Highly sensitive gas chromatographic-tandem mass spectrometric method for the determination of morphine and codeine in serum and urine in the femtomolar range

Quantitative detection of morphine based on an up-conversion luminescent system

An up-conversion luminescent material converts low-frequency excitation light into high-frequency emission light through photons and has the advantages of long fluorescence lifetime, narrow emission peak and low toxicity; thus, this material has many unique applications in the detection and identification of biomolecules. In this study, an ultrasensitive up-conversion luminescent system for the quantitative detection of morphine was developed. The principle of this system is based on infrared light as an excitation light source to convert light with lower energy into excitation light with higher energy. The up-conversion luminescent material is used as a label and through the processing and analysis of the excitation light intensity, the quantitative detection of morphine concentration is achieved. At the same time, the excitation light can avoid the interference and scattering phenomenon of the autofluorescence of the biological sample, which improves the system's detection sensitivity. An algorithm for light intensity processing is added to process image data, reduce the interference caused by noise during image acquisition and improve the accuracy of morphine detection. The T/C value is calculated to achieve the quantitative detection of morphine with a detection limit of 0.1 ng mg-1 and detection time within 0.5 min. The up-conversion luminescent system has the advantages of quantitative detection, convenience, portability, short detection time and low price. Thus, the system can be used for the detection of other biomolecules or for other applications such as food analysis, environmental detection, national security, etc.

Fabrication of a sensitive electrochemical sensor based on electrospun magnetic nanofibers for morphine analysis in biological samples

A sensitive electrochemical sensor for detection of morphine (MPH) at the surface of electrode modified with electrospun magnetic nanofibers (MNFs) was prepared. The features of constructed sensor were evaluated by scanning electron microscopy (SEM), X ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS). The modified sensor was used for MPH analysis using of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) method. The calibration curve has been composed of a linear portion in the concentration range of 0.0033-55 μM and 55-245 μM and the detection limit was 1.9 nM. The reproducibility of the peak current with a reliable relative standard deviation (RSD) value was acquired. Based on the results, the fabricated sensor has good stability and reproducibility, as well as the sensitive and selective analysis of MPH in human serum samples as real samples had effectively been feasible. The results of the actual sample were measured by HPLC procedure, and the results were compared with the results of the electrochemical method and corroborated them.

Cobalt Oxide Nanoparticles/Graphene/Ionic Liquid Crystal Modified Carbon Paste Electrochemical Sensor for Ultra-sensitive Determination of a Narcotic Drug

Purpose: Drug-abuse, namely morphine (MO) affects the metabolism of neurotransmitters such as dopamine (DA). Therefore, it is crucial to devise a sensitive sensing technique to simultaneously determine both compounds in real samples. Methods: The fabrication of the sensor is based on in situ modification of a carbon paste (CP) electrode with cobalt oxide nanoparticles, graphene, and ionic liquid crystal in presence of sodium dodecyl sulfate; CoGILCCP-SDS. The modified sensor is characterized using scanning electron microscopy, electrochemical impedance spectroscopy and voltammetry measurements. Results: Electron transfer kinetics and analytical performance of the proposed sensor were enhanced due to the synergistic role of all the modifiers. The simultaneous determination of MO and DA achieved low detection limits of 0.54 nmol L-1 and 0.25 nmol L-1, respectively. Besides, a carbon-based electrochemical sensor is fabricated for the nano-molar determination of MO in real samples and formulations. The sensor showed fouling resistance and anti-interference ability in presence of other species in human fluids. The real sample analysis of MO was successfully achieved with good recovery results in urine samples and pharmaceutical tablets. Linear dynamic range, sensitivity, detection limit and quantification limit of MO in urine were 5 nmol L-1 to 0.6 μmol L-1, 6.19 μA/μmol L-1, 0.484 nmol L-1 and 1.61 nmol L-1, respectively. Conclusion: This sensor has great ability to be extended for electrochemical applications in assaying of many drugs.

Sensitivity Enhancement for Direct Injection Capillary Electrophoresis to Determine Morphine in Human Serum via In-capillary Derivatization

Rapid and simple micellar electrokinetic chromatography (MEKC) with in-capillary derivatization and fluorescence detection has been developed to determine morphine in human serum. The sample was introduced into a background electrolyte (BGE) containing potassium ferricyanide, whereas morphine was oxidized into highly fluorescent product, pseudomorphine. Different parameters for derivatization and subsequent separation were systematically investigated for the analysis of morphine in serum. Efficient performance of the developed MEKC system was carried out in a single run using BGE made up of 70 mM sodium tetraborate decahydrate (pH 10.5), 0.30 mM potassium ferrricyanide, 80 mM sodium dodecyl sulfate, and applied voltage of 9 kV. The combination of MEKC with in-capillary derivatization of morphine was successfully achieved with a high degree of sensitivity. The validation of the method showed good linearity between areas of morphine and the corresponding concentrations over the range of 5-5000 ng/mL. Excellent accuracy and precision were obtained at all concentration levels. The mean recoveries of morphine were ranging from 83.86 to 94.45%. The validated MEKC method successfully permitted determination of morphine in clinical samples after a single oral dose of controlled release morphine sulfate tablets.

Quantitative detection of codeine in human plasma using surface-enhanced Raman scattering via adaptation of the isotopic labelling principle

In this study surface-enhanced Raman scattering (SERS) combined with the isotopic labelling (IL) principle has been used for the quantification of codeine spiked into both water and human plasma.

Efficient solid phase extraction of codeine from human urine samples using a novel magnetic molecularly imprinted nanoadsorbent and its spectrofluorometric determination

From a medical or clinical point of view, to assess toxicity, adverse effects, interactions and therapeutic efficiency, monitoring drug levels in body fluids, such as urine and plasma, has become increasingly necessary.

Different interaction of codeine and morphine with DNA: a concept for simultaneous determination

In this study, the interaction between codeine and morphine with dsDNA was assessed at pH 7.0. Poly(diallyldimethylammonium chloride), PDDA, was used as a dispersant of MWCNTs. Using differential pulse voltammetry (DPV) at pencil graphite electrode (PGE) showed that both molecules were electrochemically oxidized due to the presence of phenolic and amino groups in their structures. When DNA was added to the solution, the electrochemical signal of codeine and morphine was decreased and shifted to more negative and positive potentials, respectively. The interaction modes were respectively electrostatic for codeine and intercalation for morphine with two anodic peaks of codeine being merged into them when DNA concentration was increased. At high DNA concentrations, a sharp anodic wave for codeine and a clear discrimination of codeine and morphine oxidation peaks were observed. Finally, a pencil graphite electrode was modified with carbon nanotubes and DNA was tested in order to determine codeine and morphine in solution. Electrochemical oxidation of codeine and morphine bonded on dsDNA/MWCNTs-PDDA/PGE was used to obtain an analytical signal. Allowing five min as an accumulation time, a linear dependence was observed between 0.05 and 40 μg mL(-1) for codeine and 0.05 and 42 μg mL(-1) for morphine. Detection limits of 0.041 and 0.043 μg mL(-1) were obtained for codeine and morphine, respectively. The biosensor was applied to validate its capability for the analysis of codeine and morphine in blood serum, urine samples and pharmaceutical formulations.

Chemometric approach for development, optimization, and validation of different chromatographic methods for separation of opium alkaloids

The excessive and continuously growing interest in the simultaneous determination of poppy alkaloids imposes the development and optimization of convenient high-throughput methods for the assessment of the qualitative and quantitative profile of alkaloids in poppy straw. Systematic optimization of two chromatographic methods (gas chromatography (GC)/flame ionization detector (FID)/mass spectrometry (MS) and reversed-phase (RP)-high-performance liquid chromatography (HPLC)/diode array detector (DAD)) for the separation of alkaloids from Papaver somniferum L. (Papaveraceae) was carried out. The effects of various conditions on the predefined chromatographic descriptors were investigated using chemometrics. A full factorial linear design of experiments for determining the relationship between chromatographic conditions and the retention behavior of the analytes was used. Central composite circumscribed design was utilized for the final method optimization. By conducting the optimization of the methods in very rational manner, a great deal of excessive and unproductive laboratory research work was avoided. The developed chromatographic methods were validated and compared in line with the resolving power, sensitivity, accuracy, speed, cost, ecological aspects, and compatibility with the poppy straw extraction procedure. The separation of the opium alkaloids using the GC/FID/MS method was achieved within 10 min, avoiding any derivatization step. This method has a stronger resolving power, shorter analysis time, better cost/effectiveness factor than the RP-HPLC/DAD method and is in line with the "green trend" of the analysis. The RP-HPLC/DAD method on the other hand displayed better sensitivity for all tested alkaloids. The proposed methods provide both fast screening and an accurate content assessment of the six alkaloids in the poppy samples obtained from the selection program of Papaver strains.

Simultaneous determination of codeine, ephedrine, guaiphenesin and chlorpheniramine in beagle dog plasma using high performance liquid chromatography coupled with tandem mass spectrometric detection: application to a bioequivalence study

A rapid and sensitive method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the simultaneous determination of codeine, ephedrine, guaiphenesin and chlorpheniramine in beagle dog plasma has been developed and validated. Following liquid-liquid extraction, the analytes were separated on a reversed-phase C(18) column (150 mm × 2.0 mm, 3 μm) using formic acid:10 mM ammonium acetate:methanol (0.2:62:38, v/v/v) as mobile phase at a flow rate of 0.2 mL/min and analyzed by a triple-quadrupole mass spectrometer in the selected reaction monitoring (SRM) mode. The method was linear for all analytes over the following concentration (ng/mL) ranges: codeine 0.08-16; ephedrine 0.8-160; guaiphenesin 80-16,000; chlorpheniramine 0.2-40. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. It is the first time that the validated HPLC-MS/MS method was successfully applied to a bioequivalence study in 6 healthy beagle dogs.

Determination of morphine at gold nanoparticles/Nafion® carbon paste modified sensor electrode

A novel and effective electrochemical sensor for the determination of morphine (MO) in 0.04 mol L(-1) universal buffer solution (pH 7.4) is introduced using gold nanoparticles electrodeposited on a Nafion modified carbon paste electrode. The effect of various experimental parameters including pH, scan rate and accumulation time on the voltammetric response of MO was investigated. At the optimum conditions, the concentration of MO was determined using differential pulse voltammetry (DPV) in a linear range of 2.0 × 10(-7) to 2.6 × 10(-4) mol L(-1) with a correlation coefficient of 0.999, and a detection limit of 13.3 × 10(-10) mol L(-1), respectively. The effect of common interferences on the current response of morphine namely ascorbic acid (AA) and uric acid (UA) is studied. The modified electrode can be used for the determination of MO spiked into urine samples, and excellent recovery results were obtained.

Kinetic spectrophotometric method for the determination of morphine in biological samples

In this paper a simple, selective and inexpensive kinetic method was developed for the determination of morphine based on its inhibitory effect on the Janus green-bromate system in sulfuric acid media. The reaction was monitored spectrophotometrically at 618 nm by a fixed time method. The effect of different parameters such as concentration of reactants and temperature on the rate of reaction was investigated and optimum conditions were obtained. The calibration curve was linear in the concentration range 0.07-7.98 mg L(-1) of morphine, and detection limit of the method was 3.0x10(-2)mg L(-1). The relative standard deviation for five determinations of 3.74 mg L(-1) of morphine was 0.57%. Finally, the proposed method was successfully applied to the determination of morphine in human urine and serum as real samples.

Urinary excretion of morphine and biosynthetic precursors in mice

It has been firmly established that humans excrete a small but steady amount of the isoquinoline alkaloid morphine in their urine. It is unclear whether it is of dietary or endogenous origin. There is no doubt that a simple isoquinoline alkaloid, tetrahydropapaveroline (THP), is found in human and rodent brain as well as in human urine. This suggests a potential biogenetic relationship between both alkaloids. Unlabeled THP or [1,3,4-D(3)]-THP was injected intraperitoneally into mice and the urine was analyzed. This potential precursor was extensively metabolized (96%). Among the metabolites found was the phenol-coupled product salutaridine, the known morphine precursor in the opium poppy plant. Synthetic [7D]-salutaridinol, the biosynthetic reduction product of salutaridine, injected intraperitoneally into live animals led to the formation of [7D]-thebaine, which was excreted in urine. [N-CD(3)]-thebaine was also administered and yielded [N-CD(3)]-morphine and the congeners [N-CD(3)]-codeine and [N-CD(3)]-oripavine in urine. These results show for the first time that live animals have the biosynthetic capability to convert a normal constituent of rodents, THP, to morphine. Morphine and its precursors are normally not found in tissues or organs, presumably due to metabolic breakdown. Hence, only that portion of the isoquinoline alkaloids excreted in urine unmetabolized can be detected. Analysis of urine by high resolution-mass spectrometry proved to be a powerful method for tracking endogenous morphine and its biosynthetic precursors.

Sample preparation and separation techniques for bioanalysis of morphine and related substances

In present time the use or misuse of morphine and its derivatives are monitored by assaying the presence of the drug and its metabolites in biofluids. In the present review, focus is placed on the sample preparation and on the separation techniques used in the current best practices of bioanalysis of morphine and its major metabolites. However, as methods for testing the misuse of heroin, a morphine derivative, often involve bioanalytical methods that cover a number of other illicit drug substances, such methods are also included in the review. Furthermore, the review also includes bioanalysis in a broader perspective as analysis of plant materials, cell cultures and environmental samples. The review is not intended to cover all publications that include bioanalysis of morphine but is more to be considered a view into the current best practices of bioanalysis of morphine, its metabolites and other related substances.

Determining plasma morphine levels using GC-MS after solid phase extraction to monitor drug levels in the postoperative period

OBJECTIVE

To implement a selective and sensitive analytical method to quantify morphine in small volumes of plasma by gas-liquid chromatography-mass spectrometry (GC-MS), aimed at post-operatively monitoring the drug.

METHOD

A gas-liquid chromatographic method with mass detection has been developed to determine morphine concentration in plasma after solid phase extraction. Morphine-d3 was used as an internal standard. Only 0.5 mL of plasma is required for the drug solid-phase extraction in the Bond Elut-Certify, followed by the quantification of morphine derivative by GC-MS using a linear temperature program, a capillary fused silica column, and helium as the carrier and make-up gas. The method was applied to determine morphine content in plasma samples of four patients during the postoperative period of cardiac surgery. Patient-controlled analgesia with morphine was performed by a venous catheter, and a series of venous blood samples were collected. After the oro-After the orotracheal extubation, morphine plasma levels were monitored for up to 36 hours.

RESULTS

The run time was 16 minutes because morphine and the internal standard were eluted after 8.8 minutes. The GC-MS method had 0.5 -1000 ng/mL linearity range (r(2)=0.9995), 0.1 ng/mL limit of detection, intraday and interday precision equivalent to 1.9% and 6.8%, and 0.1% and 0.8% systematic error (intraday and interday, respectively). The analytical method showed optimal absolute (98%) and relative (100.7%) recoveries. Morphine dose requirements and plasma levels are discussed.

CONCLUSION

The analytical gas-liquid chromatography-mass spectrometry method is selective and adequate for morphine measurements in plasma for applications in clinical studies.

Hair analysis for methamphetamine, ketamine, morphine and codeine by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

We established a capillary electrophoretic method with high sensitivity and specificity for testing hair taken from addicts. After pretreatment of hair sample, the cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-Sweep-MEKC) was used to test for the presence of abused drugs in human hair. These drugs include morphine (M), codeine (C), ketamine (K) and methamphetamine (MA). First, an uncoated fused-silica capillary (40 cm, 50 microm I.D.) was filled with phosphate buffer (50 mM, pH 2.5) containing 30% methanol, followed by high conductivity buffer (100 mM phosphate, 6.9 kPa for 99.9 s). Electrokinetic injection (10 kV, 600 s) was used to load samples and to enhance sensitivity. Stacking steps and separations were performed at -20 kV with detection at 200 nm, using phosphate buffer (25 mM, pH 2.5) containing 20% methanol and 100 mM sodium dodecyl sulfate. Using CSEI-Sweep-MEKC, the analytes could be simultaneously analyzed and have a detection limit down to the level of picogram per milligram hair. During method validation, calibration plots were linear (r > or = 0.999) over a range of 0.15-80 ng/mg hair for MA and K, 0.3-30 ng/mg hair for C and 0.5-50 ng/mg hair for M. The limits of detection were 50 pg/mg hair for MA and K, 100 pg/mg hair for C and 200 pg/mg hair for M (S/N=3, sampling 600 s at 10 kV). Our method was applied for analysis of real hair samples taken from addicts. The addicts' specimens were also analyzed by LC-MS, and showed good coincidence of results. This method has proven feasible for application in detecting trace levels of abused drugs in forensic analysis.

Determination of morphine and codeine in urine using poly(dimethylsiloxane) microchip electrophoresis with electrochemical detection

In this paper, a poly(dimethylsiloxane) (PDMS) microchip with electrochemical (EC) detection was developed for rapid separation and detection of morphine and codeine. It was found that morphine and codeine were well separated within 140 s in phosphate buffer solution (PBS) (pH 6.6, 40 mM)-beta-cyclodextrin (beta-CD) (20 mM)-acetonitrile (30%, v/v). The detection limit was 0.2 microM for morphine and 1 microM for codeine. The protocol was successfully applied to monitoring the amount of morphine and codeine in human urine. Compared with the conventional methods, the presented method had many advantages such as lower instrument cost, less reagent consumption and shorter analysis time.

Endogenous morphine: opening new doors for the treatment of pain and addiction

Nitric oxide (NO) signalling is at the forefront of intense research interest because its many effects remain controversial and seemingly contradictory. This paper examines its role as a potential mediator of pain and tolerance. Within this context discussion covers endogenous morphine, documenting its ability to be made in animal tissues, including nervous tissue, and in diverse animal phyla. Supporting morphine as an endogenous signalling molecule is the presence of the newly cloned mu3 opiate receptor subtype found in animal (including human) immune, vascular and neural tissues, which is coupled to NO release. Importantly, this mu opiate receptor subtype is morphine-selective and opioid peptide-insensitive, further highlighting the presence of morphinergic signalling coupled to NO release. These findings provide novel insights into pain and tolerance as morphinergic signalling exhibits many similarities with NO actions. Taken together, a select morphinergic signalling system utilising NO opens the gate for the development of novel pharmaceuticals and/or the use of old pharmaceuticals in new ways.

Direct and sensitive analysis of methamphetamine, ketamine, morphine and codeine in human urine by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

Cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-Sweep-MEKC) was directly used to test some abuse drugs in human urine, including morphine (M), codeine (C), ketamine (K) and methamphetamine (MA). First, phosphate buffer (50 mM, pH 2.5) containing 30% methanol was filled into uncoated fused silica capillary (40 cm, 50 microm I.D.), then high conductivity buffer (100 mM phosphate, 6.9 kPa for 99.9 s) was followed. Electrokinetic injection (10 kV, 500 s) was used to load samples and to enhance sensitivity. The stacking step and separation were performed at -20 kV and 200 nm using phosphate buffer (25 mM, pH 2.5) containing 20% methanol and 100 mM sodium dodecyl sulfate. Using CSEI-Sweep-MEKC, the analytes could be simultaneously analyzed and have a detection limit down to ppb level. It was unnecessary to have sample pretreatments. During method validation, calibration plots were linear (r>or=0.9982) over a range of 150-3,000 ng/mL for M and C, 250-5,000 n g/mL for MA, and 50-1,000 ng/mL for K. The limits of detection were 15 ng/mL for M and C, and 5 ng/mL for MA and K (S/N=3, sampling 500 s at 10 kV). Comparing with capillary zone electrophoresis, the results indicated that this stacking method could increase 6,000-fold sensitivity for analysis of MA. Our method was applied for analysis of 28 real urine samples. The results showed good coincidence with immunoassay and GC-MS. This method was feasible for application to detect trace levels of abused drugs in forensic analysis.

How human neuroblastoma cells make morphine

Recently, our laboratory demonstrated that human neuroblastoma cells (SH-SY5Y) are capable of synthesizing morphine, the major active metabolite of opium poppy. Now our experiments are further substantiated by extending the biochemical studies to the entire morphine pathway in this human cell line. L-[1,2,3-13C3]- and [ring-2',5',6'-2H3]dopa showed high isotopic enrichment and incorporation in both the isoquinoline and the benzyl moiety of the endogenous morphine. [2,2-2H2]Dopamine, however, was exclusively incorporated only into the isoquinoline moiety. Neither the trioxygenated (R,S)-[1,3-13C2]norcoclaurine, the precursor of morphine in the poppy plant, nor (R)-[1,3,4-2H3]norlaudanosoline showed incorporation into endogenous morphine. However, (S)-[1,3,4-2H3]norlaudanosoline furnished a good isotopic enrichment and the loss of a single deuterium atom at the C-9 position of the morphine molecule, indicating that the change of configuration from (S)- to (R)-reticuline occurs via the intermediacy of 1,2-dehydroreticuline. Additional feeding experiments with potential morphinan precursors demonstrated substantial incorporation of [7-2H]salutaridinol, but not 7-[7-2H]episalutaridinol, and [7-2H,N-C2H3]oripavine, and [6-2H]codeine into morphine. Human morphine biosynthesis involves at least 19 chemical steps. For the most part, it is a reflection of the biosynthesis in opium poppy; however, there is a fundamental difference in the formation of the key intermediate (S)-reticuline: it proceeds via the tetraoxygenated initial isoquinoline alkaloid (S)-norlaudanosoline, whereas the plant morphine biosynthesis proceeds via the trioxygenated (S)-norcoclaurine. Following the plant biosynthetic pathway, (S)-reticuline undergoes a change of configuration at C-1 during its transformation to salutaridinol and thebaine. From thebaine, there is a bifurcate pathway leading to morphine proceeding via codeine or oripavine, in both plants and mammals.

Endogenous formation of morphine in human cells

Morphine is a plant (opium poppy)-derived alkaloid and one of the strongest known analgesic compounds. Studies from several laboratories have suggested that animal and human tissue or fluids contain trace amounts of morphine. Its origin in mammals has been believed to be of dietary origin. Here, we address the question of whether morphine is of endogenous origin or derived from exogenous sources. Benzylisoquinoline alkaloids present in human neuroblastoma cells (SH-SY5Y) and human pancreas carcinoma cells (DAN-G) were identified by GC/tandem MS (MS/MS) as norlaudanosoline (DAN-G), reticuline (DAN-G and SH-SY5Y), and morphine (10 nM, SH-SY5Y). The stereochemistry of reticuline was determined to be 1-(S). Growth of the SH-SY5Y cell line in the presence of (18)O(2) led to the [(18)O]-labeled morphine that had the molecular weight 4 mass units higher than if grown in (16)O(2), indicating the presence of two atoms of (18)O per molecule of morphine. Growth of DAN-G cells in an (18)O(2) atmosphere yielded norlaudanosoline and (S)-reticuline, both labeled at only two of the four oxygen atoms. This result clearly demonstrates that all three alkaloids are of biosynthetic origin and suggests that norlaudanosoline and (S)-reticuline are endogenous precursors of morphine. Feeding of [ring-(13)C(6)]-tyramine, [1-(13)C, N-(13)CH(3)]-(S)-reticuline and [N-CD(3)]-thebaine to the neuroblastoma cells led each to the position-specific labeling of morphine, as established by GC/MS/MS. Without doubt, human cells can produce the alkaloid morphine. The studies presented here serve as a platform for the exploration of the function of "endogenous morphine" in the neurosciences and immunosciences.

Sensitive determination of pethidine in body fluids by gas chromatography-tandem mass spectrometry

We have presented a simple and sensitive method for determining pethidine, a narcotic analgesic drug in body fluids by gas chromatography-tandem mass spectrometry (GC-MS/MS). Pethidine and 4'-piperidinoacetophenone (internal standard) were extracted from body fluids with Bond Elut C(18) columns; the recoveries were above 85% for both compounds. The calibration curves for blood and urine showed good linearities in the range of 1.25-40 ng/ml. Its detection limits (signal-to-noise ratio=3) were estimated to be approximately 0.5 ng/ml of whole blood and urine.

Pharmacokinetic modelling of morphine, morphine-3-glucuronide and morphine-6-glucuronide in plasma and cerebrospinal fluid of neurosurgical patients after short-term infusion of morphine

AIMS

Concentrations in the cerebrospinal fluid (CSF) are a useful approximation to the effect site for drugs like morphine. However, CSF samples, are available only in rare circumstances. If they can be obtained they may provide important insights into the pharmacokinetics/pharmacodynamics of opioids.

METHODS

Nine neurological and neurosurgical patients (age 19-69 years) received 0.5 mg kg-1 morphine sulphate pentahydrate as an intravenous infusion over 30 min. Plasma and CSF were collected for up to 48 h. Concentration time-course and interindividual variability of morphine (M), morphine-3-glucuronide (M3G) and morphine-6 glucuronide (M6G) were analysed using population pharmacokinetic modelling.

RESULTS

While morphine was rapidly cleared from plasma (total clearance = 1838 ml min-1 (95% CI 1668, 2001 ml min-1)) the glucuronide metabolites were eliminated more slowly (clearance M3G = 44.5 ml min-1 (35.1, 53.9 ml min-1), clearance M6G = 42.1 ml min-1 (36.4, 47.7 ml min-1)) and their clearance could be described as a function of creatinine clearance. The central volumes of distribution were estimated to be 12.7 l (11.1, 14.3 l) for morphine. Transfer from the central compartment into the CSF was also rapid for M and considerably slower for both glucuronide metabolites. Maximum concentrations were achieved after 102 min (M), 417 min (M3G) and 443 min (M6G). A P-glycoprotein exon 26 polymorphism previously found to be linked with transport activity could be involved in CSF accessibility, since the homozygous mutant genotype was associated (P < 0.001) with high maximum CSF concentrations of M but not M3G or M6G.

CONCLUSIONS

From the population pharmacokinetic model presented, CSF concentration profiles can be derived for M, M3G and M6G on the basis of dosing information and creatinine clearance without collecting CSF samples. Such profiles may then serve as the link between dose regimen and effect measurements in future clinical effect studies.

Phenytoin pharmacokinetics and clinical effects in African children following fosphenytoin and chloramphenicol coadministration

AIMS

Some children with malaria and convulsions also have concurrent bacterial meningitis. Chloramphenicol is used to treat the latter whereas phenytoin is used for convulsions. Since chloramphenicol inhibits the metabolism of phenytoin in vivo, we studied the effects of chloramphenicol on phenytoin pharmacokinetics in children with malaria.

METHODS

Multiple intravenous (i.v.) doses of chloramphenicol succinate (CAP) (25 mg kg-1 6 hourly for 72 h) and a single intramuscular (i.m.) seizure prophylactic dose of fosphenytoin (18 mg kg-1 phenytoin sodium equivalents) were concomitantly administered to 15 African children with malaria. Control children (n = 13) with malaria received a similar dose of fosphenytoin and multiple i.v. doses (25 mg kg-1 8 hourly for 72 h) of cefotaxime (CEF). Blood pressure, heart rate, respiratory rate, oxygen saturation, level of consciousness and convulsion episodes were monitored. Cerebrospinal fluid (CSF) and plasma phenytoin concentrations were determined.

RESULTS

The area under the plasma unbound phenytoin concentration-time curve (AUC(0, infinity ); means (CAP, CEF): 58.5, 47.6 micro g ml-1 h; 95% CI for difference between means: -35.0, 11.4), the peak unbound phenytoin concentrations (Cmax; medians: 1.12, 1.29 micro g ml-1; 95% CI: -0.5, 0.04), the times to Cmax (tmax; medians: 4.0, 4.0 h; 95% CI: -2.0, 3.7), the CSF:plasma phenytoin ratios (means: 0.21, 0.22; 95% CI: -0.8, 0.10), the fraction of phenytoin unbound (means: 0.06, 0.09; 95% CI: -0.01, 0.07) and the cardiovascular parameters were not significantly different between CAP and CEF groups. However, mean terminal elimination half-life (t1/2,z) was significantly longer (23.7, 15.5 h; 95% CI: 1.71, 14.98) in the CAP group compared with the CEF group. Seventy per cent of the children had no convulsions during the study period.

CONCLUSIONS

Concomitant administration of chloramphenicol and a single i.m. dose of fosphenytoin alters the t1/2,z but not the other pharmacokinetic parameters or clinical effects of phenytoin in African children with severe malaria. Moreover, a single i.m. dose of fosphenytoin provides anticonvulsant prophylaxis in the majority of the children over 72 h. However, a larger study would be needed to investigate the effect of concomitant administration of multiple doses of the two drugs in this population of patients.

Diclofenac does not interact with codeine metabolism in vivo: a study in healthy volunteers

BACKGROUND

Previously, we have demonstrated a marked inhibition of codeine glucuronidation by diclofenac in human liver tissue homogenate. We therefore aimed to investigate whether diclofenac inhibits glucuronidation of codeine also in vivo in healthy volunteers.

METHODS

In a randomised, placebo-controlled, double-blind, cross-over study, 12 healthy volunteers received a singe of 100 mg codeine phosphate plus 50 mg diclofenac sodium or codeine phosphate plus placebo. Over a 36 hour period serum concentrations of codeine and its metabolites as well as urinary excretion were analysed using LC-mass spectrometry. Side effects were recorded and analgesic efficacy was determined using the cold pressor test (0-6 h).

RESULTS

A single dose of diclofenac did not alter the formation of codeine-6-glucuronide in healthy volunteers. Metabolic clearance of codeine to morphine was not affected by diclofenac. In terms of side effects, both treatments were well tolerated. Diclofenac did not significantly influence the analgesic effects of codeine in the cold pressor test.

CONCLUSIONS

In contrast to recent in vitro data, a single oral dose of diclofenac did not alter the glucuronidation of codeine in healthy volunteers.

Gas chromatography/negative-ion chemical ionisation mass spectrometry for the quantitative analysis of morphine in human plasma using pentafluorobenzyl carbonate derivatives

A sensitive and specific method for the quantitative determination of morphine in human plasma is presented. Morphine was extracted from plasma by solid phase extraction on C18 and converted to its pentafluorobenzyl carbonate trimethylsilyl derivative. The derivatives were analysed without further purification. Using gas chromatography/negative ion chemical ionisation mass spectrometry, a useful diagnostic fragment ion at m/z 356 is obtained at high relative abundance. Deuterated morphine was used as internal standard. Calibration graphs were linear within the range 1.25 to 320 nmol/L. Intra-day precision was 3.82% (15 nmol/L), 2.85% (75 nmol/L) and 4.13% (225 nmol/L), inter-day variability was found to be 1.77% (15 nmol/L), 4.95% (75 nmol/L) and 9.88% (225 nmol/L). Inter-day accuracy showed deviations of 2.18% (15 nmol/L), -0.72% (75 nmol/L) and -0.13% (225 nmol/L). The method is rugged and robust and has been applied to the batch analysis of morphine during pharmacokinetic profiling of the drug.

Quantitative analysis of morphine in human plasma by gas chromatography-negative ion chemical ionization mass spectrometry

A sensitive and specific method for the quantitative determination of morphine in human plasma is presented. Morphine was extracted from plasma by solvent extraction with ethyl acetate and derivatized to its heptafluorobutyrate derivative. The derivatives were measured by gas chromatography-negative ion chemical ionization mass spectrometry without any further purification. Using this detection mode, a diagnostic useful fragment ion at m/z 637 is obtained at high relative abundance. Deuterated morphine was used as an internal standard. Calibration graphs were linear within a range of 0.78 ng/ml and 50 ng/ml. Inter-assay precision was 2.3% (2.85 ng/ml) and 1.4% (14.25 ng/ml), intra-assay variability was found to be 1.5% (3.71 ng/ml) and 0.5% (14.54 ng/ml). Accuracy showed deviations of -9.3% (2.85 ng/ml) and -4.2% (14.25 ng/ml). The method is rugged and robust and has been applied to the batch analysis of morphine during pharmacokinetic profiling of the drug.