Determination of codeine and its metabolites in human blood plasma and in microsomal incubates by high-performance liquid chromatography with ultraviolet detection

On the assessment of drug metabolism by assays of codeine and its main metabolites

Codeine and its main metabolites appear to have advantages for assessing drug metabolic phenotypes. The authors have further developed a high-performance liquid chromatography (HPLC) method for the quantification of codeine and six of its metabolites in urine. Quantification was performed by electrochemical detection for morphine, normorphine, morphine-6-glucuronide, and the internal standard 4-O-methyldopamine; and by ultraviolet detection for codeine, norcodeine, and morphine-3-glucuronide. The method had a detection limit of 2 nmol/L(-1) for morphine and normorphine, 4 nmol/L(-1) for morphine-6-glucuronide, 3 nmol/L for the internal standard, 20 nmol/L(-1) for morphine-3-glucuronide, and 60 nmol/L(-1) for codeine and norcodeine. The coefficients of variations were <9% for intraday and <10% for interday analyses. The recovery of codeine and its metabolites ranged from 55% (for morphine-3-glucuronide) to 90% (for codeine, norcodeine, morphine, and morphine-6-glucuronide). Eleven healthy volunteers were phenotyped for CYP2D6 using codeine as well as debrisoquine and dextromethorphan. Ten subjects were extensive metabolizers (EM) and one a poor metabolizer (PM) of codeine, debrisoquine, and dextromethorphan. Significant correlations between the metabolic ratios (MRs) of the different probe drugs were obtained (r2 > 0.95, p < 0.001). This HPLC method is simple, sensitive, accurate, and reproducible for assessing the CYP2D6 phenotype.

Head-column field-amplified sample stacking in binary system capillary electrophoresis. Preparation of extracts for determination of opioids in microliter amounts of body fluids

Head-column field-amplified sample stacking (head-column FASS) is an efficient, on-line sample concentration technique that can easily provide a sensitivity enhancement of three orders of magnitude. Application of head-column FASS to the capillary electrophoretic analysis of opioid extracts prepared from 20 to 100 microliters of human plasma, serum or urine is reported. In the described approach, efficient concentration of cationic opiates from low conductivity extracts of body fluids is effected across a water plug, with separation taking place in a binary buffer comprising 60% (v/v) ethylene glycol, 75 mM Na2HPO4 and 25 mM NaH2PO4 (pH 7.9), and detection is effected at 210 nm. Sample extracts are prepared in 55% (v/v) ethylene glycol containing 100 microM H3PO4. Application of mixed-mode polymer solid-phase resins is shown to provide extracts that are either too salty or contain quite a large number of endogenous substances that could interfere with certain opioids. Liquid-liquid extraction with hexane, dichloromethane, ethyl acetate and dichloromethane-isopropanol is shown to provide extracts that are sufficiently clean. At a given pH, however, only closely related opioids can be extracted. Using ethyl acetate at alkaline pH, dihydrocodeine and nordihydrocodeine can reproducibly be recovered from 20-100 microliters of plasma, serum and urine. Application of head-column FASS and UV absorption detection thereby leads to the determination of ppb concentrations (> or = 1 ng/ml) of these compounds, an approach that only requires microliter amounts of sample and organic solvents.

Simultaneous determination of codeine and its seven metabolites in plasma and urine by high-performance liquid chromatography with ultraviolet and electrochemical detection

A sensitive and selective high-performance liquid chromatography method has been developed for the measurement of codeine and its seven metabolites, norcodeine, morphine, normorphine, codeine-6-glucuronide, morphine-6-glucuronide, morphine-3-glucuronide and norcodeine glucuronide, in plasma and urine. The compounds were recovered from plasma and urine using solid-phase extraction with C18 cartridges and separated on a reversed-phase C8 column with a mobile phase consisting of 77% buffer (5 mM sodium phosphate monobasic and 0.70 mM sodium dodecyl sulfate, pH 2.35) and 23% acetonitrile. Codeine, norcodeine, codeine-6-glucuronide, norcodeine glucuronide and morphine-3-glucuronide were detected by ultraviolet detection at 214 nm, with a detection limit of 0.02 nmol/ml for each compound in plasma. Morphine-6-glucuronide, normorphine and morphine were monitored by electrochemical detection at 350 mV, with a detection limit of 0.003 nmol/ml for each compound in plasma. The assay showed good reproducibility and accuracy using external standardization. The recovery and inter-day variation for all compounds in plasma samples were 63.40-77.90% and 3.49-16.77% (R.S.D.) and while in urine were 64.98-90.13% and 2.93-9.96% (R.S.D.), respectively.

Glucuronidation of dihydrocodeine by human liver microsomes and the effect of inhibitors

1. Glucuronidation is the major route of metabolism of dihydrocodeine (DHC) and accounts for 25-30% of an oral dose in urine. The kinetics of DHC-6-glucuronide formation in liver microsomes from five human donors and the effect of a number of potential inhibitor drugs were examined using a newly developed and validated HPLC assay. 2. The formation of DHC-6-glucuronide exhibited atypical kinetics that conformed to the Hill equation. The mean intrinsic dissociation constant (Ks) and maximum velocity (Vmax) values were 1566 micromol/L and 0.043 micromol/min per g, respectively. The Ks and Vmax values varied 1.5- and 3.5-fold, respectively. 3. Seven drugs were tested for inhibitory effects on DHC glucuronidation at low (50 micromol/L) and high (500 micromol/L) concentrations. At 50 micromol/L, only diclofenac produced greater than 50% inhibition, while at concentrations of 500 micromol/L inhibition was greater than 35% for diclofenac, amitriptyline, oxazepam, naproxen, chloramphenicol and probenecid, but not paracetamol. 4. The present study found little interindividual variation in the activity of human liver microsomes for glucuronidation of DHC. Comparison of the results from the inhibition studies with those reported previously for codeine and morphine suggest that the UDP-glucuronosyltransferase isoform UGT2B7 is involved in the glucuronidation of DHC.

Patient-controlled analgesia (PCA) with codeine for postoperative pain relief in ten extensive metabolisers and one poor metaboliser of dextromethorphan

Postoperative pain relief with codeine was evaluated in 11 women undergoing hysterectomy. Patient-controlled analgesia (PCA) was used to administer codeine. After the study the patients were phenotyped with respect to the O-demethylation of dextromethorphan (cytochrome P4502D6 polymorphism). Ten were extensive metabolisers and one a poor metaboliser. There was a nine-fold variation in the minimum plasma concentration of codeine consistent with pain relief (40-350 ng ml-1). Two patients did not experience any effect of codeine, one of whom was a poor metaboliser of dextromethorphan, confirmed by genotyping. In the other nine patients the effective dose of codeine varied from 4.8-25.3 mg h-1.

Determination of codeine and its metabolites in microsomal incubates by high-performance liquid chromatography

A rapid and sensitive HPLC method has been developed for the determination of codeine, norcodeine and morphine in small volumes of a biological matrix, using a cyanopropyl column and a combination of coulometric and UV detection. The compounds were isolated using C18 solid-phase extraction cartridges prior to quantitative analysis. The limit of detection was 250 pg/ml for morphine and 5 ng/ml for both norcodeine and codeine. Recovery of each compound was greater than 90% and intra- and inter-assay precision was better than 10%. The method has been used to study the metabolism of codeine in microsomal incubations.

Pharmacokinetics and metabolism of codeine in humans

Codeine (30 mg phosphate) was metabolized by eight human volunteers to the following six metabolites: codeine-6-glucuronide 81.0 +/- 9.3 per cent, norcodeine 2.16 +/- 1.44 per cent, morphine 0.56 +/- 0.39 per cent, morphine-3-glucuronide 2.10 +/- 1.24 per cent, morphine-6-glucuronide 0.80 +/- 0.63 per cent, and normorphine 2.44 +/- 2.42 per cent. Two out of eight volunteers were unable to O-dealkylate codeine into morphine and lack therefore the cytochrome P450 IID6 isoenzyme. The half-life of codeine was 1.47 +/- 0.32 h, that of codeine-6-glucuronide 2.75 +/- 0.79 h, and that of morphine-3-glucuronide 1.71 +/- 0.51 h. The systemic clearance of codeine was 2280 +/- 840 ml min-1, the renal clearance of codeine was 93.8 +/- 29.8 ml min-1, and that of codeine-6-glucuronide was 122 +/- 39.2 ml min-1. The plasma AUC of codeine-6-glucuronide is approximately 10 times higher than that of codeine. Protein binding of codeine and codeine-6-glucuronide in vivo was 56.1 +/- 2.5 per cent and 34.0 +/- 3.6 per cent, respectively. The in vitro protein binding of norcodeine was 23.5 +/- 2.9 per cent; of morphine, 46.5 +/- 2.4 per cent; of normorphine, 23.5 +/- 3.5 per cent; of morphine-3-glucuronide, 27.0 +/- 0.8 per cent; and of morphine-6-glucuronide, 36.7 +/- 3.8 per cent.

Direct determination of codeine, norcodeine, morphine and normorphine with their corresponding O-glucuronide conjugates by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method has been developed for the detection, separation and measurement of codeine and its metabolites norcodeine, morphine and normorphine, with their glucuronide conjugates. The glucuronidase Escherichia coli type VIIA hydrolyses codeine-6-glucuronide completely and is used for the construction of the calibration curves of codeine-6-glucuronide. Enzymic hydrolysis of codeine-6-glucuronide depends on the specific activity of the glucuronidase applied. Examples are shown of a volunteer who is able to form morphine from codeine and one who is unable to do so.

Morphine metabolism in children

1. The metabolism of morphine was studied in 12 children and nine premature neonates on a continuous infusion of morphine (10-360 micrograms kg-1 h-1). 2. The mean plasma clearance of morphine was significantly higher in children than neonates (25.7 and 4.7 ml min-1 kg-1, respectively) (P less than 0.01). 3. All the neonates and children had detectable concentrations of morphine-3-glucuronide (M3G) in plasma. All the children and five neonates had detectable concentrations of morphine-6-glucuronide (M6G) in plasma or urine. 4. The M3G/morphine ratios in plasma and urine, and M6G/morphine ratios in urine were significantly higher in children than neonates (P less than 0.01), suggesting that morphine glucuronidation capacity is enhanced after the neonatal period. 5. There was no difference in the M3G/M6G ratio in children and neonates, indicating a parallel development of both glucuronidation pathways.