Actions and metabolism of codeine (methylmorphine) administration by continuous intravenous infusion to humans

The challenges of LC–MS/MS analysis of opiates and opioids in urine

Opioids are some of the most commonly prescribed and abused drugs around the world. Primarily used for anesthesia or pain management, other opioids can also be used in the treatment of opioid addiction. Given these facts, clinicians often randomly test or monitor their patients to determine compliance or abstinence from these drugs via immunoassay methods. When a positive screen is obtained, a confirmatory assay is carried out and although the gold standard has been GC–MS, LC–MS/MS is fast becoming a valid and popular alternative. This review will discuss opioids, the complex metabolic pathways, the measurement of these drugs, the challenges involved and, finally, will describe some LC–MS/MS methods published from 2003 until 2013.

Hydrophilic interaction LC–MS/MS analysis of opioids in urine: significance of glucuronide metabolites

Background: In clinical laboratories, a large proportion of the toxicology workload is drug confirmations. Our GC–MS method for opioid confirmation detects total codeine, morphine, hydrocodone, hydromorphone, oxycodone and oxymorphone. The objective of this study was to develop a LC–MS/MS assay measuring the above drugs and glucuronide metabolites. In addition, to determine if measuring free drug only would lead to false negative results. Results: In 85 patient urines, 43% were positive for morphine glucuronide, but not morphine, 48% were positive for hydromorphone glucuronide, but not hydromorphone, 33% were positive for codeine glucuronide, but not codeine, and 44% were positive for oxymorphone glucuronide, but not oxymorphone. Conclusion: We developed an LC–MS/MS assay capable of detecting codeine, morphine, hydrocodone, hydromorphone, oxycodone, oxymorphone and glucuronide metabolites. Detection of free drug only led to false negative confirmations.

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.

Disposition and metabolism of codeine after single and chronic doses in one poor and seven extensive metabolisers

1. The pharmacokinetics, metabolism and partial clearances of codeine to morphine, norcodeine and codeine-6-glucuronide after single (30 mg) and chronic (30 mg 8 h for seven doses) administration of codeine were studied in eight subjects (seven extensive and one poor metaboliser of dextromethorphan). Codeine, codeine-6-glucuronide, morphine and norcodeine were measured by high performance liquid chromatographic assays. 2. After the single dose, the time to achieve maximum plasma codeine concentrations was 0.97 +/- 0.31 h (mean +/- s.d.) and for codeine-6-glucuronide it was 1.28 +/- 0.49 h. The plasma AUC of codeine-6-glucuronide was 15.8 +/- 4.5 times higher than that of codeine. The AUC of codeine in saliva was 3.4 +/- 1.1 times higher than that in plasma. The elimination half-life of codeine was 3.2 +/- 0.3 h and that of codeine-6-glucuronide was 3.2 +/- 0.9 h. 3. The renal clearance of codeine was 183 +/- 59 ml min-1 and was inversely correlated with urine pH (r = 0.81). These data suggest that codeine undergoes filtration at the glomerulus, tubular secretion and passive reabsorption. The renal clearance of codeine-6-glucuronide was 55 +/- 21 ml min-1, and was not correlated with urine pH. Its binding to human plasma was less than 10%. These data suggest that codeine-6-glucuronide undergoes filtration at the glomerulus and tubular reabsorption. This latter process is unlikely to be passive. 4. After chronic dosing, the pharmacokinetics of codeine and codeine-6-glucuronide were not significantly different from the single dose pharmacokinetics. 5. After the single dose, 86.1 +/- 11.4% of the dose was recovered in urine, of which 59.8 +/- 10.3% was codeine-6-glucuronide, 7.1 +/- 1.1% was total morphine, 6.9 +/- 2.1% was total norcodeine and 11.8 +/- 3.9% was unchanged codeine. These recoveries were not significantly different (P greater than 0.05) after chronic administration. 6. After the single dose, the partial clearance to morphine was 137 +/- 31 ml min-1 in the seven extensive metabolisers and 8 ml min-1 in the poor metaboliser; to norcodeine the values were 103 +/- 33 ml min-1 and 90 ml min-1; to codeine-6-glucuronide the values were 914 +/- 129 ml min-1 and 971 ml min-1; and intrinsic clearance was 1568 +/- 103 ml min-1 and 1450 ml min-1. These values were not significantly (P greater than 0.05) altered by chronic administration.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphine formation from codeine in rat brain: a possible mechanism of codeine analgesia

The O-demethylation of codeine to morphine was demonstrated in rat brain homogenate. Maximal formation occurred at 10 minutes, with a Vmax of 5.93 +/- 0.16 nmol/g brain/h and Km of 37.82 +/- 4.99 microM. The formation was significantly (P less than 0.05) greater in the microvessel-rich brain fraction. Intraperitoneal injection of codeine in the rat resulted in brain concentrations of morphine which could not be solely attributed to transfer of morphine from the blood stream across the blood-brain barrier. Morphine formed in the brain after codeine administration may be an important mechanism for codeine-induced analgesia.

Direct determination of codeine-6-glucuronide in plasma and urine using solid-phase extraction and high-performance liquid chromatography with fluorescence detection

A sensitive and selective method was developed for the direct determination of codeine-6-glucuronide in plasma and urine using high-performance liquid chromatography (HPLC) with fluorescence detection. Codeine-6-glucuronide was synthesised and its purity estimated using acid and enzyme hydrolysis. The hydrolysis of codeine-6-glucuronide by beta-glucuronidase was incomplete and urine reduced the extent of hydrolysis. Codeine-6-glucuronide was recovered from plasma using a solid-phase extraction column and separated on a reversed-phase C18 HPLC column. The assay showed good reproducibility and accuracy (within 10%), and standard curves were linear between 32 and 1600 ng/ml in plasma and between 0.32 and 160 micrograms/ml in urine. The assay has been applied to the study of the pharmacokinetics and metabolism of codeine in patients.

Adverse reactions to intravenous codeine phosphate in children. A report of three cases

Adverse reactions ranging from tachycardia and cutaneous vasodilatation to severe hypotension and apnoea occurred in three children who were given codeine phosphate intravenously. The cause of these reactions is discussed and a review of the literature on the parenteral use of codeine phosphate is presented. The findings indicate that the standard reference formularies and pharmacopeoiae, with one exception, deal inadequately with the parenteral use of codeine phosphate. On the evidence of the cases presented we would support the conclusion of the American Medical Association's drug evaluations, that codeine phosphate should not be used intravenously in children.

Pharmacokinetics of drug overdose

Pharmacokinetics of drugs taken in overdose may differ from those observed following therapeutic doses. Differences are due both to dose-dependent changes and to effects of drugs or pathophysiological consequences of the overdose on kinetics. Dose-dependent changes in rate and extent of absorption, bioavailability (saturation of first-pass metabolism), distribution (saturation of protein binding sites) and metabolism are discussed. Gastrointestinal motility is affected both by specific drug actions, such as delayed gastric emptying by anticholinergic drugs, and by general nervous system depression caused by many drugs. Drug-induced circulatory insufficiency may retard tissue distribution and reduce clearance. Disturbances in blood and urine pH may alter distribution and clearance of weak acids and bases. Drug-induced renal or hepatic failure can significantly decrease clearance. Hypothermia is a common complication of drug overdose and might retard distribution and also reduce clearance. The data concerning pharmacokinetics during overdose are usually incomplete and difficult to interpret. Doses and times of ingestion are uncertain, duration of blood and urine sampling is often inadequate to distinguish absorption from distribution and elimination phases, active metabolites are not measured, protein binding is not determined and clinical features of patients not adequately described. We have, however, reviewed available data for salicylate, paracetamol (acetaminophen), barbiturates, ethchlorvynol, glutethimide, chloral hydrate, tricyclic antidepressants, lithium, phenytoin, ethanol, theophylline, digoxin, amphetamine and phencyclidine.