The bioavailability and pharmacokinetics of subcutaneous, nebulized and oral morphine-6-glucuronide

The role of drug efflux and uptake transporters in the plasma pharmacokinetics and tissue disposition of morphine and its main metabolites

Morphine is a widely used opioid for the treatment of pain. Differences in drug transporter expression and activity may contribute to variability in morphine pharmacokinetics and response. Using appropriate mouse models, we investigated the impact of the efflux transporters ABCB1 and ABCG2 and the OATP uptake transporters on the pharmacokinetics of morphine, morphine-3-glucuronide (M3G), and M6G. Upon subcutaneous administration of morphine, its plasma exposure in Abcb1a/1b-/-;Abcg2-/--, Abcb1a/1b-/-;Abcg2-/-;Oatp1a/1b-/-;Oatp2b1-/- (Bab12), and Oatp1a/1b-/-;Oatp2b1-/- mice was similar to that found in wild-type mice. Forty minutes after dosing, morphine brain accumulation increased by 2-fold when mouse (m)Abcb1 and mAbcg2 were ablated. Relative recovery of morphine in small intestinal content was significantly reduced in all the knockout strains. In the absence of mOatp1a/1b and mOatp2b1, plasma levels of M3G were markedly increased, suggesting a lower elimination rate. Moreover, Oatp-deficient mice displayed reduced hepatic and intestinal M3G accumulation. Mouse Oatps similarly affected plasma and tissue disposition of subcutaneously administered M6G. Human OATP1B1/1B3 transporters modestly contribute to the liver accumulation of M6G. In summary, mAbcb1, in combination with mAbcg2, limits morphine brain penetration and its net intestinal absorption. Variation in ABCB1 activity due to genetic polymorphisms/mutations and/or environmental factors might, therefore, partially affect morphine tissue exposure in patients. The ablation of mOatp1a/1b increases plasma exposure and decreases the liver and small intestinal disposition of M3G and M6G. Since the contribution of human OATP1B1/1B3 to M6G liver uptake was quite modest, the risks of undesirable drug interactions or interindividual variation related to OATP activity are likely negligible.

Subcutaneous administration of drugs and hydration in acute palliative care units: Physician attitudes and beliefs in the United States and Canada

OBJECTIVES

The objective of this study was to compare the attitudes and beliefs of PCU physicians leaders in the United States versus Canada regarding the subcutaneous method in the administration of medications and hydration in order to gain a better understanding as to why variations in practice exist.

METHODS

This survey trial took place from November 2022 to May 2023. The MD Anderson Cancer Center institutional review board in Houston, Texas, approved this study. The participants were the physician leaders of the acute palliative care units (PCUs) in the United States and Canada. The survey comprised questions formulated by the study investigators regarding the perceived comfort, efficiency, and preference of using the subcutaneous versus the intravenous method. The consent form and survey links were emailed to the participants.

RESULTS

Sixteen PCUs were identified in the United States and 15 PCUs in Canada. Nine US and 8 Canadian physicians completed the survey. Physicians in Canada were more likely to use the subcutaneous route for administering opioids, antiemetics, neuroleptics, and hydration. They preferred subcutaneous over intravenous or intramuscular routes (p = 0.017). Canadian physicians felt their nursing staff was more comfortable with subcutaneous administration (p = 0.022) and that it was easier to administer (p = 0.02). US physicians felt the intravenous route was more efficient (p = 0.013).

SIGNIFICANCE OF RESULTS

The study results suggest that exposure to the subcutaneous route influences a physician's perception. Further research is needed to explore ways to incorporate its use to a greater degree in the US healthcare system.

Nalbuphine-6-glucuronide is a potent analgesic with superior safety profiles by altering binding affinity and selectivity for mu-/kappa-opioid receptors

Although nalbuphine, a semi-synthetic analgesic compound, is less potent than morphine in terms of alleviating severe pain, our recent findings have revealed that nalbuphine-6-glucuronide (N6G), one of the glucuronide metabolites of nalbuphine, promotes a significantly more robust analgesic effect than its parent drug. Nevertheless, despite these promising observations, the precise mechanisms underlying the analgesic effects of nalbuphine glucuronides have yet to be determined. In this study, we aim to elucidate the mechanisms associated with the analgesic effects of nalbuphine glucuronides. Pharmacokinetic and pharmacodynamic studies were conducted to investigate the relationship between the central and peripheral compartments of nalbuphine and its derivatives. The analgesic responses of these compounds were evaluated based on multiple behavioral tests involving thermal and mechanical stimuli. Radioligand binding assays were also performed to determine the binding affinity and selectivity of these compounds for different opioid receptors. The results of these tests consistently confirmed that the heightened analgesic effects of N6G are mediated through its enhanced binding affinity for both mu- and kappa-opioid receptors, even comparable to those of morphine. Notably, N6G exhibited fewer side effects and did not induce sudden death, thereby highlighting its superior safety profile. Additionally, pharmacokinetic studies indicated that N6G could cross the blood-brain barrier when administered peripherally, offering pain relief. Overall, N6G provides great analgesic efficacy and enhanced safety. These findings highlight the potential value of nalbuphine glucuronides, particularly N6G, as promising candidates for the development of novel analgesic drugs.

Hydrocodone, Oxycodone, and Morphine Metabolism and Drug-Drug Interactions

Awareness of drug interactions involving opioids is critical for patient treatment as they are common therapeutics used in numerous care settings, including both chronic and disease-related pain. Not only do opioids have narrow therapeutic indexes and are extensively used, but they have the potential to cause severe toxicity. Opioids are the classical pain treatment for patients who suffer from moderate to severe pain. More importantly, opioids are often prescribed in combination with multiple other drugs, especially in patient populations who typically are prescribed a large drug regimen. This review focuses on the current knowledge of common opioid drug-drug interactions (DDIs), focusing specifically on hydrocodone, oxycodone, and morphine DDIs. The DDIs covered in this review include pharmacokinetic DDI arising from enzyme inhibition or induction, primarily due to inhibition of cytochrome p450 enzymes (CYPs). However, opioids such as morphine are metabolized by uridine-5'-diphosphoglucuronosyltransferases (UGTs), principally UGT2B7, and glucuronidation is another important pathway for opioid-drug interactions. This review also covers several pharmacodynamic DDI studies as well as the basics of CYP and UGT metabolism, including detailed opioid metabolism and the potential involvement of metabolizing enzyme gene variation in DDI. Based upon the current literature, further studies are needed to fully investigate and describe the DDI potential with opioids in pain and related disease settings to improve clinical outcomes for patients. SIGNIFICANCE STATEMENT: A review of the literature focusing on drug-drug interactions involving opioids is important because they can be toxic and potentially lethal, occurring through pharmacodynamic interactions as well as pharmacokinetic interactions occurring through inhibition or induction of drug metabolism.

Approaches for estimating the clinical starting dose of new dosage forms: An example of a long-acting injectable formulation of finasteride

In our previous study, a long-acting injectable (LAI) formulation of finasteride was prepared as a new dosage form of PROPECIA®, and in vivo pharmacokinetics (PKs)-pharmacodynamics (PDs) was evaluated in beagle dogs. The resulting PK-PD profiles of the formulation showed pharmacological effects and achievability for monthly delivery. In this study, a first-in-human (FIH) dose of the LAI formulation loaded with finasteride was predicted. The three approaches were used for estimating a FIH dose of the LAI formulation: (1) No observed adverse effect level (NOAEL)-based approach; (2) Pharmacokinetically-guided approach; (3) Pharmacokinetic/pharmacodynamic model-based approach. The advantage, assumptions, limitations, and estimated FIH dose from each approach was discussed and compared since there is no consensus on the best approach. For the prediction of clinical exposures and estimation of FIH doses, the clinical PK-PD parameters were allometrically scaled from the nonclinical data, extracted from reported clinical studies, or fixed from published literature. The starting dose range of the LAI formulation (as finasteride) was estimated to be 16.80-81.06 mg from the three approaches, and the PK/PD model-based approach suggests the most optimal starting dose (16.80 mg) of the LAI formulation. The approaches for estimating starting doses presented in the study could be used as a basis for an Investigational New Drug (IND) application of new dosage forms.

[Neuraxial Morphine for Postoperative Analgesia after Caesarean Deliveries]

The use of neuraxial morphine, in combination with nonopioid analgesic regimens for postoperative analgesia after Caesarean deliveries is common practice, especially in the Anglo-American world. Neuraxial morphine offers a longer-lasting superior analgesia than intravenous opioids or patient-controlled analgesia. If neuraxial anaesthesia is being used for a caesarean delivery, it may be recommended to concomitantly administer neuraxial morphine for the postoperative analgesia.A low dose of neuraxial morphine in a healthy parturient bears a low morbidity and mortality risk. The optimal frequency, duration and modality of respiratory monitoring for patients at low risk for respiratory depression is dependent on the dose of morphine administered and the patient-specific and obstetric risk profile.

Drivers of absolute systemic bioavailability after oral pulmonary inhalation in humans

There are few studies in humans dealing with the relationship between physico-chemical properties of drugs and their systemic bioavailability after administration via oral inhalation route (Fpulm). Getting further insight in the determinants of Fpulm after oral pulmonary inhalation could be of value for drugs considered for a systemic delivery as a result of poor oral bioavailability, as well as for drugs considered for a local delivery to anticipate their undesirable systemic effects. To better delineate the parameters influencing the systemic delivery after oral pulmonary inhalation in humans, we studied the influence of physico-chemical and permeability properties obtained in silico on the rate and extent of Fpulm in a series of 77 compounds with or without marketing approval for pulmonary delivery, and intended either for local or for systemic delivery. Principal component analysis (PCA) showed mainly that Fpulm was positively correlated with Papp and negatively correlated with %TPSA, without a significant influence of solubility and ionization fraction, and no apparent link with lipophilicity and drug size parameters. As a result of the small sample set, the performance of the different models as predictive of Fpulm were quite average with random forest algorithm displaying the best performance. As a whole, the different models captured between 50 and 60% of the variability with a prediction error of less than 20%. Tmax data suggested a significant positive influence of lipophilicity on absorption rate while charge apparently had no influence. A significant linear relationship between Cmax and dose (R² = "0.79) highlighted that Cmax was primarily dependent on dose and absorption rate and could be used to estimate Cmax in humans for new inhaled drugs.

Misuse of Tramadol in the United States: An Analysis of the National Survey of Drug Use and Health 2002-2017

Objective:

To analyze the rates of misuse - that is, use in any way not directed by a doctor - of products containing oral tramadol, a Schedule IV opioid, from the National Survey of Drug Use and Health (NSDUH), as compared to comparator Schedule II opioids (morphine, oxycodone, and hydrocodone) and alprazolam, a commonly prescribed Schedule IV controlled substance in the U.S.

Methods:

The NSDUH is a congressionally mandated household survey that collects information on tobacco, alcohol, and drug use, mental health and other health-related issues in the US. A cross-sectional surveillance study design was used to examine lifetime and past year misuse of oral tramadol and comparators of interest among NSHUH respondents aged 12 years or older. Based on when particular data were available, the past-year misuse analysis includes NSDUH data from 2015 to 2017, and the lifetime misuse analysis includes NSDUH data from 2002 to 2014.

Results:

In 2015 to 2017, past-year misuse of oral tramadol was approximately 4% of the total number of prescriptions, versus 7% to 8% for all of the comparators when adjusted for drug availability. In 2002 to 2014, lifetime misuse of oral tramadol remained at 1.5% or less over the 13-year period, and was lower than reported for hydrocodone (6%) and oxycodone (4%), respectively. Comparison of oral tramadol and alprazolam showed misuse of tramadol was also much lower than alprazolam. Too few reports of tramadol misuse by injection (n = 7) were reported, versus 570, 1096, and 32 reports of injection of morphine, oxycodone, and hydrocodone, respectively, during the 16-year analysis period to allow for any population-based estimation. Only morphine has an intravenous formulation available and tramadol was not available as an intravenous formulation in the U.S. during that time period.

Conclusions:

This analysis shows a low prevalence of oral tramadol misuse, relative to other commonly prescribed opioids, in a nationally representative sample of noninstitutionalized US residents. Estimates of reported oral tramadol misuse have remained relatively stable over time and are substantially lower than those reported for comparators when adjusted for prescription volume. Reports of oral tramadol misuse are also much less than alprazolam, another Schedule IV drug.

Nebulized versus intravenous morphine titration for the initial treatment of severe acute pain in the emergency department: study protocol for a multicenter, prospective randomized and controlled trial, CLIN-AEROMORPH

BACKGROUND

Intravenous morphine titration (IVMT) is the French gold standard for opioid treatment in the emergency department (ED). Nebulized morphine titration (NMT) may represent an alternative without venous access, but it has not been adequately studied in adults. We test the hypothesis that NMT is at least as effective as IVMT to initially manage severe acute pain in the ED.

METHODS/DESIGN

We designed a multicenter (10 French EDs), single-blind, randomized and controlled trial. Adults between 18 and 75 years with visual analog scale (VAS) ≥ 70/100 or numeric rating scale (NRS) ≥ 7/10 will be enrolled. We will randomize 850 patients into two groups to compare two routes of MT as long as VAS >  30 or NRS >  3. In group A (425), patients will receive an initial NMT for 5-25 min associated with titration of an intravenously (IV) administered placebo of physiologic serum (PS). In group B (425), patients will receive IVMT plus nebulized PS placebo. NMT is defined as a minimum of 1 and a maximum of 3 5-min nebulized boluses of 10 mg or 15 mg (weight ≥ 60 kg), at 10-min fixed intervals. IVMT is defined as a minimum of 1 and a maximum of 6 boluses of 2 mg or 3 mg (weight ≥ 60 kg), at 5-min fixed intervals. Nebulized placebo titration will be performed every 10 min. IV titration of PS will be performed every 5 min. In both groups, after 25 min, if VAS > 30/100 or NRS > 3/10, routine IVMT will be continued until pain relief. Pain severity, vital signs, bronchospasm, and Ramsay score will be recorded every 5 min. The primary outcome is the rate of relief obtained 1 h from the start of drug administration. Complete pain relief in both groups will be compared with a non-inferiority design. Secondary outcomes are pain relief at 30 min (the end of NMT) and at 2 h and median pain relief. We will compare final doses, and study the feasibility and tolerance of NMT (protocol deviations, respiratory or hemodynamic depression, sedation, and minor vegetative side effects). Co-analgesia will be recorded. Discharge criteria from the ED and hospital are defined.

DISCUSSION

This trial is the first multicenter randomized and controlled NMT protocol for severe pain in the ED using the titration concept. We propose an original approach of combined titration with an endpoint at 1 h and a non-inferiority design.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03257319 . Registered on 22 August 2017.

A Prospective Population Pharmacokinetic Study on Morphine Metabolism in Cancer Patients

Background

Oral and subcutaneous morphine is widely used for the treatment of cancer-related pain; however, solid pharmacokinetic data on this practice are lacking. Furthermore, it is largely unknown which factors contribute to the variability in clearances of morphine and its metabolites and whether morphine clearance is related to treatment outcome.

Methods

Blood samples from 49 cancer patients treated with oral and/or subcutaneous morphine were prospectively collected and were used to develop a population pharmacokinetic model for morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). The influence of age, gender, renal function and several polymorphisms possibly related to the pharmacokinetics of the three compounds was investigated. In addition, the relation between treatment failure and morphine and metabolite clearances was explored.

Results

A one-compartment model including an extensive first-pass effect adequately described the data of morphine and its metabolites. Estimated mean area under the plasma concentration–time curve (AUC) ratios following oral versus subcutaneous administration were: M3G/morphine 29.7:1 vs. 11.1:1; M6G/morphine 5.26:1 vs. 1.95:1; and M3G/M6G 5.65:1 vs. 5.70:1. Renal function was significantly correlated with clearance of the metabolites, which increased 0.602 L/h per every 10 mL/min/1.73 m² increase of estimated glomerular filtration rate (eGFR), reaching a plateau for eGFR >90 mL/min/1.73 m². The clearance of morphine or its metabolites was not found to be correlated with treatment failure.

Conclusion

The influence of age-, gender- and pharmacokinetic-related polymorphisms was not identified on the pharmacokinetics of morphine. Clearance of morphine or its metabolites was not found to explain treatment outcome; however, large variations in plasma concentrations of morphine, M3G and M6G support further studies on the relation between plasma concentrations and treatment outcome.

Dutch Trial Register ID: NTR4369.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-016-0471-7) contains supplementary material, which is available to authorized users.

Simultaneous determination of morphine-6-d-glucuronide, morphine-3-d-glucuronide and morphine in human plasma and urine by ultra-performance liquid chromatography-tandem mass spectrometry: Application to M6G injection pharmacokinetic study

A robust ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the determination of morphine-6-d-glucuronide (M6G), morphine-3-d-glucuronide (M3G) and morphine (MOR) in human plasma and urine has been developed and validated. The analytes of interest were extracted from plasma by protein precipitation. The urine sample was prepared by dilution. Both plasma and urine samples were chromatographed on an Acquity UPLC HSS T₃ column using gradient elution. Detection was performed on a Xevo TQ-S tandem mass spectrometer in multiple reaction monitoring mode using positive electrospray ionization. Matrix interferences were not observed at the retention time of the analytes and internal standard, naloxone-D5. The lower limits of quantitation of plasma and urine were 2/0.5/0.5 and 20/4/2 ng/mL for M6G/M3G/MOR, respectively. Calibration curves were linear over the concentration ranges of 2-2000/0.5-500/0.5-500 and 20-20,000/4-4000/2-2000 ng/mL for M6G/M3G/MOR in plasma and urine samples, respectively. The precision was <7.14% and the accuracy was within 85-115%. Furthermore, stability of the analytes at various conditions, dilution integrity, extraction recovery and matrix effect were assessed. Finally, this quantitative method was successfully applied to the pharmacokinetic study of M6G injection in Chinese noncancer pain patients.

Sugar Derivatives of Morphine: A New Window for the Development of Potent Anesthetic Drugs

This review provides a short account of carbohydrate derivatives of an important natural drug, morphine, along with their comparative efficacies as anesthetic agent. Sugar derivatives are found to have more prospect as anesthetic drug than morphine itself owing to their enhanced bioavailability. Synthetic schemes of these sugar derivatives and information on related patents are also included in this manuscript.

Effect of 12-oxochenodeoxycholate on the pharmacokinetics and pharmacodynamics of morphine 6-glucuronide in Wistar rats

Objectives

The semi-synthetic bile salt, 12-oxochenodeoxycholate (OCDC also known as 12-monoketocholate), has been shown to enhance drug permeation across biological membranes with low cytotoxicity. Its effect on the analgesic potency and brain concentration of morphine 6-glucuronide (M6G) was studied in male Wistar rats.

Methods

Four groups of animals (n = 8) were given 5, 10 or 20 mg/kg OCDC or normal saline (control) by subcutaneous injection 30 min before a subcutaneous injection of 5 mg/kg M6G after which the hotplate test was performed on each rat at various times. After a 2 week wash-out period, the same rats (n = 30) were randomized to two equal groups and given OCDC (20 mg/kg) or normal saline 30 min before 5 mg/kg M6G. At five time points up to 3 h after M6G administration, three rats from each group were euthanized and blood and brain analyzed for M6G.

Key findings

The area under the analgesic effect versus time curve (AUAE) was found to be significantly (P &lt; 0.05) greater in rats given 20 mg/kg OCDC than in control rats. Area under the curve (AUC) for M6G in both plasma and brain was greater in OCDC-treated rats than in control rats, but the brain : plasma AUC ratio was lower.

Conclusions

OCDC enhances the analgesic effect of M6G but gives a lower brain : plasma ratio due to increasing M6G plasma levels probably by reducing its renal clearance.

Accidental subcutaneous remifentanil infusion as a cause of delayed awakening after craniotomy

We report a case of accidental subcutaneous infusion of remifentanil as a cause of delayed awakening after a craniotomy.

Impact of transporters in oral absorption: a case study of in vitro and in vivo organic anion absorption

A key determinant for oral bioavailability of a drug candidate is the intestinal epithelial permeation of the drug candidate. This intestinal permeation may be affected by interactions on membrane transporters expressed in the intestinal epithelial cells. The purpose of the present study was to investigate whether transporters were involved in the intestinal absorption of an organic anion A275 and to compare the impact of interactions related to transporters in the Caco-2 cell model versus the in vivo rat model of intestinal absorption. In both models, it was investigated whether intestinal permeation of A275 was concentration dependent and affected by inhibitors or competitive organic anions. Interactions related to transporters in intestinal permeation was clearly demonstrated in the Caco-2 cell model but was not directly evident for in vivo rat absorption. However, an observed biphasic in vivo absorption and a large intervariability between rats might mask a dose-dependent absorption of A275. To avoid these suggested interactions, a dose of at least 10 mg/kg, which saturates the intestinal transporters involved in A275 absorption, should be administered, but at doses below that the risk of such drug interactions should be taken into account.

Morphine-6-glucuronide: potency and safety compared with morphine

BACKGROUND

In contemporary medicine, morphine remains the drug of choice in the treatment of severe postoperative pain. Nevertheless, morphine has several side effects, which can seriously compromise its analgesic effectiveness and the patient safety/compliance. The search for opioid analgesics with a better side-effect profile than morphine has led to a morphine metabolites, morphine-6-glucuronide (M6G).

OBJECTIVE

The objectives of the current paper are to give an overview of the analgesic properties of M6G, assess the dose range at which it produces equianalgesia to morphine and explore its side-effect profile.

METHODS

A review of published clinical studies (Phase II - III) on M6G in the treatment of experimental and clinical pain is given.

RESULTS/CONCLUSIONS

M6G > 0.2 mg/kg is an effective analgesic with a slower onset but longer duration of action (> 12 h) compared with morphine. Side effects, most importantly postoperative nausea and vomiting, occur less frequent after M6G treatment. M6G is an attractive alternative to morphine in the treatment of severe postoperative pain.

Pharmacokinetics of morphine-6-glucuronide following oral administration in healthy volunteers

AIM

After oral administration, morphine-6-glucuronide (M6G) displays an atypical absorption profile with two peak plasma concentrations. A proposed explanation is that M6G is hydrolysed to morphine in the colon, which is then absorbed and subsequently undergoes metabolism in the liver to morphine-3-glucuronide (M3G) and M6G. The aims of this study were to confirm and elucidate the biphasic absorption profile as well as clarify the conversion of M6G to morphine after a single oral administration of M6G in healthy volunteers.

METHODS

The study was conducted accordingly to a nonblinded, randomised, balanced three-way crossover design in eight healthy male subjects. The subjects received 200 mg oral M6G, 50 mg oral M6G and 30 mg oral morphine. Blood samples were collected until 72 h after M6G administration and until 9 h after morphine administration. Paracetamol and sulfasalazine were coadministered with M6G as markers for the gut contents reaching the duodenum and colon, respectively.

RESULTS

The plasma concentration peaks of M6G were seen at 4.0 (2.0-6.0) and 18 (12.0-24.0) h after 200 mg M6G and at 3.5 (2.0-6.0) and 21.3 (10.0-23.3) h after 50 mg M6G, which was in agreement with previously published results. The K(M6G_abs)/K(M6G_M6G) ratio was found to be 10.

CONCLUSION

The pharmacokinetic profile of M6G after oral administration was confirmed and with the presence of M3G and morphine in plasma after oral administration of M6G, proof seems to be found of the constant and prolonged absorption of M6G. The K(M6G_abs)/K(M6G_M6G) ratio of 10 indicates that the second absorption peak of M6G consists of approximately 10 times more absorbed M6G than reglucuronidated M6G. However, further studies are required to determine the precise kinetics of the second absorption peak.

Blood-brain distribution of morphine-6-glucuronide in sheep

BACKGROUND AND PURPOSE

At present there are few data regarding the rate and extent of brain-blood partitioning of the opioid active metabolite of morphine, morphine-6-glucuronide (M6G). In this study the cerebral kinetics of M6G were determined, after a short-term intravenous infusion, in chronically instrumented conscious sheep.

EXPERIMENTAL APPROACH

Five sheep received an intravenous infusion of M6G 2.2 mg kg(-1) over a four-minute period. Non-linear mixed-effects analysis, with hybrid physiologically based kinetic models, was used to estimate cerebral kinetics from the arterio-sagittal sinus concentration gradients and cerebral blood flow measurements.

KEY RESULTS

A membrane limited model was selected as the final model. The blood-brain equilibration of M6G was relatively slow (time to reach 50% equilibration of the deep compartment 5.8 min), with low membrane permeability (PS, population mean, 2.5 ml min(-1)) from the initial compartment (V1, 13.7 ml) to a small deep distribution volume (V2) of 18.4 ml. There was some between-animal variability (%CV) in the initial distribution volume (29%), but this was not identified for PS or V2.

CONCLUSION AND IMPLICATIONS

Pharmacokinetic modelling of M6G showed a delayed equilibration between brain and blood of a nature that is primarily limited by permeability across the blood-brain-barrier, in accordance with its physico-chemical properties.

Analgesia and local anesthesia during invasive procedures in the neonate

BACKGROUND

Preterm and full-term neonates admitted to the neonatal intensive care unit or elsewhere in the hospital are routinely subjected to invasive procedures that can cause acute pain. Despite published data on the complex behavioral, physiologic, and biochemical responses of these neonates and the detrimental short- and long-term clinical outcomes of exposure to repetitive pain, clinical use of pain-control measures in neonates undergoing invasive procedures remains sporadic and suboptimal. As part of the Newborn Drug Development Initiative, the US Food and Drug Administration and the National Institute of Child Health and Human Development invited a group of international experts to form the Neonatal Pain Control Group to review the therapeutic options for pain management associated with the most commonly performed invasive procedures in neonates and to identify research priorities in this area.

OBJECTIVE

The goal of this article was to review and synthesize the published clinical evidence for the management of pain caused by invasive procedures in preterm and full-term neonates.

METHODS

Clinical studies examining various therapies for procedural pain in neonates were identified by searches of MEDLINE (1980-2004), the Cochrane Controlled Trials Register (The Cochrane Library, Issue 1, 2004), the reference lists of review articles, and personal files. The search terms included specific drug names, infant-newborn, infant-preterm, and pain, using the explode function for each key word. The English-language literature was reviewed, and case reports and small case series were discarded.

RESULTS

The most commonly performed invasive procedures in neonates included heel lancing, venipuncture, IV or arterial cannulation, chest tube placement, tracheal intubation or suctioning, lumbar puncture, circumcision, and SC or IM injection. Various drug classes were examined critically, including opioid analgesics, sedative/hypnotic drugs, nonsteroidal anti-inflammatory drugs and acetaminophen, injectable and topical local anesthetics, and sucrose. Research considerations related to each drug category were identified, potential obstacles to the systematic study of these drugs were discussed, and current gaps in knowledge were enumerated to define future research needs. Discussions relating to the optimal design for and ethical constraints on the study of neonatal pain will be published separately. Well-designed clinical trials investigating currently available and new therapies for acute pain in neonates will provide the scientific framework for effective pain management in neonates undergoing invasive procedures.

Effect of device inhalational resistance on the three-dimensional configuration of the upper airway

Entrainment and de-aggregation of aerosol particles from dry powder inhalers (DPIs) is achieved by a forceful inhalation from the device by the patient and by the airflow resistance built into the device. The aerodynamic shear stress imposed by the upper airway also plays an important role in the de-aggregation process. In this study the effect of device airflow resistance on the upper airway shape is determined. Seven healthy subjects inhaled via a test inhaler of different resistances (0.2 x 10(5) to 2.2 x 10(5) N(0.5).s.m(-4)) while the upper airway was imaged using magnetic resonance imaging. Decreasing the test inhaler resistance led to an increase in the cross-sectional areas of the upper airway at the oral cavity, oropharynx and larynx, while the cross-sectional areas of the upper trachea remained rather constant. The mean volume of the upper airway also increased from 72 (22) cm3 (mean (SD)) to 101 (25) cm3 by decreasing device airflow resistance from 2.2 x 10(5) to 0.2 x 10(5) N(0.5).s.m(-4). In conclusion, this study shows a significant variation in the shape of the upper airway during inhalation via devices with different resistances. This may aid understanding of drug deposition in the lungs from DPIs.

Synthesis and in vitro biological evaluation of a carbon glycoside analogue of morphine-6-glucuronide

Attachment of a glucose moiety to 6-beta-aminomorphine afforded compound 3, where the glucose moiety was linked to the C-6 nitrogen atom by a two-carbon bridge. The synthesis of 3 was accomplished in eight steps from 3-triisopropylsilyl-6-beta-aminomorphine and 2,3,4,6-tetra-O-benzyl-D-glucose. The C-glycoside 3 was prepared with the objective of examining a metabolically stable analogue of morphine-6-glucuronide and determining the potency and selectivity of opioid receptor binding. Competition binding assays showed that 3 bound to the mu opioid receptor with a Ki value of 3.5 nM. The C-glycoside 3 exhibited delta/mu and kappa/mu selectivity ratios of 76 and 165, respectively. The synthetic intermediate (i.e., benzyl precursor, compound 11) bound to the mu opioid receptor with a Ki value of 0.5 nM, was less selective for the mu opioid receptor. The [35S]GTPgammaS assay was used to evaluate the functional properties of compounds 3 and 11. Compound 3 was determined to be a full agonist at the mu opioid receptor, whereas compound 11 was found to be a partial agonist. Compound 3 was determined to be very stable in the presence of human liver S9, and rat and monkey liver microsomes: no detectable loss of 3 was observed up to 90 min. Compound 3 was also very stable at pH 2 and pH 7.4, suggesting that 3 possessed properties for sustained duration of action.

Morphine-6-glucuronide: Actions and mechanisms

Morphine-6-glucuronide (M6G) appears to show equivalent analgesia to morphine but to have a superior side-effect profile in terms of reduced liability to induce nausea and vomiting and respiratory depression. The purpose of this review is to examine the evidence behind this statement and to identify the possible reasons that may contribute to the profile of M6G. The vast majority of available data supports the notion that both M6G and morphine mediate their effects by activating the micro-opioid receptor. The differences for which there is a reasonable consensus in the literature can be summarized as: (1) Morphine has a slightly higher affinity for the micro-opioid receptor than M6G, (2) M6G shows a slightly higher efficacy at the micro-opioid receptor, (3) M6G has a lower affinity for the kappa-opioid receptor than morphine, and (4) M6G has a very different absorption, distribution, metabolism, and excretion (ADME) profile from morphine. However, none of these are adequate alone to explain the clinical differences between M6G and morphine. The ADME differences are perhaps most likely to explain some of the differences but seem unlikely to be the whole story. Further work is required to examine further the profile of M6G, notably whether M6G penetrates differentially to areas of the brain involved in pain and those involved in nausea, vomiting, and respiratory control or whether micro-opioid receptors in these brain areas differ in either their regulation or pharmacology.

Synthesis and biological evaluation of some 6-arylamidomorphines as analogues of morphine-6-glucuronide

A series of 6-beta-arylamidomorphines was synthesized and biologically evaluated. Various aryl substituents were introduced into the arylamidomorphines to examine substituent structure-activity relationships. Competition binding assays showed that compounds 10a-h bound to the mu opioid receptor with high affinity (0.2-0.6 nM). Functional assays showed that compounds 10a-h acted as full mu opioid receptor agonists. The ED(50) of compound 10e.HCl as an analgesic was 12.6 mg/kg in the tail flick latency test in the rat.

Design, Chemical Synthesis, and Biological Evaluation of Thiosaccharide Analogues of Morphine- and Codeine-6-Glucuronide

A series of 6-beta-thiosaccharide analogues of morphine-6-glucuronide (M6G) and codeine-6-glucuronide (C6G) were synthesized and evaluated with the objective of preparing an analogue of M6G with improved biological activity. The affinity of the thiosaccharide analogues of M6G and C6G was examined by competitive binding assays at mu, delta, and kappa opioid receptors. The thiosaccharide compounds in the morphine series 5b, 5e, 6a, and 6c showed 1.5-2.4-fold higher affinity for the mu receptor than M6G, but were generally less selective than M6G. The functional activity of the M6G and C6G analogues was examined with the [35S]GTP-gamma-S assay. Compounds 5b and 5e were determined to be full mu agonists, whereas compounds 6a and 6c were partial mu agonists. The in vivo antinociceptive activity of compound 5b was evaluated by the tail flick latency test, giving an ED50 of 2.5 mg/kg.

Developmental pharmacokinetics of morphine and its metabolites in neonates, infants and young children

BACKGROUND

Descriptions of the pharmacokinetics and metabolism of morphine and its metabolites in young children are scant. Previous studies have not differentiated the effects of size from those related to age during infancy.

METHODS

Postoperative children 0-3 yr old were given an intravenous loading dose of morphine hydrochloride (100 micro g kg(-1) in 2 min) followed by either an intravenous morphine infusion of 10 micro g h(-1) kg(-1) (n=92) or 3-hourly intravenous morphine boluses of 30 micro g kg(-1) (n=92). Additional morphine (5 micro g kg(-1)) every 10 min was given if the visual analogue (VAS, 0-10) pain score was >/=4. Arterial blood (1.4 ml) was sampled within 5 min of the loading dose and at 6, 12 and 24 h for morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). The disposition of morphine and formation clearances of morphine base to its glucuronide metabolites and their elimination clearances were estimated using non-linear mixed effects models.

RESULTS

The analysis used 1856 concentration observations from 184 subjects. Population parameter estimates and their variability (%) for a one-compartment, first-order elimination model were as follows: volume of distribution 136 (59.3) litres, formation clearance to M3G 64.3 (58.8) litres h(-1), formation clearance to M6G 3.63 (82.2) litres h(-1), morphine clearance by other routes 3.12 litres h(-1) per 70 kg, elimination clearance of M3G 17.4 (43.0) litres h(-1), elimination clearance of M6G 5.8 (73.8) litres h(-1). All parameters are standardized to a 70 kg person using allometric 3/4 power models and reflect fully mature adult values. The volume of distribution increased exponentially with a maturation half-life of 26 days from 83 litres per 70 kg at birth; formation clearance to M3G and M6G increased with a maturation half-life of 88.3 days from 10.8 and 0.61 litres h(-1) per 70 kg respectively at birth. Metabolite formation decreased with increased serum bilirubin concentration. Metabolite clearance increased with age (maturation half-life 129 days), and appeared to be similar to that described for glomerular filtration rate maturation in infants.

CONCLUSION

M3G is the predominant metabolite of morphine in young children and total body morphine clearance is 80% that of adult values by 6 months. A mean steady-state serum concentration of 10 ng ml(-1) can be achieved in children after non-cardiac surgery in an intensive care unit with a morphine hydrochloride infusion of 5 micro g h(-1) kg(-1) at birth (term neonates), 8.5 micro g h(-1) kg(-1) at 1 month, 13.5 micro g h(-1) kg(-1) at 3 months and 18 micro g h(-1) kg(-1) at 1 year and 16 micro g h(-1) kg(-1) for 1- to 3-yr-old children.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

The pharmacokinetics of the interstitial space in humans

BACKGROUND

The pharmacokinetics of extracellular solutes is determined by the blood-tissue exchange kinetics and the volume of distribution in the interstitial space in the different organs. This information can be used to develop a general physiologically based pharmacokinetic (PBPK) model applicable to most extracellular solutes.

METHODS

The human pharmacokinetic literature was surveyed to tabulate the steady state and equilibrium volume of distribution of the solutes mannitol, EDTA, morphine-6-glucuronide, morphine-3-glucuronide, inulin and beta-lactam antibiotics with a range of protein binding (amoxicillin, piperacillin, cefatrizine, ceforanide, flucloxacillin, dicloxacillin). A PBPK data set was developed for extracellular solutes based on the literature for interstitial organ volumes. The program PKQuest was used to generate the PBPK model predictions. The pharmacokinetics of the protein (albumin) bound beta-lactam antibiotics were characterized by two parameters: 1) the free fraction of the solute in plasma; 2) the interstitial albumin concentration. A new approach to estimating the capillary permeability is described, based on the pharmacokinetics of the highly protein bound antibiotics.

RESULTS

About 42% of the total body water is extracellular. There is a large variation in the organ distribution of this water - varying from about 13% of total tissue water for skeletal muscle, up to 70% for skin and connective tissue. The weakly bound antibiotics have flow limited capillary-tissue exchange kinetics. The highly protein bound antibiotics have a significant capillary permeability limitation. The experimental pharmacokinetics of the 11 solutes is well described using the new PBPK data set and PKQuest.

CONCLUSIONS

Only one adjustable parameter (systemic clearance) is required to completely characterize the PBPK for these extracellular solutes. Knowledge of just this systemic clearance allows one to predict the complete time course of the absolute drug concentrations in the major organs. PKQuest is freely available http://www.pkquest.com.

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.