Topical ophthalmic atropine in horses, pharmacokinetics and effect on intestinal motility

BACKGROUND

Topical ophthalmic atropine sulfate is an important part of the treatment protocol in equine uveitis. Frequent administration of topical atropine may cause decreased intestinal motility and colic in horses due to systemic exposure. Atropine pharmacokinetics are unknown in horses and this knowledge gap could impede the use of atropine because of the presumed risk of unwanted effects. Additional information could therefore increase safety in atropine treatment.

RESULTS

Atropine sulfate (1 mg) was administered in two experiments: In part I, atropine sulfate was administered intravenously and topically (manually as eye drops and through a subpalpebral lavage system) to six horses to document atropine disposition. Blood-samples were collected regularly and plasma was analyzed for atropine using UHPLC-MS/MS. Atropine plasma concentration was below lower limit of quantification (0.05 μg/L) within five hours, after both topical and IV administration. Atropine data were analyzed by means of population compartmental modeling and pharmacokinetic parameters estimated. The typical value was 1.7 L/kg for the steady-state volume of distribution. Total plasma clearance was 1.9 L/h‧kg. The bioavailability after administration of an ophthalmic preparation as an eye drop or topical infusion were 69 and 68%, respectively. The terminal half-life was short (0.8 h). In part II, topical ophthalmic atropine sulfate and control treatment was administered to four horses in two dosing regimens to assess the effect on gastro-intestinal motility. Borborygmi-frequency monitored by auscultation was used for estimation of gut motility. A statistically significant decrease in intestinal motility was observed after administration of 1 mg topical ophthalmic atropine sulfate every three hours compared to control, but not after administration every six hours. Clinical signs of colic were not observed under any of the treatment protocols.

CONCLUSIONS

Taking the plasma exposure after topical administration into consideration, data and simulations indicate that eye drops administrated at a one and three hour interval will lead to atropine accumulation in plasma over 24 h but that a six hour interval allows total washout of atropine between two topical administrations. If constant corneal and conjunctival atropine exposure is required, a topical constant rate infusion at 5 μg/kg/24 h offers a safe alternative.

Pharmacokinetics after a single dose of naloxone administered as a nasal spray in healthy volunteers

BACKGROUND

There is increasing interest in the use of intranasal naloxone to reverse adverse opioid effects during management of procedural pain in children and in adults after overdose. There are limited data on the pharmacokinetics of intranasal naloxone so in this study we aimed to detail the pharmacokinetic profile of the commercially marketed injectable solution of naloxone 0.4 mg/ml when administered as an intranasal spray.

METHODS

Twenty healthy volunteers received naloxone as an intranasal spray at a dose of 10 μg/kg. Venous blood sampling was carried out for 90 min after administration to determine the time profile of the plasma concentrations of using tandem mass spectrometry. Pharmacokinetic parameters were calculated using a one-compartment model.

RESULTS

Median time to maximum naloxone concentration (Tmax) was 14.5 (95% CI: 9.0-16.5) min, mean maximum naloxone concentration (Cmax) was 1.09 ± 0.56 ng/ml and mean AUC_{0-90 min} was 37.1 ± 15.0 ng*min/ml. Elimination half-life estimated from the median concentration data was 28.2 min.

CONCLUSION

Our results show a faster uptake of intranasal naloxone to maximum concentration compared with previous studies although with a marked variation in maximum concentration. The findings are consistent with our clinical experience of the time profile for reversing the effects of sufentanil sedation in children.

Nickel in equine sports drug testing - pilot study results on urinary nickel concentrations

RATIONALE

The issue of illicit performance enhancement spans human and animal sport in presumably equal measure, with prohibited substances and methods of doping conveying both ways. Due to the proven capability of unbound ionic cobalt (Co(2) (+) ) to stimulate erythropoiesis in humans, both human and equine anti-doping regulations have listed cobalt as a banned substance, and in particular in horse drug testing, thresholds for cobalt concentrations applying to plasma and urine have been suggested or established. Recent reports about the finding of substantial amounts of undeclared nickel in arguably licit performance- and recovery-supporting products raised the question whether the ionic species of this transition metal (Ni(2) (+) ), which exhibits similar prolyl hydroxylase inhibiting properties to Co(2) (+) , has been considered as a substitute for cobalt in doping regimens.

METHODS

Therefore, a pilot study with 200 routine post-competition doping control horse urine samples collected from animals participating in equestrian, gallop, and trotting in Europe was conducted to provide a first dataset on equine urinary Ni(2) (+) concentrations. All specimens were analyzed by conventional inductively coupled plasma mass spectrometry (ICP-MS) to yield quantitative data for soluble nickel.

RESULTS

Concentrations ranging from below the assay's limit of quantification (LOQ, 0.5 ng/mL) up to 33.4 ng/mL with a mean value (± standard deviation) of 6.1 (±5.1) ng/mL were determined for the total nickel content.

CONCLUSIONS

In horses, nickel is considered a micronutrient and feed supplements containing nickel are available; hence, follow-up studies are deemed warranted to consolidate potential future threshold levels concerning urine and blood nickel concentrations in horses using larger sets of samples for both matrices and to provide in-depth insights by conducting elimination studies with soluble Ni(2) (+) -salt species. Copyright © 2016 John Wiley & Sons, Ltd.

A quantitative approach to analysing cortisol response in the horse

The cortisol response to glucocorticoid intervention has, in spite of several studies in horses, not been fully characterized with regard to the determinants of onset, intensity and duration of response. Therefore, dexamethasone and cortisol response data were collected in a study applying a constant rate infusion regimen of dexamethasone (0.17, 1.7 and 17 μg/kg) to six Standardbreds. Plasma was analysed for dexamethasone and cortisol concentrations using UHPLC-MS/MS. Dexamethasone displayed linear kinetics within the concentration range studied. A turnover model of oscillatory behaviour accurately mimicked cortisol data. The mean baseline concentration range was 34-57 μg/L, the fractional turnover rate 0.47-1.5 1/h, the amplitude parameter 6.8-24 μg/L, the maximum inhibitory capacity 0.77-0.97, the drug potency 6-65 ng/L and the sigmoidicity factor 0.7-30. This analysis provided a better understanding of the time course of the cortisol response in horses. This includes baseline variability within and between horses and determinants of the equilibrium concentration-response relationship. The analysis also challenged a protocol for a dexamethasone suppression test design and indicated future improvement to increase the predictability of the test.

Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015

REASONS FOR PERFORMING STUDY

Hypoglycin A (HG) appears to cause atypical myopathy (AM), but to our knowledge, detection of HG in affected and unaffected horses and concurrently in plants that they were exposed to has not previously been reported.

OBJECTIVES

To investigate HG in samples from horses exposed to Acer pseudoplatanus (European sycamore maple) and in such plant material, at the time of clinical cases of AM in the herd.

STUDY DESIGN

Cross-sectional study.

METHODS

Blood was collected from 2 horses with AM and 22 clinically healthy co-grazing horses in 2 Swedish farms within one week of onset of signs (May 2014) and one month later, after horses were moved to other pastures. Ten healthy control horses from unaffected farms were sampled once. Samaras, seedlings, flowers and leaves from Acer pseudoplatanus and from Acer platanoides L (Norway maple) were collected from affected pastures. Hypoglycin A was analysed using chemical derivatisation with dansyl chloride (DNS) and ultra high performance liquid chromatography-tandem mass spectrometry. Hypoglycin A was detected as derivatised compound HG-DNS [M+H]+ with selected reaction monitoring.

RESULTS

Hypoglycin A was detected in the horses affected with AM, and also in 20 out of 22 co-grazing horses. One month later, a surviving case horse and 9/20 co-grazing horses were still positive for HG. Controls from other farms were negative for HG. Hypoglycin A was detected in plant material from Acer pseudoplatanus, but not from Acer platanoides L.

CONCLUSIONS

Horses grazing in pastures with HG-containing Acer pseudoplatanus were positive for HG in blood, and some showed severe signs of myopathy. Ethical animal research: Ethical consent for blood sampling was granted (C113/11) and horse owners gave their informed consent to inclusion of horses in the study.

SOURCE OF FUNDING

National Veterinary Institute, Sweden. Competing interests: None declared.

Cetirizine in horses: pharmacokinetics and effect of ivermectin pretreatment

The pharmacokinetics of the histamine H(1)-antagonist cetirizine and the effects of pretreatment with the antiparasitic macrocyclic lactone ivermectin on the pharmacokinetics of cetirizine were studied in horses. After oral administration of cetirizine at 0.2 mg/kg bw, the mean terminal half-life was 3.4 h (range 2.9-3.7 h) and the maximal plasma concentration 132 ng/mL (101-196 ng/mL). The time to reach maximal plasma concentration was 0.7 h (0.5-0.8 h). Ivermectin (0.2 mg/kg bw) given orally 1.5 h before cetirizine did not affect its pharmacokinetics. However, ivermectin pretreatment 12 h before cetirizine increased the area under the plasma concentration-time curve by 60%. The maximal plasma concentration, terminal half-life and mean residence time also increased significantly following the 12 h pretreatment. Ivermectin is an inhibitor of P-glycoprotein, which is a major drug efflux transporter in cellular membranes at various sites. The elevated plasma levels of cetirizine following the pretreatment with ivermectin may mainly be due to decreased renal secretion, related to inhibition of the P-glycoprotein in the proximal tubular cells of the kidney. The pharmacokinetic properties of cetirizine have characteristics which are suitable for an antihistamine, and this substance may be a useful drug in horses.

Clinical pharmacology of buprenorphine in healthy, lactating goats

The pharmacokinetics and the effects of the opioid buprenorphine on behavior, cardiovascular parameters, plasma concentrations of cortisol and vasopressin were studied in the goat. After intravenous injection at a dosage of 0.02 mg/kg bw, the terminal half-life was 73.8+/-19.9 min (mean+/-SD), the apparent volume of distribution 5.22+/-1.01 L/kg, and total body clearance 79.1+/-18.5 mL/min/kg. After intramuscular administration of buprenorphine at the same dosage, bioavailability was complete and clearance was 54.7+/-16.6 mL/min/kg. Heart rate, blood pressure and concentrations of cortisol and vasopressin in plasma increased after drug administration. The goats became agitated and stopped ruminating. The effects were more pronounced the first time the animals received the drug, especially the influence on the hormone levels. The concentrations of cortisol and vasopressin in plasma remained unaffected after the second dose despite a wash-out period of 3-6 weeks. Buprenorphine may be an unsuitable drug in goats because of the profound inhibition of rumination and the agitation it causes. The short half-life of buprenorphine may limit its use if long-term analgesia is required but be advantageous if a short acting drug is desirable.

Effect of erythromycin on the absorption of fexofenadine in the jejunum, ileum and colon determined using local intubation in healthy volunteers

OBJECTIVE

To investigate the in vivo intestinal absorption mechanism(s) and systemic availability of fexofenadine in the jejunum, ileum and colon in humans.

METHOD

A single dose of fexofenadine hydrochloride (60 mg as solution) was applied under fasting conditions, either alone or directly after a solution of erythromycin lactobionate (corresponding to a dose of 250 mg erythromycin), to the jejunum, ileum and colon in 6 healthy volunteers (3 male and 3 female) using a regional intubation dosing technology (Bioperm AB, Lund, Sweden). A total of 36 fexofenadine administrations were performed. The administration of fexofenadine to the specified location either alone or in combination with erythromycin was conducted in a randomized manner on 2 consecutive days with a 5-day washout period between doses.

RESULTS

The plasma AUC for fexofenadine (mean +/- SEM) was higher (2.7-to 2.3-fold, p < 0.001) after application to the jejunum (1090 +/- 134 h x ng/ml) than to the ileum (404 +/- 102 h x ng/ml) or colon (476 +/- 212 h x ng/ml). No significant differences were found between application to the ileum and colon. The administration of erythromycin affected the absorption rate after jejunal application with a prolonged tmax from a median of 40 min (range 10-90 min) to a median of 3 hours (range 10-180 min) (p = 0.009). A change in tmax was not observed with application to the ileum and colon. The concomitant administration of erythromycin in the jejunum tended to increase the plasma AUC of fexofenadine from 1090 +/- 134 to 1750 +/- 305 h x ng/ml (p = 0.069).

CONCLUSIONS

The systemic availability of fexofenadine was significantly higher after jejunal administration in accordance with a low permeability compound. The effects of erythromycin suggest that absorption of fexofenadine involves an uptake transport in addition to passive diffusion in the jejunum and predominantly passive diffusion in the ileum and colon.

Fexofenadine in horses: pharmacokinetics, pharmacodynamics and effect of ivermectin pretreatment

The pharmacokinetics and the effects on inhibition of histamine-induced cutaneous wheal formation of the histamine H1-antagonist fexofenadine were studied in horse. The effect of ivermectin pretreatment on the pharmacokinetics of fexofenadine was also examined. After intravenous infusion of fexofenadine at 0.7 mg/kg bw the mean terminal half-life was 2.4 h (range: 2.0-2.7 h), the apparent volume of distribution 0.8 L/kg (0.5-0.9 L/kg), and the total body clearance 0.8 L/h/kg (0.6-1.2 L/h/kg). After oral administration of fexofenadine at 10 mg/kg bw bioavailability was 2.6% (1.9-2.9%). Ivermectin pretreatment (0.2 mg/kg, p.o.) 12 h before oral fexofenadine decreased the bioavailability to 1.5% (1.4-2.1%). In addition, the area under the plasma concentration-time curve decreased 27%. Ivermectin did not affect the pharmacokinetics of i.v. administered fexofenadine. Ivermectin may influence fexofenadine absorption by interfering in intestinal efflux and influx pumps, such as P-glycoprotein and the organic anion transport polypeptide family. Oral and i.v. fexofenadine significantly decreased histamine-induced wheal formation, with a maximal duration of 6 h. A pharmacokinetic/pharmacodynamic link model indicated that fexofenadine in horse has antihistaminic effects at low plasma concentrations (EC50 = 16 ng/mL). However, oral treatments of horses with fexofenadine may not be suitable due to the low bioavailability.

Clinical pharmacology of clemastine in healthy dogs

The pharmacokinetic properties of clemastine were investigated in six healthy dogs and compared with the effect of the drug recorded as inhibition of wheal formation induced by intradermal injections of histamine. Clemastine clearance was high (median: 2.1 L h(-1) kg(-1)) and the volume of distribution large (13.4 L kg(-1)). The half-life after intravenous administration was 3.8 h and the plasma protein binding level in vitro was 98%. After oral administration, the bioavailability was only 3%. Given intravenously, clemastine (0.1 mg kg(-1)) inhibited wheal formation completely for 7 h, whereas the effect after oral administration (0.5 mg kg(-1)) was minor. The data show that most dosage regimens suggested in the literature for the oral administration of clemastine to dogs are likely to give too low a systemic exposure of the drug to allow effective therapy.

Pharmacokinetics and pharmacodynamics of clemastine in healthy horses

Clemastine is an H1 antagonist used in certain allergic disorders in humans and tentatively also in horses, although the pharmacology of the drug in this species has not yet been investigated. In the present study we determined basic pharmacokinetic parameters and compared the effect of the drug measured as inhibition of histamine-induced cutaneous wheal formation in six horses. The most prominent feature of drug disposition after intravenous dose of 50 microg/kg bw was a very rapid initial decline in plasma concentration, followed by a terminal phase with a half-life of 5.4 h. The volume of distribution was large, Vss = 3.8 L/kg, and the total body clearance 0.79 L/h kg. Notably, oral bioavailability was only 3.4%. There was a strong relationship between plasma concentrations and effect. The effect maximum (measured as reduction in histamine-induced cutaneous wheal formation) was 65% (compared with controls where saline was injected) and the effect duration after i.v. dose was approximately 5 h. The effect after oral dose of 200 microg/kg was minor. The results indicate that clemastine is not appropriate for oral administration to horses because of low bioavailability. When using repeated i.v. administration, the drug has to be administered at least three to four times daily to maintain therapeutic plasma concentrations because of the short half-life. However, if sufficient plasma concentrations are maintained the drug is efficacious in reducing histamine-induced wheal formations.

Identification of phase I and phase II metabolites of ketobemidone in patient urine using liquid chromatography-electrospray tandem mass spectrometry

Ketobemidone and five of its phase I metabolites were identified in the urine of four patients post intravenous administration of Ketogan Novum. Furthermore, indications of the presence of the glucuronide conjugates of ketobemidone and norketobemidone is presented. Both hydrolyzed (beta-glucuronidase) and unhydrolyzed human urine was extracted on a mixed-mode slightly polar cation-exchange SPEC cartridge prior to analysis with LC-ESI-MS-MS. The phase I metabolites were identified by comparison of their daughter spectra with those of synthesized standards. The glucuronides were identified by their molecular mass and interpretation of the daughter spectra, as no standards were available for these compounds.

Non-aqueous capillary electrophoretic separation of enantiomeric amines with (-)-2,3:4,6-di-O-isopropylidene-2-keto-L-gulonic acid as chiral counter ion

(-)-2,3:4,6-Di-O-isopropylidene-2-keto-L-gulonic acid [(-)-DIKGA] has been introduced as a chiral counter ion in non-aqueous capillary electrophoresis. High enantioresolutions (R(s)> or =3) were obtained for amines, e.g., pronethalol, labetalol and bambuterol. Methanol containing NaOH and (-)-DIKGA was used as the background electrolyte. The counter ion concentration and the nature of the injection medium were found to affect the chiral separation. Covalent coating of the fused-silica capillary reduced the electro-osmotic flow resulting in improved enantioresolutions.

Simultaneous analysis of endogenous neurotransmitters and neuropeptides in brain tissue using capillary electrophoresis--microelectrospray-tandem mass spectrometry

Capillary electrophoresis was combined with highly sensitive microelectrospray-tandem mass spectrometry to simultaneously detect classical small molecule neurotransmitters as well as neuropeptides from discrete regions of the marmoset brain. A mixture of four classical neurotransmitters (glutamate, gamma-aminobutyric acid, acetylcholine, dopamine) and four neuropeptides (neurotensin, methionine-enkephalin, leucine-enkephalin and substance P 1-7) was studied to optimize the capillary electrophoresis conditions for separation, injection volume, and analysis time. Gamma-aminopropyltriethoxysilane-coated capillaries and acetic acid electrolytes were used to avoid interactions between the sample and the capillary surface and to obtain a high anodic electroosmotic flow, which resulted in a short analysis time. Detection was performed using tandem mass spectrometry in the selected reaction monitoring mode using a triple quadrupole mass spectrometer. Samples were dissolved in ammonium acetate to achieve a transient-isotachophoretic concentration step at the beginning of the separation and to make it possible to inject larger sample volumes, up to 140 nL. Small amounts of tissue from specific regions of the marmoset monkey brain were pretreated using solid-phase extraction as a clean-up and concentrating step. In the striatum we could detect endogenous glutamate, gamma-aminobutyric acid (GABA), acetylcholine and dopamine, as well as the neuropeptides methionine-enkephalin and substance P 1-7 in the same analysis, using only 58 mm3 of brain tissue.

Selective effects of somatostatin analogs on human drug-metabolizing enzymes

Pharmacologic or surgical manipulation with growth hormone secretion or with the physiologic release of somatostatin and growth hormone-releasing hormone affects some rat liver enzymes, especially the sex-differentiated ones. We investigated the effects of two somatostatin analogs on several enzyme functions in six patients with carcinoid syndrome, using codeine as a probe drug. Codeine was given intravenously and its N- and O-demethylation, as well as 6-glucuronidation catalyzed by CYP3A, CYP2D6, and uridine diphosphate-glucuronosyltransferase, respectively, were studied before and during treatment with somatostatins. After 3 days of treatment with somatostatins the partial metabolic clearance of codeine by N-demethylation decreased by 21% to 64% in all patients (mean change, 44%; p < 0.05), and the clearance by O-demethylation was decreased by 20% to 69% in five of the patients (mean change in all patients, 35%; p < 0.05). In contrast, the partial clearance by 6-glucuronidation and the total systemic clearance of codeine were unchanged. Our results may be caused by the inhibition of growth hormone secretion induced by the somatostatins, inasmuch as direct metabolic interactions with these peptide drugs are improbable. The decline in CYP3A4 and CYP2D6 activity might have clinical implications when substrates of these enzymes with low therapeutic indices are combined with somatostatin analogs. Because the formation of morphine from codeine was altered, the analgesic effect of this drug may be reduced during concomitant treatment with somatostatins.

Determination of ropivacaine and [2H3]ropivacaine in biological samples by gas chromatography with nitrogen-phosphorus detection or mass spectrometry

Bioanalytical methods for determining the total concentration of the new local anaesthetic drug ropivacaine in blood plasma, urine and tissues are presented. Ropivacaine is a drug mainly used in connection with surgery and for post-operative pain relief. The biological samples were prepared using liquid-liquid extraction and analysed using capillary gas chromatography with nitrogen-phosphorus detection or mass spectrometry. The methods are highly selective and reliable with a between-day precision, given as the relative standard deviation, generally below 6%. More than 20000 samples have been analysed using the methods described.

Excretion of ketobemidone in human breast milk

The excretion of ketobemidone into human breast milk was investigated in three women who obtained ketobemidone as postoperative pain relief after Cesarean section and two women premedicated with 5 mg of ketobemidone before currettage after delivery. The highest observed concentration of ketobemidone in breast milk was 36 ng/ml three hours after administration, and 4-7 hours after administration the concentration was 3-5 fold that in maternal plasma. It could be estimated that the newborn will be exposed to less than 2 micrograms of ketobemidone during the first 24 hours.

CSF and serum concentrations of clozapine and its demethyl metabolite: a pilot study

With the aim of exploring putative correlations between serum and CSF levels of clozapine and its demethyl metabolite, lumbar puncture was performed on four male and five female schizophrenic patients during long-term treatment with clozapine. Three consecutive 6-ml fractions were collected after at least 8 h of bedrest and fasting. On comparing serum and CSF levels, a correlation was found for norclozapine in the third (13-18 ml) CSF fraction. Norclozapine in the first (0-6 ml) CSF correlated significantly with height. The CSF/serum ratio of clozapine in the first fraction was correlated significantly with body weight. No correlations were found between serum levels of clozapine and norclozapine, or between the serum and CSF levels of clozapine. The study suffers from a small number of patients (for ethical reasons), but the present results might be explicable if the first (0-6 ml) CSF fraction represents a cul-du-sac of the CSF, mirroring the previous day's drug levels. The second fraction, then, will represent the CSF level in the steady state during the night.

Clozapine disposition covaries with CYP1A2 activity determined by a caffeine test

In a previous study we showed that the disposition of clozapine after a single oral dose is unrelated to either debrisoquine or S-mephenytoin hydroxylation polymorphism. The same 14 healthy subjects studied in that investigation were given 150 mg of caffeine. The reciprocal of plasma clozapine AUC (0,24), was correlated with an index of the N3-demethylation of caffeine (rs = 0.84; P = 0.0024), used as a measure of cytochrome P4501A2 (CYP1A2) activity. N1- and N7-demethylation indices of caffeine also reflect CYP1A2 activity and were also correlated with clozapine clearance (rs = 0.89 and 0.85; P = 0.0013 and 0.0023; respectively). No significant relationships with xanthine oxidase and N-acetyl transferase activity, also assessed by a caffeine test, were found. This study suggests that clozapine is metabolised by CYP1A2 to a major extent.

Fluvoxamine inhibition and carbamazepine induction of the metabolism of clozapine: evidence from a therapeutic drug monitoring service

Therapeutic drug monitoring data for clozapine were used to study interactions with other drugs. The distribution of the ratio concentration/dose (C/D) of clozapine was compared in four matched groups--patients simultaneously treated with benzodiazepines, patients on drugs that inhibit the cytochrome P450 enzyme CYP2D6, patients taking carbamazepine, and those not taking any of these drugs. No difference was seen among the monotherapy, CYP2D6, and benzodiazepine groups. Patients on carbamazepine had a mean 50% lower C/D than the monotherapy group (p < 0.001), indicating that carbamazepine is an inducer of the metabolism of clozapine. The C/D was inversely correlated to the daily dose of carbamazepine. Intraindividual comparisons in eight patients, with analyses both on and off carbamazepine, confirmed a substantial decrease of the clozapine concentration when carbamazepine was introduced. Four patients treated with clozapine were concomitantly given the antidepressant fluvoxamine. Three of them exhibited a much higher C/D ratio when on fluvoxamine compared with the monotherapy group. Two had their clozapine levels analyzed when on and off fluvoxamine. The dose-normalized clozapine concentration increased by a factor of 5-10 when fluvoxamine was added. We conclude that carbamazepine causes decreased clozapine plasma levels, while fluvoxamine increases the levels. The pathways are not known with certainty, but CYP1A2 may be of major importance for the metabolism of clozapine, since fluvoxamine is a potent inhibitor of this enzyme. A recent panel study suggests that determination of CYP1A2 activity with the caffeine test may be very useful for the dosing of clozapine. The induction of clozapine metabolism by carbamazepine might be partly mediated by CYP3A4.

Disposition of clozapine in man: lack of association with debrisoquine and S-mephenytoin hydroxylation polymorphisms

A large interindividual variability has previously been demonstrated in the bioavailability, steady-state plasma concentrations and clearance of clozapine, an atypical neuroleptic drug. To evaluate the importance of genetic factors in the metabolism of clozapine, its disposition after a single oral dose of 10 mg was studied in 15 healthy Caucasian volunteers. Five of the subjects were poor metabolisers (PM) of debrisoquine, five were PM of S-mephenytoin, and the remaining five were extensive metabolisers (EM) of both probe drugs. There was a 10-fold interindividual variation in Cmax and a 14-fold variation in AUC(0, 24) of clozapine among the 15 subjects studied. The mean (s.d.) Cmax was 117 (81) nmol l-1 and the mean AUC(0,24) value was 890 (711) nmol l-1 h. The value of t1/2,z varied 3-fold with a mean (s.d.) of 13.3 (5.0) h. There were no significant differences in the plasma concentrations or any of the pharmacokinetic parameters of clozapine between PM and EM of debrisoquine, or between the two S-mephenytoin hydroxylation phenotypes. We conclude that neither of the major genetic polymorphisms of oxidative drug metabolism contribute to the large interindividual variability in clozapine pharmacokinetics.

Analgesic effect and plasma concentrations of codeine and morphine after two dose levels of codeine following oral surgery

A double blind randomised cross over investigation was carried out in 25 male patients undergoing two oral surgical extractions, one for each lower wisdom tooth. The two extractions were performed about 6 weeks apart and were carried out under local anaesthesia. One hour after each extraction the patients randomly received 90 or 45 mg codeine. During the following 5 h the patients rated the intensity of their pain on a visual analogue scale. Blood was simultaneously sampled and assayed for codeine and its metabolite morphine. Mean pain intensity difference was just significantly higher after 90 mg codeine compared to 45 mg. The mean plasma concentrations of codeine and morphine were significantly higher after the 90 mg dose. However, for the two dose levels of codeine there was no obvious relationship between the difference in analgesic effect and the difference in the plasma concentration of codeine or morphine. The plasma concentrations of morphine were 2-3% of those of codeine and the levels were relatively low. Local formation of morphine from codeine within the human brain should therefore be investigated. Four patients were unable to demethylate codeine to a detectable plasma concentration of morphine after 90 mg codeine. In those patients the analgesic effect during the first hours was better after 90 mg codeine than after 45 mg. This suggests some analgesic effect of codeine itself.

Transplacental passage of isradipine in the treatment of pregnancy-induced hypertension

The aim of this study was to assess the concentration of isradipine in maternal and fetal plasma, and in amniotic fluid under steady-state conditions. Eight women were treated with 5-mg isradipine tablets twice daily and eight women were given slow-release isradipine capsules (SRO) twice daily for hypertension in pregnancy. Blood and amniotic fluid sampling for analysis of drug concentration was performed at delivery. In the isradipine tablet group, maternal and fetal plasma levels were 788 +/- 701 pg/mL (mean +/- SD) and 270 +/- 90 pg/mL, respectively. The corresponding levels in the SRO-treated group were 463 +/- 217 pg/mL and 185 +/- 95 pg/mL, respectively. In the amniotic fluid, the concentration was 74 +/- 42 pg/mL in the tablet group and 45 +/- 14 pg/mL in the SRO group. Therefore, isradipine passes the placental barrier, but its concentration is considerably lower in the fetal compartments.

Infants and young children metabolise codeine to morphine. A study after single and repeated rectal administration

1. Codeine was administered rectally to thirteen infants and young children undergoing elective surgery. Nine infants (6-10 months old) received a 4 mg suppository and four children (3-4 years old) an 8 mg suppository. Codeine and its metabolite morphine were measured in plasma by GC/MS. 2. The mean concentrations of codeine at 3, 4 and 5 h after administration were 240, 163 and 123 nmol l-1 in the younger and 309, 251 and 169 nmol l-1 in the older patients. The corresponding concentrations of morphine were 8.3, 7.4 and 4.5 nmol l-1 and 6.8, 5.5 and 2.8 nmol l-1 respectively. One patient in each age group had no detectable amounts of morphine. 3. In the four children, the rectal dose was repeated 6-hourly for four doses. The plasma concentrations of codeine and morphine following the fifth dose were similar to those after the first dose. The mean AUC(0,5 h) of morphine was 1.6% that of codeine. 4. In the infants the mean plasma half-lives of codeine and morphine were 2.6 and 2.5 h. The two infants with the lowest body weights had the longest half-lives. 5. The mean morphine/codeine concentration ratio was 4.3% in the infants and 1.6% in the children, suggesting impaired glucuronidation of morphine in the former group. The hourly concentration ratios were almost identical following the first and fifth dose in the children. 6. We conclude that at the age of 6 months infants are capable of O-demethylating codeine to morphine.

Nifedipine as an antihypertensive drug in patients with renal failure--pharmacokinetics and effects

Pharmacokinetics and pharmacodynamics of nifedipine were studied in 12 patients with renal failure and hypertension, after a single dose and during an 18-week treatment period. The plasma concentrations of nifedipine and its first pyridine metabolite were measured by gas chromatography mass spectrometry. The oral plasma clearance of nifedipine was 1189 +/- 876 ml min-1, and the mean plasma half-life (t1/2) was 5.99 +/- 3.05 h. The pyridine metabolite was not retained. Plasma concentrations of nifedipine were found to be significantly correlated with the effects on blood pressure, forearm blood flow and peripheral resistance, and these effects did not vary with the degree of renal failure. Normotension was achieved in eight of the nine patients observed over a period of 4 months with doses in the range 20-40 mg, administered twice daily. The mean Cr-EDTA clearance remained unchanged during the study (initial value 31.4 +/- 12.3 ml min-1; final value 32.7 +/- 14.4 ml min-1), and in three patients it increased. Nifedipine induces a slight increase in metabolic rate in patients with renal failure, but it is not necessary to modify the dose. It is effective in lowering blood pressure, has mild side-effects and may improve renal function in some patients.

Reduced glutamate decarboxylase activity in the subthalamic nucleus in patients with tardive dyskinesia

Glutamate decarboxylase (GAD) activity was measured in the nuclei of the basal ganglia in patients with neuroleptic-induced tardive dyskinesia (TD) and controls matched for age and premortem state. In five TD patients, who all had a sudden death, a significant decrease in GAD activity was found in the subthalamic nucleus (STN). The lowered GAD activity in the STN may represent a biochemical substrate for neuroleptic-induced TD.

Liquid-chromatographic quantification compared with gas-chromatographic-mass-spectrometric determination of verapamil and norverapamil in plasma

A high-performance liquid chromatographic (HPLC) method for determining verapamil and norverapamil in plasma is presented and compared with gas chromatography/mass spectrometry (GC-MS). The plasma samples were extracted at alkaline pH with hexane containing 2-butanol (20 mL/L) and then back-extracted into phosphate buffer (0.1 mol/L, pH 3.0). For chromatography we used a reversed-phase column (Supelcosil LC-18 DB) with a mobile phase of the phosphate buffer and acetonitrile (70/30 by vol). Fluorescence detection was used (excitation at 203 nm, emission at 320 nm). Overall analytical recovery was 85%. Standard curves were linear from 1 to 1000 micrograms/L. The detection limit was 1 microgram/L. The assays are accurate and precise. We found no interferences by those substances tested. Results by HPLC and GC-MS agreed well (r = 0.99) for both verapamil and norverapamil determinations.

Liquid-chromatographic quantification compared with gas-chromatographic-mass-spectrometric determination of verapamil and norverapamil in plasma

A high-performance liquid chromatographic (HPLC) method for determining verapamil and norverapamil in plasma is presented and compared with gas chromatography/mass spectrometry (GC-MS). The plasma samples were extracted at alkaline pH with hexane containing 2-butanol (20 mL/L) and then back-extracted into phosphate buffer (0.1 mol/L, pH 3.0). For chromatography we used a reversed-phase column (Supelcosil LC-18 DB) with a mobile phase of the phosphate buffer and acetonitrile (70/30 by vol). Fluorescence detection was used (excitation at 203 nm, emission at 320 nm). Overall analytical recovery was 85%. Standard curves were linear from 1 to 1000 micrograms/L. The detection limit was 1 microgram/L. The assays are accurate and precise. We found no interferences by those substances tested. Results by HPLC and GC-MS agreed well (r = 0.99) for both verapamil and norverapamil determinations.

Cardiorespiratory and sedative effects of a combination of acepromazine, xylazine and methadone in the horse

Cardiorespiratory and sedative effects of a combination of acepromazine, xylazine and methadone were studied in the horse. Acepromazine and xylazine produced cardiovascular effects whereas methadone mainly affected respiratory rate. Decreases in heart rate, arterial blood pressure and respiratory rate were seen. Sedation was superior to that of acepromazine, xylazine or a combination of these. No serious side effects were seen.

Determination of clozapine and its N-demethylated metabolite in plasma by use of gas chromatography-mass spectrometry with single ion detection

A gas chromatographic-mass spectrometric method with single ion detection has been developed for determination of clozapine and its N-demethylated metabolite norclozapine in plasma. Propylnorclozapine was used as internal standard and the mass spectrometer was adjusted to record the ion m/z 373 for the compounds analyzed. The precision of the method was found to be high, with a relative standard deviation of 6% or less for replicated samples. The limit of determination was 1.0 ng/ml for clozapine and 5.0 ng/ml norclozapine. A significant correlation was obtained between the daily oral dose of clozapine within the dose interval 100-800 mg/day and the plasma level of clozapine in 22 chronic schizophrenic patients. The plasma levels of clozapine and norclozapine were also significantly correlated. The quotient norclozapine/clozapine showed great interindividual variation and was not correlated to the daily dose of clozapine. The method is rapid and sensitive to allow evaluation of the pharmacokinetic properties of clozapine in the treatment of schizophrenic patients.

Clinical pharmacokinetics of clozapine in chronic schizophrenic patients

The clinical pharmacokinetics of clozapine, an atypical neuroleptic, was evaluated in 10 chronic schizophrenic male patients after intravenous and oral administration. The mean equilibrium-state concentration ratio between blood and plasma was experimentally determined to be 0.87. The average values for blood clearance, hepatic extraction ratio and oral bioavailability were 250 ml/min, 0.2 and 0.27, respectively. Plasma concentration peaked on average at 3 h. The mean volume of distribution at steady-state and the terminal half-life was 1.6 l/kg and 10.3 h, respectively. A large fraction of the dose is most probably metabolized by some extrahepatic presystemic routes. The large inter-individual variability in the bioavailability and clearance is probably the main reason for large variation in the steady-state plasma level in patients receiving the same oral dosage regimen.

Metabolism of mono-(2-ethylhexyl)phthalate in fetal, neonatal and adult rat liver

The aim of the investigation was to study to what extent maturity influences the metabolism of mono-(2-ethylhexyl)phthalate (MEHP), the primary metabolite of the plasticizer di-(2-ethylhexyl)phthalate. The conversion of MEHP to its (omega-1)-hydroxylated product was determined in liver microsomes from fetal, neonatal (1- and 5-day-old) and adult rats. Product formation was determined by gas chromatography-mass spectrometry. The results show that fetal and neonatal as well as adult rat livers are capable of metabolizing MEHP by (omega-1)-hydroxylation. Preparations from 1- and 5-day-old rats were much more efficient than those from fetal rats. The transition into adult life gave no further increase in hydroxylase activity as compared to that in 5-day-old rats. The work shows that there is a rapid postnatal development of MEHP (omega-1)-hydroxylase activity in the rat.

CSF and plasma pharmacokinetics of pethidine and norpethidine in man after epidural and intrathecal administration of pethidine

The disposition of pethidine and its main metabolite, norpethidine, in cerebrospinal fluid (CSF) and plasma was studied in 11 thoracic surgery patients after lumbar epidural (100 mg; n = 6) or lumbar intrathecal (25 mg; n = 5) administration of pethidine. Pethidine appeared more slowly in plasma after intrathecal than after epidural administration (tmax 2.3 h and 14 min, respectively), but systemic bioavailability was similar. The CSF concentrations of pethidine were higher than those in plasma after both routes of administration. The maximal CSF/plasma concentration ratio was 6000 to 45,000 after intrathecal administration but was only 26 to 97 after the epidural route. Pethidine was rapidly distributed in CSF; nine to ten h after the intrathecal and epidural injections the CSF/plasma concentration ratios were 12 to 89 and 2 to 33, respectively. The calculated bioavailability in CSF of epidural pethidine was 10.3%. The terminal elimination half-life of pethidine was 6.0 h (CSF) and 5.4 h (plasma) after intrathecal administration and 8.6 h (CSF) and 8.8 h (plasma) after epidural injection. The volume of distribution of unchanged pethidine in the subarachnoid space was 13 ml.kg-1 and clearance from the CSF was 15 microliters.kg-1.min-1. In all patients receiving intrathecal pethidine and in some patients after epidural pethidine, CSF norpethidine concentrations were higher than those in plasma; the maximum CSF norpethidine was 102 to 1211 ng.ml-1 and 14 to 210 ng.ml-1 and the maximum CSF/plasma norpethidine concentration ratios were 21 to 652 and 0.6 to 14 times after intrathecal and epidural administration, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Constant-rate infusion of nicotine and cotinine. I. A physiological pharmacokinetic analysis of the cotinine disposition, and effects on clearance and distribution in the rat

The tissue partition of cotinine was measured by a GC-MS method following a 6-day constant-rate input of nicotine and cotinine to male rats by means of an osmotic minipump. The tissue-to-blood partition coefficients of cotinine were calculated for adipose (0.08), brain (0.48), heart muscle (0.51), following the cotinine infusion. When nicotine was infused the tissue partitioning of cotinine increased by a factor of 2.3-4.9, depending on the tissue sampled. Another group of animals were killed at timed intervals from 10 min to 30 hr, after having received a single intravenous bolus dose of 0.5 mg cotinine, and the washout of cotinine was traced in blood and tissues. A physiological model was used to simulate the disposition of cotinine. Generally, the model-predicted concentrations were consistent with those found experimentally. The fractional uptake of cotinine into various tissues was simulated. Blood, intestinal, and skeletal muscle tissues embodied more than 70% of the total body load of the drug. Clearance (Cl), volume of distribution (Vd), and the biological half-life (t1/2) were calculated both from the infusion study and by fitting a monoexponential model to the iv blood data of the rat. Significant differences were found in the apparent clearance calculated from the single iv bolus dose compared to the constant rate infusion. The volume of distribution was, however, consistent from both studies. The impact of a change in clearance was also simulated.

Effects of buprenorphine in heroin addicts

Twelve heroin addicts on the 8th day after withdrawal, and 8 healthy volunteers were given a single i.m. injection of buprenorphine 0.6 mg and their subjective response rated on 10 psychological variables. Pre-injection rating differed significantly between addicts and controls on 7 variables out of 10. Following buprenorphine more subjective changes were noted in the control group which became more calm, depressed, more aware of the environment, sleepy, tired, intoxicated, dizzy and nauseated. The drug addicts reported changes only in 2 variables (less tense and dysphoric) but otherwise showed no significant changes. These findings support the notion that buprenorphine induces low or normalizing effects in heroin addicts. This drug might thus be suitable for maintenance therapy in opiate addiction.

Verapamil and norverapamil in plasma and breast milk during breast feeding

The concentrations of verapamil and norverapamil have been measured in milk and plasma samples from a 32 year-old woman treated with verapamil 80 mg tds while breast-feeding her child. The average steady-state concentrations of verapamil and noverapamil in milk were, respectively, 60% and 16% of the concentrations in plasma. The breast-fed child received less than 0.01% of the dose of verapamil given to the mother. No verapamil or norverapamil (less than 1 ng/ml) could be detected in the plasma from the child.

Pharmacokinetics of haloperidol in psychotic patients

Nine psychotic patients under continuous oral treatment with haloperidol were randomly given a test dose of 1.5-5 mg haloperidol orally and/or intravenously. Serum levels of haloperidol were determined by high performance liquid chromatography and serum concentration data obtained were submitted to pharmacokinetic analysis. The steady state concentration ratio between blood and plasma was determined and found to be 0.79 +/- 0.03. The blood clearance was then calculated to be 550 +/- 133 ml/min. The mean hepatic extraction ratio was intermediate (0.37). Consequently, for a drug mainly eliminated by hepatic metabolism like haloperidol, the total blood clearance and the extent of oral bioavailability can be affected by changes in hepatic blood flow, hepatic enzyme activities and drug binding. During continuous oral treatment with haloperidol, however, it can be shown that changes in the total metabolic capacity of the liver due to hepatic enzyme induction or inhibition should be important for the therapeutic effects of haloperidol. The volume of distribution at steady state (Vdss) was large (7.9 +/- 2.5 l/kg). The terminal half-life was 18.8 h after intravenous and 18.1 h after oral administration. The oral bioavailability (0.60 +/- 0.18) were in accordance with previous results in healthy subjects. A mean lag time after oral dose was 1.3 +/- 1.1 h and a longer absorption half-life (1.9 +/- 1.4 h) was found in the patients compared with healthy volunteers.

Spontaneous chewing movements in rats during acute and chronic antipsychotic drug administration

Single intraperitoneal doses of various antipsychotic drugs (clozapine 6, 12, 25 mg/kg, sulpiride 100 mg/kg, haloperidol 0.5, 1.0, 2.0 mg/kg, fluphenazine 0.5, 1.0, 2.0 mg/kg) induced a depression of the spontaneous chewing movement (SCM) rate in rats during the first 6-8 hours. Haloperidol and fluphenazine elicited a rebound increase in SCM on day 2-5, while clozapine and sulpiride did not. Atropine (5 mg/kg) reduced the SCM rate. During chronic administration for 10 months clozapine (50 mg/kg/day) caused no changes in the SCM rate. Sulpiride (120 mg/kg/day) gave a marginal rise above control levels, while thioridazine (40 mg/kg/day), chlorpromazine (30 mg/kg/day), fluphenazine (0.6 mg/kg/day) and haloperidol (0.4 mg/kg/day) produced highly significant increases in SCM rates. It is suggested that the present animal model may prove useful for monitoring the risk of tardive dyskinesia with individual drugs.

Analysis of pethidine disposition in the pregnant rat by means of a physiological flow model

The disposition of pethidine (meperidine) in the pregnant rat is described by means of a physiological flow model. The model includes arterial and venous blood, brain, fat, fetal, hepatic, intestinal, muscular, pulmonar, and renal tissues. The concentration-time profiles of pethidine calculated by the model are consistent with experimental data, except for the brain and renal tissues, where the model predicts initially higher concentrations. Simulations are carried out to further explore the contribution from different organs on the kinetics in blood and tissues. The tissue-to-blood partition coefficients vary over a range from 5 to 316, where fat has the lowest and liver the highest after a correction is made due to hepatic extraction. Rapid uptake occurs into highly perfused organs such as brain, kidneys, liver, and lungs, followed by fetus, intestines, muscle, and fat. Data indicate no marked membrane resistance to pethidine of the investigated organs, except for fetal tissues, but rather a perfusion-limited uptake. Simulations suggest that muscles and adipose tissue play an important role in the rat, becoming the major reservoir of drug during the intermediate and terminal elimination phase, respectively. Volume of distribution and the biological half-life agree with reported findings. Pethidine is subject to a high systemic blood clearance, which exceeds the total hepatic blood flow in the rat. No degradation of pethidine is found in blood, and therefore a pulmonary expression for pethidine clearance is added as a potential source of pethidine elimination. The elimination of pethidine after a single i.v. bolus does is found to be dependent on simulated changes in cardiac output and hepatic blood flow. A simulation is performed with the scaled model to mimic the human concentration-time profiles in maternal blood and brain tissues and fetal tissue during repetitive doses of pethidine.

Pharmacokinetics of verapamil in patients with hypertension

Twelve hypertensive patients (WHO Stage I-II) were given oral verapamil (Isoptin) b.d. or t.d.s. as long-term treatment. The pharmacokinetics of verapamil and norverapamil were studied both after single and b.d. and t.d.s. doses of verapamil 240, 360 or 480 mg daily adjusted according to the blood pressure response. The apparent oral clearance of verapamil was decreased after both the twice and thrice daily dosage regimens (1.38 and 1.841/min, respectively) as compared to the single dose (4.391/min). The plasma half-life of verapamil was increased from 3.34 h (single dose) to 4.65 h (b.i.d.). Decreased elimination of norverapamil was also found after multiple doses of verapamil, as shown by an increase in the adjusted AUC of norverapamil (adjusted to a verapamil dose of 80 mg), namely from 574.9 h X ng X ml-1 (single dose) to 1172 h X ng X ml-1 (b.d.) and to 841 h X ng X ml-1 (t.d.s.). The plasma half-life of norverapamil increase from 5.68 h to 7.34 h during twice daily dosing. During thrice daily verapamil, no increase in plasma half-life was found either for verapamil or norverapamil, probably due to the relatively short sampling time (6 h). The plasma concentration of verapamil and the reduction in supine systolic and diastolic blood pressure were correlated. The mean decrease in supine systolic blood pressure was 5.8 mm Hg per 100 ng verapamil/ml plasma, and for diastolic pressure 2.9 mm Hg per 100 ng verapamil/ml plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of di-(2-ethylhexyl) phthalate and five of its metabolites on rat testis in vivo and in in vitro

In an attempt to establish which compound or compounds are responsible for the testicular damage observed after administration of di-(2-ethylhexyl) phthalate (DEHP) in rats, the effects of the parent compound and five of its major metabolites (mono-(2-ethylhexyl) phthalate (MEHP), 2-ethylhexanol (2-EH), mono-(5-carboxy-2-ethylpentyl) phthalate, mono-(2-ethyl-5-oxohexyl) phthalate and mono-(2-ethyl-5-hydroxyhexyl) phthalate) were investigated in vivo and in vitro. The concentrations of MEHP and the three MEHP-derived metabolites in plasma were determined after single and multiple oral doses of DEHP. The plasma concentrations and areas under the plasma concentration-time curves (AUC's) of each of the MEHP-derived metabolites were considerably lower than those of MEHP both after single and after repeated administration of 2.7 mmol of DEHP/kg body weight. The mean elimination half-life of MEHP was significantly shorter in animals given repetitive doses than in those given a single dose, but there was no statistically significant difference between the mean AUC values. No testicular damage was observed in young rats given oral doses of 2.7 mmol of DEHP or 2-EH/kg body weight daily for five days. In animals which received corresponding doses of MEHP the number of degenerated spermatocytes and spermatids was increased, whereas no such effects were found in animals given the MEHP-derived metabolites. MEHP was also the only compound that enhanced germ cell detachment from mixed primary cultures of Sertoli and germ cells.

Distribution of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in experimental animals studied by postiron emission tomography and whole body autoradiography

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a selective potent neurotoxin which has induced a syndrome similar to parkinsonism both in man and in monkeys. At autopsy degeneration of pigmented nerve cells in the pars compacta of the substantia nigra has been confirmed. The regional distribution of intravenously administered 1-(11C-methyl)-4-phenyl-1,2,3,6-tetrahydropyridine (11C-MPTP) in the brain of Rhesus monkeys was studied by positron emission tomography and the whole body distribution in mice was documented by autoradiography and by impulse counting of selected tissues. A very rapid and high uptake of 11C-MPTP derived radioactivity was seen in areas corresponding to striatum and midbrain, including the substantia nigra area. No elimination from these regions was seen during the study period of 2 h. The uptake was in the order of 7-8 times the homogenous distribution of the radioactivity in the monkey. The uptake was generally high also in other regions of the brain, but there some elimination could be distinguished. Pretreatment of the monkey with spiperone, a selective dopamine receptor antagonist, did not alter uptake nor the kinetics of the 11C-MPTP derived radioactivity. Thus 11C-MPTP does not have a high affinity for postsynaptic dopamine receptors. A remarkably high uptake of 11C-MPTP derived radioactivity was seen in the eye of the monkey. The selective uptake of radioactivity in the eye was also confirmed in pigmented but not in albino mice. The melanin affinity of MPTP may cause high intracellular concentrations of the compound or its metabolites in the melanin containing nerve cells in substantia nigra, which may explain the serious vulnerability of these neurons to MPTP.

Receptor binding of N-(methyl-11C) clozapine in the brain of rhesus monkey studied by positron emission tomography (PET)

By means of positron emission tomography the uptake and kinetics of N-(methyl-11C)clozapine in different brain regions have been studied in Rhesus monkeys. 11C-clozapine rapidly entered the brain and maximum radioactive uptake was seen 5-12 min after administration. Highest uptake was measured in the striatum. Other regions with an uptake higher than in the cerebellum were thalamus and mesencephalon. The radioactivity from different brain regions decreased with an elimination half-life of about 5 h and parallelled the plasma kinetics of unlabelled clozapine. The striatum/cerebellum ratio of 11C-clozapine-derived radioactivity remained constant during the period studied and did not change after pretreatment with atropine. In contrast, the striatum/cerebellum ratio was somewhat lower after pretreatment with N-methylspiperone (NMSP), indicating competition for the same binding sites in the striatum. After pretreatment with increasing doses of clozapine, a dose-dependent protection of binding sites in the striatum for 11C-NMSP was seen. It is concluded that clozapine is more loosely bound to dopamine receptors in the striatum than N-methylspiperone and that the kinetics of clozapine in the brain parallel that in the plasma. The binding properties of clozapine within the brain may explain some of the clinical properties of the drug.

Plasma concentrations of codeine and its metabolite, morphine, after single and repeated oral administration

Plasma concentrations of codeine and its demethylated metabolite, morphine, were determined after single and repeated oral administration of codeine. Twelve healthy volunteers received two doses of codeine 60 mg, 2.8 h apart. In order to achieve steady-state conditions codeine 60 mg was then taken every 8 h for a further five doses. The plasma concentrations of codeine and morphine after the first, second and seventh doses were analyzed by GC-MS. The maximum plasma concentrations of codeine and morphine were reached about 1 h after administration and this time interval did not change on repeated administration. The peak plasma codeine was higher after the second dose of codeine than after the first and the concentration resembled that at steady-state. For morphine, the plasma concentration did not increase significantly after the second dose. Both after a single dose and during steady-state the plasma concentration of morphine was only 2-3% of that of codeine. It seems unlikely that morphine plays a significant role in the analgesic efficacy of single or repeated doses of codeine.