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Biomedical subjects

Jörn Lötsch

Publications and source records attributed to Jörn Lötsch.

At least 19 recordsLinked to original sources
PubMed2006

GTP cyclohydrolase and tetrahydrobiopterin regulate pain sensitivity and persistence.

We report that GTP cyclohydrolase (GCH1), the rate-limiting enzyme for tetrahydrobiopterin (BH4) synthesis, is a key modulator of peripheral neuropathic and inflammatory pain. BH4 is an essential cofactor for catecholamine, serotonin and nitric oxide production. After axonal injury, concentrations of BH4 rose in primary sensory neurons, owing to upregulation of GCH1. After peripheral inflammation, BH4 also increased in dorsal root ganglia (DRGs), owing to enhanced GCH1 enzyme activity. Inhibiting this de novo BH4 synthesis in rats attenuated neuropathic and inflammatory pain and prevented nerve injury-evoked excess nitric oxide production in the DRG, whereas administering BH4 intrathecally exacerbated pain. In humans, a haplotype of the GCH1 gene (population frequency 15.4%) was significantly associated with less pain following diskectomy for persistent radicular low back pain. Healthy individuals homozygous for this haplotype exhibited reduced experimental pain sensitivity, and forskolin-stimulated immortalized leukocytes from haplotype carriers upregulated GCH1 less than did controls. BH4 is therefore an intrinsic regulator of pain sensitivity and chronicity, and the GTP cyclohydrolase haplotype is a marker for these traits.

Adult↗
PubMed2006

The clinical significance of electrophysiological measures of olfactory function.

AIM: To establish the detectability of olfactory event-related potentials (OERP) in relation to the results from psychophysical tests of olfactory function. METHODS: Fifty-nine men and 64 women (aged 19-89 years) participated all of whom presented themselves to a specialized "Smell and Taste Clinic" because of chemosensory complaints. Their olfactory function was assessed by means of psychophysical tests, e.g., assessment of odor threshold, odor discrimination, and odor identification, which were combined in a composite "Threshold Discrimination Identification" score ("TDI score"). OERP were obtained in response to the olfactory stimulant phenyl ethyl alcohol; their presence/absence was judged by a trained observer. Using logistic regression the TDI score was calculated in relation to the subjects' olfactory function at which the probability of the presence of OERP became greater than chance. RESULTS: Based on psychophysical tests, 40 subjects were diagnosed with functional anosmia, 40 with hyposmia, and 43 subjects scored within the normal range. Causes of hyposmia and anosmia included congenital anosmia, Parkinson's disease, head trauma, infections of the upper respiratory tract, and sinunasal disease. A TDI score of 22.6 equivalent to "pronounced hyposmia" was identified as the turning point at which the probability of detection of OERP was higher than 50%. Its 95% confidence interval of 16.1-27.8 well reflected the range of hyposmia, i.e., was above significant loss of olfactory function (functional anosmia, TDI score<15.5) and below normal olfactory function (TDI score>30.5). CONCLUSION: The present results indicate that the probability to detect an OERP becomes greater than 50% within a range of olfactory function that separates functional anosmia from normosmia. Presence of OERP clearly signifies presence of olfactory function while this is not always the other way around with absence of OERP.

Adult↗
PubMed2006

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.

Adult↗
PubMed2006

Modulation of the central nervous effects of levomethadone by genetic polymorphisms potentially affecting its metabolism, distribution, and drug action.

AIM: Our aim was to judge the importance of candidate pharmacogenetic modulators of the central nervous effects of levomethadone by both magnitude of the modulatory effect and frequency of the mutation to assess the utility of genotyping for clinical levomethadone therapy in a random sample of subjects that, by distribution of genotypes, resembled the clinical setting. METHODS: Candidate pharmacogenetic modulators were polymorphisms reported to be of functional consequence and therefore potentially important for metabolism, distribution, or pharmacodynamic action of levomethadone, consisting of genes coding for cytochrome P450 (CYP) 2B6 and 3A, as well as 1A2, 2C8, 2C9, 2C19, and 2D6, for P-glycoprotein (ABCB1), and for mu-opioid receptors (OPRM1). The central nervous effects of levomethadone were investigated by means of measuring pupil size in a random sample of 51 healthy volunteers for 9 hours after oral administration of 0.075 mg/kg levomethadone. Plasma concentrations of levomethadone and its metabolites were assessed concomitantly, and to judge the role of metabolites, the affinities of levomethadone and its metabolites at mu-opioid receptors were estimated by use of displacement of the selective mu-opioid receptor agonist [(3)H]-DAMGO ((3)H-[D-Ala(2),N-MePhe(4),Gly-ol(5)]-enkephalin). RESULTS: Pupil size decreased to -41.8% +/- 9.6% from baseline at 3.5 +/- 1.1 hours after levomethadone administration. Miosis was still manifest to a lower degree (-25.1% +/- 12.3%) at the end of the observation period. In carriers of the variant 118G allele (118A>G single-nucleotide polymorphism) of the mu-opioid receptor gene (OPRM1), levomethadone had a 1.74 times (95% confidence interval, 1.4-2.2 times) lower miotic potency (P < .001) as compared with noncarriers (concentration at half-maximum effects, 52.3 nmol/L; 95% confidence interval, 36.7-66.2 nmol/L). The maximum percent decrease in pupil diameter from baseline was 44.9% +/- 7.6%, 33% +/- 6.5%, and 24% +/- 6.9% for carriers of the OPRM1 118AA, AG, and GG genotypes, respectively (P < .001 for AG and GG versus wild type, without significant differences between AG and GG). Other candidate polymorphisms in the ABCB1 or in CYP genes had no significant influence on the effects of levomethadone, either because of lack of functional consequences or because of their low allelic frequency. The metabolites of levomethadone did not contribute to the effects as indicated by low metabolite plasma concentrations and their 120- to 1300-fold lower affinities at mu-opioid receptors as compared with levomethadone. CONCLUSIONS: Among polymorphisms in OPRM1, ABCB1, and CYP genes previously associated with functional consequences in a different context, the most important pharmacogenetic factor modulating the short-term effects of levomethadone is a polymorphism (OPRM1 118A>G) affecting mu-opioid receptors.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

The cyclooxygenase 2 genetic variant -765G>C does not modulate the effects of celecoxib on prostaglandin E2 production.

OBJECTIVE: Our objective was to assess the role of the reportedly functional PTGS2 (prostaglandin-endoperoxide synthase 2/cyclooxygenase [COX] 2) promoter mutation -765G>C for the COX-2-inhibiting effects of celecoxib. METHODS: Twenty healthy carriers of the -765GG genotype and -765CC genotype (n = 10 each) received 200 mg of celecoxib orally. Blood samples were drawn at baseline and at 1, 3, 6, 9, and 24 hours after administration. Plasma concentrations of celecoxib and concentrations of prostaglandin E(2) (PGE(2)) produced by peripheral blood monocytes stimulated ex vivo with bacterial lipopolysaccharide (LPS) were analyzed by liquid chromatography-tandem mass spectrometry. Expression of COX-2 messenger ribonucleic acid and protein expression with and without LPS stimulation were analyzed by real-time polymerase chain reaction and Western blotting, respectively. RESULTS: LPS induced PGE(2) production (P < .001), and celecoxib reduced PGE(2) production from 19.3 +/- 7.2 ng/mL at baseline to 7.4 +/- 4.8 ng/mL at 1 hour (P < .001). The effect of celecoxib lasted for 9 hours (repeated-measures ANOVA, P .28). LPS up-regulated COX-2 messenger ribonucleic acid expression (P = .016) but was independent of genotype (P = .36). COX-2 protein expression was similar for both -765G>C genotypes (P = .63). CONCLUSION: The PTGS2 -765G>C single-nucleotide polymorphism does not modulate COX-2 inhibitory effects of celecoxib as assessed by an ex vivo whole blood assay. Thus the results indicate the need for further investigation toward PTGS2 pharmacogenetics-based prescription of celecoxib.

Adult↗
PubMed2006

The human mu-opioid receptor gene polymorphism 118A > G decreases cortical activation in response to specific nociceptive stimulation.

The authors sought to investigate the role of a common single nucleotide polymorphism in the mu-opioid receptor gene (OPRM1) 118A > G for nociceptive sensory processing using event-related potentials (ERPs). Specific nociceptive (carbon dioxide [CO-sub-2]: 40% volume-to-volume [vol/vol] and 60% vol/vol) and nonnociceptive (hydrogen sulfide, 2 parts per million [ppm] and 4 ppm) stimuli were applied to the nasal mucosa of 45 volunteers. ERPs were recorded from a central lead. In this random sample, we found 37 noncarriers, 7 heterozygous carriers, and 1 homozygous carrier of the variant OPRM1 118G allele (allelic frequency, 10%). Amplitudes of nociceptive ERP in carriers of this allele were, on average, half as high as those of noncarriers. In discriminant analysis, ERP amplitude N1 response to the weaker nociceptive stimuli was the only ERP parameter that discriminated statistically significantly between carriers and noncarriers of the variant 118G allele. On the basis of N1-CO-sub-2 (40% vol/vol), the authors correctly backclassified 68.6% of the cases as carriers or noncarriers of the allele. The OPRM1 118A > G polymorphism specifically modulates nociceptive but not nonnociceptive cortical activation.

Adult↗
PubMed2006

The mu-opioid receptor gene polymorphism 118A>G depletes alfentanil-induced analgesia and protects against respiratory depression in homozygous carriers.

AIM: To investigate whether OPRM1 118A>G polymorphism affects analgesic and respiratory depressive effects of alfentanil and assess its role for the therapeutic range of alfentanil. METHODS: In an open-label, single-occasion design, 10 non-carriers, four heterozygous and six homozygous carriers of the variant OPRM1 118G allele received a computerized infusion of alfentanil to achieve target effect-site concentrations of 0, 33.33, 66.67 and 100 ng/ml. At each concentration level, analgesia was assessed by means of electrically and chemically induced pain, and respiratory depression was quantified by hypercapnic challenge and breathing frequency. RESULTS: The relationship between the percent change of tolerance to electrical stimuli and measured alfentanil concentrations, described by power models, was flatter in carriers of the 118G variant allele than in non-carriers, indicating decreased opioid analgesia (P<0.05). For chemically induced pain, a flatter analgesia versus concentration relationship was found only for homozygous carriers of the 118G allele (P<0.05). The relationship between the percent changes in respiratory parameters was significantly flatter (P<0.01) only in homozygous carriers as compared to heterozygous carriers and non-carriers of the 118G allele. Higher alfentanil concentrations were needed in homozygous carriers as compared to wild-type subjects (2-4 times) to produce the same degree of analgesia, whereas 10-12 times higher alfentanil concentrations were needed to produce the same degree of respiratory depression. CONCLUSION: OPRM1 118A>G polymorphism affects both analgesic and respiratory depressive effects of alfentanil. However, while the analgesic effects are already partly decreased in heterozygous carriers, depending on the pain model, the respiratory depressive effects are decreased in homozygous carriers of the variant 118G allele. The therapeutic range of alfentanil was only broadened in homozygous carriers.

Adult↗
PubMed2006

Clinical significance of results from olfactory testing.

BACKGROUND: Although widely used in healthy subjects and patients with olfactory loss, the significance of changes of scores from validated olfactory tests is unknown. AIM AND METHODS: The aim of the present study was to relate the self-assigned changes of olfactory function in terms of "better," "unchanged," and "worse" in patients with smell disorders with the results from olfactory testing by means of a validated test set. Olfactory function of 83 anosmic or hyposmic patients (40 women, 43 men; age 12-84 yr) was tested on two occasions (mean interval 136 days, minimum 7 days, maximum 6.7 yr). Olfactory function was assessed using a validated technique ("Sniffin' Sticks"). This test consists of three subtests, one for odor threshold (T), odor discrimination (D), and odor identification (I), with possible results ranging up to 16 points each. From the sum of the results from the three subtests a composite "TDI" score was obtained. RESULTS: Forty-four patients indicated an improvement of olfactory function, whereas 39 patients reported no change. No subject reported deterioration of olfactory sensitivity. Subjects assigned to group BETTER had higher TDI scores in the second olfactory tests than subjects assigned to the group UNCHANGED, both in absolute terms and as compared with the first olfactory test (effect "test occasion" by "self-assessed improvement," P < .001). There was no significant difference between groups with respect to age and sex (P = .99 and .84, respectively). Logistic regression showed that more than 60% of the subjects reported an improvement of olfactory sensitivity when the TDI score increased by 5.5 points. CONCLUSION: We show that there is a statistically significant relation between measured and perceived improvement of olfactory function in patients who first presented with the diagnosis of anosmia or hyposmia. The results indicate that improved olfactory function in patients with olfactory deficiency is perceived as such in everyday life and is quantitatively related to an improvement in the composite TDI score of the "Sniffin' Sticks" olfactory test battery. This is the basis for the application of a specific therapy for olfactory loss because of a possible gain in quality of life for the patients.

Adolescent↗
PubMed2006

Nimodipine plasma concentration and retinal blood flow in healthy subjects.

PURPOSE: Calcium antagonists are strong vasodilators, and nimodipine is known to improve cerebral blood flow. The purpose of this study was to measure retinal blood flow and nimodipine plasma concentrations during repeated oral dosing. METHODS: In a double-blind, two-way, crossover study, 20 healthy subjects (mean age, 22.8 +/- 3.7 years) underwent examination of retinal perfusion and nimodipine plasma concentrations. In a placebo-controlled fashion, nimodipine was orally administered at a dosage of 30 mg three times a day for two periods of 5 days including a 9-day washout interval. At days 1, 5, 15, and 19, plasma concentrations of nimodipine and retinal perfusion were measured 11 times within 3 hours. Stereoselective analysis of nimodipine plasma concentrations was performed with the use of liquid chromatography-tandem mass spectrometry. Scanning laser Doppler flowmetry was used to measure the microcirculation of the juxtapapillary retina. Perfusion images were evaluated with the automatic full-field evaluation procedure (AFFPIA). RESULTS: Areas under the plasma concentration versus time curves were similar at day 1 and day 5 of nimodipine administration (t test: P = 0.64). Values of C(max) displayed a large interindividual variance and ranged from 0 ng/mL to 57.5 ng/mL. On average, maximum nimodipine plasma concentrations (C(max)) were 16.6 +/- 14.9 ng/mL and 12.0 +/- 10.3 ng/mL at day 1 and day 5, respectively (P = 0.068). They were observed at 81 +/- 50 and at 93 +/- 40 minutes (t(max)) after the administration of nimodipine at day 1 and day 5, respectively (P = 0.43). Retinal microcirculation was greater after nimodipine than after placebo, as reflected in significantly larger areas under the curves of percentage change in blood flow from baseline versus time (P < 0.01). The maximum increase of retinal blood flow from baseline was significantly more pronounced after nimodipine (28.5% +/- 14.4% and 39.6% +/- 21.4% at day 1 and day 5, respectively) than after placebo (20.5% +/- 16.8% and 31.9% +/- 14.6% at day 1 and day 5, respectively; P = 0.032). CONCLUSIONS: Oral nimodipine significantly increases retinal perfusion in healthy subjects.

Administration, Oral↗
PubMed2006

Fatal respiratory depression after multiple intravenous morphine injections.

A 26-year-old female was treated with morphine within the first 2 hours after knee surgery, in an attempt to titrate analgesia. The patient received a total of four intravenous injections of morphine 35 mg in total. Soon after the last injection the patient had adequate pain relief, was in a good clinical state and had adequate blood oxygenation. However, 40 minutes later, the patient had a deep respiratory depression followed by a fatal cardiac arrest. Solving the case in a medico-legal context was possible by applying results of clinical pharmacokinetic research on opioid analgesics, most importantly morphine, to this particular clinical case. This knowledge made it possible to estimate the probable concentrations of morphine at the site of its effect, the brain, during the time of the fatal event, and to show that these concentrations could have produced respiratory depression. We mainly attribute the fatal intoxication of morphine to the lag period needed for the transfer of morphine across the blood-brain barrier. Because of its slow transfer between plasma and the effect site, the CNS effects of morphine are delayed from its plasma concentrations to a clinically relevant degree. Successive injections at short intervals of relatively high amounts of morphine increase the clinical relevance of this delay. The present report demonstrates an important application of clinical pharmacokinetics for explaining clinical observations at a scientific level and transferring theoretical knowledge from clinical pharmacokinetics into daily clinical practice as a basis for rational opioid selection.

Adult↗
PubMed2006

Rapid identification of three functionally relevant polymorphisms in the OATP1B1 transporter gene using Pyrosequencing.

INTRODUCTION: Clinical evidence suggests there are three single nucleotide polymorphisms (SNPs) of the solute carrier organic anion transporter family member B1 (SLCO1B1) gene for which in vivo evidence for a functional relevance for organic anion transporter polypeptides subgroup C (OATP1B1, formerly OATP-C) has been provided. These genetic variants have been shown to lead to altered pharmacokinetics of OATP1B1 substrates, mainly pravastatin, but also the irinotecan metabolite SN-38, estrone-3-sulfate, and estradiol-17beta-glucuronide. The authors therefore developed reliable and quick screening assays to identify the SLCO1B1 SNPs -11187G>A, 388A>G and 521T>C, in order to facilitate the judgment of their clinical role and to identify allelic frequencies of SNPs and haplotypes in a Caucasian random sample. METHODS: Three simplex Pyrosequencing assays were developed and the three selected SLCO1B1 SNPs were screened for in 250 DNA samples from healthy young female and male unrelated volunteers of Caucasian ethnicity. SLCO1B1 haplotypes involving DNA positions -11187, 388 and 521 were identified by in silico haplotyping. RESULTS: A clear identification of the three single nucleotide polymorphisms in the 250 DNA samples was possible and was verified by routine implementation of 40 control samples obtained by conventional sequencing. The frequencies of the variant alleles -11187A, 388G and 521C were 0.09, 0.47 and 0.12, respectively. All observed frequencies of heterozygous of homozygous carriers of SLCO1B1 alleles were in agreement with the Hardy-Weinberg equilibrium. SLCO1B1 haplotypes reportedly associated with altered substrate pharmacokinetics, i.e., SLCO1B1*15B (-11187G/388G/521C) and *17 (-11187A/388G/521C), were found at allelic frequencies of 0.09 and 0.02, respectively. CONCLUSION: The presently developed Pyrosequencing assays allowed for quick and reliable identification of those SLCO1B1 SNPs that had been proposed to cause functional alternations in OATP1B1 with shown consequences for the pharmacokinetics of drugs that are OATP1B1 substrates.

Adult↗
PubMed2006

Pyrosequencing-based screening for genetic polymorphisms in cytochrome P450 2B6 of potential clinical relevance.

OBJECTIVES: Three exonic single nucleotide polymorphisms (SNPs) in the cytochrome P450 2B6 (CYP2B6) gene, 516G>T, 785A>G and 1459C>T, have been described to be associated with functional changes in the CYP2B6 catalytic activity or protein expression. They are therefore of potential clinical importance for drug efficacy and safety of CYP2B6 substrates, in particular of antiretroviral therapy regimes that include efavirenz. Therefore, we aimed at providing genetic screening assays for these three SNPs. METHODS: Simplex Pyrosequencing assays were developed for the selected CYP2B6 SNPs. A total of 273 DNA samples from healthy volunteers of Caucasian ethnicity were genotyped. RESULTS: The presently developed Pyrosequencing assays afford an accurate determination of the three SNPs in the 273 DNA samples. The assays were verified by routine implementation of control samples obtained by conventional sequencing. The frequencies for the variant alleles 516T, 785G and 1459T were 0.22, 0.24 and 0.13, respectively. All genotype frequencies were in agreement with the Hardy-Weinberg equilibrium. CYP2B6 alleles CYP2B6*5A (1459T), CYP2B6*6 (516T/785G) and *7B (516T/785G/1459T) were found at allelic frequencies of 0.12, 0.20 and 0.01. CONCLUSION: The present reliable and quick Pyrosequencing assays afford facilitating future research on the importance of CYP2B6 pharmacogenetics for personalized drug therapy with CYP2B6 substrates.

Adult↗
PubMed2005

Rapid genotyping for relevant CYP1A2 alleles by pyrosequencing.

OBJECTIVE: To develop a rapid and reliable screening method for identifying the relevant cytochrome P450 (CYP) 1A2 alleles CYP1A2*1D (-2467Tdel), *1F (-163A>C), and *1K (-739T>G, -729C>T, -163A>C) that are in linkage disequilibrium with the functionally relevant CYP1A2 polymorphisms and therefore are considered to be predictive for the CYP1A2 phenotype. METHODS: CYP1A2 single nucleotide polymorphisms (SNPs) -2467Tdel, -739T>G, -729C>T, and -163A>C were screened for in 495 healthy Caucasian volunteers using newly developed pyrosequencing duplex and simplex assays. Conventional sequencing of randomly selected samples served as quality control. RESULTS: Frequencies were 7.9% for CYP1A2*1D, 31.8% for *1F, and 0.4% for *1K. The observed distribution of homozygous and heterozygous carriers of the alleles corresponded to the predicted one according to the Hardy-Weinberg law. It also corresponded to reported allelic frequencies from Caucasians but differed significantly from the distribution seen in other ethnicities. The most frequent haplotype was -2467T/-739T/-729C/-163A (allelic frequency 61.6%), followed by -2467T/-739T/-729C/-163C (30.5%), -2467Tdel/-739T/-729C/-163A (5.1%), -2467Tdel/-739G/-729C/-163A (1.2%), and -2467Tdel/-739T/-729C/-163C (1.1%). Complete linkage disequilibrium (value of D' nearly 1) existed between -2467Tdel, -739T>G, and -729C>T and between -729T>G and -163A>C. CONCLUSIONS: Pyrosequencing facilitates rapid and reliable detection of those CYP1A2 alleles that, based on current knowledge, can be considered predictive for the CYP1A2 phenotype.

Alleles↗
PubMed2005

The 5-hydroxytryptamine 4 receptor agonist mosapride does not antagonize morphine-induced respiratory depression.

BACKGROUND: On the basis of experiments in rats, serotonin 4 receptor (5-hydroxytryptamine 4 [5-HT4]) agonists have been proposed as a novel therapeutic strategy for the selective treatment of respiratory depression caused by opioids while leaving analgesic effects unaffected. The effects in rats have been seen with the 5-hydroxytryptamine 4a (5-HT4a) agonist BIMU8, which is currently not available for use in humans. METHODS: In a proof-of-applicability study, the clinically recommended dose of 5 mg mosapride, currently the only 5-HT4 agonist available for clinical use, was given in a placebo-controlled manner 3 times daily for 5 days to 12 healthy men and women. During the actual experiments, a further 15 mg mosapride was administered. After baseline measurements of respiratory depression, by use of a carbon dioxide rebreathing method, and of pain, by use of electrical and chemical pain stimuli, 30 mg morphine per 70 kg body weight was administered intravenously within 2 hours. After assessment of respiratory depression and pain, 2 mg naloxone was intravenously administered within 20 minutes, followed by a third assessment of respiratory depression and pain. In ancillary experiments 10 rats received 100 mg/kg mosapride orally or placebo 50 minutes before intraperitoneal injection of 10 mg/kg morphine, followed 20 minutes later by injection of naloxone, and the respiratory frequency was monitored. RESULTS: With placebo coadministration, the slope of the relationship between expiratory volume and CO2 concentration in the inspired air was significantly reduced, from 1.11 +/- 0.46 L/mm Hg CO2 at baseline to 0.39 +/- 0.25 L/mm Hg CO2 at the end of the morphine infusion (P < .001). Coadministration of mosapride had no effect on respiratory depression induced by morphine (slope of 0.39 +/- 0.19 L/mm Hg CO2, P > .7). In contrast, naloxone significantly reversed the slope to 0.78 +/- 0.36 L/mm Hg CO2 (P = .001). Morphine produced significant effects on electrical and chemical pain stimuli, which were partially reversed by naloxone, but mosapride did not affect the analgesic effects of morphine. In rats mosapride similarly failed to prevent a slowing of the breathing frequency after morphine administration but naloxone reversed the respiratory depression. CONCLUSION: Our results show that, with mosapride, opioid-induced respiratory depression cannot be prevented, and because other 5-HT4 agonists are not currently available for clinical use, a cure for opioid-induced respiratory depression as promised by the previous successful experiments in laboratory animals is not yet available in clinical practice.

Adult↗
PubMed2005

Opioid metabolites.

The metabolism of opioids closely relates to their chemical structure. Opioids are subject to O-dealkylation, N-dealkylation, ketoreduction, or deacetylation leading to phase-I metabolites. By glucuronidation or sulfatation, phase-II metabolites are formed. Some metabolites of opioids have an activity themselves and contribute to the effects of the parent compound. This can go as far that the main clinical activity is exerted through active metabolites while the parent compounds are only weak agonist at mu-opioid receptors, as in the case of codeine and tilidine. The clinical effects of tramadol also involve an important contribution of its active metabolite. With morphine, the active metabolite morphine-6-glucuronide exerts important clinical opioid effects when it accumulates in the plasma of patients with renal failure. However, after short-term administration of morphine, its contribution to the central nervous effects of morphine is probably poor. Morphine-6-glucuronide has recently been identified to exert important peripheral opioid effects. By this, it may play an important role in the clinical effects of morphine. Several other opioids, such as meperidine and perhaps also morphine and hydromorphone, produce metabolites with neuroexcitatory effects. In sum, the evidence suggests that the metabolites of several opioids account for an important part of the clinical effects that must be considered in clinical practice.

Animals↗
PubMed2005

Pharmacokinetic-pharmacodynamic modeling of opioids.

The effects of opioids usually parallel the plasma concentrations but with a temporal shift. This temporal shift differs between opioids. It is small with alfentanil or remifentanil and very long with the active metabolite of morphine, morphine-6-glucuronide (M6G). The mathematical and experimental techniques for modeling these pharmacokinetic-pharmacodynamic (PK/PD) relationships were developed in the late 1970s. The delay between plasma concentrations and effects is accounted for by the introduction of a hypothetic effect compartment, which is linked to the plasma compartment by a first-order transfer function with a rate constant k(e0). The effects are then linked to the concentrations at effects site by standard pharmacodynamic models such as sigmoid ("E(max)") models or power models, depending on the actual effect measure. These principles were first applied to the opioids fentanyl and alfentanil in 1985. Since then, PK/PD of opioids have been repeatedly assessed, using EEG derived parameters, pupil size, and experimental and clinical pain as effect measures. The opioids of the fentanyl group, methadone, morphine, and piritramid, are today well characterized with respect to their PK/PD properties. Alfentanil and remifentanil are very fast equilibrating opioids with equilibration half-lives between plasma and effect site of about 1 minute. They are followed by fentanyl and sufentanil, each with equilibration half-lives of about 6 min. Methadone equilibrates with a half-life of about 8 min. Morphine, in contrast, equilibrates with a half-life of 2-3 h. The slowest opioid with respect to plasma-effect site transfer is M6G, with an equilibration half-life of about 7 h. PK/PD modeling has advanced the understanding of the time course of the clinical effects of opioids after various dosing regimens. It may provide a rational basis for the selection of opioids in clinical circumstances. PK/PD modeling of opioids may also be employed for the design and the interpretation of experiments addressing clinical effects of opioids.

Humans↗