Prodrugs as empowering tools in drug discovery and development: recent strategic applications of drug delivery solutions to mitigate challenges associated with lead compounds and drug candidates

The delivery of a drug to a specific organ or tissue at an efficacious concentration is the pharmacokinetic (PK) hallmark of promoting effective pharmacological action at a target site with an acceptable safety profile. Sub-optimal pharmaceutical or ADME profiles of drug candidates, which can often be a function of inherently poor physicochemical properties, pose significant challenges to drug discovery and development teams and may contribute to high compound attrition rates. Medicinal chemists have exploited prodrugs as an informed strategy to productively enhance the profiles of new chemical entities by optimizing the physicochemical, biopharmaceutical, and pharmacokinetic properties as well as selectively delivering a molecule to the site of action as a means of addressing a range of limitations. While discovery scientists have traditionally employed prodrugs to improve solubility and membrane permeability, the growing sophistication of prodrug technologies has enabled a significant expansion of their scope and applications as an empowering tool to mitigate a broad range of drug delivery challenges. Prodrugs have emerged as successful solutions to resolve non-linear exposure, inadequate exposure to support toxicological studies, pH-dependent absorption, high pill burden, formulation challenges, lack of feasibility of developing solid and liquid dosage forms, first-pass metabolism, high dosing frequency translating to reduced patient compliance and poor site-specific drug delivery. During the period 2012-2022, the US Food and Drug Administration (FDA) approved 50 prodrugs, which amounts to 13% of approved small molecule drugs, reflecting both the importance and success of implementing prodrug approaches in the pursuit of developing safe and effective drugs to address unmet medical needs.

Improving Drug Delivery While Tailoring Prodrug Activation to Modulate Cmax and Cmin by Optimization of (Carbonyl)oxyalkyl Linker-Based Prodrugs of Atazanavir

Structure-property relationships associated with a series of (carbonyl)oxyalkyl amino acid ester prodrugs of the marketed HIV-1 protease inhibitor atazanavir (1), designed to enhance the systemic drug delivery, were examined. Compared to previously reported prodrugs, optimized candidates delivered significantly enhanced plasma exposure and trough concentration (C_min at 24 h) of 1 in rats while revealing differentiated PK paradigms based on the kinetics of prodrug activation and drug release. Prodrugs incorporating primary amine-containing amino acid promoieties offered the benefit of rapid bioactivation that translated into low circulating levels of the prodrug while delivering a high C_max value of 1. Interestingly, the kinetic profile of prodrug cleavage could be tailored for slower activation by structural modification of the amino terminus to either a tertiary amine or a dipeptide motif, which conferred a circulating depot of the prodrug that orchestrated a sustained release of 1 along with substantially reduced C_max and a further enhanced C_min.

An Open Label, Phase 1, Randomized, Seven-treatment, Seven-period, Crossover Study to Assess the Relative Bioavailability, pH Effect, Food Effect, and Dose Proportionality of CC-292, a Potent and Orally Available Bruton's Tyrosine Kinase Inhibitor

BACKGROUND AND OBJECTIVE

CC-292 is a potent, selective, orally administered small molecule inhibitor of Bruton's tyrosine kinase (BTK). To support the clinical investigation of CC-292, a randomized, seven-treatment, seven-period, crossover study was conducted to assess the relative bioavailability, pH effect, food effect, and dose-proportionality of two formulated tablets of CC-292.

METHODS

Healthy subjects (n = 24) were enrolled in the study and randomly assigned into different treatment sequences. Blood samples were collected at pre-specified time points to measure the drug concentrations in plasma. Statistical analyses were performed to compare the pharmacokinetics of CC-292 under different conditions.

RESULTS

The relative bioavailability of the newly developed formulation [spray-dried dispersion (SDD)] to the reference formulation (P22) was 1.24. When a single dose of CC-292 SDD tablet was administered under fed conditions, the area under the plasma concentration-time curve from time zero to infinity (AUC_∞) increased by 10.9% and the maximum plasma drug concentration C_max) decreased by 19.4% compared to when CC-292 was administered under fasted conditions. When a single dose of CC-292 SDD tablet was administered after multiple doses of omeprazole, the area under the plasma concentration-time curve from time zero to infinity (AUC_∞) decreased by 36.8% and the maximum plasma drug concentration C_max) decreased by 48.1% compared to when CC-292 was administered alone. Over a dose range of 100-300 mg (SDD formulation), CC-292 exhibited more than dose-proportional increases of drug exposures.

CONCLUSIONS

CC-292 was well tolerated when administered to healthy subjects as single oral doses under all conditions. Food intake had no clinically relevant impact on CC-292 pharmacokinetics compared to fasted conditions. Therefore, CC-292 can be administered with or without food. Co-administration of CC-292 with multiple doses of omeprazole (40 mg) decreased the pharmacokinetic exposure of CC-292. However, the effect was not clinically relevant.

CLINICAL TRIALS REGISTRATION

NCT02433457.

Pharmacokinetic effects of proton pump inhibitors on the novel PARP inhibitor fluzoparib: a single-arm, fixed-sequence trial in male healthy volunteers

Purpose To assess the pharmacokinetic (PK) effect of proton pump inhibitors on the novel poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitor fluzoparib, and observe the safety of its co-administration with omeprazole. Patients and methods Sixteen male healthy volunteers (HVs) were enrolled in a single-center, single-arm, open-label, fixed-sequence study. HVs took fluzoparib (100 mg, p.o.) after meal consumption on day-1, took omeprazole 40 mg (p.o.) under a fasting condition from day-5 to day-9, and took fluzoparib (100 mg, p.o.) after meal consumption on day-9. Blood samples were collected at predetermined timepoints for PK analyses. Safety was assessed via clinical laboratory tests. The study was registered with the Clinical Trials Registry on 30 September 2019 (NCT04108676). Results The peak plasma concentrations (Cmax) after fluzoparib administration was 2395.17 ± 418.27 ng/mL, the area under the curve (AUC) within 72 h (AUC0 - 72 h) was 26669.09 ± 7320.12 h·ng/mL, and AUC0-∞ was 26897.44 ± 7573.61 h·ng/mL. The Cmax after co-administration of fluzoparib and omeprazole was 2489.43 ± 423.72 ng·mL, AUC0 - 72 h was 30300.49 ± 8350.08 h·ng/mL, and AUC0-∞ was 30678.74 ± 8595.55 h·ng/mL. The geometric mean ratio of Cmax, AUC0 - 72 h and AUC0-∞ was 104.0% (90%CI: 94.8-114.0%), 113.6% (104.2-123.9%) and 104.1% (104.5-124.6%). The number of HVs with adverse reactions was identical (eight) for administration of fluzoparib and co-administration of fluzoparib and omeprazole. Conclusions The proton pump inhibitor omeprazole did not have a significant influence on the PK behavior of fluzoparib, and its safety profile was good upon co-administration with omeprazole. (NCT04108676, 30 September 2019).

(Carbonyl)oxyalkyl linker-based amino acid prodrugs of the HIV-1 protease inhibitor atazanavir that enhance oral bioavailability and plasma trough concentration

We describe the design, synthesis and pharmacokinetic (PK) evaluation of a series of amino acid-based prodrugs of the HIV-1 protease inhibitor atazanavir (1) derivatized on the pharmacophoric secondary alcohol using a (carbonyl)oxyalkyl linker. Prodrugs of 1 incorporating simple (carbonyl)oxyalkyl-based linkers and a primary amine in the promoiety were found to exhibit low chemical stability. However, chemical stability was improved by modifying the primary amine moiety to a tertiary amine, resulting in a 2-fold enhancement of exposure in rats following oral dosing compared to dosing of the parent drug 1. Further refinement of the linker resulted in the discovery of 22 as a prodrug that delivered the parent 1 to rat plasma with a 5-fold higher AUC and 67-fold higher C₂₄ when compared to oral administration of the parent drug. The PK profile of 22 indicated that plasma levels of this prodrug were higher than that of the parent, providing a more sustained release of 1 in vivo.

Prevalence of potential drug-drug interactions in patients of the Swiss HIV Cohort Study in the era of HIV integrase inhibitors

BACKGROUND

Prevalence of potential drug-drug interactions (PDDIs) between antiretroviral drugs (ARVs) and comedications was high in 2008 in a Swiss HIV Cohort Study (SHCS) survey. We reassessed the prevalence of PDDIs in the era of HIV integrase inhibitors (INIs), characterized by more favorable interaction profiles.

METHODS

The prevalence of PDDIs in treated HIV positive individuals was assessed for the period: 01-12/2018 by linkage of the Liverpool HIV drug interactions and SHCS databases. PDDIs were categorized as harmful (red flagged), of potential clinical relevance (amber flagged) or of weak clinical significance (yellow flagged).

RESULTS

In 9'298 included individuals, median age was 51 years (IQR 43; 58), and 72% were males. Individuals received unboosted INIs (40%), boosted ARVs (30%), and non-nucleoside reverse transcriptase inhibitors (NNRTIs) (32%) based regimens. In the entire cohort, 68% received > 1 comedication, 14% had polypharmacy (> 5 comedications) and 29% had > 1 PDDI. Among individuals with comedication, the prevalence of combined amber and yellow PDDIs was 43% (33% amber - mostly with cardiovascular drugs - and 20% yellow flagged PDDIs) compared to 59% in 2008. Two percent had red flagged PDDIs (mostly with corticosteroids), the same as in the 2008 survey. Compared to 2008, fewer individuals received boosted ARVs (-24%) and NNRTIs (-13%) but the use of comedications was higher.

CONCLUSIONS

Prevalence of PDDIs was lower with more widespread use of INIs in 2018 than in 2008. Continued use of boosted regimens and increasing needs for comedications in this aging population impeded lower rates of PDDIs.

The challenge of HIV treatment in an era of polypharmacy

INTRODUCTION

The availability of potent antiretroviral therapy has transformed HIV infection into a chronic disease such that people living with HIV (PLWH) have a near normal life expectancy. However, there are continuing challenges in managing HIV infection, particularly in older patients, who often experience age-related comorbidities resulting in complex polypharmacy and an increased risk for drug-drug interactions. Furthermore, age-related physiological changes may affect the pharmacokinetics and pharmacodynamics of both antiretrovirals and comedications thereby predisposing elderly to adverse drug reactions. This review provides an overview of the therapeutic challenges when treating elderly PLWH (i.e. >65 years). Particular emphasis is placed on drug-drug interactions and other common prescribing issues (i.e. inappropriate drug use, prescribing cascade, drug-disease interaction) encountered in elderly PLWH.

DISCUSSION

Prescribing issues are common in elderly PLWH due to the presence of age-related comorbidities, organ dysfunction and physiological changes leading to a higher risk for drug-drug interactions, drugs dosage errors and inappropriate drug use.

CONCLUSIONS

The high prevalence of prescribing issues in elderly PLWH highlights the need for ongoing education on prescribing principles and the optimal management of individual patients. The knowledge of adverse health outcomes associated with polypharmacy and inappropriate prescribing should ensure that there are interventions to prevent harm including medication reconciliation, medication review and medication prioritization according to the risks/benefits for each patient.

Food, Acid Supplementation and Drug Absorption - a Complicated Gastric Mix: a Randomized Control Trial

PURPOSE

The purpose of this study was to determine the impact of food on gastric pH and the ability of over the counter betaine hydrochloride (BHCl) acid to reacidify gastric pH after food-induced elevations in gastric pH.

METHODS

This open-label cross over clinical study (NCT02758015) included 9 subjects who were randomly assigned to one of 16 possible, 4-period cross-over sequences to determine the impact and relationship of food and gastric pH with acid supplementation. Subjects were administered various doses (1500 mg, 3000 mg and 4500 mg) of betaine hydrochloride (BHCl) to determine the ability of acid supplementation to reacidify gastric pH after the elevation of gastric pH caused by the ingestion of food.

RESULTS

Following the administration of food and the resulting elevation in gastric pH, time to return to baseline gastric pH levels without acid supplementation was 49.7 ± 14.0 min. Administering 4500 mg of BHCl acid in capsules was able to reacidify gastric pH levels back to baseline following the administration of food in approximately 17.3 ± 5.9 min. AUC_pH of each treatment were similar and not statistically different. Mean max pH following the administration of food was 3.20 ± 0.55.

CONCLUSION

The ability of food to elevate and maintain gastric pH levels in the presence of acid supplementation was made evident throughout the study. A 4500 mg dose of BHCl was required to reacidify gastric pH after the administration of food. This study details the difficulty faced by clinicians in dosing a poorly soluble, weakly basic drug to patients receiving acid reducing agents where administration with food is recommended to avoid gastric side effects.

TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT02758015.

Prescribing issues in elderly individuals living with HIV

Introduction: Combined antiretroviral therapy has transformed HIV infection into a chronic disease thus people living with HIV (PLWH) live longer. As a result, the management of HIV infection is becoming more challenging as elderly experience age-related comorbidities leading to complex polypharmacy and a higher risk for drug-drug or drug-disease interactions. Furthermore, age-related physiological changes affect pharmacokinetics and pharmacodynamics thereby predisposing elderly PLWH to incorrect dosing or inappropriate prescribing and consequently to adverse drug reactions and the subsequent risk of starting a prescribing cascade. Areas covered: This review discusses the demographics of the aging HIV population, physiological changes and their impact on drug response as well as comorbidities. Particular emphasis is placed on common prescribing issues in elderly PLWH including drug-drug interactions with antiretroviral drugs. A PubMed search was used to compile relevant publications until February 2019. Expert opinion: Prescribing issues are highly prevalent in elderly PLWH thus highlighting the need for education on geriatric prescribing principles. Adverse health outcomes potentially associated with polypharmacy and inappropriate prescribing should promote interventions to prevent harm including medication reconciliation, medication review, and medication prioritization according to the risks/benefits for a given patient. A multidisciplinary team approach is recommended for the care of elderly PLWH.

Coupling of an Acyl Migration Prodrug Strategy with Bio-activation To Improve Oral Delivery of the HIV-1 Protease Inhibitor Atazanavir

HIV-1 protease inhibitors (PIs), which include atazanavir (ATV, 1), remain important medicines to treat HIV-1 infection. However, they are characterized by poor oral bioavailability and a need for boosting with a pharmacokinetic enhancer, which results in additional drug-drug interactions that are sometimes difficult to manage. We investigated a chemo-activated, acyl migration-based prodrug design approach to improve the pharmacokinetic profile of 1 but failed to obtain improved oral bioavailability over dosing the parent drug in rats. This strategy was refined by conjugating the amine with a promoiety designed to undergo bio-activation, as a means of modulating the subsequent chemo-activation. This culminated in a lead prodrug that (1) yielded substantially better oral drug delivery of 1 when compared to the parent itself, the simple acyl migration-based prodrug, and the corresponding simple l-Val prodrug, (2) acted as a depot which resulted in a sustained release of the parent drug in vivo, and (3) offered the benefit of mitigating the pH-dependent absorption associated with 1, thereby potentially reducing the risk of decreased bioavailability with concurrent use of stomach-acid-reducing drugs.

A review of drug-drug interactions in older HIV-infected patients

INTRODUCTION

The number of older HIV-infected people is growing due to increasing life expectancies resulting from the use of antiretroviral therapy (ART). Both HIV and aging increase the risk of other comorbidities, such as cardiovascular disease, osteoporosis, and some malignancies, leading to greater challenges in managing HIV with other conditions. This results in complex medication regimens with the potential for significant drug-drug interactions and increased morbidity and mortality. Area covered: We review the metabolic pathways of ART and other medications used to treat medical co-morbidities, highlight potential areas of concern for drug-drug interactions, and where feasible, suggest alternative approaches for treating these conditions as suggested from national guidelines or articles published in the English language. Expert commentary: There is limited evidence-based data on ART drug interactions, pharmacokinetics and pharmacodynamics in the older HIV-infected population. Choosing and maintaining effective ART regimens for older adults requires consideration of side effect profile, individual comorbidities, interactions with concurrent prescriptions and non-prescription medications and supplements, dietary patterns with respect to dosing, pill burden and ease of dosing, cost and affordability, patient preferences, social situation, and ART resistance history. Practitioners must remain vigilant for potential drug interactions and intervene when there is a potential for harm.

Design strategies in the prodrugs of HIV-1 protease inhibitors to improve the pharmaceutical properties

Combination antiretroviral therapy (cART) is currently the most effective treatment for HIV-1 infection. HIV-1 protease inhibitors (PIs) are an important component of some regimens of cART. However, PIs are known for sub-optimal ADME properties, resulting in poor oral bioavailability. This often necessitates high drug doses, combination with pharmacokinetic enhancers and/or special formulations in order to effectively deliver PIs, which may lead to a high pill burden and reduced patient compliance. As a remedy, improving the ADME properties of existing drugs via prodrug and other approaches has been pursued in addition to the development of next generation PIs with improved pharmacokinetic, resistance and side effect profiles. Phosphate prodrugs have been explored to address the solubility-limiting absorption and high excipient load. Prodrug design to target carrier-mediated drug delivery has also been explored. Amino acid prodrugs have been shown to improve permeability by engaging active transport mechanisms, reduce efflux and mitigate first pass metabolism while acyl migration prodrugs have been shown to improve solubility. Prodrug design efforts have led to the identification of one marketed agent, fosamprenavir, and clinical studies with two other prodrugs. Several of the reported approaches lack detailed in vivo characterization and hence the potential preclinical or clinical benefits of these approaches are yet to be fully determined.

Patient-centered Outcomes with Concomitant Use of Proton Pump Inhibitors and Other Drugs

PURPOSE

We performed a systematic review of patient-centered outcomes after the concomitant use of proton pump inhibitors (PPIs) and other drugs.

METHODS

We searched 4 databases in July 2016 to find studies that reported mortality and morbidity after the concomitant use of PPIs and other drugs. We conducted direct meta-analyses using a random-effects model and graded the quality of evidence according to the Grading of Recommendations Assessment, Development and Evaluation working group approach.

FINDINGS

We included data from 17 systematic reviews and meta-analyses, 16 randomized controlled trials, and 16 observational studies that examined the concomitant use of PPIs with medications from 10 drug classes. Low-quality evidence suggests that the use of PPIs is associated with greater morbidity when administered with antiplatelet drugs, bisphosphonates, antibiotics, anticoagulants, metformin, mycophenolate mofetil, or nelfinavir. Concomitant PPIs reduce drug-induced gastrointestinal bleeding and are associated with greater docetaxel and cisplatin response rates in patients with metastatic breast cancer. For demonstrated statistically significant relative risks and benefits from concomitant PPIs, the magnitudes of the effects are small, with <100 attributable events per 1000 patients treated, and the effects are inconsistent among specific drugs. Among individual PPIs, the concomitant use of pantoprazole or esomeprazole, but not omeprazole or lansoprazole, is associated with an increased risk for all-cause mortality, nonfatal myocardial infarction, or stroke. Clopidogrel is associated with a greater risk for myocardial infarction compared with prasugrel. Conflicting results between randomized controlled trials and observational studies and high risk for bias in the body of evidence lessened our confidence in the results.

IMPLICATIONS

Available evidence suggests a greater risk for adverse patient outcomes after the concomitant use of PPIs and medications from 9 drug classes and warns against inappropriate drug combinations.

Meal Effects Confound Attempts to Counteract Rabeprazole-Induced Hypochlorhydria Decreases in Atazanavir Absorption

PURPOSE

Clinically relevant pharmacokinetic interactions exist between gastric acid-reducing agents and certain weakly basic drugs that rely on acidic environments for optimal oral absorption. In this study, we examine whether the administration of betaine hydrochloride under fed conditions can enhance the absorption of atazanavir, an HIV-1 protease inhibitor, during pharmacologically-induced hypochlorhydria.

METHODS

In this randomized, single-dose, 3 period, crossover study healthy volunteers received ritonavir-boosted atazanavir (atazanavir/ritonavir 300/100 mg) alone, following pretreatment with the proton pump inhibitor rabeprazole (20 mg twice daily), and with 1500 mg of betaine HCl after rabeprazole pretreatment. Atazanavir was administered with a light meal and gastric pH was monitored using the Heidelberg Capsule.

RESULTS

Pretreatment with rabeprazole resulted in significant reductions in atazanavir C_max (p < 0.01) and AUC_0-last (p < 0.001) (71 and 70%, respectively), and modest decreases in ritonavir C_max and AUC_last (p < 0.01) (40% and 41%, respectively). The addition of betaine HCl restored 13% of ATV C_max and 12% of AUC_last lost due to rabeprazole.

CONCLUSIONS

The co-administration of rabeprazole with atazanavir resulted in significant decreases in atazanavir exposure. The addition of betaine HCl did not sufficiently mitigate the loss of ATV exposure observed during RAB-induced hypochlorhydria. Meal effects lead to a marked difference in the outcome of betaine HCl on atazanavir exposure than we previously reported for dasatanib under fasting conditions.

The use of betaine HCl to enhance dasatinib absorption in healthy volunteers with rabeprazole-induced hypochlorhydria

Many orally administered, small-molecule, targeted anticancer drugs, such as dasatinib, exhibit pH-dependent solubility and reduced drug exposure when given with acid-reducing agents. We previously demonstrated that betaine hydrochloride (BHCl) can transiently re-acidify gastric pH in healthy volunteers with drug-induced hypochlorhydria. In this randomized, single-dose, three-way crossover study, healthy volunteers received dasatinib (100 mg) alone, after pretreatment with rabeprazole, and with 1500 mg BHCl after rabeprazole pretreatment, to determine if BHCl can enhance dasatinib absorption in hypochlorhydric conditions. Rabeprazole (20 mg b.i.d.) significantly reduced dasatinib Cmax and AUC0-∞ by 92 and 78%, respectively. However, coadministration of BHCl significantly increased dasatinib Cmax and AUC0-∞ by 15- and 6.7-fold, restoring them to 105 and 121%, respectively, of the control (dasatinib alone). Therefore, BHCl reversed the impact of hypochlorhydria on dasatinib drug exposure and may be an effective strategy to mitigate potential drug-drug interactions for drugs that exhibit pH-dependent solubility and are administered orally under hypochlorhydric conditions.

Understanding and preventing drug-drug and drug-gene interactions

Concomitant administration of multiple drugs can lead to unanticipated drug interactions and resultant adverse drug events with their associated costs. A more thorough understanding of the different cytochrome P450 isoenzymes and drug transporters has led to new methods to try to predict and prevent clinically relevant drug interactions. There is also an increased recognition of the need to identify the impact of pharmacogenetic polymorphisms on drug interactions. More stringent regulatory requirements have evolved for industry to classify cytochrome inhibitors and inducers, test the effect of drug interactions in the presence of polymorphic enzymes, and evaluate multiple potentially interacting drugs simultaneously. In clinical practice, drug alert software programs have been developed. This review discusses drug interaction mechanisms and strategies for screening and minimizing exposure to drug interactions. We also provide future perspectives for reducing the risk of clinically significant drug interactions.

Gastric reacidification with betaine HCl in healthy volunteers with rabeprazole-induced hypochlorhydria

Previous studies have demonstrated that increased gastric pH from the use of acid-reducing agents, such as proton-pump inhibitors or H2-receptor antagonists, can significantly impact the absorption of weakly basic drugs that exhibit pH-dependent solubility. Clinically practical strategies to mitigate this interaction have not been developed. This pilot study evaluated the extent and time course of gastric reacidification after a solid oral dosage form of anhydrous betaine HCl in healthy volunteers with pharmacologically induced hypochlorhydria. Six healthy volunteers with baseline normochlorhydria (fasting gastric pH < 4) were enrolled in this single period study. Hypochlorhydria was induced via 20 mg oral rabeprazole twice daily for four days. On the fifth day, an additional 20 mg dose of oral rabeprazole was given and gastric pH was monitored continuously using the Heidelberg pH capsule. After gastric pH > 4 was confirmed for 15 min, 1500 mg of betaine HCl was given orally with 90 mL of water and gastric pH was continuously monitored for 2 h. Betaine HCl significantly lowered gastric pH by 4.5 (± 0.5) units from 5.2 (± 0.5) to 0.6 (± 0.2) (P < 0.001) during the 30 min interval after administration. The onset of effect of betaine HCl was rapid, with a mean time to pH < 3 of 6.3 (± 4.3) min. The reacidification period was temporary with a gastric pH < 3 and < 4 lasting 73 (± 33) and 77 (± 30) min, respectively. Betaine HCl was well tolerated by all subjects. In healthy volunteers with pharmacologically induced hypochlorhydria, betaine HCl was effective at temporarily lowering gastric pH. The rapid onset and relatively short duration of gastric pH reduction gives betaine HCl the potential to aid the absorption of orally administered weakly basic drugs that exhibit pH-dependent solubility when administered under hypochlorhydric conditions.

Pharmacokinetic drug interaction profile of omeprazole with adverse consequences and clinical risk management

BACKGROUND

Omeprazole, a proton pump inhibitor (PPI), is widely used for the treatment of dyspepsia, peptic ulcer, gastroesophageal reflux disease, and functional dyspepsia. Polypharmacy is common in patients receiving omeprazole. Drug toxicity and treatment failure resulting from inappropriate combination therapy with omeprazole have been reported sporadically. Systematic review has not been available to address the pharmacokinetic drug-drug interaction (DDI) profile of omeprazole with adverse consequences, the factors determining the degree of DDI between omeprazole and comedication, and the corresponding clinical risk management.

METHODS

Literature was identified by performing a PubMed search covering the period from January 1988 to March 2013. The full text of each article was critically reviewed, and data interpretation was performed.

RESULTS

Omeprazole has actual adverse influences on the pharmacokinetics of medications such as diazepam, carbamazepine, clozapine, indinavir, nelfinavir, atazanavir, rilpivirine, methotrexate, tacrolimus, mycophenolate mofetil, clopidogrel, digoxin, itraconazole, posaconazole, and oral iron supplementation. Meanwhile, low efficacy of omeprazole treatment would be anticipated, as omeprazole elimination could be significantly induced by comedicated efavirenz and herb medicines such as St John's wort, Ginkgo biloba, and yin zhi huang. The mechanism for DDI involves induction or inhibition of cytochrome P450, inhibition of P-glycoprotein or breast cancer resistance protein-mediated drug transport, and inhibition of oral absorption by gastric acid suppression. Sometimes, DDIs of omeprazole do not exhibit a PPI class effect. Other suitable PPIs or histamine 2 antagonists may be therapeutic alternatives that can be used to avoid adverse consequences. The degree of DDIs associated with omeprazole and clinical outcomes depend on factors such as genotype status of CYP2C19 and CYP1A2, ethnicity, dose and treatment course of precipitant omeprazole, pharmaceutical formulation of object drug (eg, mycophenolate mofetil versus enteric-coated mycophenolate sodium), other concomitant medication (eg, omeprazole-indinavir versus omeprazole-indinavir-ritonavir), and administration schedule (eg, intensified dosing of mycophenolate mofetil versus standard dosing).

CONCLUSION

Despite the fact that omeprazole is one of the most widely prescribed drugs internationally, clinical professionals should enhance clinical risk management on adverse DDIs associated with omeprazole and ensure safe combination use of omeprazole by rationally prescribing alternatives, checking the appropriateness of physician orders before dispensing, and performing therapeutic drug monitoring.

Lack of a clinically significant drug-drug interaction in healthy volunteers between the HCV protease inhibitor boceprevir and the proton pump inhibitor omeprazole

OBJECTIVES

Proton pump inhibitors (PPIs) can limit the solubility of concomitant drugs, which can lead to decreased absorption and exposure. Reduced efficacy can be a consequence and in the case of an antimicrobial agent this may contribute to development of resistance. Patients chronically infected with the hepatitis C virus can be treated with a boceprevir-containing regimen and it is relevant to know if interactions between PPIs and boceprevir exist. This study was designed to investigate the influence of a frequently used PPI, omeprazole, on the pharmacokinetics of boceprevir and vice versa.

METHODS

In this open-label, three-period, randomized, cross-over, Phase I study, healthy subjects were randomly assigned to 40 mg of omeprazole once daily for 5 days, 800 mg of boceprevir three times daily for 5 days and 40 mg of omeprazole once daily + 800 mg of boceprevir three times daily for 5 days, or the same treatment in a different order. Every treatment was followed by a wash-out period. At day 5 of every treatment pharmacokinetic blood sampling was performed for 8 h after medication intake. ClinicalTrials.gov: NCT01470690.

RESULTS

All 24 subjects (15 males) completed the study and no serious adverse events were reported. Geometric mean ratios (90% CI) of the area under the plasma concentration-time curve up to 8 h (AUC0-8) and maximum plasma concentration (Cmax) of boceprevir with omeprazole versus boceprevir alone were 0.92 (0.87-0.97) and 0.94 (0.86-1.02), respectively. For omeprazole these values were 1.06 (0.90-1.25) for AUC0-8 and 1.03 (0.85-1.26) for Cmax for the combination versus omeprazole alone.

CONCLUSIONS

Omeprazole did not have a clinically significant effect on boceprevir exposure, and boceprevir did not affect omeprazole exposure.

Atazanavir pharmacokinetics, efficacy and safety in pregnancy: a systematic review

BACKGROUND

For some antiretroviral therapies, drug concentrations are reduced during pregnancy, potentially compromising effective virological suppression.

METHODS

Data on atazanavir boosted with ritonavir in pregnancy are reviewed.

RESULTS

With standard atazanavir/ritonavir 300/100 mg once-daily dosing: atazanavir area-under-the-concentration-time curves were reduced during pregnancy in most studies, but overall interpretation differed according to the data used for comparison; atazanavir concentration 24 h post-dose was maintained >150 ng/ml in 97.6% of women; no instance of mother-to-child transmission occurred in treatment-adherent mothers; and infant hyperbilirubinaemia was not elevated beyond levels expected in the neonatal period.

CONCLUSIONS

With concurrent medications that reduce atazanavir drug concentrations, optimal therapy during pregnancy may require once-daily atazanavir/ritonavir 400/100 mg; however, using this dose during the third trimester doubled maternal grade 3-4 hyperbilirubinaemia rates.

A population pharmacokinetic-pharmacogenetic analysis of atazanavir

Atazanavir is a first-line HIV protease inhibitor commonly co-dosed with ritonavir. Ritonavir inhibits atazanavir metabolism, decreasing variability and increasing plasma concentrations. However, ritonavir use results in higher costs and increased drug-related adverse events. Elucidating atazanavir pharmacokinetics might allow for individualized ritonavir boosting. We previously demonstrated that genetically determined CYP3A5 nonexpression was associated with slower atazanavir clearance CL/F and higher trough concentrations. This effect was prominent in non-African-American men but absent in African-Americans. The present study considers additional genetic predictors of atazanavir CL/F with a focus on race differences. Nine polymorphisms in CYP3A4, ABCG2, NR1I2 (PXR), and SLCO1B1 were evaluated; 330 plasma samples from 30 HIV-negative volunteers, balanced by sex, race, and CYP3A5 expressor status, were available. Analyses were performed using nonlinear mixed-effects modeling (NONMEM). The following factors were univariately associated with atazanavir CL/F (% effect) : African-American race (decreased 35%), female sex (decreased 25%), older age (decreased 1.7%/year), CYP3A5 nonexpressors (decreased 26%), ABCB1 CGC haplotype carriers (1236C/2677G/3435C) (decreased 33%), and CYP3A4*1B carriers (decreased 31%). However, an independent genetic explanation for the differential race effect could not be identified. An interaction was observed with PXR 63396 C>T and CYP3A5 expressor status (p=0.0002). CYP3A5 nonexpressors with a PXR 63396 CC genotype had 37% slower CL/F versus those with CT or TT genotypes. For CYP3A5 expressors, those with a PXR 63396 CC genotype had 63% faster CL/F versus those with CT or TT genotypes. Although this study has as its main limitation a small overall sample size, these results nonetheless provide new leads and impetus to evaluate ways to individualize the need for ritonavir boosting using demographic and genetic predictors of atazanavir pharmacokinetics.

Antiretroviral therapy adherence and drug-drug interactions in the aging HIV population

It is estimated that by 2015 more than half of all HIV-infected individuals in the United States will be 50 years of age or older. As this population ages, the frequency of non-AIDS related comorbidities increases, which includes cardiovascular, metabolic, gastrointestinal, genitourinary and psychiatric disorders. As a result, medical management of the aging HIV population can be complicated by polypharmacy and higher pill burden, leading to poorer antiretroviral therapy (ART) adherence. Adherence to ART is generally better in older populations when compared to younger populations; however, cognitive impairment in elderly patients can impair adherence, leading to worse treatment outcomes. Practical monitoring tools can improve adherence and increase rates of viral load suppression. Several antiretroviral drugs exhibit inhibitory and/or inducing effects on cytochrome P450 isoenzymes, which are responsible for the metabolism of many medications used for the treatment of comorbidities in the aging HIV population. The combination of ART with polypharmacy significantly increases the chance of potentially serious drug-drug interactions (DDIs), which can lead to drug toxicity, poorer ART adherence, loss of efficacy of the coadministered medication, or virologic breakthrough. Increasing clinicians awareness of common DDIs and the use of DDI programs can prevent coadministration of potentially harmful combinations in elderly HIV-infected individuals. Well designed ART adherence interventions and DDI studies are needed in the elderly HIV population.

Darunavir : a nonpeptidic protease inhibitor for antiretroviral-naive and treatment-experienced adults with HIV infection

INTRODUCTION

Darunavir , a nonpeptidic inhibitor of the HIV-1 protease with potent activity against resistant virus, was initially approved by the FDA (2006) and the EMA (2007) for the treatment of antiretroviral-experienced adults, and later for naive adults. Darunavir/ritonavir (600/100 mg twice daily, ideally given with two other active antiretrovirals) demonstrated superior efficacy compared to lopinavir/ritonavir and other protease inhibitors in highly experienced patients. Darunavir/ritonavir (800/100 mg once daily) was demonstrated to be safe and effective for the treatment of naive patients and those with limited darunavir resistance-associated mutations (RAMs). Because darunavir must be coadministered with ritonavir, cytochrome P450 drug-drug interactions can be problematic.

AREAS COVERED

The chemistry, pharmacokinetics, pharmacodynamics, efficacy and safety of darunavir are reviewed in this paper. A PubMed search was conducted using the search terms 'randomized', 'darunavir' and 'efficacy'. Review articles and studies that primarily focused on other drugs were excluded.

EXPERT OPINION

Because darunavir exhibits efficacy against virus with significant protease inhibitor resistance mutations, it is critically important in the treatment of experienced patients, although viral suppression rates may be lower in those with a high baseline viral load or a greater number of cumulative darunavir RAMs. Darunavir/ritonavir is efficacious and well tolerated as a once-daily regimen in naive patients.

Atazanavir/ritonavir-based combination antiretroviral therapy for treatment of HIV-1 infection in adults

In the past 15 years, improvements in the management of HIV infection have dramatically reduced morbidity and mortality. Similarly, rapid advances in antiretroviral medications have resulted in the possibility of life-long therapy with simple and tolerable regimens. Protease inhibitors have been important medications in regimens of combination antiretroviral therapy for the treatment of HIV. One of the recommended and commonly used therapies in this class is once-daily-administered atazanavir, pharmacologically boosted with ritonavir (atazanavir/r). Clinical studies and practice have shown these drugs, in combination with other antiretroviral agents, to be potent, safe and easy to use in a variety of settings. Atazanavir/r has minimal short-term toxicity, including benign bilirubin elevation, and has less potential for long-term complications of hyperlipidemia and insulin resistance compared with other protease inhibitors. A high genetic barrier to resistance and a favorable resistance profile make it an excellent option for initial HIV treatment or as the first drug utilized in the protease inhibitors class. Atazanavir/r is also currently being studied in novel treatment strategies, including combinations with new classes of antiretrovirals to assess nucleoside reverse transcriptase inhibitor-sparing regimens. In this article we review atazanavir/r as a treatment for HIV infection and discuss the latest information on its pharmacology, efficacy and toxicity.

Atazanavir metabolism according to CYP3A5 status: an in vitro-in vivo assessment

The current study was a follow-up to an in vivo study in which atazanavir oral clearance was shown to be dependent on genetically determined CYP3A5 expression status, but only in non-African Americans. The aim of this study was to identify atazanavir metabolites generated by CYP3A5 and to evaluate this metabolite pattern in the African-American versus non-African-American CYP3A5 expressors from the previous study. First, the in vitro metabolism of atazanavir was evaluated using human liver microsomes (HLM) and CYP3A4 and CYP3A5 isoforms. Second, the metabolite pattern generated by CYP3A5 was evaluated in human plasma samples from the previous study. Atazanavir metabolites were analyzed using liquid chromatography-tandem mass spectrometry methods. Metabolite areas under the time-concentration curves (AUCs) were normalized to atazanavir AUC to generate an AUC ratio. Sixteen metabolites were observed in human liver microsomal incubations representing five "phase I" biotransformation pathways. Mono-oxidation products (M1 and M2) were formed by CYP3A5 at a faster rate than CYP3A4 by 32- and 2.6-fold, respectively. This finding was replicated in HLM from a genetically determined CYP3A5 expressor versus nonexpressor. In the in vivo samples, the M1 and M2 AUC ratios were approximately 2-fold higher in CYP3A5 expressors versus nonexpressors (P < 0.05), and the difference was similar in African Americans and non-African Americans. Thus, CYP3A5 produced a unique metabolite "signature" for atazanavir in vitro and in vivo, independent of race. Therefore, other pharmacological factors are likely to explain the apparent lack of effect of genetically determined CYP3A5 expressor status on atazanavir oral clearance in African Americans from the previous study.