin alone for 4 days. After a washout period of 10 days, the volunteers were crossed over to the alternative treatment arm. Blood samples were collected during a 10-h period after intake of the last metformin dose. The primary endpoint was the area under the plasma concentration-time curve (AUC0-12h) and the maximum plasma metformin concentration (C max).

RESULTS

In healthy subjects, dipyridamole did not significantly affect Cmax nor AUC0-12h of metformin under steady-state conditions.

CONCLUSIONS

Previous in vitro studies report that dipyridamole inhibits the ENT4 transporter that mediates gastrointestinal uptake of metformin. In contrast, co-administration of dipyridamole at therapeutic dosages to healthy volunteers does not have a clinically relevant effect on metformin plasma steady-state exposure. This observation is reassuring for patients who are treated with this combination of drugs.

Development of pH-Independent Drug Release Formulation Using Lipocalin-Type Prostaglandin D Synthase

The purpose of this study was to develop a pH-independent drug release formulation using lipocalin-type prostaglandin D synthase, a member of the lipocalin superfamily, with the function of forming complexes together with various small lipophilic molecules. Dipyridamole, a poorly water-soluble drug, showing a pH-dependent solubility profile, was used as the model drug. The solubilization of dipyridamole was achieved by a simple complex formulation method with lipocalin-type prostaglandin D synthase. The complex formulation was produced successfully by spray drying, and the obtained powder formulation showed complete dissolution in fasted-state simulated gastric fluid (pH, 1.6) and phosphate-buffered solution (pH, 6.8). In addition, the potential stability of the complex formulation was assessed, and the dissolution profile of the produced powder at pH 6.8 was maintained after 4-week storage under several storage conditions. Furthermore, a pharmacokinetic study using hypochlorhydria model rats was performed to verify the improvement of the intestinal absorption behavior, and eventually the complex formulation overcame the problematic absorption profile of dipyridamole in the elevated gastric pH conditions. These results, taken together, demonstrate that the use of this well-designed drug-delivery carrier is feasible for the development of pH-independent drug release formulations.

Effects of gastric pH on oral drug absorption: In vitro assessment using a dissolution/permeation system reflecting the gastric dissolution process

The aim of the present study was to evaluate the effects of gastric pH on the oral absorption of poorly water-soluble drugs using an in vitro system. A dissolution/permeation system (D/P system) equipped with a Caco-2 cell monolayer was used as the in vitro system to evaluate oral drug absorption, while a small vessel filled with simulated gastric fluid (SGF) was used to reflect the gastric dissolution phase. After applying drugs in their solid forms to SGF, SGF solution containing a 1/100 clinical dose of each drug was mixed with the apical solution of the D/P system, which was changed to fasted state-simulated intestinal fluid. Dissolved and permeated amounts on applied amount of drugs were then monitored for 2h. Similar experiments were performed using the same drugs, but without the gastric phase. Oral absorption with or without the gastric phase was predicted in humans based on the amount of the drug that permeated in the D/P system, assuming that the system without the gastric phase reflected human absorption with an elevated gastric pH. The dissolved amounts of basic drugs with poor water solubility, namely albendazole, dipyridamole, and ketoconazole, in the apical solution and their permeation across a Caco-2 cell monolayer were significantly enhanced when the gastric dissolution process was reflected due to the physicochemical properties of basic drugs. These amounts resulted in the prediction of higher oral absorption with normal gastric pH than with high gastric pH. On the other hand, when diclofenac sodium, the salt form of an acidic drug, was applied to the D/P system with the gastric phase, its dissolved and permeated amounts were significantly lower than those without the gastric phase. However, the oral absorption of diclofenac was predicted to be complete (96-98%) irrespective of gastric pH because the permeated amounts of diclofenac under both conditions were sufficiently high to achieve complete absorption. These estimations of the effects of gastric pH on the oral absorption of poorly water-soluble drugs were consistent with observations in humans. In conclusion, the D/P system with the gastric phase may be a useful tool for better predicting the oral absorption of poorly water-soluble basic drugs. In addition, the effects of gastric pH on the oral absorption of poorly water-soluble drugs may be evaluated by the D/P system with and without the gastric phase.

Appropriate prescribing and important drug interactions in older adults

Polypharmacy, specifically the overuse and misuse of medications, is associated with adverse health events, increased disability, hospitalizations, and mortality. Mechanisms through which polypharmacy may increase adverse health outcomes include decreased adherence, increased drug side effects, higher use of potentially inappropriate medications, and more frequent drug-drug interactions. This article reviews clinical problems associated with polypharmacy and presents a framework to optimize prescribing for older adults.

Immediate utility of two approved agents to target both the metabolic mevalonate pathway and its restorative feedback loop

New therapies are urgently needed for hematologic malignancies, especially in patients with relapsed acute myelogenous leukemia (AML) and multiple myeloma. We and others have previously shown that FDA-approved statins, which are used to control hypercholesterolemia and target the mevalonate pathway (MVA), can trigger tumor-selective apoptosis. Our goal was to identify other FDA-approved drugs that synergize with statins to further enhance the anticancer activity of statins in vivo. Using a screen composed of other FDA approved drugs, we identified dipyridamole, used for the prevention of cerebral ischemia, as a potentiator of statin anticancer activity. The statin-dipyridamole combination was synergistic and induced apoptosis in multiple myeloma and AML cell lines and primary patient samples, whereas normal peripheral blood mononuclear cells were not affected. This novel combination also decreased tumor growth in vivo. Statins block HMG-CoA reductase (HMGCR), the rate-limiting enzyme of the MVA pathway. Dipyridamole blunted the feedback response, which upregulates HMGCR and HMG-CoA synthase 1 (HMGCS1) following statin treatment. We further show that dipyridamole inhibited the cleavage of the transcription factor required for this feedback regulation, sterol regulatory element-binding transcription factor 2 (SREBF2, SREBP2). Simultaneously targeting the MVA pathway and its restorative feedback loop is preclinically effective against hematologic malignancies. This work provides strong evidence for the immediate evaluation of this novel combination of FDA-approved drugs in clinical trials.

Netazepide, a gastrin receptor antagonist, normalises tumour biomarkers and causes regression of type 1 gastric neuroendocrine tumours in a nonrandomised trial of patients with chronic atrophic gastritis

INTRODUCTION

Autoimmune chronic atrophic gastritis (CAG) causes hypochlorhydria and hypergastrinaemia, which can lead to enterochromaffin-like (ECL) cell hyperplasia and gastric neuroendocrine tumours (type 1 gastric NETs). Most behave indolently, but some larger tumours metastasise. Antrectomy, which removes the source of the hypergastrinaemia, usually causes tumour regression. Non-clinical and healthy-subject studies have shown that netazepide (YF476) is a potent, highly selective and orally-active gastrin/CCK-2 receptor antagonist. Also, it is effective in animal models of ECL-cell tumours induced by hypergastrinaemia.

AIM

To assess the effect of netazepide on tumour biomarkers, number and size in patients with type I gastric NETs.

METHODS

We studied 8 patients with multiple tumours and raised circulating gastrin and chromogranin A (CgA) concentrations in an open trial of oral netazepide for 12 weeks, with follow-up 12 weeks later. At 0, 6, 12 and 24 weeks, we carried out gastroscopy, counted and measured tumours, and took biopsies to assess abundances of several ECL-cell constituents. At 0, 3, 6, 9, 12 and 24 weeks, we measured circulating gastrin and CgA and assessed safety and tolerability.

RESULTS

Netazepide was safe and well tolerated. Abundances of CgA (p<0.05), histidine decarboxylase (p<0.05) and matrix metalloproteinase-7(p<0.10) were reduced at 6 and 12 weeks, but were raised again at follow-up. Likewise, plasma CgA was reduced at 3 weeks (p<0.01), remained so until 12 weeks, but was raised again at follow-up. Tumours were fewer and the size of the largest one was smaller (p<0.05) at 12 weeks, and remained so at follow-up. Serum gastrin was unaffected.

CONCLUSION

The reduction in abundances, plasma CgA, and tumour number and size by netazepide show that type 1 NETs are gastrin-dependent tumours. Failure of netazepide to increase serum gastrin further is consistent with achlorhydria. Netazepide is a potential new treatment for type 1 NETs. Longer, controlled trials are justified.

TRIAL REGISTRATION

European Union EudraCT database 2007-002916-24 https://www.clinicaltrialsregister.eu/ctr-search/search?query=2007-002916-24ClinicalTrials.gov NCT01339169 http://clinicaltrials.gov/ct2/show/NCT01339169?term=yf476&rank=5.

Pharmacokinetics and pharmacodynamics of the antiplatelet combination aspirin (acetylsalicylic acid) plus extended-release dipyridamole are not altered by coadministration with the potent CYP2C19 inhibitor omeprazole

BACKGROUND

The fixed-dose combination of aspirin (acetylsalicylic acid) 25 mg plus extended-release dipyridamole 200 mg (ASA+ER-DP) is used for long-term secondary stroke prevention in patients who have experienced non-cardioembolic stroke or transient ischemic attack. Although the theoretical risk is low that the antiplatelet activity of ASA+ER-DP will be affected by concomitant use of a proton pump inhibitor (PPI), no formal drug-drug interaction studies have been conducted.

OBJECTIVE

This study aimed to determine whether the PPI omeprazole influences the pharmacokinetic (PK) and pharmacodynamic (PD) behavior of ASA+ER-DP.

STUDY DESIGN AND SETTING

This was a randomized, open-label, multiple-dose, crossover, drug-drug interaction study carried out in a clinical trial unit.

PARTICIPANTS

Sixty healthy male and female volunteers aged 18-50 years were included in the study.

INTERVENTION

Participants were randomized to one of two treatment sequences (ABCD or CDAB), each comprising four 7-day treatments with a washout of ≥14 days between the second and third treatments. Treatment A=ASA+ER-DP 25 mg/200 mg (Aggrenox®) twice daily (BID) alone; B=ASA+ER-DP 25 mg/200 mg BID+omeprazole (Prilosec®) 80 mg once daily (QD) following ASA+ER-DP alone for 7 days; C=omeprazole 80 mg QD alone; D=omeprazole 80 mg QD+ASA+ER-DP 25 mg/200 mg BID following omeprazole alone for 7 days.

MAIN OUTCOME MEASURES

The main outcome measures were systemic PK exposure to ER-DP and ASA inhibition of arachidonic acid-induced platelet aggregation.

RESULTS

Systemic exposure to ER-DP was similar with and without omeprazole, based on steady-state area under the concentration-time curve (AUC) from 0 to 12 h (AUC0-12,ss, ng·h/mL) and maximum plasma concentration (Cmax,ss, ng/mL). For the treatment comparison D versus A, the percent mean ratios were 96.38 (90% confidence interval [CI] 90.96-102.13) for AUC0-12,ss and 92.03 (86.95-97.40) for Cmax,ss. The ER-DP concentration versus time profiles were nearly superimposable. There was no effect on the PDs of the ASA component: the extent of ASA inhibition of arachidonic acid-induced platelet aggregation was almost identical with and without omeprazole, with a percent mean ratio for treatment D versus A = 99.02 (90 % CI 98.32-99.72) at 4 h after last dose. All treatments were well tolerated.

CONCLUSION

The PK and PD behavior of ASA + ER-DP was not altered by concurrent administration of omeprazole.

Targeting adenosine receptors in the development of cardiovascular therapeutics

Adenosine receptor stimulation has negative inotropic and dromotropic actions, reduces cardiac ischemia-reperfusion injury and remodeling, and prevents cardiac arrhythmias. In the vasculature, adenosine modulates vascular tone, reduces infiltration of inflammatory cells and generation of foam cells, and may prevent the development of atherosclerosis as a result. Modulation of insulin sensitivity may further add to the anti-atherosclerotic properties of adenosine signaling. In the kidney, adenosine plays an important role in tubuloglomerular feedback and modulates tubular sodium reabsorption. The challenge is to take advantage of the beneficial actions of adenosine signaling while preventing its potential adverse effects, such as salt retention and sympathoexcitation. Drugs that interfere with adenosine formation and elimination or drugs that allosterically enhance specific adenosine receptors seem to be most promising to meet this challenge.

Rationale in diagnosis and screening of atrophic gastritis with stomach-specific plasma biomarkers

BACKGROUND AND AIMS

Atrophic gastritis (AG) results most often from Helicobacter pylori (H. pylori) infection. AG is the most important single risk condition for gastric cancer that often leads to an acid-free or hypochlorhydric stomach. In the present paper, we suggest a rationale for noninvasive screening of AG with stomach-specific biomarkers.

METHODS

The paper summarizes a set of data on application of the biomarkers and describes how the test results could be interpreted in practice.

RESULTS

In AG of the gastric corpus and fundus, the plasma levels of pepsinogen I and/or the pepsinogen I/pepsinogen II ratio are always low. The fasting level of gastrin-17 is high in AG limited to the corpus and fundus, but low or non-elevated if the AG occurs in both antrum and corpus. A low fasting level of G-17 is a sign of antral AG or indicates high intragastric acidity. Differentiation between antral AG and high intragastric acidity can be done by assaying the plasma G-17 before and after protein stimulation, or before and after administration of the proton pump inhibitors (PPI). Amidated G-17 will rise if the antral mucosa is normal in structure. H. pylori antibodies are a reliable indicator of helicobacter infection, even in patients with AG and hypochlorhydria.

CONCLUSIONS

Stomach-specific biomarkers provide information about the stomach health and about the function of stomach mucosa and are a noninvasive tool for diagnosis and screening of AG and acid-free stomach.

Effect of diallyl trisulfide on the pharmacokinetics of dipyridamole in rats

This study was aimed to evaluate the effect of diallyl trisulfide (DATS), a major component derived from garlic used to inhibit platelet thromboxane formation, on the pharmacokinetics of dipyridamole. Pharmacokinetic parameters of dipyridamole were determined in rats following intragastric (80 mg/kg suspension or 40 mg/kg solution) or intravenous (3 mg/kg) administration of dipyridamole with coadministration (20 mg/kg) and long-term pretreatment of DATS (10 or 20 mg/kg/day for 15 consecutive days). In addition, everted gut sac models were used to assess transepithelial transport of dipyridamole and the effect of DATS on the intestinal absorption of dipyridamole. After coadministration and long-term pretreatment of DATS, significantly lower Cmax and AUC(0-24 h) were observed for intragastric administration of dipyridamole, whereas little change was noted after intravenous dipyridamole administration. After adding DATS (10 and 50 μg/mL) in the everted gut sacs, absorption of dipyridamole was remarkably decreased in the ileum and jejunum (p < 0.01). In conclusion, DATS reduced the oral exposure of dipyridamole in rats likely by the modification of the dissolution rate and intestinal absorption of dipyridamole, indicating that combined use of DATS or DATS-containing supplements with dipyridamole may require caution as low plasma concentrations of dipyridamole may lead to a subtherapeutic effect of this agent.

Therapeutic modulation of cerebral microhemorrhage in a mouse model of cerebral amyloid angiopathy

BACKGROUND AND PURPOSE

The aging brain demonstrates frequent MRI and pathological evidence of cerebral microbleeds, which are often associated with cerebral amyloid angiopathy. To develop new therapeutic strategies for this disorder, we studied cerebral microhemorrhage in a well-characterized mouse model of cerebral amyloid angiopathy.

METHODS

Tg2576 mice were studied at ages ranging from 2 to 21 months. Spontaneous and induced microscopic bleeding was analyzed with and without a passive anti-amyloid immunization regimen and dietary supplementation of ischemic stroke prevention medication dipyridamole.

RESULTS

Areas of microhemorrhage were easily demonstrated and were significantly more prominent in the oldest mice and in animals treated with anti-amyloid immunotherapy. Dipyridamole supplementation in the diet generated plasma levels >790 ng/mL within the range seen clinically. Dipyridamole treatment did not worsen frequency and size of cerebral microscopic bleeding.

CONCLUSIONS

The Tg2576 mouse is a useful model to study progression and modification of spontaneous and immunotherapy-induced cerebral microhemorrhage. Absence of microhemorrhage worsening with dipyridamole treatment suggests a potential therapeutic role of this agent when ischemic and microhemorrhagic lesions coexist.

Using absorption simulation and gastric pH modulated dog model for formulation development to overcome achlorhydria effect

Impaired absorption of weakly basic drugs in patients with reduced gastric acidity can lead to loss of efficacy of the therapeutic agent. Hence, a robust formulation which can provide adequate exposure in achlorhydric patients is imperative to achieve the desired efficacy. In this report, formulation development of a weakly basic Merck compound A is described. Compound A shows lower solubility at higher pH and thus is prone to reduced exposure under conditions of achlorhydria, as the compound's solubility increases only in environments of less than pH 2. Several formulations with or without an acidifier were developed and characterized by in vitro dissolution and in gastric pH modified dog model to assess their bioperformance in high gastric pH conditions. To predict the bioperformance of these formulations in humans, a dissolution based absorption model was developed and validated against the observed PPI-interaction data in the clinic and the gastric pH-adjusted dog data. An additional absorption model was developed to allow for incorporation of the dog PK data to provide translation of preclinical to clinical exposure. Based on the in vitro dissolution, in silico absorption modeling and preclinical in vivo data, a citric acid-based formulation (F2) was selected for a human pharmacokinetic study. This study showed that exposures from F2 were not meaningfully different in the presence of proton pump inhibitor (PPI) as compared to non-PPI, thus confirming that the F2 formulation was successful in overcoming the achlorhydria effect. These efforts also highlighted that the complementary use of in vitro/in silico/in vivo (IVISIV) tools may be a helpful strategy in the development of formulations to overcome the achlorhydria effect and achieve adequate exposure in patients with high gastric pH.

Review and management of side effects associated with antiplatelet therapy for prevention of recurrent cerebrovascular events

The risk of secondary events following noncardioembolic ischemic stroke or transient ischemic attack (TIA) is high and especially pronounced in the first days and weeks following the initial event; to reduce this risk, it is recommended that antiplatelet therapy be initiated immediately. Although the risk and impact of antiplatelet-associated side effects are generally far less substantial than those of secondary events, some (especially bleeding) can be severe and even life-threatening, and others may reduce adherence to antiplatelet regimens. Therefore, clinicians should implement strategies to reduce the risk of side effects and to manage those that occur. Three antiplatelet regimens have demonstrated substantial reductions in secondary event risk and are currently recommended by consensus panels: aspirin monotherapy at 50-325 mg/day; the combination of aspirin plus extended-release dipyridamole (ER-DP); and clopidogrel monotherapy. Bleeding is potentially the most significant antiplatelet-associated side effect. As bleeding risk with aspirin monotherapy is dose dependent, while preventive efficacy appears similar at all doses above 50 mg/day, aspirin doses should be kept as low as possible. Clopidogrel bleeding risk is similar to aspirin, although a reduced incidence of gastrointestinal bleeding events suggests lower gastrotoxicity. Clopidogrel should not be combined with aspirin after stroke or TIA, as the combination increases bleeding risk without improving antiplatelet efficacy. Patients should be assessed for bleeding risk (especially gastrointestinal bleeding) before initiating antiplatelet therapy; those at elevated risk should be made aware of the signs and symptoms of bleeding events to facilitate prompt treatment. The addition of ER-DP to aspirin does not increase bleeding risk, although ER-DP is associated with risk of headache, which may be severe. The prevalence of headache drops rapidly following initiation of ER-DP, suggesting most patients are able to "push through" this side effect; for those who find headache intolerable, short-term use of a reduced-dose regimen may be helpful.

The developability classification system: application of biopharmaceutics concepts to formulation development

A revised classification system for oral drugs was developed using the biopharmaceutics classification system (BCS) as a starting point. The revised system is designed to have a greater focus on drug developability. Intestinal solubility, the compensatory nature of solubility and permeability in the small intestine and an estimate of the particle size needed to overcome dissolution rate limited absorption were all considered in the revised system. The system was then validated by comparison with literature on the in vivo performance of a number of test compounds. Observations on the test compounds were consistent with the revised classification, termed the developability classification system (DCS), showing it to be of greater value in predicting what factors are critical to in vivo performance than the widely used BCS.

Common drug interactions leading to adverse drug events in the intensive care unit: management and pharmacokinetic considerations

Critically ill patients are predisposed to drug interactions because of the complexity of the drug regimens they receive in the intensive care setting. Drugs may affect the absorption, distribution, metabolism, and/or elimination of an object drug and consequently alter the intended pharmacologic response and potentially lead to an adverse event. Certain disease states that afflict critically ill patients may also amplify an intended pharmacologic response and potentially result in an unintended effect. A team approach is important to identify, prevent, and address drug interactions in the intensive care setting and optimize patient outcomes.

Antiplatelet agents and proton pump inhibitors - personalizing treatment

Introduction:

Antiplatelet therapy remains one of the cornerstones in the management of non-cardioembolic ischemic stroke. However, a significant percentage of patients have concomitant gastroesophageal reflux or peptic ulcer disease that requires acid-reducing medications, the most powerful and effective being the proton pump inhibitors (PPIs). Antiplatelet efficacy, at least in vivo, and particularly for clopidogrel, has been shown to be reduced with concomitant proton pump inhibitor use. Whether this is clinically relevant is not clear from the limited studies available.

Methods:

We conducted an extensive review of studies available on Medline related to pharmacodynamic interactions between the antiplatelet medications and proton pump inhibitors as well as clinical studies that addressed this potential interaction.

Results:

Based on the present pharmacodynamic and clinical studies we did not find a significant interaction that would reduce the efficacy of antiplatelet agents with concomitant user of proton pump inhibitors.

Conclusions:

Patients on antiplatelet agents after a transient ischemic attack or ischemic stroke can safely use aspirin, and extended release dipyridamole/aspirin with proton pump inhibitors. Patients on clopidogrel may use other acid-reducing drugs besides proton pump inhibitors. In rare cases where proton pump inhibitors and clopidogrel have to be used concurrently, careful close monitoring for recurrent vascular events is required.

Systematic review: impaired drug absorption related to the co-administration of antisecretory therapy

BACKGROUND

Due to suppression of gastric acidity during antisecretory therapy, an impaired absorption of co-administered drugs may occur.

AIM

To review evidence of impaired drug absorption related to the use of co-administered PPIs or H2RAs.

METHODS

Systematic search of MEDLINE/EMBASE/SCOPUS databases (1980-September 2008) for English articles with keywords: drug malabsorption and absorption, stomach, anti-secretory/acid inhibitory drugs, histamine H2 antagonists, PPIs, gastric acid, pH, hypochlorhydria, gastric hypoacidity. From 2126 retrieved articles, 16 randomized crossover studies were identified investigating impaired absorption of nine different drugs in association with co-administration of PPIs or H2RAs. Information on investigated drug, study type, features of investigated subjects, study design, type of intervention, and study results were extracted.

RESULTS

The identified studies investigated the absorption kinetics of nine drugs. Acid suppression reduced absorption of ketoconazole, itraconazole, atazanavir, cefpodoxime, enoxacin and dipyridamole (median C(max) reduction by 66.5%). An increased absorption of nifedipine and digoxin (median AUC increase by 10%) and a 2-fold-increase in alendronate bioavailability were observed.

CONCLUSIONS

Gastric pH appears relevant for absorption of some cardiovascular or infectious disease agents. Antisecretory treatment may significantly modify the absorption of co-administered drugs.

Statistical Evaluation of Influence of Xanthan Gum and Guar Gum Blends on Dipyridamole Release from Floating Matrix Tablets

The present investigation explored the use of xanthan gum and guar gum for development of floating drug delivery system of dipyridamole using factorial design approach. The content of polymer blends (X(1)) and ratio of xanthan gum to guar gum (X(2)) were selected as independent variables. The diffusion exponent (n), release rate constant (k), percentage drug release at 1 hr (Q(1)) and 6 hr (Q(6)) were selected as dependent variables. Tablets of all batches had desired buoyancy characteristics. Multiple regression analysis with two way ANOVA revealed that both the factors had statistically significant influence on the response studied (p<0.05). Results of Tukey test showed the relative contribution of each level of different factors for the response studied. It was concluded that the ratio of xanthan to gaur gum had equal or dominant role as controlling factor on kinetics of drug release compared to content of polymer blends.

Aspirin Plus Dipyridamole Versus Aspirin for Prevention of Vascular Events After Stroke or TIA

Background and Purpose— This meta-analysis systematically reviewed randomized controlled trials comparing aspirin plus dipyridamole with aspirin alone in patients with stroke and TIA to determine the efficacy of these agents in preventing recurrent cerebral and systemic vascular events.

Methods— We performed separate analyses of the incidences of stroke alone and composite outcome of stroke, myocardial infarction, or vascular death. We also performed two subset analyses, planned a priori, to examine effect size based on trials using (1) exclusively immediate-release and (2) predominantly extended-release dipyridamole.

Results— The summary results indicate a significant reduction in the overall risk ratio in favor of aspirin plus dipyridamole for stroke alone with relative risk 0.77 (0.67 to 0.89) and the composite end point with relative risk 0.85 (0.76 to 0.94). Studies using immediate-release dipyridamole showed a nonstatistically significant trend in favor of the combination for stroke alone with relative risk 0.83 (0.59 to 1.15) and for the composite outcome with relative risk 0.95 (0.75 to 1.19). Studies using predominantly extended-release dipyridamole showed a statistically significant difference in favor of the combination for stroke alone with relative risk 0.76 (0.65 to 0.89) and for the composite outcome with relative risk 0.82 (0.73 to 0.92).

Conclusions— The combination of aspirin plus dipyridamole is more effective than aspirin alone in preventing stroke and other serious vascular events in patients with minor stroke and TIAs. The risk reduction was greater and statistically significant for studies using primarily extended release dipyridamole, which may reflect a true pharmacological effect or lack of statistical power in studies using immediate release dipyridamole.

Antiplatelet agents for stroke prevention following transient ischemic attack

Regardless of extent or duration of acute effects, transient ischemic attack (TIA) is a marker for cerebrovascular ischemia and carries risk for secondary stroke comparable to that associated with ischemic stroke. Pharmacologic and nonpharmacologic interventions aimed at reducing risk of secondary stroke should be implemented as soon as possible after characterization of the initial event. Medical strategies for secondary prevention include modifying general cardiovascular risk factors but are centered on the specific reduction of stroke risk by antiplatelet agents. Aspirin and clopidogrel have each demonstrated efficacy in reducing secondary event risk; however, clopidogrel has not been shown specifically to prevent secondary events in patients who have had a TIA or stroke. Combination therapy using aspirin plus dipyridamole is the only combination approach to demonstrate additive benefit that is significantly greater than that conferred by aspirin. In contrast, the combination of clopidogrel plus aspirin has not demonstrated significant benefit over monotherapy with either agent and has been associated with increased risk of bleeding episodes.