Alfentanil-induced miosis as a surrogate measure of alfentanil pharmacokinetics in patients with mild and moderate liver cirrhosis

Intrasubject Variability in Intravenous and Oral Probes for Hepatic and First-Pass CYP3A Activity

BACKGROUND AND OBJECTIVES

Clearances and the area under the plasma concentration-time curve extrapolated to infinity (AUC0-∞) of intravenous (IV) and oral midazolam and alfentanil are probes for hepatic and first-pass cytochrome P450 3A (CYP3A) activity, drug interactions, and phenotyping. Single-time plasma concentrations are also used as a proxy for clearance and AUC0-∞. Pupil diameter change is a noninvasive surrogate for plasma alfentanil. An ideal probe should have minimal intrasubject (interday) variability. Despite their widespread use, the intrasubject variability of CYP3A probes is not well characterized. This investigation determined the intrasubject (interday) variability of midazolam and alfentanil metrics of hepatic and first-pass CYP3A.

METHODS

Twelve volunteers were studied in a four-period protocol, with each period identical and separated by approximately 2 weeks. In each period, participants received 1 mg IV midazolam then 15 μg/kg IV alfentanil 1 h later. The next day, they received 3 mg oral midazolam then 60 μg/kg oral alfentanil. Plasma drug concentrations were determined by liquid chromatography-mass spectrometry (LCMS). Dark-adapted pupil diameters were measured coincident with blood sampling. Plasma concentrations and pupil effects (miosis) were analyzed using noncompartmental methods. The results were the coefficient of variation (%CV, mean ± SD) across four sessions in 12 participants.

RESULTS

For IV midazolam: AUC0-∞, clearance, and 5 h concentration, the %CVs were 12 ± 3, 12 ± 3, and 18 ± 8. For IV alfentanil AUC0-∞, clearance, 2 h concentration, and area under the effect curve from time zero to infinity (AUEC0-∞), the %CVs were 16 ± 5, 15 ± 4, 22 ± 7, and 50 ± 28. For oral midazolam AUC0-∞, clearance, and 5 h concentration, %CVs were 19 ± 5, 18 ± 4, and 28 ± 11. For oral alfentanil: AUC0-∞, clearance, 4 h concentration, and AUEC0-∞, %CVs were 20 ± 4, 21 ± 4, 42 ± 26, and 37 ± 14.

CONCLUSIONS

Midazolam and alfentanil had comparable intrasubject variabilities of clearance and AUC0-∞. Single-time point metrics had greater intrasubject variability than AUC0-∞ and clearance. Miosis was a surrogate for alfentanil concentrations and provided real-time results, but intrasubject variability was greater than that of clearances and AUC0-∞.

The impact of gene polymorphism and hepatic insufficiency on voriconazole dose adjustment in invasive fungal infection individuals

Voriconazole (VRZ) is a broad-spectrum antifungal medication widely used to treat invasive fungal infections (IFI). The administration dosage and blood concentration of VRZ are influenced by various factors, posing challenges for standardization and individualization of dose adjustments. On the one hand, VRZ is primarily metabolized by the liver, predominantly mediated by the cytochrome P450 (CYP) 2C19 enzyme. The genetic polymorphism of CYP2C19 significantly impacts the blood concentration of VRZ, particularly the trough concentration (Ctrough), thereby influencing the drug's efficacy and potentially causing adverse drug reactions (ADRs). Recent research has demonstrated that pharmacogenomics-based VRZ dose adjustments offer more accurate and individualized treatment strategies for individuals with hepatic insufficiency, with the possibility to enhance therapeutic outcomes and reduce ADRs. On the other hand, the security, pharmacokinetics, and dosing of VRZ in individuals with hepatic insufficiency remain unclear, making it challenging to attain optimal Ctrough in individuals with both hepatic insufficiency and IFI, resulting in suboptimal drug efficacy and severe ADRs. Therefore, when using VRZ to treat IFI, drug dosage adjustment based on individuals' genotypes and hepatic function is necessary. This review summarizes the research progress on the impact of genetic polymorphisms and hepatic insufficiency on VRZ dosage in IFI individuals, compares current international guidelines, elucidates the current application status of VRZ in individuals with hepatic insufficiency, and discusses the influence of CYP2C19, CYP3A4, CYP2C9, and ABCB1 genetic polymorphisms on VRZ dose adjustments and Ctrough at the pharmacogenomic level. Additionally, a comprehensive summary and analysis of existing studies' recommendations on VRZ dose adjustments based on CYP2C19 genetic polymorphisms and hepatic insufficiency are provided, offering a more comprehensive reference for dose selection and adjustments of VRZ in this patient population.

Sources of Interindividual Variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in others. A significant source of this variability in drug response is drug metabolism, where differences in presystemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C_max, and/or C_min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is recognized that both intrinsic factors (e.g., genetics, age, sex, and disease states) and extrinsic factors (e.g., diet , chemical exposures from the environment, and the microbiome) play a significant role. For drug-metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, upregulation and downregulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less predictable and time-dependent manner. Understanding the mechanistic basis for variability in drug disposition and response is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that will improve outcomes in maintaining health and treating disease.

Physiologically Based Pharmacokinetic Modeling for Olaparib Dosing Recommendations: Bridging Formulations, Drug Interactions, and Patient Populations

We report physiologically based pharmacokinetic-modeling analyses to determine olaparib (tablet or capsule) drug-drug interactions (DDIs). Verified DDI simulations provided dose recommendations for olaparib coadministration with clinically relevant CYP3A4 modulators to eliminate potential risk to patient safety or olaparib efficacy. When olaparib is given with strong/moderate CYP3A inhibitors, the dose should be reduced to 100/150 mg b.i.d. (tablet), and 150/200 mg b.i.d. (capsule). Olaparib administration is not recommended with strong/moderate CYP3A inducers. No dose reductions are required with weak CYP3A inhibitors/inducers. Olaparib was shown to be a weak inhibitor of CYP3A (1.6-fold increase in exposure of a sensitive CYP3A probe) and to have no effect on P-glycoprotein or UGT1A1 substrates. Finally, this model was used to simulate exposure in scenarios where clinical data of olaparib are lacking, such as severe renal or hepatic impairment populations, and provided initial dosing recommendations in pediatric patients.

Objective methods for the assessment of the spinal and supraspinal effects of opioids

BACKGROUND AND PURPOSE

Opioids are potent analgesics. Opioids exert effects after interaction with opioid receptors. Opioid receptors are present in the peripheral- and central nervous system (CNS), but the analgesic effects are primarily mediated via receptors in the CNS. Objective methods for assessment of opioid effects may increase knowledge on the CNS processes responsible for analgesia. The aim of this review was to provide an overview of the most common objective methods for assessment of the spinal and supraspinal effects of opioids and discuss their advantages and limitations.

METHOD

The literature search was conducted in Pub Med (http://www.ncbi.nlm.nih.gov/pubmed) from November 2014 to June 2016, using free-text terms: "opioid", "morphine" and "oxycodone" combined with the terms "pupillometry," "magnetic resonance spectroscopy," "fMRI," "BOLD," "PET," "pharmaco-EEG", "electroencephalogram", "EEG," "evoked potentials," and "nociceptive reflex". Only original articles published in English were included.

RESULTS

For assessment of opioid effects at the supraspinal level, the following methods are evaluated: pupillometry, proton magnetic resonance spectroscopy, functional resonance magnetic imaging (fMRI), positron emission tomography (PET), spontaneous electroencephalogram (EEG) and evoked potentials (EPs). Pupillometry is a non-invasive tool used in research as well as in the clinical setting. Proton magnetic resonance spectroscopy has been used for the last decades and it is a non-invasive technique for measurement of in vivo brain metabolite concentrations. fMRI has been a widely used non-invasive method to estimate brain activity, where typically from the blood oxygen level-dependent (BOLD) signal. PET is a nuclear imaging technique based on tracing radio labeled molecules injected into the blood, where receptor distribution, density and activity in the brain can be visualized. Spontaneous EEG is typically quantified in frequency bands, power spectrum and spectral edge frequency. EPs are brain responses (assessed by EEG) to a predefined number of short phasic stimuli. EPs are quantified by their peak latencies and amplitudes, power spectrum, scalp topographies and brain source localization. For assessment of opioid effects at the spinal level, the following methods are evaluated: the nociceptive withdrawal reflex (NWR) and spinal EPs. The nociceptive withdrawal reflex can be recorded from all limbs, but it is standard to record the electromyography signal at the biceps femoris muscle after stimulation of the ipsilateral sural nerve; EPs can be recorded from the spinal cord and are typically recorded after stimulation of the median nerve at the wrist.

CONCLUSION AND IMPLICATIONS

The presented methods can all be used as objective methods for assessing the centrally mediated effects of opioids. Advantages and limitations should be considered before implementation in drug development, future experimental studies as well as in clinical settings. In conclusion, pupillometry is a sensitive measurement of opioid receptor activation in the CNS and from a practical and economical perspective it may be used as a biomarker for opioid effects in the CNS. However, if more detailed information is needed on opioid effects at different levels of the CNS, then EEG, fMRI, PET and NWR have the potential to be used. Finally, it is conceivable that information from different methods should be considered together for complementary information.

Estimation of the plasma effect site equilibration rate constant of sufentanil in children using the time to peak effect of heart rate and blood pressure

Objectives:

Although targeting the effect site concentration may offer advantages over the traditional forms of administering intravenous anesthetics, it is not applicable for sufentanil in children because its plasma effect site equilibration rate constant (k_e0) is not known yet. We estimated k_e0 of sufentanil in children using the time to peak effect (t_peak) method.

Materials and Methods:

Under general anesthesia, sufentanil t_peak was measured after administration of a submaximal bolus dose by means of the decrease in heart rate, blood pressure and calculated approximate entropy (ApEn) of electroencephalogram in 105 children (age range: 3–11 years). k_e0 was estimated using t_peak and known sufentanil pharmacokinetic parameters in normal children.

Results:

The mean t_peaks were measured as 44 ± 22 s and 227 ± 91 s by heart rate and by mean blood pressure respectively. The estimated k_e0 were 5.16/min and 0.49/min by heart rate and blood pressure respectively. t_peak could not be measured using the ApEn, thus k_e0 could not be calculated by ApEn in children.

Conclusions:

Shorter measured sufentanil t_peak by heart rate compared to blood pressure indicate that the heart rate decrease faster than decreasing of blood pressure. Moreover, the calculated sufentanil k_e0 in children depends on the pharmacodynamics parameters.

CYP3A activity: towards dose adaptation to the individual

INTRODUCTION

Co-medication, gene polymorphisms and co-morbidity are main causes for high variability in expression and function of the CYP3A isoenzymes. Pharmacokinetic variability is a major source of interindividual variability of drug effect and response of CYP3A substrates. While CYP3A genotyping is of limited use, direct testing of enzyme function ('phenotyping') may be more promising to achieve individualized dosing of CYP3A substrates.

AREAS COVERED

We will discuss available phenotyping strategies for CYP3A isoenzymes and causes of intra- and interindividual variability of CYP3A. The impact of phenotyping on the dose selection and pharmacokinetics of CYP3A substrates (docetaxel, irinotecan, tyrosine kinase inhibitors, ciclosporin, tacrolimus) are reviewed. Pubmed searches were conducted during March-November 2015 to retrieve articles related to CYP3A enzyme, phenotyping, drug interactions with CYP3A probe substrates, and phenotyping-guided dosing algorithms.

EXPERT OPINION

While ample data is available on the choice appropriate phenotyping drugs (midazolam, alfentanil, aplrazolam, buspirone, triazolam), less clinical trial data is available concerning strategies to usefully guide dosing in the clinical practice. Implementation into the clinical routine necessitates further research to identify (1) an easy-to-use and cheap test for CYP3A activity that (2) adequately predicts drug exposure to (3) allow a sound decision on dose adaptation and hence (4) improve clinical outcome and/or reduce the intensity or frequency of adverse drug effects.

Opioid Drugs in Patients With Liver Disease: A Systematic Review

CONTEXT

The liver, one of the most important organs of the body, is known to be responsible for several functions. The functional contribution of the liver to the metabolism of carbohydrates, protein, drugs and toxins, fats and cholesterol and many other biological processes are still unknown. Liver disorders are classified into two types: acute and chronic. Different drugs are used in liver diseases to treat and control pain. Most pain relief medications such as opioids are metabolized via the liver; therefore, the adverse reactions of drugs are probably higher for patients with liver disease. The current study aimed to evaluate the effects of opioid drugs on patients with liver disease; therefore, it is necessary to select suitable opioids for such patients.

EVIDENCE ACQUISITION

This review was written by referring to research literature including 70 articles and four textbooks published from 1958 to 2015 on various reputable sites. Searches were carried out on the key phrases of narcotic pain relievers (opioids), acute and chronic hepatic failure, opioid adverse drug reactions, drug-induced liver injury (DILI) and other similar keywords. References included a variety of research papers (descriptive and analytical), intervention and review articles.

RESULTS

In patients with liver disease, administration of opioid analgesics should be observed, accurately. As a general rule, lower doses of drugs should be administered at regular intervals based on the signs of drug accumulation. Secondly, the interactions of opioid drugs with different levels of substrates of the P450 cytochrome enzyme should be considered.

CONCLUSIONS

Pain management in patients with liver dysfunction is always challenging to physicians because of the adverse reactions of drugs, especially opioids. Opioids should be used cautiously since they can cause sedation, constipation and sudden encephalopathy effects. Since the clearance of these drugs in patients with hepatic insufficiency is decreased, the initial dose must be decreased, the intervals between doses should be increased and some patients need to be continuously assessed.

Brivaracetam disposition in mild to severe hepatic impairment

Brivaracetam is a high-affinity synaptic vesicle protein 2A (SV2A) ligand in clinical development for epilepsy. This open-label, single-dose study evaluated brivaracetam disposition in participants with different degrees of hepatic impairment versus matched healthy controls. Twenty-six participants (38-72 years; 19 males and 7 females) with hepatic impairment classified by Child-Pugh score (mild, n = 6; moderate, n = 7; severe, n = 7) or normal hepatic function (n = 6) received a single oral dose of 100 mg brivaracetam. The pharmacokinetics of brivaracetam and its three main metabolites (acid, hydroxy, hydroxyacid) were determined and correlated with impairment severity. Dynamic liver function tests correlated with hepatic impairment severity. The plasma half-life of brivaracetam was 9.8, 14.2, 16.4, and 17.4 hours and the area under the plasma concentration-time curve was 29.7, 44.6, 46.7, and 47.1 µg h/mL in healthy controls and participants with mild, moderate, and severe liver impairment, respectively. Production of the acid metabolite was increased and the hydroxylated metabolites were decreased in participants with hepatic impairment versus healthy controls. Exposure to brivaracetam increased by 50-60% in patients with hepatic impairment, irrespective of severity. The relative importance of biotransformation pathways was altered; cytochrome P450 (CYP)-dependent hydroxylation decreased; CYP-independent acid metabolite formation increased concomitantly.

Analgesics in patients with hepatic impairment: pharmacology and clinical implications

The physiological changes that accompany hepatic impairment alter drug disposition. Porto-systemic shunting might decrease the first-pass metabolism of a drug and lead to increased oral bioavailability of highly extracted drugs. Distribution can also be altered as a result of impaired production of drug-binding proteins or changes in body composition. Furthermore, the activity and capacity of hepatic drug metabolizing enzymes might be affected to various degrees in patients with chronic liver disease. These changes would result in increased concentrations and reduced plasma clearance of drugs, which is often difficult to predict. The pharmacology of analgesics is also altered in liver disease. Pain management in hepatically impaired patients is challenging owing to a lack of evidence-based guidelines for the use of analgesics in this population. Complications such as bleeding due to antiplatelet activity, gastrointestinal irritation, and renal failure are more likely to occur with nonsteroidal anti-inflammatory drugs in patients with severe hepatic impairment. Thus, this analgesic class should be avoided in this population. The pharmacokinetic parameters of paracetamol (acetaminophen) are altered in patients with severe liver disease, but the short-term use of this drug at reduced doses (2 grams daily) appears to be safe in patients with non-alcoholic liver disease. The disposition of a large number of opioid drugs is affected in the presence of hepatic impairment. Certain opioids such as codeine or tramadol, for instance, rely on hepatic biotransformation to active metabolites. A possible reduction of their analgesic effect would be the expected pharmacodynamic consequence of hepatic impairment. Some opioids, such as pethidine (meperidine), have toxic metabolites. The slower elimination of these metabolites can result in an increased risk of toxicity in patients with liver disease, and these drugs should be avoided in this population. The drug clearance of a number of opioids, such as morphine, oxycodone, tramadol and alfentanil, might be decreased in moderate or severe hepatic impairment. For the highly excreted morphine, hydromorphone and oxycodone, an important increase in bioavailability occurs after oral administration in patients with hepatic impairment. Lower doses and/or longer administration intervals should be used when these opioids are administered to patients with liver disease to avoid the risk of accumulation and the potential increase of adverse effects. Finally, the pharmacokinetics of phenylpiperidine opioids such as fentanyl, sufentanil and remifentanil appear to be unaffected in hepatic disease. All opioid drugs can precipitate or aggravate hepatic encephalopathy in patients with severe liver disease, thus requiring cautious use and careful monitoring.