Pharmacokinetics, adverse effects and effects on thermal nociception following administration of three doses of codeine to horses

BACKGROUND

In humans, codeine is a commonly prescribed analgesic that produces its therapeutic effect largely through metabolism to morphine. In some species, analgesic effects of morphine have also been attributed to the morphine-6-glucuronide (M6G) metabolite. Although an effective analgesic, administration of morphine to horses produces dose-dependent neuroexcitation at therapeutic doses. Oral administration of codeine at a dose of 0.6 mg/kg has been shown to generate morphine and M6G concentrations comparable to that observed following administration of clinically effective doses of morphine, without the concomitant adverse effects observed with morphine administration. Based on these results, it was hypothesized that codeine administration would provide effective analgesia with decreased adverse excitatory effects compared to morphine. Seven horses received a single oral dose of saline or 0.3, 0.6 or 1.2 mg/kg codeine or 0.2 mg/kg morphine IV (positive control) in a randomized balanced 5-way cross-over design. Blood samples were collected up to 72 hours post administration, codeine, codeine 6-glucuronide, norcodeine morphine, morphine 3-glucuronide and M6G concentrations determined by liquid chromatography- mass spectrometry and pharmacokinetic analysis performed. Pre- and post-drug related behavior, locomotor activity, heart rate and gastrointestinal borborygmi were recorded. Response to noxious stimuli was evaluated by determining thermal threshold latency.

RESULTS

Morphine concentrations were highest in the morphine dose group at all times post administration, however, M6G concentrations were significantly higher in all the codeine dose groups compared to the morphine group starting at 1 hour post drug administration and up to 72-hours in the 1.2 mg/kg group. With the exception of one horse that exhibited signs of colic following administration of 0.3 and 0.6 mg/kg, codeine administration was well tolerated. Morphine administration, led to signs of agitation, tremors and excitation. There was not a significant effect on thermal nociception in any of the dose groups studied.

CONCLUSIONS

The current study describes the metabolic profile and pharmacokinetics of codeine in horses and provides information that can be utilized in the design of future studies to understand the anti-nociceptive and analgesic effects of opioids in this species with the goal of promoting judicious and safe use of this important class of drugs.

Metabolism, pharmacokinetics and selected pharmacodynamic effects of codeine following a single oral administration to horses

OBJECTIVE

To describe the pharmacokinetics and selected pharmacodynamic variables of codeine and its metabolites in Thoroughbred horses following a single oral administration.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 12 Thoroughbred horses, nine geldings and three mares, aged 4-8 years.

METHODS

Horses were administered codeine (0.6 mg kg-1) orally and blood was collected before administration and at various times until 120 hours post administration. Plasma and urine samples were collected and analyzed for codeine and its metabolites by liquid chromatography-mass spectrometry, and plasma pharmacokinetics were determined. Heart rate and rhythm, step counts, packed cell volume and total plasma protein were measured before and 4 hours after administration.

RESULTS

Codeine was rapidly converted to the metabolites norcodeine, codeine-6-glucuronide (C6G), morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). Plasma codeine concentrations were best represented using a two-compartment model. The Cmax, tmax and elimination t½ were 270.7 ± 136.0 ng mL-1, 0.438 ± 0.156 hours and 2.00 ± 0.534 hours, respectively. M3G was the main metabolite detected (Cmax 492.7 ± 35.5 ng mL-1), followed by C6G (Cmax 96.1 ± 33.8 ng mL-1) and M6G (Cmax 22.3 ± 4.96 ng mL-1). Morphine and norcodeine were the least abundant metabolites with Cmax of 3.17 ± 0.95 and 1.42 ± 0.79 ng mL-1, respectively. No significant adverse or excitatory effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Following oral administration, codeine is rapidly metabolized to morphine, M3G, M6G, C6G and norcodeine in horses. Plasma concentrations of M6G, a presumed active metabolite of morphine, were comparable to concentrations reported previously following administration of an analgesic dose of morphine to horses. Codeine was well tolerated based on pharmacodynamic variables and behavioral observations.

Combating opioid addiction and abuse-2 ways to effectively intervene in the cycle of addiction through pharmacogenomics

OBJECTIVES

The objectives of this commentary are to: (1) briefly describe the ongoing challenges of addressing opioid abuse, (2) examine codeine metabolism in terms of pharmacogenomics, (3) describe 2 points of patient contact where pharmacogenomics can be implemented to determine the appropriateness of opioid therapy, and (4) briefly explore the value of pharmacogenomics in opioid-abuse and dependency research.

SUMMARY

Opioid abuse is one of the most significant medical, social, and economic threats facing our country today. Yet for some patients, opioids are the only effective treatment option in achieving pain relief. Differentiating patients who are susceptible to abuse and addiction from those who are not has been absent in standard statistics-based medication prescribing. Pharmacogenomics (PGX) is a burgeoning science that examines how gene variations (variants) influence drug metabolism. With an estimated 23% of the U.S. population unable to properly metabolize codeine and related analogs, PGX could play an immediate role in the management of opioid therapy if applied (1) as part of regular pre-operative screening assessments and (2) prior to or in conjunction with pain-management referral.

CONCLUSION

Using PGX to identify patients who should not begin or continue treatment with opioids because of abnormal metabolic pathways could (1) reduce the number of opioid prescriptions written; (2) reduce related costs; (3) guide more patient-centric, pain-management treatment plans, away from opioids as necessary; and (4) reduce the potential for opioid abuse and addiction.

Refining the excretion factors of methadone and codeine for wastewater analysis - Combining data from pharmacokinetic and wastewater studies

Analysing drug residues in wastewater (wastewater analysis) to monitor the consumption of those drugs in the population has become a complementary method to epidemiological surveys. In this method, the excretion factor of a drug (or the percentage of drug metabolites excreted through urine) is a critical parameter for the back-estimation of the consumption of a drug. However, this parameter is usually derived from a small database of human pharmacokinetic studies. This is true for methadone and codeine, the two most commonly used opioids and also common substances of abuse. Therefore, we aimed to refine the current excretion factors used for estimating methadone and codeine by analysing published data from the literature on the excretion of methadone, its main metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), and codeine. Our review included both human drug pharmacokinetic studies and wastewater analysis studies. We found that while the commonly used excretion factor of methadone (~27.5%) was relatively accurate, the excretion factor of EDDP, a better biomarker for methadone consumption in sewer epidemiology, should be twice that of methadone (i.e. 55%) instead of the current equal or half values. For codeine, the excretion factor should be ~30% instead of 63.5% or 10% as previously used in wastewater analysis studies. Data from wastewater analysis studies could be used in this way to refine the excretion factors of the drugs of interest.

Two Relations to Estimate Membrane Permeability Using Milestoning

Prediction of passive permeation rates of solutes across lipid bilayers is important to drug design, toxicology, and other biological processes such as signaling. The inhomogeneous solubility-diffusion (ISD) equation is traditionally used to relate the position-dependent potential of mean force and diffusivity to the permeability coefficient. The ISD equation is derived via the Smoluchowski equation and assumes overdamped system dynamics. It has been suggested that the complex membrane environment may exhibit more complicated damping conditions. Here we derive a variant of the inhomogeneous solubility diffusion equation as a function of the mean first passage time (MFPT) and show how milestoning, a method that can estimate kinetic quantities of interest, can be used to estimate the MFPT of membrane crossing and, by extension, the permeability coefficient. We further describe a second scheme, agnostic to the damping condition, to estimate the permeability coefficient from milestoning results or other methods that compute a probability of membrane crossing. The derived relationships are tested using a one-dimensional Langevin dynamics toy system confirming that the presented theoretical methods can be used to estimate permeabilities given simulation and milestoning results.

[Paracetamol-codeine, an always actual choice for the treatment of pain]

Acute pain of mild to moderate intensity is one of the problems most frequently encountered in primary care and emergency medicine and is a major reason of request for visit by patients. In recent years the focus has been more on the treatment of chronic pain, perhaps ignoring the negative impact of acute pain on quality of life and functional status of the patient, despite a growing number of evidence indicating the need to treat optimally also acute pain to avoid it prolongs in time. The remarkable progress achieved in the understanding of the physiological mechanisms of the nociceptive stimulus, as well as those common to biochemical inflammation and acute pain, highlighted the active and complex role of central nervous system in the genesis and maintenance of pain that from acute, if not promptly and adequately treated, can become chronic. In this article, after a brief introduction on the most recent advances on the transition from acute to chronic pain, we have focused on paracetamol, an analgesic drug widely used for over a century for its demonstrated efficacy and tolerability. Paracetamol that, thanks to a complex and not yet fully defined mechanism of action, certainly localized in the central nervous system, can have a significant role in the early treatment of acute pain aimed to reduce the risk of chronicization. Pharmacokinetic parameters and pharmacodynamic studies are outlined, as well as the latest acquisitions in terms of metabolism of this drug and the risks related to its misuse. Are also discussed the recommendations issued by scientific societies and recent articles that indicate paracetamol as the drug of first choice for mild to moderate pain in various clinical settings, such as post-operative pain, post-traumatic and osteoarticular diseases, alone or in association with weak opioids, in particular with codeine. Most recent findings about metabolism and analgesic effect of codeine and its metabolites are highlighted, and how, in combination with acetaminophen, there is an increase in analgesic efficacy without increasing side effects, offering the chance of obtaining a better pain control.

Clinical practice guideline: CYP2D6 genotyping for safe and efficacious codeine therapy

This guideline is intended to provide a basis for informed decision-making regarding genetic testing to identify those individuals who will not benefit from codeine therapy, as well as those who are at an increased risk for codeine-induced toxicity. This guideline addresses the following key questions: 1) Should genetic testing for CYP2D6 be performed in patients prior to the initiation of codeine therapy? 2) How should patients with an indication for codeine therapy be managed based on their genotyping results for CYP2D6?

Quantitative study of controlled substance bedside wasting, disposal and evaluation of potential ecologic effects

Drugs in wastewater arise from many sources. For health care, these include excretion and direct disposal (bedside wasting). The present study reports on the dispensing and wasting of 15 controlled substances (CS) at two health care facilities in Albany, NY over a nearly two year period. The study considered measures of ecotoxicity, drug metabolism, excretion and disposal of these CS. Potential alternatives to flushing of CS into wastewaters from healthcare facilities are discussed. Drug medication and waste collection records (12,345) included: numbers of drugs dispensed, returned and wasted. Overall, 8528 g of 15 CS were wasted. Three (midazolam, acetaminophen-codeine and fentanyl) accounted for 87.5% of the total wasted. Wasting varied by hospital, 14 CS at the academic medical center hospital and 8 at the surgical care center were wasted. Liquids were more frequently wasted than tablets or pills. Some combination drugs (acetaminophen (APAP)-codeine) were frequently (50% of drug dispensed) wasted while others were less wasted (APAP-hydrocodone-6.3%; APAP-oxycodone-1.3%). The 8 CS judged more hazardous to aquatic life were: APAP-codeine, APAP-hydrocodone, APAP-oxycodone, alprazolam, diazepam, fentanyl, midazolam, and testosterone. Ketamine, morphine, oxycodone and zolpidem were of lesser acute toxicity based on available LC50 values. These CS might provide a therapeutically equivalent alternative to the more environmentally harmful drugs. In health care facilities, professionals dispose of CS by bedside wasting into water or other receptacles. This can be avoided by returning CS to the hospital's pharmacy department, thence to a licensed distributor. Study of this process of drug wasting can identify opportunities for process improvements. We found 3 CS (APAP-codeine, midazolam and testosterone) where ½ to 1/3 of the drug was wasted and 5 others with 30 to 13% wasted. Knowledge of the adverse impacts from the release of highly toxic drugs into the environment might influence CS selection and disposal alternatives.

Genotypic screening of the main opiate-related polymorphisms in a cohort of 139 sickle cell disease patients

Because no frequency data are available for the main opiate-related polymorphisms in sickle-cell disease (SCD) populations, we decided to perform such a genotyping in a cohort of 139 individuals. For pharmacodynamics,the OPRM1 A118G and the COMT G322A single nucleotide polymorphisms (SNPs) were chosen for their negative effects on the m receptors [1,2]. For pharmacokinetics [3], important SNPs for the CYP2D6 gene (codeine to morphine conversion) and for three genes involved in morphine elimination (namely CYP3A, UGT2B7, and ABCB1) were genotyped. The allelic frequencies of the OPRM1 and COMT SNPs appeared very low (0.01 to 0.05-no double mutant homozygous),as well as the proportion of CYP2D6 poor metabolizers (1.4%)and CYP3A wild-type (17.9%) which are associated with a low morphine exposure. On the contrary, up to 35% of SCD patients may have unfavorable ABCB1 and UGT2B7 genotypes for a good morphine exposure.Obviously, pharmacokinetic studies with precise phenotype/genotype correlations are required to draw definitive conclusions.

Dispositional study of opioids in mice pretreated with sympathomimetic agents

Brain and plasma levels of morphine and codeine were determined by an assay method involving solid-phase extraction and ion-pair reversed phase HPLC. Detection was by a variable wavelength UV-detector (for codeine) and an amperometric electrochemical detector (for morphine) coupled in series. Ephedrine or phenylpropanolamine pretreatment did not interfere with the plasma disposition of morphine, evidenced by overlapping plasma concentration-time profiles. Brain opioid levels were equally unaffected by sympathomimetic pretreatment. The relative ratios of brain to plasma concentrations at the time corresponding to the respective peak anti-nociceptive activity for morphine and codeine revealed no significant differences. It is concluded that single doses of ephedrine and phenylpropanolamine do not affect the disposition of morphine and codeine in mice.

Preparation of Codeine-Resinate and Chlorpheniramine-Resinate Sustained-Release Suspension and its Pharmacokinetic Evaluation in Beagle Dogs

Using ion exchange resins (IERs) as carriers, a dual-drug sustained release suspension containing codeine, and chlorpheniramine had been prepared to elevate drug safety, effectiveness and conformance. The codeine resinate and chlorpheniramine resinate beads were prepared by a batch process and then impregnated with Polyethylene glycol 4000 (PEG 4000), respectively. The PEG impregnated drug resinate beads were coated with ethylcellulose as the coating polymer and di-n-butyl-phthalate as plasticizer in ethanol and methylene chloride mixture by the Wurster process. The coated PEG impregnated drug resinate beads were dispersed in an aqueous suspending vehicle containing 0.5% w/w xanthan gum and 0.5% w/w of hydroxypropylmethylcellulose of nominal viscosity of 4000 cps, obtaining codeine resinate and chlorpheniramine resinate sustained-release suspension (CCSS). Codeine phosphate and chlorpheniramine maleate were respectively loaded onto AMBERLITE IRP 69, and PEG 4000 was used to impregnate drug resinate beads to maintain their geometry. Ethylcellulose with di-n-butyl-phthalate in ethanol and methylene chloride mixture for the coating of drug resinate beads was performed in Glatt fluidized bed coater, where the coating solution flow rate was 8-12 g/min, the inlet air temperature was 50-60 degrees C, the outlet air temperature was 32-38 degrees C, the atomizing air pressure was 2.0 bar and the fluidized air pressure was adjusted as required. Few significant agglomeration of circulating drug resinate beads was observed during the operation. The film weight gained 20% w/w and 15% w/w were suitable for the PEG impregnated codeine resinate and chlorpheniramine resinate beads, respectively. Residual solvent content increased with coating level, but inprocess drying could reduce residual solvent content. In the present study, the rates of drug release from both drug resinate beads were measured in 0.05 M and 0.5M KCl solutions. The increased ionic strength generally accelerated the release rate of both drugs. But the release of codeine from its resinate beads was much more rapid than chlorpheniramine released from its resinate beads in the same ionic strength release medium. The drug release specification of the CCSS, where release mediums were 0.05 M KCl solution for codeine and 0.5 M KCl solution for chlorpheniramine, was established to be in conformance with in vivo performance. Relative bioavailability and pharmacokinetics evaluation of the CCSS, using commercial immediate-release tablets as the reference preparation, were performed following a randomized two-way crossover design in beagle dogs. The drug concentrations in plasma were measured by a validated LC-MS/MS method to determine the pharmacokinetic parameters of CCSS. This LC-MS/MS method demonstrated high accuracy and precision for bioanalysis, and was proved quick and reliable for the pharmacokinetic studies. The results showed that the CCSS had the longer value of Tmax and the lower value of Cmax, which meant an obviously sustained release effect, and its relative bioavailability of codeine and chlorpheniramine were (103.6 +/- 14.6)% and (98.1 +/- 10.3)%, respectively, compared with the reference preparation. These findings indicated that a novel liquid sustained release suspension made by using IERs as carriers and subsequent fluidized bed coating might provide a constant plasma level of the active pharmaceutical ingredient being highly beneficial for various therapeutic reasons.

Monitoring opioid adherence in chronic pain patients: tools, techniques, and utility

Opioids are important, if not essential, agents in treating certain types of chronic pain. However, the prevalence of drug misuse, abuse, and addiction has fostered considerable consternation among physicians, who may hesitate to prescribe these medications both due to concern for patients (misuse, abuse, and addiction), and fears of prosecution and/or professional sanction. Such practice may reflect 1) inadequate knowledge about patients' susceptibility to, or current drug misuse or abuse; 2) lack of familiarity with extant assessments and/or regulations, and/or 3) an unanticipated reaction to existing guidelines, policies or laws. We posit that assessing patients' predisposition to, and patterns of, drug misuse/abuse is a vital first step toward establishing and maintaining the safe and effective use of opioid analgesics in the treatment of chronic pain. Adherence monitoring is critical to identify patients' prior and current drug use, establish treatment basis, and evaluate compliance, so as to avoid misuse and abuse, and ensure sound and proper pain management. This paper provides a review of the numerous monitoring approaches that have been described in the literature and addresses the benefits and limitations of these techniques and tools. The complex nature of the problem of drug misuse and abuse is discussed, and while no single monitoring technique can fully address this complex issue, we describe how multiple approaches to adherence monitoring may be employed to sustain the prudent use of opioids for the treatment of chronic pain.

Pharmacokinetic–pharmacodynamic modeling of the miotic effects of dihydrocodeine in humans

AIM

The purpose of this study was to evaluate the pharmacokinetic-pharmacodynamic interrelations of pupillary effects of dihydrocodeine by two different analytic approaches.

METHODS

Dihydrocodeine plasma concentrations and miotic effects were available from a previous study with 24-h measurements after administration of 60 mg dihydrocodeine to nine healthy young men. Plasma concentration versus time course was described either by a one-compartment model or by linear splines using NONMEM. Dihydrocodeine concentrations at the effect site were obtained by convolution of a first-order transfer function with the function describing the plasma concentration versus time courses, and miotic effects were related to effect-site concentrations by a sigmoidal pharmacodynamic model.

RESULTS

Bayesian individual fits of miotic effects were only slightly better with the spline approach than with the compartmental approach (median individual absolute weighted residuals 0.046 versus 0.058, respectively, Wilcoxon test p = 0.008; residual errors of an additive error model 0.0979 versus 0.184, respectively). Both approaches provided similar pharmacokinetic-pharmacodynamic population parameter values. The transfer half-life between plasma and effect site was 21.1 min (95% CI 11.1-34.7 min) and 19.8 min (95% CI 11.9-34 min) with spline and compartmental approaches, respectively, and miosis occurred with EC50 of 207 or 230 ng/ml, respectively.

CONCLUSION

Two modeling approaches to the miotic effects of dihydrocodeine provided similar transfer half-lives between plasma and effect site, which also agreed with previous independently estimated values obtained from analgesic effects, suggesting that pupil size is a valid biomarker to estimate the value of ke0 for opioid central nervous system (CNS) effects.

Apnea in a child after oral codeine: a genetic variant - an ultra-rapid metabolizer

We present a case of a 29 months old previously healthy child who experienced apnea resulting in brain injury following a dose of acetaminophen and codeine 2 days after an uneventful anesthetic for tonsillectomy. A genetic polymorphism leading to ultra-rapid metabolism of codeine into morphine resulted in narcosis and apnea. This paper discusses the use of codeine for pain relief, obstructive sleep apnea, the alteration of the CYP2D6 gene and the resulting effect on drug metabolism.

Comparative metabolic capabilities and inhibitory profiles of CYP2D6.1, CYP2D6.10, and CYP2D6.17

Polymorphisms in the cytochrome P450 2D6 (CYP2D6) gene are a major cause of pharmacokinetic variability in human. Although the poor metabolizer phenotype is known to be caused by two null alleles leading to absence of functional CYP2D6 protein, the large variability among individuals with functional alleles remains mostly unexplained. Thus, the goal of this study was to examine the intrinsic enzymatic differences that exist among the several active CYP2D6 allelic variants. The relative catalytic activities (enzyme kinetics) of three functionally active human CYP2D6 allelic variants, CYP2D6.1, CYP2D6.10, and CYP2D6.17, were systematically investigated for their ability to metabolize a structurally diverse set of clinically important CYP2D6-metabolized drugs [atomoxetine, bufuralol, codeine, debrisoquine, dextromethorphan, (S)-fluoxetine, nortriptyline, and tramadol] and the effects of various CYP2D6-inhibitors [cocaine, (S)-fluoxetine, (S)-norfluoxetine, imipramine, quinidine, and thioridazine] on these three variants. The most significant difference observed was a consistent but substrate-dependent decease in the catalytic efficiencies of cDNA-expressed CYP2D6.10 and CYP2D6.17 compared with CYP2D6.1, yielding 1.32 to 27.9 and 7.33 to 80.4% of the efficiency of CYP2D6.1, respectively. The most important finding from this study is that there are mixed effects on the functionally reduced allelic variants in enzyme-substrate affinity or enzyme-inhibitor affinity, which is lower, higher, or comparable to that for CYP2D6.1. Considering the rather high frequencies of CYP2D6*10 and CYP2D6*17 alleles for Asians and African Americans, respectively, these data provide further insight into ethnic differences in CYP2D6-mediated drug metabolism. However, as with all in vitro to in vivo extrapolations, caution should be applied to the clinical consequences.

Buprenorphine versus dihydrocodeine for opiate detoxification in primary care: a randomised controlled trial

Background

Many drug users present to primary care requesting detoxification from illicit opiates. There are a number of detoxification agents but no recommended drug of choice. The purpose of this study is to compare buprenorphine with dihydrocodeine for detoxification from illicit opiates in primary care.

Methods

Open label randomised controlled trial in NHS Primary Care (General Practices), Leeds, UK. Sixty consenting adults using illicit opiates received either daily sublingual buprenorphine or daily oral dihydrocodeine. Reducing regimens for both interventions were at the discretion of prescribing doctor within a standard regimen of not more than 15 days. Primary outcome was abstinence from illicit opiates at final prescription as indicated by a urine sample. Secondary outcomes during detoxification period and at three and six months post detoxification were recorded.

Results

Only 23% completed the prescribed course of detoxification medication and gave a urine sample on collection of their final prescription. Risk of non-completion of detoxification was reduced if allocated buprenorphine (68% vs 88%, RR 0.58 CI 0.35–0.96, p = 0.065). A higher proportion of people allocated to buprenorphine provided a clean urine sample compared with those who received dihydrocodeine (21% vs 3%, RR 2.06 CI 1.33–3.21, p = 0.028). People allocated to buprenorphine had fewer visits to professional carers during detoxification and more were abstinent at three months (10 vs 4, RR 1.55 CI 0.96–2.52) and six months post detoxification (7 vs 3, RR 1.45 CI 0.84–2.49).

Conclusion

Informative randomised trials evaluating routine care within the primary care setting are possible amongst drug using populations. This small study generates unique data on commonly used treatment regimens.

Toxicokinetics of drugs of abuse: current knowledge of the isoenzymes involved in the human metabolism of tetrahydrocannabinol, cocaine, heroin, morphine, and codeine

This review summarizes the major metabolic pathways of the drugs of abuse, tetrahydrocannabinol, cocaine, heroin, morphine, and codeine, in humans including the involvement of isoenzymes. This knowledge may be important for predicting their possible interactions with other xenobiotics, understanding pharmaco-/toxicokinetic and pharmacogenetic variations, toxicological risk assessment, developing suitable toxicological analysis procedures, and finally for understanding certain pitfalls in drug testing. The detection times of these drugs and/or their metabolites in biological samples are summarized and the implications of the presented data on the possible interactions of drugs of abuse with other xenobiotics, ie, inhibition or induction of individual polymorphic and nonpolymorphic isoenzymes, discussed.

Pharmacokinetics of codeine and its metabolite morphine in ultra-rapid metabolizers due to CYP2D6 duplication

Codeine is an analgesic drug acting on mu-opiate receptors predominantly via its metabolite morphine, which is formed almost exclusively by the genetically polymorphic enzyme cytochrome P450 2D6 (CYP2D6). Whereas it is known that individuals lacking CYP2D6 activity (poor metabolizers, PM) suffer from poor analgesia from codeine, ultra-fast metabolizers (UM) due to the CYP2D6 gene duplication may experience exaggerated and even potentially dangerous opioidergic effects and no systematical study has been performed so far on this question. A single dose of 30 mg codeine was administered to 12 UM of CYP2D6 substrates carrying a CYP2D6 gene duplication, 11 extensive metabolizers (EM) and three PM. Genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism methods and a single-base primer extension method for characterization of the gene-duplication alleles. Pharmacokinetics was measured over 24 h after drug intake and codeine and its metabolites in plasma and urine were analyzed by liquid chromatography with tandem mass spectrometry. Significant differences between the EM and UM groups were detected in areas under the plasma concentration versus time curves (AUCs) of morphine with a median (range) AUC of 11 (5-17) microg h l(-1) in EMs and 16 (10-24) microg h l(-1) in UM (P=0.02). In urine collected over 12 h, the metabolic ratios of the codeine+codeine-6-glucuronide divided by the sum of morphine+its glucuronides metabolites were 11 (6-17) in EMs and 9 (6-16) in UM (P=0.05). Ten of the 11 CYP2D6 UMs felt sedation (91%) compared to six (50%) of the 12 EMs (P=0.03). CYP2D6 genotypes predicting ultrarapid metabolism resulted in about 50% higher plasma concentrations of morphine and its glucuronides compared with the EM. No severe adverse effects were seen in the UMs in our study most likely because we used for safety reasons a low dose of only 30 mg. It might be good if physicians would know about the CYP2D6 duplication genotype of their patients before administering codeine.

Opioid disposition in human sweat after controlled oral codeine administration

BACKGROUND

Characterization of opioid excretion in sweat is important for accurate interpretation of sweat tests in drug treatment, criminal justice, and workplace drug testing programs.

METHODS

Participants (n=20) received placebo, 3 low (60 mg/70 kg) or 3 high (120 mg/70 kg) codeine sulfate doses (used as a model for opioid excretion) within 1 week. Codeine and metabolites in sweat were collected with PharmChek Sweat Patches; hourly patches were applied for 1 to 15 h (n=775) and weekly patches for 7 days (n=118). Patches were analyzed by solid-phase extraction and gas chromatography-mass spectrometry for codeine, norcodeine, morphine, normorphine, and 6-acetylmorphine. Limits of quantification were 2.5 ng/patch (codeine and morphine) and 5 ng/patch (other analytes).

RESULTS

Codeine was the only analyte identified in 12.6% of hourly patches and 83.3% of weekly sweat patches worn during dosing. Weekly patch concentrations (SD) were 38.6 (59.9) ng/patch [median (range), 15.9 (0-225.1) ng/patch] for low and 34.1 (32.7) ng/patch [24.0 (0-96.2) ng/patch] for high codeine doses. Codeine detected 1 week after dosing was 4.6 (5.3) ng/patch [median (range), 4.0 (0-17.1) ng/patch; n=11] after low and 7.7 (7.1) ng/patch [6.9 (0-20.5) ng/patch; n=10] after high doses. In total, 2.6% of hourly, 38.5% of low-dose, and 45.5% of high-dose weekly patches contained codeine at the proposed Substance Abuse and Mental Health Services Administration cutoff.

CONCLUSIONS

Codeine was the only analyte detected, at highly variable concentrations, up to 2 weeks after dosing. These results are consistent, considering the complex processes of codeine deposition in sweat. Sweat testing is a useful alternative technique for qualitative monitoring of opioid use.

Evidence for morphine-independent central nervous opioid effects after administration of codeine: Contribution of other codeine metabolites

OBJECTIVE

Our objective was to investigate whether codeine or one of its metabolites contributes substantially to central nervous effects independent from the cytochrome P450 (CYP) 2D6-mediated O-demethylation to morphine.

METHODS

After oral administration of codeine, plasma concentrations of codeine and its metabolites, as well as pupil size as a measure of central nervous effects, were measured in 11 healthy volunteers representing poor, intermediate, extensive, and ultrarapid metabolizers for CYP2D6. Subsequently, the observed plasma morphine concentrations were mimicked by use of computerized morphine infusion, and the miotic effects were compared with those observed after codeine administration. The contribution of codeine, codeine-6-glucuronide, norcodeine, morphine, morphine-6-glucuronide, and normorphine to the miotic effects was analyzed by means of pharmacokinetic-pharmacodynamic modeling.

RESULTS

The areas under the curve of the miotic effects after codeine were 1.7 +/- 2 times greater than after morphine (P <0.01). This contrasted to similar or even lower morphine concentrations after codeine than after morphine (area under the curve ratio, 0.5 +/- 0.4; P =.21). A pharmacokinetic-pharmacodynamic fit of the miotic effects by use of morphine as the only active moiety was most significantly (P <.0001) improved when codeine-6-glucuronide as a second active moiety was added.

CONCLUSION

CYP2D6-dependent formation of morphine does not explain exclusively the central nervous effects of codeine. Codeine-6-glucuronide is the most likely additional active moiety.

Dextromethorphan differentially affects opioid antinociception in rats

Opioid drugs such as morphine and meperidine are widely used in clinical pain management, although they can cause some adverse effects. A number of studies indicate that N-methyl-D-aspartate (NMDA) receptors may play a role in the mechanism of morphine analgesia, tolerance and dependence. Being an antitussive with NMDA antagonist properties, dextromethorphan (DM) may have some therapeutic benefits when coadministered with morphine. In the present study, we investigated the effects of DM on the antinociceptive effects of different opioids. We also investigated the possible pharmacokinetic mechanisms involved. The antinociceptive effects of the mu-opioid receptor agonists morphine (5 mg kg(-1), s.c.), meperidine (25 mg kg(-1), s.c.) and codeine (25 mg kg(-1), s.c.), and the kappa-opioid agonists nalbuphine (8 mg kg(-1), s.c.) and U-50,488H (20 mg kg(-1), s.c.) were studied using the tail-flick test in male Sprague-Dawley rats. Coadministration of DM (20 mg kg(-1), i.p.) with these opioids was also performed and investigated. The pharmacokinetic effects of DM on morphine and codeine were examined, and the free concentration of morphine or codeine in serum was determined by HPLC.It was found that DM potentiated the antinociceptive effects of some mu-opioid agonists but not codeine or kappa-opioid agonists in rats. DM potentiated morphine's antinociceptive effect, and acutely increased the serum concentration of morphine. In contrast, DM attenuated the antinociceptive effect of codeine and decreased the serum concentration of its active metabolite (morphine). The pharmacokinetic interactions between DM and opioids may partially explain the differential effects of DM on the antinociception caused by opioids.

Pharmacogenetics and Human Molecular Genetics of Opiate and Cocaine Addictions and Their Treatments

Opiate and cocaine addictions are major social and medical problems that impose a significant burden on society. Despite the size and scope of these problems, there are few effective treatments for these addictions. Methadone maintenance is an effective and most widely used treatment for opiate addiction, allowing normalization of many physiological abnormalities caused by chronic use of short-acting opiates. There are no pharmacological treatments for cocaine addiction. Epidemiological, linkage, and association studies have demonstrated a significant contribution of genetic factors to the addictive diseases. This article reviews the molecular genetics and pharmacogenetics of opiate and cocaine addictions, focusing primarily on genes of the opioid and monoaminergic systems that have been associated with or have evidence for linkage to opiate or cocaine addiction. This evidence has been marshalled either through identification of variant alleles that lead to functional alterations of gene products, altered gene expression, or findings of linkage or association studies. Studies of polymorphisms in the mu opioid receptor gene, which encodes the receptor target of some endogenous opioids, heroin, morphine, and synthetic opioids, have contributed substantially to knowledge of genetic influences on opiate and cocaine addiction. Other genes of the endogenous opioid and monoaminergic systems, particularly genes encoding dopamine beta-hydroxylase, and the dopamine, serotonin, and norepinephrine transporters have also been implicated. Variants in genes encoding proteins involved in metabolism or biotransformation of drugs of abuse and also of treatment agents are reviewed.

Drug interactions with the potential to prevent prodrug activation as a common source of irrational prescribing in hospital inpatients

OBJECTIVE

Our objective was to investigate the frequency of potential drug-drug interactions between the prodrugs losartan, codeine, and tramadol and drugs known to inhibit their activation in hospitalized patients.

METHODS

The frequency of coadministration between losartan and well-established cytochrome P450 (CYP) 2C9 inhibitors, as well as codeine and tramadol and CYP2D6 inhibitors, was studied by use of data from a university hospital medication database. The study population comprised all patients treated in internal medicine, pulmonary medicine, oncology, and neurology wards (105,533 treatment periods and 65,526 patients) between July 1, 1996, and June 30, 2002 (6 years).

RESULTS

Every fifth patient receiving losartan, codeine, or tramadol was concomitantly taking another drug that has the potential to inhibit the activation of these drugs. During the 6-year time period, 1999 patients were exposed to a potential interaction. Interactions occurred more commonly in internal medicine wards (odds ratio, 2.3; 95% confidence interval, 2.1-2.5) and in women (odds ratio, 1.5; 95% confidence interval, 1.4-1.7).

CONCLUSIONS

Coadministration of drugs that potentially result in inhibition of prodrug activation present a common and unrecognized source of irrational prescribing.

[Problem forte--is paracetamol-codeine combination rational?]

BACKGROUND

Combination drugs containing codeine and paracetamol are widely prescribed in Norway.

MATERIAL AND METHODS

We reviewed relevant literature identified through searches on Medline or found in the reference lists of important articles.

RESULTS

Codeine mediates its analgesic effect through the active metabolite morphine, a reaction which is catalysed by the cytochrome P450-isoenzyme CYP2D6. Approximately 7-10 % of the population does not express functional CYP2D6; for them codeine have no analgesic effect. They may, however, experience side effects from codeine. Used alone, codeine is an inefficient analgesic. Meta-analyses have shown little therapeutic advantage by adding codeine to paracetamol.

INTERPRETATION

Codeine is an opiate with uncertain and unpredictable effects. The therapeutic benefit from the codeine component in combination with paracetamol is small, even in single dose evaluations. In chronic use, the therapeutic efficacy is most likely outweighed by side effects, including development of tolerance and abuse.

Effect of λ-carrageenan-induced inflammatory pain on brain uptake of codeine and antinociception

This study investigated the potential clinical implications of lambda-carrageenan-induced inflammatory pain on brain uptake of a commonly used analgesic, codeine, in relation to the fundamental properties of the blood-brain barrier (BBB) correlated to its antinociceptive profile over a 168-h time course. BBB uptake of [14C]sucrose (a membrane impermeant marker) and [3H]codeine were investigated using an in situ brain perfusion model in the rat. Results demonstrated a significantly increased brain uptake of [14C]sucrose at 1, 3, 6 and 48 h (139+/-9%, 166+/-19%, 138+/-13% and 146+/-7% compared with control, respectively) and [3H]codeine at 3 and 48 h (179+/-6% and 179+/-12% compared with control, respectively). Capillary depletion analyses ensured that increased radioisotope associated with the brain was due to increased uptake rather than trapping in the cerebral vasculature. Antinociception studies using a radiant-heat tail flick analgesia method demonstrated that lambda-carrageenan-induced inflammatory pain enhanced the in vivo antinociceptive profile of i.p.-administered codeine (7 mg/kg) at 3 and 48 h (144+/-11% and 155+/-9% compared with control, respectively). This study demonstrated that brain uptake and antinociception of codeine are increased during lambda-carrageenan-induced inflammatory pain, suggesting that the presence of inflammatory pain may be an important consideration in therapeutic drug dosing, potential adverse effects and/or neurotoxicity.

Sensitivity, Specificity, and Efficiency in Detecting Opiates in Oral Fluid with the Cozart(R) Opiate Microplate EIA and GC-MS Following Controlled Codeine Administration

Oral fluid specimens (N = 1406) were collected from 19 subjects prior to and up to 72 h following controlled administration of oral codeine. Volunteers provided informed consent to participate in this National Institute on Drug Abuse Institutional Review Board-approved protocol. A modification of Cozart Microplate Opiate EIA Oral Fluid Kit (Opiate ELISA), employing codeine calibrators, was used for semiquantitative analysis of opiates, followed by gas chromatography-mass spectrometry (GC-MS) for the confirmation and quantitation of codeine, norcodeine, morphine, and normorphine in oral fluid. GC-MS limits of detection and quantitation were 2.5 microg/L for all analytes. The Substance Abuse and Mental Health Services Administration (SAMHSA) has proposed a 40-microg/L opiate screening and a 40-microg/L morphine or codeine confirmation cutoff for the detection of opiate use. Oral fluid opiate screening and confirmation cutoffs of 30 micro g/L are in use in the U.K. Utilizing 2.5-, 20-, 30-, and 40-microg/L GC-MS cutoffs, 26%, 20%, 19%, and 18% of the oral fluid specimens were positive for codeine or one of its metabolites. Six Opiate ELISA/confirmation cutoff criteria (2.5/2.5, 10/2.5, 20/20, 30/20, 30/30, and 40/40 microg/L) were evaluated. Calculations for Opiate ELISA sensitivity, specificity, and efficiency were determined from the number of true-positive, true-negative, false-positive, and false-negative results at each screening/confirmation cutoff. Sensitivity, specificity, and efficiency for the lowest cutoff were 91.5%, 88.6%, and 89.3%. Application of the cutoff currently used in the U.K. yielded sensitivity, specificity, and efficiency results of 79.7%, 99.0%, and 95.4% and similar results of 76.7%, 99.1%, and 95.1% when applying the SAMHSA criteria. These data indicate that the Opiate ELISA efficiently detects oral codeine use. In addition, the data, collected following controlled oral codeine administration, may aid in the interpretation of opiate oral fluid test results and in the selection of appropriate oral fluid screening and confirmation cutoffs.

The study of codeine-gluthetimide pharmacokinetic interaction in rats

A high-performance liquid chromatographic (HPLC) assay with native fluorescence detection was developed for the simultaneous quantification of codeine and its two metabolites, morphine and morphine-3-glucuronide (M-3-G), in rat plasma. Solid-phase extraction was used to separate codeine and its metabolites from plasma constituents. Extraction efficiencies of codeine, morphine and M-3-G from rat plasma samples were 97, 92 and 93%, respectively. The chromatographic separation was performed using a reversed-phase C18 column and an elution gradient at ambient temperature. Using native fluorescence detection (excitation at 245 nm and emission at 345 nm), the detection limits of 50 ng/ml for morphine, 25 ng/ml for codeine and 20 ng/ml for M-3-G were obtained. The method had good precision, accuracy and linearity, and was applied to the study of glutethimide's influence on codeine metabolism in rat, following single doses of codeine-glutethimide association. The results confirmed the fact that glutethimide was responsible for a significant increase of morphine plasma levels and for their maintenance in time, concomitant with a significant decrease of M-3-G plasma levels, explained by the inhibition of morphine glucuronidation. In conclusion, glutethimide potentiates and prolongs the analgesic effect of codeine by a pharmacokinetic mechanism.

Codeine and morphine blood concentrations increase during blood loss

During extensive blood loss, a plasma volume refill will take place by transfer of extravascular fluid into the circulation. Drugs present in this fluid may follow and cause a rise or a drop in blood drug concentration, depending on their levels and accessibility in the restoration fluid. This study explored the possible changes of codeine, and its metabolite morphine, in whole blood during a standardized exsanguination in the rat. Three doses containing 5 mg codeine were given orally. In eight rats, blood loss was accomplished by slowly withdrawing 0.8 mL blood at 10 min intervals during 70 min. In control rats, blood was withdrawn only at 0 and 70 min. At 70 min, the final/initial codeine and morphine concentration ratios were 0.70 +/- 0.38 and 0.88 +/- 0.47, respectively, in controls, but increased to 1.28 +/- 0.44 (p = 0.014) and 1.41 +/- 0.34 (p = 0.021), respectively, in exsanguinated rats. It is concluded that blood loss can affect blood drug concentrations.

Pharmacokinetic drug interactions of morphine, codeine, and their derivatives: theory and clinical reality, part I

Pharmacokinetic drug-drug interactions with morphine, hydromorphone, and oxymorphone are reviewed in this column. Morphine is a naturally occurring opiate that is metabolized chiefly through glucuronidation by uridine diphosphate glucuronosyl transferase (UGT) enzymes in the liver. These enzymes produce an active analgesic metabolite and a potentially toxic metabolite. In vivo drug-drug interaction studies with morphine are few, but they do suggest that inhibition or induction of UGT enzymes could alter morphine and its metabolite levels. These interactions could change analgesic efficacy. Hydromorphone and oxymorphone, close synthetic derivatives of morphine, are also metabolized primarily by UGT enzymes. Hydromorphone may have a toxic metabolite similar to morphine. In vivo drug-drug interaction studies with hydromorphone and oxymorphone have not been done, so it is difficult to make conclusions with these drugs.

The role of active metabolites in dihydrocodeine effects

OBJECTIVE

The metabolism of dihydrocodeine to dihydromorphine, a high affinity mu-opioid receptor ligand in membrane homogenates, is catalyzed by CYP2D6. However, it is not clear whether an active CYP2D6 enzyme is required for opioid receptor-mediated effects in man after standard dihydrocodeine doses.

METHODS

Whole cell opioid-receptor affinity and effects on cAMP accumulation of dihydrocodeine and its metabolites were determined in differentiated SH-SY5Y neuroblastoma cells. In a double-blind, 2-period, placebo-controlled randomized crossover pilot study the pharmacokinetics of dihydrocodeine (60 mg single dose) and its metabolites were examined in 5 phenotyped extensive (EMs) and 4 poor metabolizers (PMs) for CYP2D6, and pharmacodynamics were evaluated using a pain threshold model and dynamic pupillometry.

RESULTS

Displacement binding and cAMP accumulation experiments showed clearly higher affinities (100- and 50-fold) and activities (180- and 250-fold) of dihydromorphine and dihydromorphine-6-glucuronide, respectively, whereas the other metabolites had similar or lower affinities and activities as compared to dihydrocodeine. The clinical study revealed no significant difference in plasma or urine pharmacokinetics between EMs and PMs for dihydrocodeine and its glucuronide. Dihydromorphine and its glucuronides were detectable in EMs only. A clear reduction of initial pupil diameters was observed up to 6 hours postdose in both PMs and EMs, with no obvious differences between CYP2D6 phenotypes. In the pain threshold model no effects were observed in either group.

CONCLUSION

CYP2D6 phenotype has no major impact on opioid receptor-mediated effects of a single 60 mg dihydrocodeine dose, despite the essential role of CYP2D6 in formation of highly active metabolites.

Comparative biotransformation of morphine, codeine and pholcodine in rat hepatocytes: identification of a novel metabolite of pholcodine

1. Pholcodine (3-morpholinoethylmorphine), a semi-synthetic alkaloid, is widely used as an antitussive agent. 2. Norpholcodine [7,8-didehydro-4,5alpha-epoxy-3-(2-morpholinoethoxy)morphinan-6alpha-ol] (NP) and pholcodine-N-oxide [1(9a)-dehydro-(4aR,5S,7aR,9cS,12S)-4a,5,7a,8,9,9a-hexahydro-5-hydroxy-12-methyl-3-morpholinoethoxy-1H-8,9,c-(iminoethano)phenanthro[4,5-bcd] furan-12-oxide] (PNOX) were identified in incubations of pholcodine with freshly isolated rat hepatocytes by liquid chromatography/electrospray-mass spectrometry (LC/ESI-MS). 3. Synthesized NP and PNOX were characterized by mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. 4. N-oxidation was the major metabolic pathway for pholcodine, producing a previously unreported metabolite. 5. The metabolism of morphine and codeine was also determined using freshly isolated hepatocytes. 6. For morphine, 3-glucuronidation was the major metabolic pathway, whilst for codeine it was dealkylation (O- and N-). 7. Neither morphine nor its metabolites were metabolites of pholcodine. 8. This observation supports the hypothesis that the absence of analgesic activity with pholcodine may be due to less O-dealkylation in vivo. 9. Together with the slow biotransformation of pholcodine (k(met) = 0.021 microM min(-1)) in comparison with morphine (k(met) = 0.057 microM min(-1)) and codeine (k(met) = 0.112 microM min(-1)), the results obtained were consistent with its low addiction potential and suggest that its antitussive efficacy is mediated by the parent drug or one of its metabolites other than morphine.

Plasma and oral fluid pharmacokinetics and pharmacodynamics after oral codeine administration

BACKGROUND

The ease, noninvasiveness, and safety of oral fluid collection have increased the use of this alternative matrix for drugs-of-abuse testing; however, few controlled drug administration data are available to aid in the interpretation of oral fluid results.

METHODS

Single oral codeine doses (60 and 120 mg/70 kg) were administered to 19 volunteers. Oral fluid and plasma were analyzed for free codeine, norcodeine, morphine, and normorphine by solid-phase extraction combined with gas chromatography-mass spectrometry (SPE/GC-MS). Physiologic and subjective effects were examined.

RESULTS

Mean (SE) peak codeine concentrations were 214.2 +/- 27.6 and 474.3 +/- 77.0 micro g/L in plasma and 638.4 +/- 64.4 and 1599.3 +/- 241.0 micro g/L in oral fluid. The oral fluid-to-plasma ratio for codeine was relatively constant ( approximately 4) from 1 to 12 h. The mean half-life (t(1/2)) of codeine was 2.2 +/- 0.10 h in plasma and 2.2 +/- 0.16 h in oral fluid. Significant dose-related miosis and increases in sedation, psychotomimetic effect, and "high" occurred after the high dose. Mean codeine oral fluid detection time was 21 h with a 2.5 microg/L cutoff, longer than that of plasma (12-16 h). Detection times with the proposed Substance Abuse and Mental Health Services Administration cutoff (40 microg/L) were only 7 h. Norcodeine, but not morphine or normorphine, was quantified in both plasma and oral fluid.

CONCLUSIONS

The disposition of codeine over time was similar in plasma and oral fluid, but because of high variability, oral fluid codeine concentrations did not reliably predict concurrent plasma concentrations. Oral fluid testing is a useful alternative matrix for monitoring codeine exposure with a detection window of 7-21 h for single doses, depending on cutoff concentrations. These controlled drug administration data should aid in the interpretation of oral fluid codeine results.

Growth hormone replacement therapy induces codeine clearance

BACKGROUND

The increasing clinical use of growth hormone (GH) has raised questions about other than growth-related metabolic effects of this treatment. GH regulates the expression of several hepatic drug metabolising enzymes in the rat, but it is not known whether GH treatment alters the expression of such liver enzymes in man. We have investigated the effects of GH on codeine clearance and two enzymes of the cytochrome P450 (CYP) family, CYP3A and CYP2D6, and UDP-glucuronosyl transferase (UDPGT). These enzymes have a superior importance in hepatic biotransformation of numerous drugs. In addition, CYP3A and UDPGT are catalysts of many reactions with endobiotics such as steroid hormones.

METHODS

We used codeine as a probe drug for assessment of the enzyme activities. Codeine was administered as a single-dose prior to, and after 3 months of GH substitution in GH-deficient patients. Total clearance, and clearance along each of the three primary metabolic pathways of codeine, was assessed.

RESULTS

Three months of GH substitution increased the total clearance of codeine (21%, P < 0.01) and clearance catalysed by UDPGT significantly (31%, P < 0.05). The treatment tended to increase the clearance via the CYP3A pathway (83%, P = 0.05).

CONCLUSIONS

The effects of GH replacement therapy on drug metabolism may have clinical implications when combined with drugs that are substrates of UDPGT and CYP3A. Effects on steroid hormone metabolism with endocrine consequences can not be ruled out.

Detection of non-prescription heroin markers in urine with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

The planned introduction of a prescription heroin program in Germany created a need for differentiation between non-prescription and prescribed diamorphine use. The following substances were chosen as markers of non-prescription heroin: acetylcodeine (AC); its metabolites codeine (C) and codeine 6-glucuronide (C6G); papaverine (P); and noscapine (N). Typical heroin markers diamorphine (DAM) and its metabolites monoacetylmorphine (MAM) and morphine (M) were also determined. The drugs were extracted from urine samples with solid-phase extraction (C18) using standard 200-mg columns and 96-well microplates (100 mg). The extracts were examined with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (positive ionization) in two isocratic systems. Selected ion monitoring procedures were applied for protonated molecular masses and characteristic fragments of drugs involved. The limits of detection were in the range of 0.5-1 ng/mL urine. The occurrence of selected heroin markers was investigated in 25 urine samples collected from heroin abusers (road traffic offenders and overdosed patients). C6G was found in all samples, C in 24 samples, N in 22 samples, MAM in 16 samples, P in 14 samples, DAM in 12 samples, and AC in 4 samples. The appearance of these compounds in urine reflects their pharmacokinetic properties and the composition of non-prescription heroin.

Precipitated withdrawal following codeine administration is dependent on CYP genotype

The role of metabolic polymorphism in the development of physical dependence to codeine was assessed in cytochrome P450 2D2 (CYP2D2) deficient Dark Agouti and CYP2D2 intact Sprague-Dawley rats by assessment of the severity of naloxone precipitated withdrawal after codeine and morphine administration. Plasma morphine concentrations after codeine were significantly higher (P<0.01) in Sprague-Dawley than in Dark Agouti rats with metabolic ratios of 0.71 +/- 0.27 and 0.07 +/- 0.04, respectively. Withdrawal after codeine resulted in significantly greater hypothermia (3.5-4 degrees C, P<0.0001) in Sprague-Dawley animals compared to the other groups. Body weight loss was similar for all groups ranging from 6.2 +/- 0.4 to 8.2 +/- 0.6 g. When strain and treatment data were combined, a relationship between body temperature and plasma morphine concentration could be described by the inverse Hill equation (r(2)=0.76, EC(50)=556 +/- 121 ng/ml, n=2.9 +/- 1.5). These data indicate that dependence and withdrawal after codeine administration are dependent on its bioconversion to morphine.

[Pharmacokinetic and toxicokinetic parameters of some drugs of abuse]

This article outlines the main pharmacokinetic and toxicokinetic parameters of selected addicting compounds often being abused. Described parameters affect the way the compounds behave in the body. The article shows the usual dosage and "therapeutic", toxic and fatal concentrations. Knowledge of described parameters is important in the process of detoxication in patients poisoned with this group of psychoactive compounds.

Saliva testing after single and chronic administration of dihydrocodeine

In the present study, concentrations of dihydrocodeine and its metabolites in saliva and serum were compared after single low-dose and chronic high-dosage administration of the drug. In the first investigation, blood and saliva were collected periodically from six subjects after oral administration of 60 mg dihydrocodeine. In the second study, 20 subjects on oral dihydrocodeine maintenance provided single samples of blood and saliva simultaneously. Serum protein binding of salivary analytes and their recovery from the adsorbing material of the collection device as well as pH values of saliva samples were determined. The fluids were analyzed for dihydrocodeine and the major metabolites by high-performance liquid chromatography. In the single dose study dihydrocodeine was the only analyte found in saliva for up to 12-24 h post-dose. The half-life of dihydrocodeine in saliva was about twice that found in blood. The ratios of saliva/serum concentrations ranged from 1.2 to 17.0. After chronic high-dosage use, dihydrocodeine was the main salivary analyte and N-nordihydrocodeine was present in a few samples. Saliva/serum concentration ratios of dihydrocodeine were strongly dependent on the pH value of saliva and, to a lesser extent, on serum-protein binding. The saliva/serum ratios were more similar after chronic administration. The data suggest a passive diffusion process as the underlying mechanism for the transport of dihydrocodeine into saliva. After both single and chronic use, the presence of the drug in saliva can be used as evidence of recent substance administration.

Contribution of dihydrocodeine and dihydromorphine to analgesia following dihydrocodeine administration in man: a PK-PD modelling analysis

AIMS

It is not clear whether the analgesic effect following dihydrocodeine (DHC) administration is due to either DHC itself or its metabolite, dihydromorphine (DHM). We examined the relative contribution of DHC and DHM to analgesia following DHC administration in a group of healthy volunteers using a PK-PD link modelling approach.

METHODS

A single oral dose of DHC (90 mg) was administered to 10 healthy volunteers in a randomised, double-blind, placebo-controlled study. A computerized cold pressor test (CPT) was used to measure analgesia. On each study day, the volunteers performed the CPT before study medication and at 1.25, 2.75, 4.25 and 5.75 h postdose. Blood samples were taken at 0.25 h (predose) and then at half hourly intervals for 5.75 h postdose. PK-PD link modelling was used to describe the relationships between DHC, DHM and analgesic effect.

RESULTS

Mean pain AUCs following DHC administration were significantly different to those following placebo administration (P = 0.001). Mean pain AUC changes were 91 score x s(-1) for DHC and -17 score x s(-1) for placebo (95% CI = +/- 36.5 for both treatments). The assumption of a simple linear relationship between DHC concentration and effect provided a significantly better fit than the model containing DHM as the active moiety (AIC = 4.431 vs 4.668, respectively). The more complex models did not improve the likelihood of model fits significantly.

CONCLUSIONS

The findings suggest that the analgesic effect following DHC ingestion is mainly attributed to the parent drug rather than its DHM metabolite. It can thus be inferred that polymorphic differences in DHC metabolism to DHM have little or no effect on the analgesic affect.

The effects of collection methods on oral fluid codeine concentrations

The use of a variety of alternative biological specimens such as oral fluid for the detection and quantitation of drugs has recently been the focus of considerable scientific research and evaluation. A disadvantage of drug testing using alternative specimens is the lack of scientific literature describing the collection and analyses of these specimens and the limited literature about the pharmacokinetics and disposition of drugs in the specimen. Common methods of oral fluid collection are spitting, draining, suction, and collection on various types of absorbent swabs. The effect(s) of collection techniques on the resultant oral fluid drug concentration has not been thoroughly evaluated. Reported is a controlled clinical study (using codeine) that was designed to determine the effects of five collection techniques and devices on oral fluid codeine concentrations. The collection techniques were control (spitting), acidic stimulation, nonacidic stimulation, and use of either the Salivette or the Finger Collector (containing Accu-Sorb) oral fluid collection devices. Preliminary data were collected from two subjects using the Orasure device. The in vitro drug recovery was also evaluated for the Salivette and the Finger Collector devices. With the exception of a single time point, codeine concentrations in specimens collected by the control method (spitting) were consistently higher than concentrations in specimens collected by the other methods. The control collection concentrations averaged 3.6 times higher than concentrations in specimens collected by acidic stimulation and 1.3 to 2.0 higher than concentrations in specimens collected by nonacidic stimulation or collection using either the Salivette or the Finger Collector devices. When calculated using oral fluid codeine concentrations from the clinical study, the elimination rate constant, t(1/2), AUC and the peak oral fluid concentrations demonstrated device differences. The slope of the elimination curve for codeine using the acidic collection method exceeded that of the other four methods. As a result, the t(1/2) for the acidic method was significantly less than that of the control method (1.8 vs. 3.0 h, respectively). Oral contamination contributed to the control method having higher AUC than that calculated using the other methods. There was considerable variation in peak codeine concentrations between devices and between individuals within each collection method. When samples were collected simultaneously with the Salivette and the Finger Collector, the mean codeine concentrations were similar. We were able to recover > or = 500 microL of oral fluid from 81.8% of the clinical samples collected with the Salivette. However, we were able to recover this volume from only 25.5% of the samples collected with the Finger Collector. In addition, the in vitro drug recoveries were lower using the Finger Collector. When oral fluid was collected nearly simultaneously by the control method and by use of the Salivette, mean control codeine concentrations were 2.3 times higher, but the duration of detection was similar for both methods.

The disposition of cocaine and opiate analytes in hair and fingernails of humans following cocaine and codeine administration

This study investigated the disposition patterns of cocaine and opiates into hair and fingernail specimens collected from 8 volunteers enrolled in a 10-week inpatient clinical study. All subjects were African-American males with a confirmed drug use history. Scalp hair and fingernail scrapings were collected weekly throughout the course of the study. Head hair was collected from the posterior vertex region, and fingernail scrapings were collected along the entire ventral surface of the nail plate. The specimens were introduced to successive decontamination washes including an isopropanol wash and three phosphate buffer washes. All decontamination washes were collected and analyzed. All specimens were enzymatically digested prior to being subjected to solid-phase extraction and derivatization. Analyses were performed using electron impact gas chromatography-mass spectrometry. Analytes investigated included eight cocaine analytes and five codeine analytes. The limit of quantitation for all analytes ranged from 0.1 to 0.5 ng/mg for both matrices. Cocaine was present at the highest concentrations of any analyte in both hair and nail. Benzoylecgonine and ecgonine methyl ester were the primary metabolites in both matrices and were typically less than 15% of cocaine concentrations. Codeine was the only opiate analyte identified in either hair or nail. Observed drug disposition profiles were different for hair and nails. A significant dose-response relationship was observed for hair specimens. The mean peak concentrations in hair after low dosing were half the concentration observed after high-dose administration. Generally, no clear relationship was evident between nail drug concentrations and dose. Decontamination washes removed less than 20% of the total drug present in hair, but removed most of the drug concentrations (60-100%) in nail. This investigation demonstrated that higher concentrations of drug were found in the subjects' hair than in their fingernails and that cocaine was found in both matrices at a greater concentration than codeine. Although both hair and nail have similar physical and chemical properties and may share common mechanisms of drug incorporation, this clinical study suggests that there are distinct differences in their disposition profiles.

Identification of hydrocodone in human urine following controlled codeine administration

Allegations of illicit hydrocodone use have been made against individuals who were taking physician-prescribed oral codeine but denied hydrocodone use. Drug detection was based on positive urine opiate immunoassay results with subsequent confirmation of hydrocodone by gas chromatography-mass spectrometry (GC-MS). In these cases, low concentrations of hydrocodone (approximately 100 ng/mL) were detected in urine specimens containing high concentrations of codeine (> 5000 ng/mL). Although hydrocodone has been reported to be a minor metabolite of codeine in humans, there has been little study of this unusual metabolic pathway. We investigated the occurrence of hydrocodone excretion in urine specimens of subjects who were administered codeine. In a controlled study, two African-American and three Caucasian male subjects were orally administered 60 mg/70 kg/day and 120 mg/70 kg/day of codeine sulfate on separate days. Urine specimens were collected prior to and for approximately 30-40 h following drug administration. In a second case study, a postoperative patient self-administered 960 mg/day (240 mg four times per day) of physician-prescribed oral codeine phosphate, and urine specimens were collected on the third day of the dosing regimen. Samples from both studies were extracted on copolymeric solid-phase columns and analyzed by GC-MS. In the controlled study, codeine was detected in the first post-drug-administration specimen from all subjects. Peak concentrations appeared at 2-5 h and ranged from 1475 to 61,695 ng/mL. Codeine was detected at concentrations above the 10-ng/mL limit of quantitation for the assay throughout the 40-h collection period. Hydrocodone was initially detected at 6-11 h following codeine administration and peaked at 10-18 h (32-135 ng/mL). Detection times for hydrocodone following oral codeine administration ranged from 6 h to the end of the collection period. Confirmation of hydrocodone in a urine specimen was always accompanied by codeine detection. Codeine and hydrocodone were detected in all specimens collected from the postoperative patient, and concentrations ranged from 2099 to 4020 and 47 to 129 ng/mL, respectively. Analyses of the codeine formulations administered to subjects revealed no hydrocodone present at the limit of detection of the assay (10 ng/mL). These data confirm that hydrocodone can be produced as a minor metabolite of codeine in humans and may be excreted in urine at concentrations as high as 11% of parent drug concentration. Consequently, the detection of minor amounts of hydrocodone in urine containing high concentrations of codeine should not be interpreted as evidence of hydrocodone abuse.

In vitro interaction of codeine and diclofenac

There is very limited knowledge about possible pharmacokinetic interactions between opioid analgesics and nonsteroidal antiinflammatory drugs (NSAIDs), which are commonly used in combination for the treatment of chronic pain. The major metabolic pathway of the weak opioid codeine is glucuronidation to codeine-6-glucuronide. Therefore we investigated the influence of the NSAID diclofenac on the formation of codeine-6-glucuronide in vitro, using human liver tissue homogenate. The formation of codeine-6-glucuronide exhibited single enzyme Michaelis-Menten kinetics with an average V(max) of 93.6 +/- 35.3 pmol/mg/min. A noncompetitive inhibition of codeine-6-glucuronidation by diclofenac was observed with an average K(i) of 7.9 microM. These in vitro findings suggest that a pharmacokinetic interaction occurs in vivo, which has to be confirmed by an interaction study in human subjects. It can be speculated that in case of inhibition of glucuronidation, the amount of codeine available for other pathways especially O-demethylation to morphine is increased, resulting in higher morphine serum levels and therefore higher analgesic efficacy.