Variations in tissue selectivity amongst insulin secretagogues: a systematic review.

AIM: Insulin secretagogues promote insulin release by binding to sulfonylurea receptors on pancreatic ß-cells (SUR1). However, these drugs also bind to receptor isoforms on cardiac myocytes (SUR2A) and vascular smooth muscle (SUR2B). Binding to SUR2A/SUR2B may inhibit ischaemic preconditioning, an endogenous protective mechanism enabling cardiac tissue to survive periods of ischaemia. This study was designed to identify insulin secretagogues that selectively bind to SUR1 when given at therapeutic doses. METHODS: Using accepted systematic review methods, three electronic databases were searched from inception to 13 June 2011. Original studies measuring the half-maximal inhibitory concentration (IC(50)) for an insulin secretagogue on K(ATP) channels using standard electrophysiological techniques were included. Steady-state concentrations (C(SS)) were estimated from the usual oral dose and clearance values for each drug. RESULTS: Data were extracted from 27 studies meeting all inclusion criteria. IC(50) values for SUR1 were below those for SUR2A/SUR2B for all insulin secretagogues and addition of C(SS) values identified three distinct patterns. The C(SS) for gliclazide, glipizide, mitiglinide and nateglinide lie between IC(50) values for SUR1 and SUR2A/SUR2B, suggesting that these drugs bind selectively to pancreatic receptors. The C(SS) for glimepiride and glyburide (glibenclamide) was above IC(50) values for all three isoforms, suggesting these drugs are non-selective. Tolbutamide and repaglinide may have partial pancreatic receptor selectivity because IC(50) values for SUR1 and SUR2A/SUR2B overlapped somewhat, with the C(SS) in the midst of these values. CONCLUSIONS: Insulin secretagogues display different tissue selectivity characteristics at therapeutic doses. This may translate into different levels of cardiovascular risk.

Assessing the Impact of Factors that Influence the Ketogenic Response to Varying Doses of Medium Chain Triglyceride (MCT) Oil.

Objectives, Design, Setting: The ketogenic effect of medium chain triglyceride (MCT) oil offers potential for Alzheimer's disease prevention and treatment. Limited literature suggests a linear B-hyroxybutyrate (BHB) response to increasing MCT doses. This pharmacokinetic study evaluates factors affecting BHB response in three subject groups. PARTICIPANTS: Healthy subjects without cognitive deficits <65years, similarly healthy subjects >=65years, and those with Alzheimer's Disease were assessed. INTERVENTION: Different doses (0g,14g, 28g, 42g) of MCT oil (99.3% C8:0) were administered, followed by fasting during the study period. MEASUREMENTS: BHB measured by finger prick sampling hourly for 5 hours after ingestion. Each subject attended four different days for each ascending dose. Data was also collected on body composition, BMI, waist/hip ratio, grip strength, gait speed, nutrient content of pre-study breakfast and side effects. RESULTS: Twenty-five participants: eight healthy; average age of 44yr (25-61), nine healthy; 79yr (65-90) and eight with AD; 78.6yr (57-86) respectively. Compiled data showed the expected linear dose response relationship. No group differences, with baseline corrected area under the blood vs. time curve (r2=0.98) and maximum concentrations (r2=0.97). However, there was notable individual variability in maximum BHB response (42g dose: 0.4 -2.1mM), and time to reach maximum BHB response both, within and between individuals. Variability was unrelated to age, sex, sarcopenic or AD status. Visceral fat, BMI, waist/hip ratio and pretest meal CHO and protein content all affected the BHB response (p<0.001). CONCLUSION: There was a large inter-individual variability, with phenotype effects identified. This highlights challenges in interpreting clinical responses to MCT intake.

Pharmacokinetics of PSC 833 (valspodar) in its Cremophor EL formulation in rat.

Valspodar is a P-glycoprotein inhibitor widely used in preclinical and clinical studies for overcoming multidrug resistance. Despite this, the pharmacokinetics of valspodar in rat, a commonly used animal model, have not been reported. Here, we report on the pharmacokinetics of valspodar in Sprague-Dawley rats following intravenous and oral administration of its Cremophor EL formulation, which has been used for humans in clinical trials. After intravenous doses, valspodar displayed properties of slow clearance and a large volume of distribution. Its plasma unbound fraction was around 15% in the Cremophor EL formulation used in the study. After 10 mg kg(-1) orally it was rapidly absorbed with an average maximal plasma concentration of 1.48 mg l(-1) within approximately 2 h. The mean bioavailability of valspodar was 42.8%. In rat, valspodar showed properties of low hepatic extraction and wide distribution, similar to that of its structural analogue cyclosporine A.

Epoxyeicosatrienoic acid prevents postischemic electrocardiogram abnormalities in an isolated heart model.

Cytochrome P450 epoxygenases metabolize arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) which are in turn converted to dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH). The main objective of this study was to investigate the protective effects of EETs following ischemic injury using an ex vivo electrocardiogram (EKG) model. Hearts from C57Bl/6, transgenic mice with cardiomyocyte-specific overexpression of CYP2J2 (Tr) and wildtype (WT) littermates were excised and perfused with constant pressure in a Langendorff apparatus. Electrodes were placed superficially at the right atrium and left ventricle to assess EKG waveforms. In ischemic reperfusion experiments hearts were subjected to 20 min of global no-flow ischemia followed by 20 min of reperfusion (R20). The EKG from C57Bl/6 hearts perfused with 1 microM 14,15-EET showed less QT prolongation (QTc) and ST elevation (STE) (QTc=41+/-3, STE=2.3+/-0.3; R20: QTc=42+/-2 ms, STE=1.2+/-0.2mv) than control hearts (QTc=36+/-2, STE=2.3+/-0.2; R20: QTc=53+/-3 ms; STE=3.6+/-0.4mv). Similar results of reduced QT prolongation and ST elevation were observed in EKG recording from CYP2J2 Tr mice (QTc=35+/-1, STE=1.9+/-0.1; R20: QTc=38+/-4 ms, STE=1.3+/-0.2mv) compared to WT hearts. The putative epoxygenase inhibitor MS-PPOH (50 microM) and EET antagonist 14,15-EEZE (10 microM) both abolished the cardioprotective response, implicating EETs in this process. In addition, separate exposure to the K(ATP) channel blockers glibenclamide (1 microM) and HMR1098 (10 microM), or the PKA protein inhibitor H89 (50 nM) during reperfusion abolished the improved repolarization in both the models. Consistent with a role of PKA, CYP2J2 Tr mice had an enhanced activation of the PKAalpha regulatory II subunit in plasma membrane following IR injury. The present data demonstrate that EETs can enhance the recovery of ventricular repolarization following ischemia, potentially by facilitating activation of K(+) channels and PKA-dependent signaling.

Serum concentration of laminin, and course of the disease in patients with various malignancies.

Serum concentration of laminin was measured radioimmunologically in 96 patients suffering from various malignancies. Laminin levels were significantly elevated in patients with carcinomas and leukemias, but not in patients with sarcomas or lymphomas when compared with healthy controls. A good correlation could be found between serum laminin concentration and response to therapy in patients with carcinoma and leukemia. Elevated laminin levels were associated with a progressive course of the tumor condition. Furthermore, a close correlation has been detected between serum concentrations of laminin and carcinoembryonic antigen (CEA) in patients with carcinoma of the colon. The serum laminin level seems to be a valuable parameter for observation of the course of certain malignancies.

Clinical pharmacokinetics of ketoprofen and its enantiomers.

Ketoprofen, a potent nonsteroidal anti-inflammatory drug (NSAID) of the 2-arylpropionic acid class, has been used clinically for over 15 years in Europe, and has recently been introduced in the United States. Although it possesses a chiral centre, with only the S-enantiomer possessing beneficial pharmacological activity, all ketoprofen preparations to date are marketed as the racemate. Ketoprofen exhibits little stereoselectivity in its pharmacokinetics. The enantiomers have similar plasma time-courses and do not seem to interact with one another. Hence, the data generated using nonstereospecific assays may be used to explain the pharmacokinetics of individual enantiomers. The absorption of ketoprofen is rapid and almost complete when given orally. Sustained release dosage forms are available, which may be beneficial due to the short terminal phase half-life of ketoprofen (1 to 3h). They may also decrease local gastrointestinal side effects. Although with these preparations the peak plasma drug concentration is reduced and time to peak is prolonged, the bioavailability is the same as that with regular release counterparts. Ketoprofen binds extensively to plasma albumin, apparently in a stereoselective manner. Substantial concentrations of the drug are attained in synovial fluid, the proposed site of action of NSAIDs. It is eliminated following extensive biotransformation to inactive glucuroconjugated metabolite. There is about 10% R to S inversion upon oral administration. Conjugates are excreted in urine, and virtually no drug is eliminated unchanged. The excretion of conjugates is closely tied to renal function; accumulation of conjugates occurs in the elderly, but not in young subjects or patients. Significant drug interactions have been demonstrated for probenecid, aspirin and methotrexate. There appears to be circadian variation, particularly in the absorption of ketoprofen. The relationship between concentration and anti-inflammatory effect has yet to be elucidated for this drug.

Pharmacokinetic optimisation of the treatment of osteoarthritis.

Osteoarthritis is the most frequently encountered form of arthritis worldwide. Pharmacological therapies consisting of nonsteroidal anti-inflammatory drugs (NSAIDs) and analgesics such as paracetamol (acetaminophen), codeine and dextropropoxyphene are the principal means of symptom control. Osteoarthritis appears to have little impact on the pharmacokinetics of these drugs per se. However, other clinical features commonly associated with patients with osteoarthritis, such as advanced age, obesity or concurrent diseases and medications, may be important. A limited number of concentration-response studies have demonstrated the existence of a pharmacokinetic/pharmacodynamic relationship for these drugs. However, the information derived from patients with osteoarthritis is very limited. Simple analgesics have been shown to be as effective as NSAIDs in some studies. Furthermore, the response does not appear to be able to be predicted on the basis of clinical features of inflammation. It appears that a defined concentration-toxicity relationship exists and should be considered when dosage regimens for patients are formulated. Symptoms occur with a circadian rhythm, and similarly, there is circadian variation in the pharmacokinetic/pharmacodynamic response of a number of NSAIDs in patients with osteoarthritis. Selection of the optimal drug formulation will also be influenced by the need for continuous or intermittent therapy in these patients.

Clinical pharmacokinetics of ketorolac tromethamine.

Ketorolac is a new chiral nonsteroidal anti-inflammatory drug (NSAID) which is marketed for analgesia as the racemate. The drug is administered as the water soluble tromethamine salt and is available in tablets or as an intramuscular injection. The absorption of ketorolac is rapid, Cmax being attained between 20 to 60 min. Its oral bioavailability is estimated to range from 80 to 100%. The drug is extensively bound (> 99%) to plasma proteins and has a volume of distribution (0.1 to 0.3 L/kg) comparable with those of other NSAIDs. Only small concentrations of ketorolac are detectable in umbilical vein blood after administration to women in labour. The elimination half-life is between 4 and 6h and is moderate in comparison with other NSAIDs. The area under the plasma concentration-time curve of ketorolac is proportional to the dose after intramuscular administration of therapeutic doses to young healthy volunteers. Ketorolac is extensively metabolised through glucuronidation and oxidation; little if any drug is eliminated unchanged. Most of the dose of ketorolac is recovered in the urine as conjugated drug. Although ketorolac is excreted into the breast milk, the amount of drug transferred comprises only a small fraction of the maternal exposure. Little stereoselectivity was present in the pharmacokinetics of ketorolac in a healthy volunteer receiving single intravenous or oral doses. The elderly exhibit reduced clearance of the drug. Renal insufficiency appears to cause an accumulation of ketorolac in plasma, although hepatic disease may not affect the pharmacokinetics.

Etodolac clinical pharmacokinetics.

Etodolac is a chiral nonsteroidal anti-inflammatory drug (NSAID) that is marked as the racemate. Currently, the drug is available in several countries for the treatment of arthritis and the alleviation of pain. Etodolac possesses several unique disposition features mainly due to its stereoselective pharmacokinetics. In plasma, the concentrations of the 'inactive' R-enantiomer are about 10-fold higher than those of the active S-enantiomer, an observation that is novel among the chiral NSAIDs. In common with other NSAIDs, the drug is highly plasma protein bound, and undergoes virtually complete biotransformation to oxidised metabolites and acyl-glucuronides. Etodolac is well absorbed, with maximal plasma concentrations attained within 1 to 2 hours in healthy volunteers. The area under the plasma concentration-time curve of racemic etodolac increases linearly with doses used clinically. The elimination half-life of etodolac is between 6 and 8 hours in plasma, and is similar for both enantiomers. The volume of distribution (Vd) of racemic etodolac is higher than that of most other NSAIDs mainly because of the extensive distribution of the S-enantiomer. The very large Vd of the S-enantiomer, compared with its antipode is, at least in part, due to its less extensive plasma protein binding. In addition to the unchanged drug, substantial concentrations of the acyl-glucuronides of etodolac are found in both plasma and the synovial fluid of patients with arthritis. A limited amount of conjugated etodolac is found in the bile of patients following cholecystectomy. Hepatic cirrhosis has no effect on the pharmacokinetics of racemic etodolac, although the effect of hepatic dysfunction on the pharmacokinetics of the individual enantiomers has yet to be determined. In elderly non-arthritic individuals with excellent kidney function, aging does not affect the pharmacokinetics of etodolac. The pharmacokinetics of the drug in patients with renal failure have not been published, and may be important because the acyl-glucuronides are renally cleared.

Gomez-Lopez-Hernandez syndrome: expansion of the phenotype.

Gomez-Lopez-Hernandez syndrome (cerebello-trigeminal-dermal dysplasia) is a condition that includes abnormalities of the cerebellum (rhombencephalosynapsis), cranial nerves (trigeminal anesthesia), and scalp (alopecia). Seven patients with this condition have been documented since 1979. We now report a male with Gomez-Lopez-Hernandez syndrome who, at the age of 19 years, is the oldest patient identified to date. He has been followed since birth, allowing us to report on the progression of his physical findings and psychiatric problems including hyperactivity, depression, self-injurious behavior and bipolar disorder. In addition, he has short stature and growth hormone deficiency.

Stereoselective disposition of etodolac enantiomers in synovial fluid.

The synovial fluid (SF) uptake of the chiral nonsteroidal anti-inflammatory drug, etodolac, was studied in six arthritic patients, 2 hours (n = 1) or 12 hours (n = 5) after a single 200 mg dose of racemate. Marked stereoselectivity was seen in both SF and plasma; concentrations of pharmacologically inactive R-etodolac were up to 10-fold greater than active S-etodolac. Concentrations of S-etodolac were greater in SF than in plasma (SF:plasma ratio = 1.98 +/- 0.8): No such difference was seen for R-etodolac (SF:plasma = 0.91 +/- 0.3). Considerable concentrations of conjugated enantiomers were present in SF. In vitro equilibrium dialysis studies in drug-spiked samples showed that the unbound fraction of both enantiomers in SF was greater than in plasma; both fluids bound R more extensively than S etodolac. Therapeutically active S-etodolac has greater concentrations in synovial fluid than plasma during the post-distributive phase, which may be of possible clinical relevance.

The stereoselective pharmacokinetics of etodolac in young and elderly subjects, and after cholecystectomy.

The pharmacokinetics of the enantiomers of etodolac were studied in six young subjects (ages 28 +/- 3.3 years), 6 nonarthritic elderly subjects (ages 73 +/- 6.0 years), and in three cholecystectomy patients after single oral doses of the racemate (200 mg). In all subjects, the plasma concentrations of R-etodolac, which is pharmacologically inactive, greatly exceeded those of the pharmacologically active S-enantiomer. Stereoselectivity was reflected in the pharmacokinetics, with R > S for maximum peak plasma concentration and area under the concentration versus time curve, and S > R for apparent oral clearance and apparent volume of distribution. On average, less than 25% of the dose of each enantiomer was excreted in the urine within 24 hours as alkali-labile conjugates; little or no unchanged drug was recovered. Bile constituted a minor route of elimination of etodolac as conjugated enantiomers. There were no significant differences in the pharmacokinetics of etodolac enantiomers between the young and elderly subjects. The results reflect the importance of considering stereoselectivity in evaluating the pharmacokinetics of etodolac.

Pharmacokinetics of testosterone in hypogonadal men after transdermal delivery: influence of dose.

To assess the pharmacokinetics of testosterone after application of one, two, or three testosterone transdermal delivery systems to hypogonadal patients, 12 hypogonadal men (mean age 46.6 +/- 10.5 years) were enrolled in an open-label, randomized, crossover study. Each application period comprised 4 days: a 2-day washout period with no exogenous testosterone therapy followed by 2 days of therapy with one, two, or three transdermal systems applied daily to the patient's back. On day 4 of each period, serial blood samples were collected for determination of total and non-sex hormone binding globulin (non-SHBG) bound serum testosterone concentrations. Serum concentrations of testosterone were determined using validated radioimmunoassay methods. Residual testosterone analysis of used transdermal systems was used to estimate testosterone delivery through the skin. In general, serum concentrations of testosterone rose in accordance with an increase in dose. Using a strict bioequivalence approach to dose proportionality, the increases in area under the concentration-time curve (AUC) and morning concentrations were proportional to the increase in dose from two to three transdermal systems, but somewhat less than proportional with an increase from one to two transdermal systems. Results from the non-SHBG bound serum testosterone concentrations closely paralleled those of total serum testosterone. Use of three transdermal systems yielded serum concentrations of testosterone that tended to be above the upper limit of the normal range. The AUC and cumulative release of testosterone were linearly related to the number of applied systems. If necessary, the standard recommended dose of two testosterone transdermal delivery systems can be modified to accommodate interindividual differences in testosterone requirements of hypogonadal men.

Hematologic disposition of hydroxychloroquine enantiomers.

Hydroxychloroquine (HCQ) is a racemic antiarthritic agent that has a long half-life (t1/2) in plasma and accumulates in blood cells. To study the relationships between HCQ concentrations in plasma, serum, and whole blood and to determine the optimal blood fraction to use for therapeutic drug monitoring of the drug, we studied the relative distribution of the HCQ enantiomers in various fractions of human blood under in vivo and in vitro conditions. Substantially greater concentrations of both enantiomers were found in serum as compared with plasma because of release via platelet activation. After in vitro incubations of the separated blood cells with HCQ, high concentrations of both enantiomers were found in leukocytes, and low concentrations in erythrocytes and platelets; the R:S ratio in vitro was near unity in all of the cells examined. Unlike the in vitro cellular uptake, the concentrations of HCQ in vivo were significantly lower and stereoselective (R:S ratio = 2). There was almost no drug in the polymorphonuclear cells (PMN) in vivo, despite a substantial uptake in vitro after incubation of separated cells. The enantiomeric (R:S) ratio in the urinary excretion of the enantiomers was significantly correlated with that in plasma. The plasma-protein binding of the enantiomers was stereoselective and complimented the cellular uptake findings; the unbound fraction was dependent on the plasma concentrations of alpha 1-acid glycoprotein, but not albumin. Although concentrations in whole blood correlated well with those in lymphocytes and monocytes (the proposed site of HCQ action), stronger correlations were found between concentrations in serum and in the mononuclear cells.

Stereochemical aspects of pharmacotherapy.

Over the past 15 years stereoselectivity has become a well-recognized consideration in clinical pharmacology. Drugs that have an asymmetric center or plane of symmetry within their molecular structure are said to be chiral. They are available as pairs of nonsuperimposable mirror images, called enantiomers, that share essentially the same physicochemical properties. These three-dimensional structural differences, however, can translate into enantiospecific pharmacologic or pharmacokinetic properties, which may be important in understanding the clinical pharmacology of chiral drugs. Most chiral drugs are available as the racemate, in which equal proportions of the two enantiomers are administered concurrently. The pharmacologic and disposition properties of many chiral drugs are documented to be stereospecific, and this has influenced the regulatory requirements for the approval of new drug candidates. Due to this influence on new drug development, the possible issues surrounding racemic drugs will undoubtedly affect the types of pharmaceuticals that are used clinically in the next century. Accordingly, considerable advances have been made in producing optically pure drug. It should be emphasized, however, that stereochemically pure drugs are not necessarily superior to the respective racemates.

Enantioselective pharmacokinetics of etodolac in the rat: tissue distribution, tissue binding, and in vitro metabolism.

The nonsteroidal anti-inflammatory agent etodolac (ET) exhibits stereoselectivity in its pharmacokinetics following administration to humans and rats. To underline the factors responsible for this stereoselectivity, the tissue distribution, in vitro tissue binding, and microsomal metabolism of ET enantiomers were studied in the rat. Following iv administration of racemic ET, the S:R AUC ratios in tissues were stereoselective, and different from that in plasma. Binding of enantiomers to tissues was stereoselective, although it did not relate well with in vivo tissue distribution. Rather, the tissue distribution of enantiomers appeared to be better explained by the unbound fractions of enantiomers in plasma. With respect to in vitro glucuronidation by liver microsomes, the Vmax of S-ET was 3.4-fold greater than that of R-ET; the enantiomers possessed similar Km. There appeared to be stereoselectivity in the oxidative metabolism of ET enantiomers by liver and kidney microsomes, in favor of the R-enantiomer. The lower AUC in rat plasma of pharmacologically active S-ET as compared with its antipode is due to its relatively greater distribution to tissues, owing to a lesser degree of binding to plasma proteins, and to its higher rate of glucuronidation.

SK&F107647: a synthetic hematoregulatory peptide in patients with solid tumor malignancies: a phase I trial.

SK&F107647 is a synthetic hematoregulatory peptide (HP) increases both the number and function of progenitor cells, enabling improved survival after lethal myelosuppression, lethal fungal infection, and lethal herpes simplex virus infection in murine models. This Phase I single-blind placebo-controlled dose-rising crossover trial examined the efficacy of SK&F107647 in patients who had incurable solid tumor malignancies. Sixteen patients were treated. Six adverse events in 3 patients were considered to be possibly related to SK& F107647; all were mild to moderate in nature (mild nervousness and agitation at 0.01 ng/kg, moderate fever and mild nausea at 0.1 ng/kg, elevated hepatic enzymes at 0.1 ng/kg, and mild vomiting at 1.0 ng/kg). Plasma half-life was 2.44 hours (+/-1.07 standard deviation). The observed area volume of distribution was 16.7 L (+/-7.7 standard deviation) and clearance was 5.04 L/hour (+/-1.83 standard deviation). When administered as a single 2-hour intravenous infusion at doses ranging from 0.01 to 100 ng/kg, SK&F107647 is safe and well tolerated.

Anticholinergic drugs used in Parkinson's disease: An overlooked class of drugs from a pharmacokinetic perspective.

Anticholinergic drugs were the first pharmacological agents used in the treatment of Parkinson"s disease. Although levodopa and other centrally acting dopaminergic agonists have largely supplanted their use, they still have a place in treatment of the disease. As a therapeutic class, there is little pharmacokinetic information available for these drugs, which is inclusive of benztropine, biperiden, diphenhydramine, ethopropazine, orphenadrine, procyclidine and trihexyphenidyl. Pharmacokinetic information is largely restricted to studies involving young health volunteers given single doses. In general, this class of drugs is rapidly absorbed after oral administration to humans. Oral bioavailability is variable between the different drugs, ranging from 30% to over 70%. Each of the drugs appears to possess a large Vd in humans and animals, and distribution to tissues is rapid. The drugs are all characterized by relatively low clearance relative to hepatic blood flow, and appear to be extensively metabolized, primarily to N-dealkylated and hydroxylated metabolites. The available information suggests that excretion of parent drug and metabolite is via the urine and bile. Although the existence of a plasma concentration vs. therapeutic effect relationship has not been explored, there is some evidence suggesting a relationship between concentration and peripheral side effects. Elderly tolerate the drugs less well than do younger patients. There is a notable lack of pharmacokinetic information for these drugs in the elderly. The lack of pharmacokinetic information for multiple dose administration and in the elderly may be a possible hindrance in the safe and effective use of these drugs in patients with Parkinson"s disease.

A high-performance liquid chromatographic assay for the determination of desbutylhalofantrine enantiomers in rat plasma.

PURPOSE: To develop a stereoselective high performance liquid chromatographic assay for determination of desbutylhalofantrine (DHF) enantiomers in rat plasma. METHODS: After protein precipitation of 100 microL of rat plasma, racemic DHF and internal standard (quinidine sulfate) were extracted into hexane in the presence of pH 8 phosphate buffer. After transfer and evaporation of the hexane, the residue was derivatized using 0.25 M (+)-di-O-acetyl-L-tartaric acid anhydride at 4 degrees C. After 5 min the reaction was stopped by addition of methanol in water, and the tube contents were dried, reconstituted in the mobile phase, and injected into a C(18) analytical column under reverse phase conditions. RESULTS: The derivatized enantiomers were baseline resolved and free of interference from endogenous components in plasma. Standard curves were linear (r(2)>0.99) over the range of enantiomer concentrations from 25-1000 ng/mL. The assay was validated to concentrations as low as 25 ng/mL, based on 100 microL of rat plasma. The nature of diastereomers formed was found to be dependent on the temperature used during the derivatization step. In a preliminary experiment in the rat, stereoselectivity in the plasma concentrations of DHF were observed, indicating stereoselectivity in the pharmacokinetics of the metabolite. CONCLUSIONS: The assay was sensitive and appropriate for use in pharmacokinetic studies of DHF in the rat.

High-performance liquid chromatography assay of amiodarone in rat plasma.

PURPOSE: A high-performance liquid chromatographic method is described for the determination of amiodarone in rat plasma. METHODS: After liquid-liquid extraction, the separation of amiodarone from internal standard and endogenous components was accomplished using reversed phase chromatography. The mobile phase, a combination of monobasic potassium phosphate, methanol and acetonitrile, was run isocratically through a C(8) analytical column. The UV detection was at 254 nm for ethopropazine, the internal standard, and subsequently changed to 242 nm for amiodarone detection. RESULTS: Analytical run time was less than 13 min. Mean recovery was 75% and 82% for lower (0.5 microg/ml) and higher concentrations (5 microg/ml), respectively. The assay exhibited excellent linear relationships between peak height ratios and plasma concentrations; quantitation limit was at least 0.035 microg/ml, based on 100 microl of rat plasma. Accuracy and precision were <17% over the concentration range of 0.035 to 5 microg/ml. CONCLUSION. The assay was applied successfully to the measurement of amiodarone plasma concentrations in rats given the drug orally.