Plasma protein binding of fentanyl

Interactions of fentanyl with blood platelets and plasma proteins: platelet sensitivity to prasugrel metabolite is not affected by fentanyl under in vitro conditions

BACKGROUND

Clinical trials indicate that fentanyl, like morphine, may impair intestinal absorption and thus decrease the efficacy of oral P2Y₁₂ inhibitors, such as clopidogrel, ticagrelor, and prasugrel. However, the ability of fentanyl to directly negate or reduce the inhibitory effect of P2Y₁₂ receptor antagonists on platelet function has not been established. A series of in vitro experiments was performed to investigate the ability of fentanyl to activate platelets, potentiate platelet response to ADP, and/or diminish platelet sensitivity to prasugrel metabolite (R-138727) in agonist-stimulated platelets. The selectivity and specificity of fentanyl toward major carrier proteins has been also studied.

METHODS

Blood was obtained from healthy volunteers (19 women and 12 men; mean age 40 ± 13 years). Platelet function was measured in whole blood, platelet-rich plasma and in suspensions of isolated platelets by flow cytometry, impedance and optical aggregometry. Surface plasmon resonance and molecular docking were employed to determine the binding kinetics of fentanyl to human albumin, α₁-acid glycoprotein, apolipoprotein A-1 and apolipoprotein B-100.

RESULTS

When applied at therapeutic and supratherapeutic concentrations under various experimental conditions, fentanyl had no potential to stimulate platelet activation and aggregation, or potentiate platelet response to ADP, nor did it affect platelet susceptibility to prasugrel metabolite in ADP-stimulated platelets. In addition, fentanyl was found to interact with all the examined carrier proteins with dissociation constants in the order of 10^-4 to 10^-9 M.

CONCLUSIONS

It does not seem that the delayed platelet responsiveness to oral P2Y₁₂ inhibitors, such as prasugrel, in patients undergoing percutaneous coronary intervention, results from direct interactions between fentanyl and blood platelets. Apolipoproteins, similarly to albumin and α₁-acid glycoprotein, appear to be important carriers of fentanyl in blood.

Physiologically-Based Pharmacokinetic (PBPK) Modeling Providing Insights into Fentanyl Pharmacokinetics in Adults and Pediatric Patients

Fentanyl is widely used for analgesia, sedation, and anesthesia both in adult and pediatric populations. Yet, only few pharmacokinetic studies of fentanyl in pediatrics exist as conducting clinical trials in this population is especially challenging. Physiologically-based pharmacokinetic (PBPK) modeling is a mechanistic approach to explore drug pharmacokinetics and allows extrapolation from adult to pediatric populations based on age-related physiological differences. The aim of this study was to develop a PBPK model of fentanyl and norfentanyl for both adult and pediatric populations. The adult PBPK model was established in PK-Sim® using data from 16 clinical studies and was scaled to several pediatric subpopulations. ~93% of the predicted AUClast values in adults and ~88% in pediatrics were within 2-fold of the corresponding value observed. The adult PBPK model predicted a fraction of fentanyl dose metabolized to norfentanyl of ~33% and a fraction excreted in urine of ~7%. In addition, the pediatric PBPK model was used to simulate differences in peak plasma concentrations after bolus injections and short infusions. The novel PBPK models could be helpful to further investigate fentanyl pharmacokinetics in both adult and pediatric populations.

Performance of TCI Propofol Using the Schnider Model for Cardiac Surgery on Cardiopulmonary Bypass-A Pilot Study

OBJECTIVE

This pilot study aimed to evaluate the performance of target-controlled infusion (TCI) of propofol using the Schnider pharmacokinetic model in patients undergoing cardiac surgery requiring cardiopulmonary bypass.

DESIGN

This was a prospective pharmacokinetic study.

SETTING

A tertiary care hospital.

PARTICIPANTS

This study is comprised of 10 patients, aged between 46 and 81, who underwent elective cardiac surgery requiring the use of cardiopulmonary bypass.

INTERVENTIONS

Anesthetic technique was standardized. Hypnosis was maintained using TCI of propofol, titrated to achieve a bispectral index of 30 to 60. Calculated plasma propofol concentrations were recorded at 5 time points in total, before, during, and after cardiopulmonary bypass. Blood propofol concentration was measured at each of these time points.

MEASUREMENTS AND MAIN RESULTS

The prediction errors and absolute prediction errors were calculated for each sample. From these, the median prediction error (MDPE) and its absolute value (MDAPE) were derived. Agreement between predicted and measured propofol concentrations was assessed using a Bland-Altman plot. Mean prediction errors were also compared pre-, on, and post-bypass using the generalized linear latent and mixed model. The MDPE and MDAPE were both found to be 45%, indicating significant bias toward under-prediction in the Schnider pharmacokinetic model. This bias was increased at an average propofol concentration of 4.5 μg/mL and above. A significant decrease in mean prediction error was noted while on bypass (45.6%, 95% confidence intervals 9.2-82.1).

CONCLUSIONS

The performance of the Schnider pharmacokinetic model for TCI propofol was poor, with a tendency toward under-prediction of blood propofol concentration, especially at higher average concentrations of propofol. While mitigating the risk of awareness, the risk of other adverse effects like hypotension and cardiorespiratory depression is increased. Patients should therefore be adequately monitored, and predicted plasma propofol concentrations taken in context with other patient parameters. A lower target concentration of propofol is probably sufficient to maintain an adequate depth of anesthesia as measured by BIS.

Protein binding of fentanyl and its metabolite nor-fentanyl in human plasma, albumin and α-1 acid glycoprotein

1.Fentanyl is a highly lipophilic opioid commonly used to treat cancer pain. Plasma protein binding (PPB) of fentanyl in human plasma is reported as 80-85%, however it is unclear whether fentanyl binds primarily to albumin (ALB) or α-1 acid glycoprotein (AAG) and no studies have been conducted on the metabolite, nor-fentanyl. Fentanyl is also known to bind to plasticware and ultrafiltration (UF) devices which impacts adversely on binding experiments. 2.PPB of fentanyl and nor-fentanyl to ALB and AAG in isotonic phosphate buffer solution and seeded human plasma was quantified. PPB was also performed in plasma samples obtained from cancer patients receiving transdermal fentanyl. The adsorption of fentanyl and nor-fentanyl to UF devices and plasticware commonly used in PPB studies was also assessed. 3.Fentanyl was shown to bind primarily to ALB as opposed to AAG, with nor-fentanyl exhibiting negligible binding to plasma proteins. Total PPB of fentanyl was 86-89% in seeded human plasma. PPB in 56 cancer patient samples was 95.1 ± 3.52% for fentanyl and 32.4 ± 21.9% for nor-fentanyl. 4.UF was shown to be a reliable and convenient method for PPB studies, thereby removing the need for complex testing for adsorption of the drug to plasticware during UF.

Influence of intensive care treatment on the protein binding of sufentanil and hydromorphone during pain therapy in postoperative cardiac surgery patients

BACKGROUND

Our objective was to evaluate the effect of intensive care treatment on the protein binding of sufentanil and hydromorphone in cardiac surgery patients during postoperative analgesia using a target-controlled infusion (TCI) and patient-controlled analgesia (PCA).

METHODS

Fifty adult patients were enrolled in this prospective randomized study; of which, 49 completed the study (age range 40-81 yr). Sufentanil was administered as an analgesic intraoperatively, and hydromorphone was dosed after operation with TCI and PCA until 8 a.m. on the first postoperative day. Arterial plasma samples were collected for drug and protein concentration measurements up to 24 h after cardiac surgery. Corresponding patient data were collected from the electronic patient data system. After explorative data analysis with principal component analysis, multivariate regression analysis and non-linear mixed effects modelling was used to study the effect of treatment on protein binding.

RESULTS

Data of 35 patients were analysed. The median protein binding of sufentanil and hydromorphone was 88.4% (IQ range 85.7-90.5%) and 11.6% (IQ range 9.5-14.3%), respectively. Free fraction of sufentanil increased towards the end of the study period, whereas hydromorphone free fraction remained nearly constant. The total sufentanil concentration and volume balance were identified as significant covariates for the protein binding of sufentanil. For the protein binding of hydromorphone, no significant covariate effects were found.

CONCLUSIONS

Sufentanil protein binding was significantly dependent on changes in the total drug concentration and volume balance addressing the importance of adequate dosing and fluid-guided therapy. Hydromorphone protein binding was nearly constant throughout the study period.

CLINICAL TRIAL REGISTRATION

EudraCT 2011-003648-31 and ClinicalTrials.gov: NCT01490268.

Pharmacokinetics of non-intravenous formulations of fentanyl

Fentanyl was structurally designed by Paul Janssen in the early 1960s as a potent opioid analgesic (100-fold more potent than morphine). It is a full agonist at μ-opioid receptors and possesses physicochemical properties, in particular a high lipophilicity (octanol:water partition coefficient >700), which allow it to cross quickly between plasma and central nervous target sites (transfer half-life of 4.7-6.6 min). It undergoes first-pass metabolism via cytochrome P450 3A (bioavailability ~30 % after rapid swallowing), which can be circumvented by non-intravenous formulations (bioavailability 50-90 % for oral transmucosal or intranasal formulations). Non-intravenous preparations deliver fentanyl orally-transmucosally, intranasally or transdermally. Passive transdermal patches release fentanyl at a constant zero-order rate for 2-3 days, making them suitable for chronic pain management, as are iontophoretic transdermal systems. Oral transmucosal and intranasal routes provide fast delivery (time to reach maximum fentanyl plasma concentrations 20 min [range 20-180 min] and 12 min [range 12-21 min], respectively) suitable for rapid onset of analgesia in acute pain conditions with time to onset of analgesia of 5 or 2 min, respectively. Intranasal formulations partly bypass the blood-brain barrier and deliver a fraction of the dose directly to relevant brain target sites, providing ultra-fast analgesia for breakthrough pain. Thanks to the development of non-intravenous pharmaceutical formulations, fentanyl has become one of the most successful opioid analgesics, and can be regarded as an example of a successful reformulation strategy of an existing drug based on pharmacokinetic research and pharmaceutical technology. This development broadened the indications for fentanyl beyond the initial restriction to intra- or perioperative clinical uses. The clinical utility of fentanyl could be expanded further by more comprehensive mathematical characterizations of its parametric pharmacokinetic input functions as a basis for the rational selection of fentanyl formulations for individualized pain therapy.

Critical care sedation for neuroscience patients

In 2000, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) introduced the mandate for the implementation of standards for both pain assessment and need for therapy in hospitalized patients. The need for the appropriate titration of sedation and analgesia is particularly poignant in an intensive care unit (ICU) setting where iatrogenic discomfort often complicates patient management. Neurologically ill patients in ICUs present particularly complex sedation issues, owing to the need to monitor these patients with serial neurological exams. Hence, maximal comfort without diminishing neurological responsiveness is desirable. Here, we review the frequently applied methods of evaluating levels of pain and agitation in critically ill patients as well as discuss the appropriate classes of pharmaceutical agents common to this population, with particular emphasis on the potential neurophysiological impact of such therapy.

The pH dependency of the binding of drugs to plasma proteins in man

An analysis of pH-induced changes of drug binding may contribute to the understanding of the mechanisms involved and the clinical relevance. A literature search was performed, and acceptance criteria set up, to select reported data for quantitative evaluation. The relationship between percentage of unbound drug, fu, and pH was analyzed, and the relevance of physicochemical characteristics of the ligand drugs and the importance of hydrogen ion-induced changes in plasma proteins for the pH sensitivity of the binding were evaluated. With all basic and the majority of acidic drugs, fu depended linearly on pH. Basic drugs showed a consistent behavior with fu decreasing with increasing pH. Acidic compounds behaved differently: With some, fu increased, and with others fu decreased, with pH, and with a third group of acids fu was pH independent. Large differences in the pH sensitivity of the plasma protein binding among individual compounds were found. The fu in plasma for some bases and acids increased up to 136% and 95%, respectively, at pH values seen in severe acidemia or alkemia. These changes in fu could be clinically relevant with narrow-therapeutic-range drugs. Physicochemical properties and other characteristics of the ligands affect the pH sensitivity of the interaction with plasma proteins, but there was clear evidence indicating that pH-induced changes in the plasma proteins are also involved in the observed pH-dependent interaction with ligands. It is generally accepted that the unbound, free fraction in whole blood or plasma is an important determinant of the pharmacokinetics and pharmacodynamics of drugs. pH-dependent protein binding and consequent changes in the free fraction have been reported for many drugs. From a basic science point of view, the systematic study of pH-induced perturbations of the drug-protein interaction may provide insight into the mechanism and forces involved in the binding of drugs to plasma proteins. From a clinical viewpoint it may be of interest to know the extent of pH-induced changes in the unbound fraction of drugs under extreme acidemic or alkalemic conditions. Arterial blood pH values compatible with life reportedly range between 6.7 and 8.0. pH values as low as 6.3 have been measured in survivors of drowning accidents. To the best knowledge of the authors, a review and interpretation of pH-associated changes in the protein binding of drugs has not been attempted to date. The goals of this investigation were to (1) review published results of studies that determined the impact of pH changes on the protein binding of drugs in man, (2) select representative data using predetermined criteria, (3) determine relevant factors impacting the pH sensitivity of the drug-protein interaction, and (4) attempt to interpret the results and their clinical relevance.

pKa of Fentanyl Varies With Temperature: Implications for Acid-Base Management During Extremes of Body Temperature

OBJECTIVE

The pKa of fentanyl has not been measured previously at varying extremes of body temperature. The goal of this laboratory investigation was to test the hypothesis that the pKa of fentanyl changes with temperature.

DESIGN

The investigation involved measuring the pKa values of aqueous fentanyl at varying temperatures.

SETTING

The investigation was conducted in a controlled laboratory environment.

PARTICIPANTS

No human or animal subjects were involved.

INTERVENTIONS

Because no live subjects were involved in the investigation, no interventions were necessary.

MEASUREMENTS AND MAIN RESULTS

This paper reports the effect of temperature on the pKa of fentanyl. The pKa of aqueous fentanyl was measured at 15 degrees C, 25 degrees C, 37 degrees C, 42 degrees C, and 47.5 degrees C by potentiometric titration in 0.01 mmol/L of potassium chloride after extensive degassing. Data were analyzed using the least squares method with an appropriately fitting equation. The pKa of fentanyl was found to change in a similar manner to the neutral point of water at varying temperatures.

CONCLUSIONS

This finding has implications for the bioavailability of fentanyl at extremes of body temperature in association with the clinical acid-base management of the patient. Clinical implications for differing methods of intraoperative acid-base management at varying temperatures are discussed.

Pharmacokinetics of fentanyl following intravenous and transdermal administration in horses

REASONS FOR PERFORMING STUDY

Although fentanyl has been reported to cause CNS excitation in horses, a transdermal therapeutic system (TTS) containing this mu agonist has recently been used empirically in equine medicine to treat moderate to severe pain. A better understanding of the disposition of fentanyl following transdermal administration would facilitate the clinical use of TTS fentanyl to obtain analgesia in horses.

OBJECTIVES

To determine the pharmacokinetics of fentanyl following i.v. and TTS patch administration in healthy, mature horses and to evaluate the tolerance of horses to TTS fentanyl administration.

METHODS

The pharmacokinetics of fentanyl in serum were assessed following a single i.v. dose, a single TTS dose, and multiple TTS doses in 6 healthy horses. Physical examinations, haematology and serum biochemistry analyses during transdermal fentanyl application were then performed to determine tolerance of continuous fentanyl administration.

RESULTS

Fentanyl was very rapidly and completely absorbed following a single TTS dose. Mean serum fentanyl concentrations consistent with analgesia in other species were reached by 1 h and maintained until 32 h after patch application. Similar steady state serum concentrations were obtained when multiple doses of TTS fentanyl were administered every 48 or 72 h over 8 or 9 days, with less fluctuation in serum concentrations during the 48 h dosing interval. Three horses exhibited brief (< 12 h) episodes of increased body temperature; however, transdermal fentanyl administrations were not associated with other significant changes in haematology and biochemistry panels or physical examination findings.

CONCLUSIONS AND POTENTIAL RELEVANCE

Although the pharmacodynamics of fentanyl have not been investigated fully in horses, transdermally-administered fentanyl exhibited a favourable pharmacokinetic profile without clinically relevant side effects and may be a useful analgesic in equine patients.

Remifentanil, fentanyl, and alfentanil have no influence on the respiratory burst of human neutrophils in vitro

BACKGROUND

Anaesthetic agents inhibit certain functions of human neutrophils. The respiratory burst (RB) enzyme in the plasma membrane of neutrophils leads to the production of superoxide anion. The oxygen radicals are responsible for killing phagocytised micro-organisms. We investigated the in vitro influence of remifentanil, fentanyl, and alfentanil on the respiratory burst of human neutrophils.

METHODS

For the flow-cytometric evaluation, leukocytes were obtained as supernatant following sedimentation and were incubated with the tested drugs. The concentrations in vitro were adjusted to conform to the plasma concentrations reported for anaesthesia and also to 10-fold higher concentrations. The RB was measured by intracellular oxidation of dihydrorhodamine to fluorescent rhodamine after induction of phorbol-myristate-acetate (PMA), Escherichia coli (E. coli) or priming by tumour necrosis factor alpha followed by stimulation of n-formyl-methionyl-leucyl-phenylalanine (TNF-alpha/FMLP). In order to exclude prestimulation of the neutrophil granulocytes, negative controls were carried out. Propidium iodide (PI) was added for viability discrimination immediately prior to flow cytometry measurement.

RESULTS

Regardless of the triggering agents chosen (PMA, E. coli, TNF-alpha/FMLP), remifentanil, fentanyl, and alfentanil had no significant effect on the neutrophils' respiratory burst even in concentrations which were higher than those encountered during in vivo conditions.

CONCLUSION

With respect to peri- and postoperative risk of infection, anaesthetics and analgetics with no inhibiting effect on neutrophil function should be used. These results show that remifentanil, fentanyl, and alfentanil do not influence the neutrophils' respiratory burst in vitro.

Neonatal effects of adding epidural fentanyl to 0.5% bupivacaine for caesarean section

Epidural injection of opioids has been introduced to improve analgesia during labour and caesarean section. This study was designed to quantify placental transfer of fentanyl and to evaluate neonatal effects of adding fentanyl to 0.5% bupivacaine for epidural anaesthesia in women undergoing elective caesarean section at term. The parturients were randomly allocated to one of four groups of 20, who received either saline (control) or 50, 75 or 100 microg of fentanyl added to 20 ml of 0.5% bupivacaine. Apgar scores, time to sustained respiration and umbilical acid-base values did not differ among the groups. The median (interquartile range) umbilical artery to maternal vein fentanyl concentration ratio was 0.34 (0.26-0.48) when the fentanyl groups were taken together. Neurologic and adaptive capacity scores were evaluated at 2 and 24 h. Neonates whose mothers received fentanyl had lower scores with regard to supporting reaction at 2 h and active tone at 24 h, when compared to controls (P<0.05), but there were no differences among the groups with regard to the other test criteria in the neurobehavioural test. In conclusion, epidural injection of fentanyl 50-100 microg did not produce depression of the term neonate.

Disposition of alfentanil in patients receiving a renal transplant

The disposition of alfentanil has been investigated in 10 anaesthetized patients with chronic renal failure undergoing kidney transplantation and compared with eight age matched anaesthetized patients with normal renal function. Plasma samples were collected to 660 min following intravenous administration of alfentanil 3-5 mg (50 micrograms kg-1). Drug concentrations were measured by RIA; and alfentanil binding to plasma proteins by equilibrium dialysis against 0.1 M phosphate buffer, pH 7.4. Alfentanil binding to plasma proteins was 87.6% (s.d. 2.0) in the patients with chronic renal failure, and 89.7% (1.2) in patients with normal renal function (P = 0.025). There was no correlation between alfentanil binding and plasma albumin, total plasma proteins, plasma urea or plasma creatinine concentrations. In both groups, the drug concentration-time profile decayed in a curvilinear manner; in the chronic renal failure patients, restoration of function did not influence the decay profile. Elimination half life, mean residence time and apparent volume of distribution at steady state were not different in the two groups of patients (mean values: 142.4 and 120.2 min; 128.5 and 136.0 min; and 40.5 and 27.6 L, respectively in chronic renal failure patients and patients with normal renal function). Total drug clearance and Vd area were significantly increased in the chronic renal failure patients: 341.9 vs 211.8 mL min-1; and 69.3 and 35.5 L. There were no differences in intrinsic clearance or apparent volume of distribution at steady state for unbound drug between the two patient groups.

Sex-related differences in drug disposition in man

Sex-related differences in the disposition of some analgesics, anxiolytics and hypnotics have recently been reported. With certain benzodiazepines, sex has been shown to be a more important determinant of variability in drug disposition than age, while with other benzodiazepines an age-related decline in clearance was more pronounced in men than women. In young healthy adults these sex-related differences in drug disposition were related to the phase of the menstrual cycle, oral contraceptive steroid administration, and variations in plasma concentrations of albumin, alpha 1-acid glycoprotein, free fatty acids and sex hormones. While none of the sex-related differences so far reported necessitates the modification of a therapeutic dosage regimen, it is prudent that future protocols for pharmacokinetic studies should regard age, sex, the menstrual cycle and oral contraceptive steroids as potential sources of variability.

Pethidine binding in plasma: effects of methodological variables

Several methodological variables potentially influencing the plasma protein binding of [14C]-pethidine in vitro were investigated using equilibrium dialysis and rigorous pH control. Ionic strength of buffer, pethidine concentration and 21 days of plasma samples frozen to -8 degrees C did not affect the outcome of the binding experiments. Unbound fraction decreased with increasing temperatures between 25 degrees C and 37 degrees C. Unbound fraction decreased with increased pH between pH 7.0 and 8.0; the mean unbound fraction at an equilibrium pH of 7.4 and at 37 degrees C was 0.58 (s.d. 0.03, n = 58). It is likely that previous reports of pethidine unbound fraction as being between 0.2 and 0.4 represent artefacts caused by inadequate pH control during dialysis.

Clinical pharmacokinetics of fentanyl and its newer derivatives

Fentanyl, a synthetic opiate with a (clinical) potency of 50 to 100 times that of morphine, was introduced into clinical practice in the early 1960s. Usually administered by single intravenous doses, it developed a reputation for having a short duration of action and it was assumed that this was a consequence of rapid removal from the body. However, as clinical experience increased, it was realised that administration of multiple doses or large doses during narcotic-based anaesthesia sometimes led to delayed recovery and prolonged respiratory depression, suggesting that the duration of action was limited by redistribution within the body rather than removal from the body. Recent developments in analytical techniques have allowed pharmacokinetic studies and these have confirmed this opinion; fentanyl is rightly regarded as having a redistribution-limited duration of action after single or infrequent doses (analogous to thiopentone). However, the magnitude of the pharmacokinetic constants reported for fentanyl are remarkably inconsistent even in healthy volunteers, for reasons apparently only explainable by assay differences. Hence, estimates of apparent volume of distribution (area) range from around 60L to over 300L, estimates of terminal half-life range from about 1.5 to 6 hours (15 hours in geriatric patients) and total body clearance ranges from 0.4 to over 1.5 L/min. Renal excretion accounts for up to 10% of the dose; the remainder of the clearance would appear to be predominantly hepatic, but with contributions from other tissues. Continued clinical developments of narcotic-based anaesthetic techniques have resulted in high doses of narcotic being used, with oxygen, as the sole anaesthetic agents. At present these techniques are usually based on fentanyl, and the technique is frequently called 'stress-free anaesthesia' because of the effects in obtunding the 'stress response' caused by surgery (elevation of plasma concentrations of cortisol, glucose, ADH, etc. in the intra- and post-operative period) and the lack of deleterious effects on the cardiovascular system.(ABSTRACT TRUNCATED AT 400 WORDS)

The uptake of fentanyl by erythrocytes

Fentanyl passed rapidly into and out of erythrocytes to equilibrate with plasma concentration, and a red cell/plasma partition coefficient of 1.01 +/- 0.0083 s.e.m. was found in 15 normal subjects. Most of the binding of fentanyl by red cells was by haemoglobin. 10% was bound by the cell membrane. Partition was unaffected by haematocrit, pH, or the concentration of fentanyl up to 0.5 mg ml-1 of blood. Dilution of plasma proteins, and replacement of plasma by buffer showed that uptake of fentanyl by red cells is a linear function of the concentration of free drug in plasma. A partition coefficient for red cells/buffer of 4.91 +/- 0.032 s.e.m. was found. This relation was confirmed where binding to plasma proteins was altered in uraemia or hyperlipoproteinaemia, or by competitive displacement of fentanyl by aspirin and phenylbutazone thereby changing the size of the free fraction of fentanyl in plasma. Quinidine, however, inhibited the binding of fentanyl to plasma proteins and red cells equally, to maintain a partition coefficient of unity.

Plasma protein binding of fentanyl: the effect of hyperlipoproteinaemia and chronic renal failure

Hyperlipoproteinaemic patients with raised pre beta-, or pre beta- and beta-lipoprotein fractions showed a significant (P less than 0.001) increase in binding of fentanyl to whole plasma, compared with normal subjects. The presence of chylomicra had no significant effect on binding. In patients with chronic renal failure, a correlation of probability P less than 0.07 was found between percent binding and concentrations of pre beta-lipoprotein (P = 0.001), serum albumin (P = 0.0101), total protein minus albumin (P = 0.0576) and beta-lipoprotein (P = 0.0625). There was no significant correlation of binding with elevation of alpha- or gamma-globulins, with urea or creatinine concentrations, or with age or sex (P greater than 0.223). The magnitude of changes in the free fraction found in these patients should not produce a clinical effect as the total distribution volume of fentanyl exceeds 200 litres.