Evaluation of the nonparametric estimation method in nonmem VI: application to real data

The aim of the study was to evaluate the nonparametric estimation methods available in NONMEM VI in comparison with the parametric first-order method (FO) and the first-order conditional estimation method (FOCE) when applied to real datasets. Four methods for estimating model parameters and parameter distributions (FO, FOCE, nonparametric preceded by FO (FO-NONP) and nonparametric preceded by FOCE (FOCE-NONP)) were compared for 25 models previously developed using real data and a parametric method. Numerical predictive checks were used to test the appropriateness of each model. Up to 1000 new datasets were simulated from each model and with each method to construct 90% and 50% prediction intervals. The mean absolute error and the mean error of the different outcomes investigated were computed as indicators of imprecision and bias respectively and formal statistical tests were performed. Overall, less imprecision and less bias were observed with nonparametric methods than with parametric methods. Across the 25 models, t-tests revealed that imprecision and bias were significantly lower (P < 0.05) with FOCE-NONP than with FOCE for half of the NPC outcomes investigated. Improvements were even more pronounced with FO-NONP in comparison with FO. In conclusion, when applied to real datasets and evaluated by numerical predictive checks, the nonparametric estimation methods in NONMEM VI performed better than the corresponding parametric methods (FO or FOCE).     

Patterns of use,desired effects,and mental health status of a sample of natural psychoactive drug users

Abstract

In recent years, the use of natural psychoactive drugs (NPDs) has grown rapidly. They are classified as new psychoactive substances (NPSs), despite the reality that they have been used for centuries. We are lacking information regarding patterns of use or characteristics of users, but some evidence suggests that NPDs substantially differ from NPSs in terms of both their safety profile and patterns of use. The aim of this study was to investigate patterns of use and user characteristics by collecting data from a sample of NPD users. We designed an online questionnaire that was shared through social media. A sample of 564 NPD users was recruited from 52 different countries, with the United States being the most common (19%), followed by Spain (14.9%). The typical user in our sample is a well-educated adult individual who uses NPDs sporadically. The most used substances were Psilocybe mushrooms (88.5%) and ayahuasca (51%). Users reported that the use of NPDs positively influenced their lives, and they showed a good mental health status. Stakeholders should consider these results particularly when deciding on legal classifications for these substances, as the study findings suggest that NPDs should not be in the same class as NPSs.     

Differential inhibition of hepatic and duodenal sulfation of (−)-salbutamol and minoxidil by mefenamic acid

Objective: The aim of this investigation was to determine whether mefenamic acid and salicylic acid inhibit the sulfation of (−)-salbutamol and minoxidil in the human liver and duodenum, and if so, to ascertain whether the 50% inhibitory concentration (IC₅₀) estimates are different in the two tissues. Methods: Sulfotransferase activities were measured for 10 mM (−)-salbutamol and 5 mM minoxidil, and the concentration of 3′-phosphoadenosine-5′-phosphosulphate-[³⁵S] was 0.4 μM. Results: The IC₅₀ estimates for (−)-salbutamol and minoxidil sulfation of mefenamic acid were 72 ± 5.4 nM and 1.5 ± 0.6 μM (liver), respectively, and 161 ± 23 μM and 420 ± 18 μM (duodenum), respectively. The figures for the liver were significantly lower (P < 0.0001) than those for the duodenum. The IC₅₀ estimates for (−)-salbutamol sulfation of salicylic acid were 93 ± 11 μM (liver) and 705 ± 19 μM (duodenum, P < 0.0001). Salicylic acid was a poor inhibitor of minoxidil sulfation. Conclusion: The IC₅₀ estimates for (−)-salbutamol sulfation of mefenamic acid and salicylic acid are lower than their unbound plasma concentrations after standard dosing, suggesting that mefenamic acid and salicylic acid should inhibit the hepatic sulfation of (−)-salbutamol in vivo. Received: 11 November 1999 / Accepted in revised form: 28 April 2000     

Pharmacokinetics of bupivacaine enantiomers in sheep: Influence of dosage regimen and study design

Bupivacaine is used as a racemate. In previous studies the mean total body clearance ofR(+)-bupivacaine was found to be greater thanS(−)-bupivacaine by 65% after iv bolus dose of separate enantiomers and by 20% after iv infusion to steady state of racemate. The present studies were performed to determine whether different study designs using different iv dosage regimens could influence the pharmacokinetic parameters determined for either bupivacaine enantiomer. rac-Bupivacaine·HCl was administered iv to 6 adult Merino ewes by bolus, brief infusion, and prolonged infusion. Arterial blood concentrations ofR(+)- andS(−)-bupivacaine were measured by enantioselective HPLC. These regimens consistently produced lower arterial blood concentrations ofR(+)-bupivacaine thanS(−)-bupivacaine due toR(+)-bupivacaine having a greater initial dilution volume by 16 (95%CI=3–29)%, volume of distribution at steady state equilibrium by 32 (95%CI=17–32)% and mean total body clearance by 28 (95%CI=21–35)%. The slow half-life ofR(+)-bupivacaine, however, was found to be 15 (95%CI=0–31)% longer than that ofS(−)-bupivacaine. The difference between enantiomers in mean total body clearance thus was similar to the previous study based upon infusion to steady state of rac-bupivacaine. Differences in pharmacokinetics attributable to the dosage regimen consisted of a greater mean total body clearance forR(+)-bupivacaine along with a smaller terminal half life with the bolus regimen and a longer half-life ofS(−)-bupivacaine after prolonged infusion. Differences in pharmacokinetics between the bupivacaine enantiomers occurred consistently in both distribution and clearance but the magnitude of the effect was less than 50% in each case. Systematic differences in pharmacokinetics associated with the dosage regimen were found mainly in terminal half-life. Dosage regimen, thus, was found to influence the pharmacokinetic results found experimentally and is therefore a significant variable in its own right. The study was supported by the National Health and Medical Research Council of Australia and by the Australian New Zealand College of Anaesthetists by way of award of inaugural Douglas Joseph Professorship in Anaesthesia (to L.E.M.).     

Mechanism-based population modelling for assessment of L-cell function based on total GLP-1 response following an oral glucose tolerance test

GLP-1 is an insulinotropic hormone that synergistically with glucose gives rise to an increased insulin response. Its secretion is increased following a meal and it is thus of interest to describe the secretion of this hormone following an oral glucose tolerance test (OGTT). The aim of this study was to build a mechanism-based population model that describes the time course of total GLP-1 and provides indices for capability of secretion in each subject. The goal was thus to model the secretion of GLP-1, and not its effect on insulin production. Single 75 g doses of glucose were administered orally to a mixed group of subjects ranging from healthy volunteers to patients with type 2 diabetes (T2D). Glucose, insulin, and total GLP-1 concentrations were measured. Prior population data analysis on measurements of glucose and insulin were performed in order to estimate the glucose absorption rate. The individual estimates of absorption rate constants were used in the model for GLP-1 secretion. Estimation of parameters was performed using the FOCE method with interaction implemented in NONMEM VI. The final transit/indirect-response model obtained for GLP-1 production following an OGTT included two stimulation components (fast, slow) for the zero-order production rate. The fast stimulation was estimated to be faster than the glucose absorption rate, supporting the presence of a proximal–distal loop for fast secretion from l-cells. The fast component (st ₃  = 8.64·10⁻⁵ [mg⁻¹]) was estimated to peak around 25 min after glucose ingestion, whereas the slower component (st ₄  = 26.2·10⁻⁵ [mg⁻¹]) was estimated to peak around 100 min. Elimination of total GLP-1 was characterised by a first-order loss. The individual values of the early phase GLP-1 secretion parameter (st ₃ ) were correlated (r = 0.52) with the AUC(0–60 min.) for GLP-1. A mechanistic population model was successfully developed to describe total GLP-1 concentrations over time observed after an OGTT. The model provides indices related to different mechanisms of subject abilities to secrete GLP-1. The model provides a good basis to study influence of different demographic factors on these components, presented mainly by indices of the fast- and slow phases of GLP-1 response.     

Opposite effects of lornoxicam co-administration on phenprocoumon pharmacokinetics and pharmacodynamics

Objective: To investigate the effect of co-administration of the non-steroidal anti-inflammatory drug (NSAID) lornoxicam on the pharmacokinetics of (R)- and (S)-phenprocoumon and their effect on factor II and VII activities. Methods: Six healthy male volunteers completed an open crossover study. Plasma concentrations of (R)- and (S)-phenprocoumon and activities of coagulation factors II and VII were measured after a single oral dose of 9 mg phenprocoumon racemate. In the second session, lornoxicam administration was started 3 days before phenprocoumon administration and continued twice daily until the last blood sample was drawn. Results: Lornoxicam co-administration resulted in a statistically significant increase of the area under the concentration-time curve (AUC) of the more potent (S)-isomer of phenprocoumon from a median value of 100 (range 68–146) mg · h · l⁻¹ to 124 (92–239) mg · h · l⁻¹. For the (R)-isomer, the AUC increase from 96 (70–142) mg h · l⁻¹ in the absence to 108 (75–155) mg · h · l⁻¹ in the presence of lornoxicam was not statistically significant. In a model-based analysis, an increase of (S)-phenprocoumon and (R)-phenprocoumon bioavailability of 14% [95% CI (9%, 19%)] and 6% (2%, 10%) and a decrease of their clearances by 15% (8%, 21%) and 6% (0%, 13%) was obtained. Lornoxicam co-administration did not influence the free fractions of (R)- or (S)-phenprocoumon. Contrary to what was expected from the changes in pharmacokinetics, a statistically significant decrease in the effect of phenprocoumon on factor II and VII activity was observed for the sessions with lornoxicam co-administration. For factor VII, lornoxicam was found to increase the concentration causing half-maximal effect (C₅₀) of phenprocoumon by 70% [95% CI (38%, 111%)]. Conclusion: Co-administration of lornoxicam at the upper limit of recommended doses mainly altered the pharmacokinetics of the more potent (S)-isomer and to a lesser degree those of (R)-phenprocoumon. Despite these changes in pharmacokinetics, a decrease of the effect on factor II and VII activity was observed. These results suggest that in the case of lornoxicam co-administration in a patient treated with phenprocoumon the prothrombin time should be monitored closely. Received: 22 June 1998 / Accepted: 1 August 1998     

Approaches to handling pharmacodynamic baseline responses

A few approaches for handling baseline responses are available for use in pharmacokinetic (PK)-pharmacodynamic (PD) analysis. They include: (method 1-B1) estimation of the typical value and interindividual variability (IIV) of baseline in the population, (B2) inclusion of the observed baseline response as a covariate acknowledging the residual variability, (B3) a more general version of B2 as it also takes the IIV of the baseline in the population into account, and (B4) normalization of all observations by the baseline value. The aim of this study was to investigate the relative performance of B1-B4. PD responses over a single dosing interval were simulated from an indirect response model in which a drug acts through stimulation or inhibition of the response according to an Emax model. The performance of B1-B4 was investigated under 22 designs, each containing 100 datasets. NONMEM VI beta was used to estimate model parameters with the FO and the FOCE method. The mean error (ME, %) and root mean squared error (RMSE, %) of the population parameter estimates were computed and used as an indicator of bias and imprecision. Absolute ME (|ME|) and RMSE from all methods were ranked within the same design, the lower the rank value the better method performance. Average rank of each method from all designs was reported. The results showed that with B1 and FOCE, the average of |ME| and RMSE across all typical individual parameters and all conditions was 5.9 and 31.8%. The average rank of |ME| for B1, B2, B3, and B4 was 3.7, 3.8, 3.3, and 5.2 for the FOCE method, and 4.6, 4.3, 4.7, and 6.4 for the FO method. The smallest imprecision was noted with the use of B1 (rank of 3.1 for FO, and 2.9 for FOCE) and increased, in order, with B3 (3.9-FO and 3.6-FOCE), B2 (4.8-FO; 4.7-FOCE), and B4 (6.4-FO; 6.5-FOCE). We conclude that when considering both bias and imprecision B1 was slightly better than B3 which in turn was better than B2. Differences between these methods were small. B4 was clearly inferior. The FOCE method led to a smaller bias, but no marked reduction in imprecision of parameter estimates compared to the FO method.     

Association between drug prescribing and quality of life in primary care

Objective To evaluate quality of life among patients of Family Health Strategy Units and how it relates to the prescribing complexity and to the number of psychotropic medications prescribed, including adjustments for sociodemographic characteristics. Setting Family Health Strategy Units in a municipality in the Brazilian state of Rio Grande do Sul. Method Cross-sectional study using face-to-face interviews and prescribing analysis among users of Family Health Strategy Units. Patients were recruited by consecutive sampling. Multiple linear regression models were fitted to the different domains of quality of life in the WHOQOL-Bref questionnaire. The response rate for the patients who completed the interview was 97%. The prescribed medication data and sociodemographic characteristics of the sample were included as covariates. Prescribing complexity was analyzed by means of the Medication Regimen Complexity Index. The assumptions in the estimated models were tested and the models were validated. Main outcome measure Quality of life among patients of Family Health Strategy Units. Results At total, 336 patients answered the questionnaire. Through multiple linear regression, it was observed that higher prescribing complexity was associated with significantly low scores in the physical (−2.01, 95% CI = −2.89 to −1.35) and overall (−1.93, 95% CI = −2.81 to −0.99) quality of life domains. Greater amounts of psychotropic medications prescribed were associated with significantly low scores in the physical (−1.02, 95% CI = −1.29 to −0.56), psychological (−2.52, 95% CI = −3.15 to −1.65) and overall (−0.97, 95% CI = −2.06 to −0.33) domains of the interviewees’ quality of life. The estimated models were adjusted for the sociodemographic characteristics of the sample and presented good predictive capacity. Conclusions The evaluated aspects of the prescribed medication (complexity and presence of psychotropic medications) were associated with low scores in the physical, psychological and overall quality of life domains. This may be an intrinsic characteristic of the interviewed patients, like having the quality of life at such a low level before starting the treatment, that the medication could not improve it to normal levels. Also, it can be a demonstration of the ineffectiveness of these treatments within primary health care.     

Cytotoxic,radical scavenging and antimicrobial activities of sesquiterpenoids from the Tahitian liverwort <Emphasis Type="Italic">Mastigophora diclados</Emphasis> (Brid.) Nees (Mastigophoraceae)

A drimane, (+)-drimenol (1), five known herbertanes, (−)-α-herbertenol (2), (−)-herbertenediol (3), mastigophorene A (4), (−)-mastigophorene C (5) and (−)-mastigophorene D (6), a pimarane, (−)-e nt-pimara-8(14),15-dien-19-oic acid (7), and two eudesmanolides, (−)-diplophyllolide A (8) and (−)-diplophyllin (9) were isolated from the Tahitian Mastigophora diclados (Brid.) Nees. Herbertane sesquiterpenes (2, 3, 5 and 6) showed cytotoxicity against HL-60 and KB cell lines, radical scavenging activity and antimicrobial activity against Bacillus subtilis. (−)-Diplophyllolide A (8) also exhibited cytotoxicity against HL-60 and KB cell lines.     

S(−)Propranolol as a discriminative stimulus and its comparison to the stimulus effects of cocaine in rats

Rationale  Racemic propranolol (PRO), a β-adrenoceptor antagonist, has been evaluated as a test agent but not as a discriminative stimulus. Its S(−) stereoisomer is thought to subserve the effects of (±)PRO. Materials and methods  Rats were trained to discriminate S(−)PRO (5 mg/kg) from saline in a two-lever food-reinforced operant conditioning task. Results  The S(−)PRO stimulus was shown to be centrally mediated, dose-related, time dependent, and stereoselective: S(−)PRO (ED₅₀ = 2.2 mg/kg) was twice as potent as (±)PRO and approximately four times as potent as R(+)PRO. The S(−)PRO stimulus generalized fully to the β-adrenoceptor agent pindolol, the α₁-adrenoceptor agonist methoxamine, cocaine, and the serotonergic agents TFMPP and RU 24969; partial generalization occurred to (−)ephedrine and nisoxetine but not to fenfluramine or 5-OMe DMT. The S(−)PRO stimulus was blocked completely (and competitively) when prazosin, an α₁-adrenoceptor antagonist, was given in combination with the training dose of S(−)PRO. Moreover, prazosin exerted antagonism of the S(−)PRO-like effect of (±)PRO or R(+)PRO but produced only partial antagonism of the S(−)PRO-like effect of cocaine. In a second study, rats were trained to discriminate 8 mg/kg of cocaine from saline. The cocaine stimulus generalized to S(−)PRO, (±)PRO, and R(+)PRO. Prazosin partially attenuated the stimulus effect of cocaine (8 mg/kg) but completely blocked the cocaine-like effects of (±), S(−), and R(+)PRO. Conclusions  PRO and cocaine exhibited cross-substitution, but their stimulus effects were antagonized differentially by prazosin. PRO (and its optical isomers) can exert a stimulus effect that is based, at least in part, on increased α₁-adrenoceptor activity. PRO might be better characterized as an adrenoceptor partial agonist. This study was supported, in part, by the National Institute on Drug Abuse (NIDA) grant DA-01642.     

Microbial transformation of aniline to acetaminophen

In order to obtain acetaminophen, a popular analgesic-antipyretic, through microbial p-hydroxylation and N-acetylation of aniline, various fungi and bacteria were screened. Among them,Streptomyces species were chosen for strain improvement by the use of interspecific protoplast fusion technique. Two interspecific fused strains were developed betweenS. rimosus (N-cetylation function) andS. aureofaciens (p-hydroxylation function) and also betweenS. lividans andS. globisporus. For efficient protoplast fusion and cell wall regeneration, various conditions were examined. In a typical experiment of mixedS. rimosus (pro⁻ his⁻) andS. aureofaciens (ilv⁻) protoplasts with 40% (w/v) polyethylene glycol 3350 (PEG) for 3 min gave 8.3×10⁻⁷ of fusion frequency. Treatment of mixedS. lividans (pant⁻) andS. globisporus (leu⁻) protoplasts with 50% (w/v) PEG for 3 min at 30°C gave 1.2×10⁻⁶ of frequency. Among the fused strains, up to 40–50% increase in p-hydroxylation power was observed. To investigate the possibility of plasmid involvement in p-hydroxylation of acetanilide, plasmid curing was attempted. We found that cells treated with acriflavine (at the frequency of 100%) and cells regenerated from protoplsts ofS. aureofaciens (2% frequency) lost their p-hydroxylation function.     

Pharmacokinetic Modeling of Non-Linear Brain Distribution of Fluvoxamine in the Rat

Introduction A pharmacokinetic (PK) model is proposed for estimation of total and free brain concentrations of fluvoxamine. Materials and methods Rats with arterial and venous cannulas and a microdialysis probe in the frontal cortex received intravenous infusions of 1, 3.7 or 7.3 mg.kg⁻¹ of fluvoxamine. Analysis With increasing dose a disproportional increase in brain concentrations was observed. The kinetics of brain distribution was estimated by simultaneous analysis of plasma, free brain ECF and total brain tissue concentrations. The PK model consists of three compartments for fluvoxamine concentrations in plasma in combination with a catenary two compartment model for distribution into the brain. In this catenary model, the mass exchange between a shallow perfusion-limited and a deep brain compartment is described by a passive diffusion term and a saturable active efflux term. Results The model resulted in precise estimates of the parameters describing passive influx into (k _in) of 0.16 min⁻¹ and efflux from the shallow brain compartment (k _out) of 0.019 min⁻¹ and the fluvoxamine concentration at which 50% of the maximum active efflux (C ₅₀) is reached of 710 ng.ml⁻¹. The proposed brain distribution model constitutes a basis for precise characterization of the PK–PD correlation of fluvoxamine by taking into account the non-linearity in brain distribution.     

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.     

Phosphodiesterases PDE3 and PDE4 jointly control the inotropic effects but not chronotropic effects of (−)-CGP12177 despite PDE4-evoked sinoatrial bradycardia in rat atrium

Acting through a low-affinity site of the β₁-adrenoceptor (β_1LAR), CGP12177 causes sinoatrial tachycardia and positive inotropic effects in left atrium but not in the ventricle of the rat. However, inhibition of either PDE3 or PDE4 also uncovers positive inotropic effects of CGP12177 in ventricle, but whether these phosphodiesterases also control the atrial agonist effects of CGP12177 was unknown. We, therefore, investigated the effects of the PDE3-selective inhibitor cilostamide (300 nM) and PDE4 inhibitor rolipram (1 μM) on the (−)-CGP12177-evoked increases of sinoatrial beating rate and force of paced left atria of the rat. Rolipram (n = 8) increased basal sinoatrial rate by 27 ± 5 bpm but cilostamide (n = 8) had no effect. The chronotropic potency of (−)-CGP12177 (−logEC₅₀M = 7.5) was not changed by rolipram and cilostamide or their combination. (-)-CGP12177 increased left atrial force with intrinsic activity 0.25 compared to (-)-isoprenaline. Rolipram (n = 8) and cilostamide (n = 8) did not change basal force of left atria but concurrent rolipram + cilostamide (n = 8) increased force by 52 ± 9% of the effect of 200 μM (−)-isoprenaline. Neither rolipram nor cilostamide affected the inotropic potency of (−)-CGP12177 (−logEC₅₀M = 7.4) but concurrent rolipram + cilostamide caused potentiation (−logEC₅₀M = 8.2) and converted (-)-CGP12177 into a full agonist compared to (-)-isoprenaline. Cyclic AMP appears to maintain sinoatrial rate and PDE4 elicits bradycardia through hydrolysis of cAMP in a compartment distinct from the β_1LAR-induced cAMP compartment through which (−)-CGP12177 causes tachycardia. In contrast to the (−)-CGP12177-evoked tachycardia, not controlled by PDE3 and PDE4, these isoenzymes jointly reduce (−)-CGP12177-evoked increases of left atrial contractility through β_1LAR.     

Changes in gastrointestinal motility influence the absorption of desmopressin

Objective: The antidiuretic effect of desmopressin is widely utilized in the treatment of neurogenic diabetes insipidus and nocturnal enuresis in children. The objective of the present study was to assess how changes in gastrointestinal motility, induced by erythromycin and loperamide, influence the pharmacokinetics of orally administered desmopressin. Methods: This study was conducted using an open randomized, three-period, three-treatment design in 18 healthy subjects. On each study day a single oral dose of 400 μg desmopressin was administered in the morning. The desmopressin dose was either given alone (reference) or after pretreatment with either loperamide tablets (4 mg at −24, −12 h and −1 h) or erythromycin capsules (250 mg q.i.d, with the first dose in the morning 3 days before the study day and the last dose at −1 h). On each study day, blood was sampled up to 8 h after dosing for assessment of desmopressin concentration. Results: Compared with administration of 400 μg of desmopressin alone, pretreatment with loperamide produced significantly (P < 0.05) altered pharmacokinetics of desmopressin as the endpoints; area under the curve up to infinity (AUC), area up to the last determinable plasma concentration (AUC_t) and maximum plasma concentration (C_max) increased 3.1-fold (95% CI 2.3–4.2), 3.2 (2.3–4.4) and 2.3 (1.6–3.2), respectively. Although the estimates were lower, pretreatment with erythromycin did not result in any significant changes in these endpoints. There were no significant changes observed between the three treatments regarding the terminal elimination half-life (t_1/2). However, significant (P < 0.05) changes in the time to reach C_max (t_max) values (median and range) were observed as, compared with administration of desmopressin alone (1.3 h and 0.5–4.0), it was longer after pretreatment with loperamide (2.0 h and 0.5–3.0) and shorter following pretreatment with erythromycin (0.9 h and 0.5–1.3). Conclusion: Presumably due to slower gastrointestinal motility, pretreatment with loperamide significantly increases the gastrointestinal absorption of desmopressin. Except for a shortening of t_max, pretreatment with erythromycin did not significantly influence absorption of the drug. Received: 1 September 1998 / Accepted in revised form: 29 December 1998     

Enantioselective pharmacokinetics of tramadol in CYP2D6 extensive and poor metabolizers

Objective To describe in detail the intravenous, single oral and multiple oral dose enantioselective pharmacokinetics of tramadol in CYP2D6 extensive metabolizers (EMs) and poor metabolizers (PMs).Methods Eight EMs and eight PMs conducted three phases as an open-label cross-over trial with different formulations; 150 mg single oral tramadol hydrochloride, 50 mg single oral tramadol hydrochloride every 8 h for 48 h (steady state), 100 mg intravenous tramadol hydrochloride. Urine and plasma concentrations of (+/−)-tramadol and (+/−)-M1 were determined for 48 h after administration.Results In all three phases, there were significant differences between EMs and PMs in AUC and t_1/2 of (+)-tramadol (P≤0.0015), (−)-tramadol (P≤0.0062), (+)-M1 (P≤0.0198) and (−)-M1 (P≤0.0370), and significant differences in C_max of (+)-M1 (P<0.0001) and (−)-M1 (P≤0.0010). In Phase A and C, significant differences in t_max were seen for (+)-M1 (P≤0.0200). There were no statistical differences between the absolute bioavailability of tramadol in EMs and PMs. The urinary recoveries of (+)-tramadol, (−)-tramadol, (+)-M1 and (−)-M1 were statistically significantly different in EMs and PMs (P<0.05). Median antimodes of the urinary metabolic ratios of (+)-tramadol / (+)-M1 and (−)-M1 were 5.0 and 1.5, respectively, hereby clearly separating EMs and PMs in all three phases.Conclusion The impact of CYP2D6 phenotype on tramadol pharmacokinetics was similar after single oral, multiple oral and intravenous administration displaying significant pharmacokinetic differences between EMs and PMs of (+)-tramadol, (−)-tramadol, -(+)-M1 and (−)-M1. The O-demethylation of tramadol was catalysed stereospecific by CYP2D6 in the way that very little (+)-M1 was produced in PMs.     

Dose-dependent stereoselective activation of the trigeminal sensory system by nicotine in man

Rationale: Nicotine applied to the nasal cavity can evoke ‘odorous’ sensations in the concentration range near the detection threshold by the activation of the olfactory sensory system and at higher concentrations ‘burning’ and ‘stinging’ sensations by the dose-dependent recruitment of C- and Aδ-fibers of the trigeminal sensory system. Neuronal nicotinic acetylcholine receptor (nAchR) subunits are expressed in trigeminal primary afferents and could constitute the receptors involved in nicotine perception. Objective: In the present study, we dose-dependently investigated the stereoselective effects of R(+)- and S(−)-nicotine on the trigeminal and olfactory sensory system in man. Methods: Trigeminal detection thresholds for the ‘burning’ and ‘stinging’ sensations and the olfactory detection threshold for the ‘odorous’ sensation were determined. In order to quantify trigeminal activation, we recorded summated electrical responses from the respiratory nasal mucosa during stimulation with R(+)- and S(−)-nicotine vapor (40, 80, 120, 160 ng/ml; stimulus duration: 250 ms). In addition, subjects rated the intensity of ‘odorous’, ‘burning’ and ‘stinging’ sensations. For chemical stimulation with nicotine enantiomers, a vapor-dilution olfactometer (constant flow rate: 140 ml/s, humidity: 80%, temperature: 37°C, stimulus duration 250 ms) was employed. Results: We found significant stereoselective differences for the trigeminal but not for the olfactory system, i.e. higher summated responses, higher trigeminal intensity estimates, and lower trigeminal detection thresholds for S(−)- compared to R(+)-nicotine. Conclusion: Our results clearly demonstrate the different stereoselective activation of the trigeminal sensory system by R(+)- and S(−)-nicotine, indicating the presence of specific stereoselective receptors on trigeminal nociceptive Aδ- and C-fibers. Received: 16 March 1998/Final version: 14 September 1998     

Comparisons of <Emphasis Type="Italic">CYP1A2</Emphasis> genetic polymorphisms,enzyme activity and the genotype-phenotype relationship in Swedes and Koreans

Objectives To investigate the CYP1A2 genotype-phenotype relationship and to compare CYP1A2 genetic polymorphisms and enzyme activity in terms of the effect of smoking and oral contraceptive (OC) use in Swedes and Koreans. Methods CYP1A2 enzyme activity was determined in 194 and 150 healthy Swedish and Korean subjects, respectively, on the basis of the 4-h plasma paraxanthine/caffeine (17X/137X) ratio determined using high-performance liquid chromatography. Genotyping for the −3860G>A, −2467delT, −739 T>G, −729 C>T, −163C>A and −3113A>G polymorphisms was performed by PCR-restriction fragment length polymorphism analysis. Results The mean 17X/137X ratio was 1.54-fold higher in Swedes than in Koreans (mean difference: 0.16; 95% CI of the mean difference: 0.12, 0.20; p < 0.0001). Smokers had a significantly higher 17X/137X ratio (higher CYP1A2 activity) than non-smokers, while Swedish OC users had a significantly lower 17X/137X ratio than non-users (mean difference: 0.31, 95% CI of the mean difference: 0.23, 0.39; p < 0.0001). No effect of gender differences on enzyme activity was observed. Four known (CYP1A2*1A, *1D, *1F, and *1L) and two novel haplotypes (CYP1A2*1V and CYP1A2*1W) were found. CYP1A2*1K was rare in Swedes and absent in Koreans. No significant genotype-phenotype relationship was observed, with the exception of CYP1A2*1F in Swedish smokers, where it was associated with higher enzyme inducibility (p = 0.02). Koreans displayed a significantly lower mean 17X/137X ratio than Swedes having the same CYP1A2 genotype, smoking habit and OC use. Conclusions We found significant differences in CYP1A2 enzyme activity between Swedes and Koreans that could not be explained by environmental factors or the CYP1A2 haplotypes examined, despite differences in allele frequencies. None of the investigated CYP1A2 haplotypes are critical in inducing variations in enzyme activity, with the exception of CYP1A2*1F.     

Involvement of Multidrug Resistance-Associated Protein 1 in Intestinal Toxicity of Methotrexate

Purpose  Methotrexate (MTX) causes dose-limiting gastrointestinal toxicity due to exposure of intestinal tissues, and is a substrate of the multidrug resistance-associated protein (MRP) 1. Here we examine the involvement of MRP1, which is reported to be highly expressed in the proliferative crypt compartment of the small intestine, in the gastrointestinal toxicity of MTX. Methods  MTX was intraperitonealy administered to mrp1 gene knockout (mrp1 ^(−/−)) and wild-type (mrp1 ^(+/+)) mice. Body weight, food and water intake were monitored, intestinal histological studies and pharmacokinetics of MTX were examined. Results   mrp1 ^(−/−) mice more severely decreased body weight, food and water intake than mrp1 ^(+/+) mice. Almost complete loss of villi throughout the small intestine in mrp1 ^(−/−) mice was observed, whereas the damage was only partial in mrp1 ^(+/+) mice. Plasma concentration and biliary excretion profiles of MTX were similar in mrp1 ^(−/−) and mrp1 ^(+/+) mice, though accumulation of MTX in immature proliferative cells isolated from mrp1 ^(−/−) mice was much higher compared to mrp1 ^(+/+) mice. Immunostaining revealed localization of Mrp1 in plasma membrane of the intestinal crypt compartment in mrp1 ^(+/+) mice, but not in mrp1 ^(−/−) mice. Conclusion  Mrp1 determines the exposure of proliferative cells in the small intestine to MTX, followed by gastrointestinal toxicity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of nornicotine enantiomers on intravenous <Emphasis Type="Italic">S</Emphasis>(−)-nicotine self-administration and cardiovascular function in rats

Rationale Previous neurochemical evidence indicates that R(+)-nornicotine is more potent than S(−)-nornicotine in evoking dopamine release in rat nucleus accumbens slices. Objective The current study tested the hypothesis that R(+)-nornicotine is also more potent than S(−)-nornicotine in selectively decreasing intravenous S(−)-nicotine self-administration in rats. Results After acute pretreatment (1–10 mg/kg for each enantiomer), R(+)-nornicotine was more potent than S(−)-nornicotine in decreasing S(−)-nicotine self-administration; in contrast, within the same dose range, the nornicotine enantiomers were equipotent in decreasing sucrose-maintained responding. This enantioselectivity does not likely reflect a difference in bioavailability, since similar levels of nornicotine were recovered from the brain 60 min after injection (5.6 mg/kg for each enantiomer). With repeated pretreatment, tolerance did not develop to the rate-decreasing effect of either nornicotine enantiomer (3 or 5.6 mg/kg) with respect to the decrease in S(−)-nicotine self-administration, although the enantioselectivity dissipated across repeated pretreatments. While both enantiomers acutely produced a similar increase in blood pressure and heart rate, tolerance developed to the blood pressure effects of R(+)-nornicotine, but not to the effects of S(−)-nornicotine, across repeated treatments. Conclusion Both R(+)- and S(−)-nornicotine may have potential utility as a novel tobacco use cessation agent.