Effects of hyperlipidemia on the pharmacokinetics of nifedipine in the rat

Implications of Incorporating Plasma Lipoprotein Binding into a Physiologically-Based Pharmacokinetic Model: A Simulation Study with Amiodarone

Although various lipophilic drugs are bound to lipoproteins, lipoprotein binding in plasma is not usually considered in current physiologically-based pharmacokinetic (PBPK) models. Amiodarone is extensively bound to serum triglyceride-rich lipoproteins. Total plasma amiodarone concentration, which is the sum of both unbound and bound concentrations, increases with increasing serum triglyceride levels. We investigated the impact of lipoprotein binding on amiodarone pharmacokinetics using PBPK modeling and simulations. An amiodarone PBPK model that incorporates plasma lipoprotein binding (LPP model) was developed based on the correlation between serum triglyceride levels and lipoprotein-bound amiodarone. The predicted unbound fraction of amiodarone in plasma and systemic clearance in the LPP and base models (with albumin binding only) were similar, but the coefficients of variation for the LPP model were greater than those for the base model and were closer to the observed data. The total plasma amiodarone concentration predicted using the LPP model increased with higher levels of plasma lipoprotein binding and serum albumin. In contrast, changes in plasma lipoprotein binding and serum albumin levels did not influence the predicted unbound plasma amiodarone concentration at steady-state. This study demonstrates that incorporating plasma lipoprotein binding into a PBPK model improves the accuracy of predicting interindividual variabilities in amiodarone clearance by more reliably predicting the interindividual variability in the plasma unbound fraction of amiodarone. Plasma lipoprotein binding should be considered in PBPK modeling and simulations for lipoprotein-associated drugs if there is available information on the relationship between plasma lipoprotein binding and hyperlipidemia.

Nimodipine systemic exposure and outcomes following aneurysmal subarachnoid hemorrhage: a pilot prospective observational study (ASH-1 study)

Background

Nimodipine improves outcomes following aneurysmal subarachnoid hemorrhage (aSAH). Guidelines recommend that all patients should receive a fixed-dose nimodipine for 21 days. However, studies reported variability of nimodipine concentrations in aSAH. It is not clear if reduced systemic exposure contributes to worsening outcomes. The aim of this study was to compare nimodipine systemic exposure in those who experienced poor outcomes to those who experienced favorable outcomes.

Methods

This was a pilot prospective observational study in 30 adult patients admitted to the University of Alberta Hospital with aSAH. Data were collected from the electronic health records following enrollment. Blood samples were collected around one nimodipine 60 mg dose at a steady state, and nimodipine [total, (+)-R and (-)-S enantiomers] plasma concentrations were determined. The poor outcome was defined as a modified Rankin Scale (mRS) score at 90 days of 3-6, while the favorable outcome was an mRS score of 0-2. The correlation between nimodipine concentrations and percent changes in mean arterial pressure (MAP) before and after nimodipine administration was also determined. Furthermore, covariates potentially associated with nimodipine exposure were explored.

Results

In total, 20 (69%) participants had favorable outcomes and 9 (31%) had poor outcomes. Following the exclusion of those with delayed presentation (>96 h from aSAH onset), among those presented with the World Federation of Neurological Surgeons (WFNS) grade 3-5, nimodipine median (interquartile range) area under the concentration time curve (AUC0-3h) in those with favorable outcomes were 4-fold higher than in those with poor outcomes [136 (52-192) vs. 33 (23-39) ng.h/mL, respectively, value of p = 0.2]. On the other hand, among those presented with WFNS grade 1-2, nimodipine AUC0-3h in those with favorable outcomes were significantly lower than in those with poor outcomes [30 (28-36) vs. 172 (117-308) ng.h/mL, respectively, value of p = 0.03)]. (+)-R-nimodipine AUC0-3h in those who did not develop vasospasm were 4-fold significantly higher than those who had vasospasm (value of p = 0.047). (-)-S-nimodipine was significantly correlated with percentage MAP reduction. Similar results were obtained when the whole cohort was analyzed.

Conclusion

The study was the first to investigate the potential association between nimodipine exposure following oral dosing and outcomes. In addition, it suggests differential effects of nimodipine enantiomers, shedding light on the potential utility of nimodipine enantiomers. Larger studies are needed.

Effects of Hyperlipidemia on the Pharmacokinetics of Tofacitinib, a JAK 1/3 Inhibitor, in Rats

Tofacitinib, an inhibitor of Janus kinases (JAKs) 1 and 3, has been shown to be effective in the treatment of rheumatoid arthritis. The incidence of hyperlipidemia has been found to be higher in patients with rheumatoid arthritis. The present study therefore investigated the pharmacokinetics of tofacitinib after its intravenous (10 mg/kg) or oral (20 mg/kg) administration in poloxamer-407-induced hyperlipidemic (PHL) rats. The area under the plasma concentration-time curve from zero to infinity (AUC0-∞) after intravenous administration of tofacitinib was 73.5% higher in PHL than in control rats, owing to slower time-averaged nonrenal clearance (CLNR) in the former. Evaluation of in vitro metabolism showed that the intrinsic clearance (CLint) of tofacitinib was 38.6% lower in PHL than in control rats, owing to the decreased protein expression of hepatic cytochrome P450 (CYP) 3A1/2 and CYP2C11 in PHL rats. Similar results were observed in PHL rats after oral administration of tofacitinib. These results were likely due to the decreased CLNR, CLint, and P-glycoprotein (P-gp) expression in the intestines of PHL compared to control rats. Overall, these findings indicated that hyperlipidemia slowed the metabolism of tofacitinib, increasing its plasma concentrations, and that this reduced metabolism was due to alterations in expression of the proteins CYP3A1/2, CYP2C11, and P-gp in the liver and/or intestines of PHL rats.

Assessment of glibenclamide pharmacokinetics in poloxamer 407-induced hyperlipidemic rats

The aim of the present research was to describe the consequences of hyperlipidemia (HL) on the pharmacokinetics of glibenclamide (Gb) in poloxamer 407-induced hyperlipidemic rats. Rats were given intraperitoneal dose of poloxamer 407 to cause hyperlipidemia. A single oral dose of Gb (10 mg/Kg) was given to normal and HL rats. The C_max and t_max after oral dose of Gb in normal rats were 340.10 µg/ml and 3.67 h, respectively. Whereas, the C_max and t_max after oral dose of Gb in HL rats were noted as 773.39 µg/ml and 2.50 h respectively. The AUC value of Gb was found considerably higher in the HL rats. While the plasma clearance (CL) after oral dose of Gb was 2.53 ml/h and 1.39 ml/h in normal and HL rats respectively. The improved plasma concentration of Gb following oral dosing in rats with HL seems to be due to a direct influence on hepatic clearance or metabolizing enzymes. In conclusion, the Gb pharmacokinetics was considerably affected by the HL in rats. Such findings play an important role for predicting the alterations in the pharmacokinetics of drugs including GB, in cases having hyperlipidemia.

Model-based pharmacokinetic and pharmacodynamic analysis for acute effects of a small molecule inhibitor of diacylglycerol acyltransferase-1 in the TallyHo/JngJ polygenic mouse

The purpose of this study was to evaluate the acute effect of a small molecule inhibitor of DGAT-1 on triglycerides (TG) and cholesterol in polygenic type 2 diabetic TallyHo/JngJ (TH) mice. PF-04620110, a potent and selective DGAT-1 inhibitor, was used as a model compound in this study and which was administered to TH and ICR mice. The concentration of the model compound that produced 50% of maximum lowering of TG level (IC₅₀) in TH mice was not significantly different from that in ICR mice, when estimated using the model-based pharmacokinetic and pharmacodynamic assay, a two-compartmental model and an indirect response model. The clearance of the inhibitor in TH mice was fivefold higher than that in ICR mice, suggesting significantly altered pharmacokinetics. Moreover, the in vitro metabolic elimination kinetic parameters (k_e,met), determined using liver microsomes from TH and ICR mice were 1.24 ± 0.14 and 0.174 ± 0.116 min^-1, respectively. Thus, we report that the differences in the acute effects of the small molecule DAGT-1 inhibitor between TH mice and ICR mice can be attributed to altered pharmacokinetics caused by an altered metabolic rate for the compound in TH mice.

Pharmacokinetic alterations in poloxamer 407-induced hyperlipidemic rats

1. Plasma lipid profile abnormalities in hyperlipidemia can potentially alter the pharmacokinetics of a drug in a complex manner. To evaluate these pharmacokinetic alterations in hyperlipidemia and to determine the underlying mechanism(s), poloxamer 407-induced hyperlipidemic rats (HL rats), a well-established animal model of hyperlipidemia have been used. 2. In this review, we summarize findings on the pathophysiological and gene expression changes in drug-metabolizing enzymes and transporters in HL rats. We discuss pharmacokinetic changes in drugs metabolized primarily via hepatic cytochrome P450 (CYPs) in terms of alterations in hepatic intrinsic clearance (CL^'_int), free fraction in plasma (f_u) and hepatic blood flow rate (Q_H), depending on the hepatic excretion ratio, as well as drugs eliminated primarily by mechanisms other than hepatic CYPs. 3. For lipoprotein-bound drugs, increased binding to lipoproteins resulted in lower f_u values and volumes of distribution, with some exceptions. Generally, slower non-renal clearance (or total body clearance) of drugs that are substrates of hepatic CYP3A and CYP2C is well explained by the following factors: alterations in CL^'_int (due to down-regulation of hepatic CYPs), decreased f_u and/or possible decreased Q_H. 4. These consistent findings across studies in HL rats suggest more studies are needed at the clinical level for optimal pharmacotherapies for hyperlipidemia.

Quantitative prediction of the extent of drug-drug interaction using a physiologically based pharmacokinetic model that includes inhibition of drug metabolism determined in cryopreserved hepatocytes

1. A physiologically based pharmacokinetic (PBPK) model that includes inhibition constant evaluated in cryopreserved hepatocytes was used to predict drug-drug interactions (DDIs) between orally administered nifedipine, a CYP substrate, and fluconazole or ketoconazole, CYP inhibitors, in rats. 2. The Kp,uu, ratio of unbound inhibitor concentration in liver ([I]liver,u) to that in plasma ([I]sys,u), of fluconazole and ketoconazole was 1.0 and 13.0, indicating that ketoconazole accumulates in liver. The ratios of inhibition constants in rat liver microsomes (Ki,mic,u) to that in rat cryopreserved hepatocytes (Ki,hep,u) for fluconazole and ketoconazole were 1.5 and 25.5, which were similar to the Kp,uu and suggested that cryopreserved hepatocytes could mimic the hepatic accumulation of inhibitors. 3. The increases in AUC of nifedipine predicted by the minimal PBPK model using [I]liver,u/Ki,mic,u and [I]sys,u/Ki,hep,u were within 1.5-fold of the observed values for both inhibitors, whereas the model using [I]sys,u/Ki,mic,u underestimated the AUC increase caused by ketoconazole 21-fold. 4. These results indicated that hepatic accumulation factor of an inhibitor is required for a precise DDI projection and that cryopreserved hepatocytes would be useful to obtain the Ki including hepatic accumulation factor. It was demonstrated that PBPK model using Ki,hep,u could be a valuable approach for quantitative DDI projection.

Pharmacokinetics of verapamil and its metabolite norverapamil in rats with hyperlipidaemia induced by poloxamer 407

In this study, the pharmacokinetics of verapamil and its active metabolite norverapamil were evaluated following intravenous and oral administration of 10 mg/kg verapamil to rats with hyperlipidaemia (HL) induced by poloxamer 407 (HL rats). The total area under the plasma concentration time curve (AUC) of verapamil in HL rats following intravenous administration was significantly greater (by 11.2%) than in control rats due to their slower (by 11%) non-renal clearance. The oral AUC of verapamil in HL rats was also significantly greater (by 116%) compared with controls, with a larger magnitude than the data observed following intravenous administration. This may have been a result of the decreased intestinal metabolism of verapamil in HL rats. The AUC of norverapamil and AUC(norverapamil)/AUC(verapamil) ratios following intravenous and oral administration of verapamil were unchanged in HL rats. Assuming that the HL rat model qualitatively reflects similar changes in patients with HL, the findings of this study have potential therapeutic implications. Further studies in humans are required to determine whether modification of the oral verapamil dosage regimen in HL states is necessary.

Effect of rat serum lipoproteins on mRNA levels and amiodarone metabolism by cultured primary rat hepatocytes

Hyperlipidemia can significantly increase amiodarone (AM) in vivo liver uptake and decrease its velocity of microsomal metabolism. Here, hepatocytes isolated from normolipidemic (NL) and hyperlipidemic rats were incubated with AM in the presence or absence of diluted NL or hyperlipidemic serum. The serum was added either as preincubation before drug, or concurrently with drug; incubations without rat serum were used as controls. The hepatocyte levels of mRNA for several proteins and enzymes were also measured. Disappearance of AM was seen up to 72 h. There was little difference between hepatocytes from NL or hyperlipidemic animals in intrinsic clearance (CL(int) ) of AM. The effect of hyperlipidemic rat serum, either before or with AM, was profound, causing a significant reduction in the CL(int) . Reductions were seen in mRNA for cytochrome P450 1A1, 3A2, and 2D1, some transporters, and low-density lipoprotein receptors after exposure of hepatocytes to lipoprotein-rich sera. In conclusion, exposure of isolated hepatocytes to hyperlipidemic serum caused decreases in AM CL(int) and lower mRNA levels for some proteins involved in the uptake and metabolism of AM. When coincubated with serum, an additional effect of increased binding to lipoproteins seemed to further contribute to a reduced CL of AM.

Effects of poloxamer 407-induced hyperlipidemia on the pharmacokinetics of carbamazepine and its 10,11-epoxide metabolite in rats: Impact of decreased expression of both CYP3A1/2 and microsomal epoxide hydrolase

The pharmacokinetics of carbamazepine (CBZ) and its active 10,11-epoxide metabolite (CBZ-E) were evaluated after intravenous and oral administration of 5 mg/kg CBZ to rats with hyperlipidemia induced by poloxamer 407 (HL rats) and controls. The total area under the plasma concentration-time curve (AUC) of CBZ in HL rats after intravenous administration was significantly greater than that in controls due to their slower non-renal clearance (CL(NR)). This was due to slower hepatic CL(int) for metabolism of CBZ to CBZ-E in HL rats via CYP3A1/2. This result was consistent with a previous study indicating reduced hepatic CYP3A1/2 expression in HL rats. Interestingly, the AUC of CBZ-E was also increased in HL rats, while AUC(CBZ-E)/AUC(CBZ) ratios remained unchanged. These results suggested that further metabolism of CBZ-E to the inactive metabolite trans-10,11-dihydoxyl-10,11-dihydro-CBZ (CBZ-D) via microsomal epoxide hydrolase (mEH) was also slowed in HL rats. The significantly reduced hepatic mRNA level and expression of mEH protein in HL rats compared to controls confirmed the above hypothesis. Similar pharmacokinetic changes were observed in HL rats after oral administration of CBZ. These findings have potential therapeutic implications assuming that the HL rat model qualitatively reflects similar changes in patients with hyperlipidemia. Caution is required regarding pharmacotherapy in the hyperlipidemic state in cases where drugs that are metabolized principally by CYP3A1/2 or mEH and have a narrow therapeutic range are in use.

Effect of experimental hyperlipidaemia on the electrocardiographic effects of repeated doses of halofantrine in rats

BACKGROUND AND PURPOSE

Halofantrine can cause a prolongation of the cardiac QT interval, leading to serious ventricular arrhythmias. Hyperlipidaemia elevates plasma concentration of halofantrine and may influence its tissue uptake. The present study examined the effect of experimental hyperlipidaemia on QT interval prolongation induced by halofantrine in rats.

EXPERIMENTAL APPROACH

Normolipidaemic and hyperlipidaemic rats (induced with poloxamer 407) were given 4 doses of halofantrine (i.v., 4-40 mg·kg(-1)·d(-1)) or vehicle every 12 h. Under brief anaesthesia, ECGs were recorded before administration of the vehicle or drug and 12 h after the first and last doses. Blood samples were taken at the same time after the first and last dose of halofantrine. Hearts were also collected 12 h after the last dose. Plasma and heart samples were assayed for drug and desbutylhalofantrine using a stereospecific method.

KEY RESULTS

In the vehicle group, hyperlipidaemia by itself did not affect the ECG. Compared to baseline, QT intervals were significantly higher in both normolipidaemic and hyperlipidaemic rats after halofantrine. In hyperlipidaemic rats, plasma but not heart concentrations of the halofantrine enantiomers were significantly higher compared to those in normolipidaemic rats. Despite the lack of difference in the concentrations of halofantrine in heart, QT intervals were significantly higher in hyperlipidaemic compared to those in normolipidaemic rats.

CONCLUSIONS AND IMPLICATIONS

The unbound fraction of halofantrine appeared to be the controlling factor for drug uptake by the heart. Our data suggested a greater vulnerability to halofantrine-induced QT interval prolongation in the hyperlipidaemic state.

Effects of experimental hyperlipidaemia on the pharmacokinetics of docetaxel in rats

Hyperlipidaemia correlates with an increased risk of occurrence of various cancers. In this study, the effects of hyperlipidaemia on the pharmacokinetics of docetaxel, a member of the taxane class of anti-cancer drugs, were investigated in rats with experimental hyperlipidaemia; we focused on the alterations in docetaxel metabolism and plasma distribution. Docetaxel (5 mg/kg intravenously (i.v.) and 40 mg/kg per oral (p.o.)) was administered to control rats and rats with poloxamer-407 (P-407)-induced hyperlipidaemia (1 g/kg, intraperitoneally). In vitro studies were conducted on hepatic metabolism in S9 fractions and plasma protein binding using the ultrafiltration method. Hyperlipidaemia dramatically increased the area under the plasma concentration-time curve from time 0 to infinity (AUC(0-∞)) of docetaxel after i.v. (1.86-fold) or p.o. (10.8-fold) administration and decreased total body clearance (0.574-fold) and apparent volume of distribution at steady state (0.615-fold) of docetaxel after i.v. administration. Compared with the control rats, the metabolism of docetaxel by hepatic S9 fractions and the unbound fraction in the plasma in the hyperlipidaemic rats were decreased, i.e., by 20.1 and 79.8%, respectively. In conclusion, the alterations in docetaxel pharmacokinetics in rats with P-407-induced hyperlipidaemia may be due, at least in part, to a decrease in hepatic metabolism and the unbound fraction of docetaxel in the plasma. These findings have potential therapeutic implications for predicting human pharmacokinetic responses to hyperlipidaemia.

Pharmacokinetics of clomipramine, an antidepressant, in poloxamer 407-induced hyperlipidaemic model rats

Objective

This study was undertaken to investigate the effects of hyperlipidaemia on the pharmacokinetics of clomipramine, an antidepressant, particularly addressing the change of clomipramine distribution to plasma components in poloxamer 407-induced hyperlipidaemia model rats.

Methods

Clomipramine pharmacokinetic studies in hyperlipidaemic rats were performed with clomipramine continuous infusion. Furthermore, clomipramine protein binding and distribution to the brain and plasma components such as lipoproteins were investigated.

Key findings

Mean plasma concentration of clomipramine at steady state during continuous infusion (17.5 µg/min/kg) in hyperlipidaemic rats (0.45 ± 0.01 µg/ml) was significantly higher than that in the control rats (0.30 ± 0.02 µg/ml). However, the amount of clomipramine in the brain in hyperlipidaemic rats (0.31 ± 0.06 µg/g) was dramatically lower than in the control rats (1.89 ± 0.13 µg/g). However, the plasma unbound fraction in hyperlipidaemic rats (0.98 ± 0.05%) was significantly lower than that of the control rats (6.51 ± 0.62%).

Conclusions

Lower distribution to the brain and lower plasma clearance of clomipramine in hyperlipidaemic rats resulted from lower plasma unbound fraction because of higher lipid-rich protein contents in blood. Results of this study provide useful information for dosage adjustment of clomipramine in hyperlipidaemia.

Antihyperlipidaemic activity of swertiamarin, a secoiridoid glycoside in poloxamer-407-induced hyperlipidaemic rats

We have investigated antihyperlipidaemic effect of swertiamarin (50 mg/kg, oral once) isolated from the perennial herb Enicostemma littorale Blume in poloxamer 407 (P-407)-induced hyperlipidaemic rats. Rats were made hyperlipidaemic by intraperitoneal administration of P-407 (400 mg/kg). Serum lipid levels such as total cholesterol, triglycerides and low-density lipoprotein cholesterol increased significantly (P < 0.001) compared with normal control rats. All these changes were significantly prevented in the rats treated with swertiamarin. Serum high-density lipoprotein (HDL) cholesterol was found to be reduced in the P-407 control rats. However, administration of swertiamarin significantly (P < 0.01) increased HDL levels and it showed a significant lipid-lowering effect, as well as a high antiatherogenic potential. Overall swertiamarin is an effective lipid-lowering lead compound and can be useful for preventing atherosclerosis.

A review of poloxamer 407 pharmaceutical and pharmacological characteristics

Poloxamer 407 copolymer (ethylene oxide and propylene oxide blocks) shows thermoreversible properties, which is of the utmost interest in optimising drug formulation (fluid state at room temperature facilitating administration and gel state above sol-gel transition temperature at body temperature promoting prolonged release of pharmacological agents). Pharmaceutical evaluation consists in determining the rheological behaviour (flow curve or oscillatory studies), sol-gel transition temperature, in vitro drug release using either synthetic or physiological membrane and (bio)adhesion characteristics. Poloxamer 407 formulations led to enhanced solubilisation of poorly water-soluble drugs and prolonged release profile for many galenic applications (e.g., oral, rectal, topical, ophthalmic, nasal and injectable preparations) but did not clearly show any relevant advantages when used alone. Combination with other excipients like Poloxamer 188 or mucoadhesive polymers promotes Poloxamer 407 action by optimising sol-gel transition temperature or increasing bioadhesive properties. Inclusion of liposomes or micro(nano)particles in Poloxamer 407 formulations offers interesting prospects, as well. Besides these promising data, Poloxamer 407 has been held responsible for lipidic profile alteration and possible renal toxicity, which compromises its development for parenteral applications. In addition, new findings have demonstrated immuno-modulation and cytotoxicity-promoting properties of Poloxamer 407 revealing significant pharmacological interest and, hence, human trials are in progress to specify these potential applications.

EXTRAPOLATION OF PRECLINICAL PHARMACOKINETICS AND MOLECULAR FEATURE ANALYSIS OF “DISCOVERY-LIKE” MOLECULES TO PREDICT HUMAN PHARMACOKINETICS

The prediction of human pharmacokinetics from preclinical species is an integral component of drug discovery. Recent studies with a 103-compound dataset suggested that scaling from monkey pharmacokinetic data tended to be the most accurate method for predicting human clearance. Additionally, interrogation of the two-dimensional molecular properties of these molecules produced a set of associations which predict the likely extrapolative outcome (success or failure) of preclinical data to project human pharmacokinetics. However, a limitation of the previous analyses was the relative paucity of data for typical "discovery-like" molecules (molecular weight >300 and/or clogP >3). The objective of this investigation was to generate preclinical data required for extension of this dataset for additional discovery-like molecules and determine whether the aforementioned findings continue to apply for these molecules. In vivo nonrodent intravenous pharmacokinetic data were generated for 13 molecules, and data for 8 additional molecules were obtained from the literature. Additionally, the various scaling methodologies and molecular features analysis were applied to this new dataset to predict human pharmacokinetics. Whereas the predictive accuracies demonstrated across all of the various methodologies were lower for this higher clearance compound dataset, scaling from monkey liver blood flow continued to be an accurate methodology, and human volume of distribution was similarly well predicted regardless of scaling methodology. Lastly, application of the molecular feature associations, particularly data-dependent associations, afforded an improved predictivity compared with the liver blood flow scaling approaches, and provides insight into the extrapolation of high clearance compounds in the preclinical species to human.

Influence of physicochemical properties on the patterns of association of a series of aliphatic esters of halofantrine with plasma lipoproteins

Although the association of lipophilic drugs with plasma lipoproteins has not been fully characterized, there are several reports of lipoprotein association being influential in pharmacokinetic and pharmacodynamic profiles of important therapeutic agents. The current studies utilized a series of aliphatic esters of halofantrine to evaluate the role of several physicochemical properties on the interaction of the different compounds with plasma lipoproteins. Density gradient ultracentrifugation techniques were employed to determine drug association in triglyceride rich (TRL), low-density (LDL) and high-density lipoproteins (HDL), under both fasted and post-prandial conditions. Compound solubility in medium or long chain triglycerides was a useful indicator of the extent of drug-lipoprotein association, particularly for the triglyceride rich lipoproteins (chylomicrons and very low-density lipoproteins). This is likely a function of the compounds being solubilized within the apolar (triglyceride and cholesterol ester) lipid core. However, molecular size also played an important role in determining lipoprotein distribution, particularly for association with the more protein abundant lipoproteins, such as HDL. Lipoprotein association of Hf analogues containing longer unsaturated esters was best correlated with total lipoprotein surface area rather than with lipoprotein core lipid volumes.

The influence of lipids on stereoselective pharmacokinetics of halofantrine: Important implications in food-effect studies involving drugs that bind to lipoproteins

The objective of this study was to determine the effect of lipids on the pharmacokinetics of halofantrine enantiomers. Rats were given (+/-)-halofantrine HCl 2 mg/kg i.v., or 7 mg/kg orally. Some rats were rendered hyperlipidemic by intraperitoneal administration of poloxamer 407 1 g/kg, followed by (+/-)-halofantrine HCl intravenously. In other normolipidemic rats, (+/-)-halofantrine was administered under fasted conditions, or after peanut oil given orally. Halofantrine enantiomer plasma concentrations were considerably (>10-fold) increased in hyperlipidemia. Decreases were noted in the clearance, volume of distribution and the unbound fraction in plasma of the hyperlipidemic rats. Peanut oil caused a significant 28% reduction in clearance of the (-), but not the (+) enantiomer (mean clearance reduced 11%) of halofantrine. After oral halofantrine, peanut oil resulted in a two- to threefold increase in the plasma area under the curves of halofantrine enantiomers. Halofantrine enantiomer pharmacokinetics are highly dependent upon plasma lipid concentrations. Oral lipids may result in a stereoselective interaction at the level of clearance. Because lipids may affect clearance of drugs that bind to lipoproteins, in determining bioavailability of such drugs in food-effect studies, reference intravenous groups should be included to separate true increase in bioavailability from the effects of decreased clearance.

Lipids, lipophilic drugs, and oral drug delivery-some emerging concepts

Lipid-based dose forms, which encompass a wide variety of compositional and functional characteristics, can be advantageously utilized for the formulation of lipophilic drugs. There has been a traditional reluctance to develop lipid-based dose forms due to potential problems of chemical and physical instability, and a paucity of knowledge regarding formulation design algorithms and technology transfer issues. However, there is a current resurgence of interest in lipid-based dose forms due to potential commercial and pharmaceutical benefits, and the industry trend towards the discovery/development of increasingly hydrophobic (and potent) new chemical entities. This mini-review describes some emerging formulation and biopharmaceutic strategies that hold promise for better understanding how to design and evaluate lipid-based dose forms.