The effects of acute falciparum malaria on the disposition of caffeine and the comparison of saliva and plasma-derived pharmacokinetic parameters in adult Nigerians

Objectives: The pharmacokinetics of caffeine and its dimethylxanthine metabolites were evaluated in Nigerians, for whom it is normal to consume caffeine-containing beverages during ill health and recuperation in the belief that caffeine aids early recovery from illness; however, there are no data defining the kinetics of caffeine in healthy and ill Nigerians. Materials and methods: A single oral dose of 300 mg caffeine was given to ten healthy adult Nigerians and ten adults suffering from acute uncomplicated Plasmodium falciparum malaria infection. Caffeine and its dimethylxanthine metabolites were measured in plasma and saliva of healthy subjects and in plasma of patients suffering from malaria using high-performance liquid chromatography. Results: The plasma pharmacokinetics of caffeine per se in both groups was similar (P > 0.05). The maximum plasma concentration (C_max) of paraxanthine was significantly lower (P < 0.05) in malaria (0.9 ± 0.4 μg/ml) than in healthy controls (1.4 ± 0.5 μg/m1), and the paraxanthine:caffeine area under the plasma concentration–time curve ratio, an index of cytochrome P₄₅₀ (CYP)IA2 activity was significantly lower (P < 0.05) in malaria patients (0.5 ± 0.1) than in healthy controls (0.3 ± 0.2). The elimination half-life of theophylline was longer in malaria, while the area under the plasma concentration–time curve of theobromine was significantly higher (P < 0.05) in malaria (7.1 ± 3.4 μg ml⁻¹ h) than in healthy adults (4.1 ± 2.2 μg ml⁻¹ h). Excellent correlations were found between saliva and plasma concentrations of caffeine (r ²=0.98) with a mean saliva:plasma concentrations ratio of 0.7 ± 0.1. The plasma concentrations (C_max and AUC) were therefore higher than the corresponding salivary levels, so that the apparent oral clearance calculated for saliva exceeded the true oral clearance based on plasma data. Conclusions: Acute Plasmodium falciparum malaria produced significant changes in the disposition of caffeine metabolites. Analysis of concentrations in saliva is a useful non-invasive method for monitoring the kinetics of caffeine and paraxanthine in Nigerians. Received: 14 April 1999 / Accepted in revised form: 30 November 1999     

Pharmacokinetics and pharmacodynamics of a premixed formulation of soluble and protamine-retarded insulin aspart

Objective: With the aim to obtain a premixed rapid-acting insulin with a serum insulin profile more closely resembling the endogenous meal-stimulated serum insulin profiles, a 30/70 (rapid/intermediate-acting) premixed suspension of the rapid-acting insulin analogue insulin aspart (BIAsp30) was compared with a similar premixed suspension of biphasic human insulin 30/70 (BHI30) after a single subcutaneous injection. Methods: The study had a randomised, double-blind, two-period crossover design. Twenty-four healthy male subjects received a single subcutaneous dose of either 0.2 U · kg⁻¹ bodyweight of BIAsp30 or BHI30 on two study days. Results: BIAsp30 was absorbed faster than BHI30, as reflected in the area under the insulin concentration-time curve from 0 to 90 min after dosing [AUC_{(0–90 min)}]. This was significantly larger for BIAsp30 than for BHI30 (1403 ± 372 versus 752 ± 191 mU · l⁻¹ · min⁻¹ [mean ± SD]; P < 0.0001). Furthermore, the time to maximum serum insulin concentration (t_max) of BIAsp30 was approximately half the t_max of BHI30 (60 [45–70] versus 110 [90–180] min [median, interquartile range]; P=0.0001) and the maximum insulin concentration (C_max) was significantly higher for BIAsp30 than for BHI30 (23.4 ± 5.3 versus 15.5 ± 3.7 mU · l⁻¹ [mean ± SD]; P < 0.0001). The serum glucose profiles showed a significantly earlier onset of the glucose-lowering effect following BIAsp30 than following BHI30. Conclusions: The improved absorption properties of soluble insulin aspart in its premixed formulation provide a basis for a more efficient meal-related glucose control and immediate pre-meal delivery when compared with a similar human premixed insulin in the treatment of diabetes mellitus. Received: 22 November 1999 / Accepted in revised form: 7 April 2000     

Inhibition of IK,ACh current may contribute to clinical efficacy of class I and class III antiarrhythmic drugs in patients with atrial fibrillation

Inward rectifier potassium currents I_K1 and acetylcholine activated I_K,ACh are implicated in atrial fibrillation (AF) pathophysiology. In chronic AF (cAF), I_K,ACh develops a receptor-independent, constitutively active component that together with increased I_K1 is considered to support maintenance of AF. Here, we tested whether class I (propafenone, flecainide) and class III (dofetilide, AVE0118) antiarrhythmic drugs inhibit atrial I_K1 and I_K,ACh in patients with and without cAF. I_K1 and I_K,ACh were measured with voltage clamp technique in atrial myocytes from 58 sinus rhythm (SR) and 35 cAF patients. The M-receptor agonist carbachol (CCh; 2 μM) was employed to activate I_K,ACh. In SR, basal current was not affected by either drug indicating no effect of these compounds on I_K1. In contrast, all tested drugs inhibited CCh-activated I_K,ACh in a concentration-dependent manner. In cAF, basal current was confirmed to be larger than in SR (at −80 mV, −15.2 ± 1.2 pA/pF, n = 88/35 vs. −6.5 ± 0.4 pA/pF, n = 194/58 [myocytes/patients]; P < 0.05), whereas CCh-activated I_K,ACh was smaller (−4.1 ± 0.5 pA/pF vs. −9.5 ± 0.6 pA/pF; P < 0.05). In cAF, receptor-independent constitutive I_K,ACh contributes to increased basal current, which was reduced by flecainide and AVE0118 only. This may be due to inhibition of constitutively active I_K,ACh channels. In cAF, all tested drugs reduced CCh-activated I_K,ACh. We conclude that in cAF, flecainide and AVE0118 reduce receptor-independent, constitutively active I_K,ACh, suggesting that they may block I_K,ACh channels, whereas propafenone and dofetilide likely inhibit M-receptors. The efficacy of flecainide to terminate AF may in part result from blockade of I_K,ACh.     

High thiamine diphosphate concentrations in erythrocytes can be achieved in dialysis patients by oral administration of benfotiamine

Objective: The influence of either orally administered S-benzoylthiamine-O-monophosphate (benfotiamine) or thiamine nitrate on the thiamine status was tested in a randomised, two-group comparison study in 20 end-stage renal disease (ESRD) patients. Main outcome measures were the pharmacokinetics of thiamine diphosphate (TDP) in blood, the in vitro erythrocyte transketolase activity, its activation coefficient (α-ETK) and the TDP concentration in erythrocytes. Methods: After ingestion of a single dose of either 100 mg thiamine nitrate (corresponding to 305 μmol thiamine) or 100 mg benfotiamine (corresponding to 214 μmol thiamine), the blood levels of thiamine phosphate esters were analysed by means of high-performance liquid chromatography for a 24-h period. The TDP concentration in erythrocytes was calculated using the haematocrit and TDP concentration in blood. Erythrocyte transketolase activity and α-ETK were measured before and 10 h after administration. The pharmacokinetics of TDP in blood were compared with healthy subjects of other studies retrieved from database query. Results: Regarding the blood concentrations of TDP, the patients with ESRD had a 4.3 times higher area under the concentration–time curve after benfotiamine administration than after thiamine nitrate. After benfotiamine administration, the peak plasma concentration of TDP exceeded that in healthy subjects by 51%. In the ESRD patients, after 24 h, the mean TDP concentration in erythrocytes increased from 158.7 ± 30.9 ng/ml initially to 325.8 ± 50.9 ng/ml after administration of benfotiamine and from 166.2 ± 51.9 ng/ml to 200.5 ± 50.0 ng/ml after thiamine nitrate administration. The ratio between the maximum erythrocyte TDP concentration and basal concentration was 2.66 ± 0.6 in the benfotiamine group and 1.44 ± 0.2 in the group receiving thiamine nitrate (P < 0.001). After 24 h, it was 2.11 ± 0.4 and 1.23 ± 0.2, respectively. The transketolase activity increased from 3.54 ± 0.7 μkat/l initially to 3.84 ± 0.6 μkat/l after benfotiamine intake (P=0.02) and from 3.71 ± 0.8 μkat/l to 4.02 ± 0.7 μkat/l after thiamine nitrate intake (P=0.08). Likewise, α-ETK decreased from initially 1.10 ± 0.07 to 1.04 ± 0.04 (P=0.04) and from 1.12 ± 0.05 to 1.08 ± 0.06 (P=0.09). After 24 h, the phosphorylation ratio in whole blood decreased from 12.9 ± 6.9 initially to 5.6 ± 3.2 after benfotiamine administration (P=0.02) and from 13.5 ± 7.3 to 9.0 ± 4.8 (P=0.03) after administration of thiamine nitrate. No correlation between erythrocyte TDP concentration and transketolase activity and/or α-ETK was observed in ESRD patients, either before or 10 h after administration. Conclusion: Compared with thiamine nitrate, the oral administration of benfotiamine leads to higher TDP concentrations in erythrocytes accompanied with a significant improvement of the erythrocyte transketolase activity in ESRD patients. Received: 4 October 1999 / Accepted: 15 March 2000     

Inhibition of metoprolol metabolism and potentiation of its effects by paroxetine in routinely treated patients with acute myocardial infarction (AMI)

Objective To investigate the influence of paroxetine on metoprolol concentrations and its effect in patients treated for acute myocardial infarction (AMI) who are routinely given paroxetine as a co-treatment of depression. Methods We recruited 17 depressed AMI patients who received metoprolol as a routine part of their therapy (mean dose 75 ± 39 mg/day). Patients were genotyped for CYP2D6 *3, *4 and gene duplication. Metoprolol and α-hydroxy-metoprolol were analyzed in plasma 0, 2, 6 and 12 h post-dose. Heart rates (HR) at rest were registered after each sampling. Paroxetine 20 mg daily was then administered, and all measurements were repeated on day 8. Results All patients were genotypically extensive metabolizers (EMs) (nine with *1/*1 and eight with *1/*3 or *4). Following the administration of paroxetine, mean metoprolol areas under the concentration–time curve (AUC) increased (1064 ± 1213 to 4476 ± 2821 nM × h/mg per kg, P = 0.0001), while metabolite AUCs decreased (1492 ± 872 to 348 ± 279 n M × h/mg per kg, P < 0.0001), with an increase of metabolic ratios (MR) (0.9 ± 1.3 to 26 ± 29; P < 0.0001). Mean HRs were significantly lower after the study week at each time point. Mean area under the HR versus time curve (AUEC) decreased (835 ± 88 to 728 ± 84 beats × h/min; P = 0.0007). Metoprolol AUCs correlated with patients’ AUECs at the baseline (Spearman r  = −0.64, P < 0.01), but not on the eighth day of the study. A reduction of metoprolol dose was required in two patients due to excessive bradycardia and severe orthostatic hypotension. No other adverse effects of the drugs were identified. Conclusion A pronounced inhibition of metoprolol metabolism by paroxetine was observed in AMI patients, but without serious adverse effects. We suggest, however, that the metoprolol dose is controlled upon initiation and withdrawal of paroxetine.     

Gender differences in the prevalence,risk and clinical correlates of tardive dyskinesia in Chinese schizophrenia

Objective  Despite extensive use of antipsychotic drug treatment, few studies address the prevalence of tardive dyskinesia (TD) in homogeneous ethnic groups such as the Chinese. This study examined gender-specific relationships between TD and symptom levels in schizophrenia among Han Chinese, which have previously received little systematic study. Materials and methods  Five hundred and twenty-two inpatients with schizophrenia receiving long-term treatment with antipsychotics were evaluated with the AIMS. The patient’s psychopathology was assessed with the Positive and Negative Syndrome Scale (PANSS). Demographic and clinical data were collected from a detailed questionnaire and medical records. Results  The overall TD prevalence was 33.7% with rates of 39.2% (138/352) in males and 22.4% (38/170) in females (χ ² = 14.6, df = 1, p < 0.0001; adjust odds ratio 2.06; CI, 1.32–3.16). The AIMS score in patients with TD was lower in females than males (5.3 ± 3.9 vs 6.7 ± 3.7, t = 2.52, p < 0.01) after adjustment for the significant covariates. TD was associated with the negative symptoms on the PANSS in both genders, and with age, PANSS total and positive symptoms in men, not women. Conclusion  Our present findings suggest that there are gender differences in the prevalence, risk, and clinical correlates of TD in schizophrenia. Although this study is limited by cross-sectional designs, the magnitude of these gender-specific differences is substantial and deservers further prospective study.     

Short- and long-term treatments with iloprost in diabetic patients with peripheral vascular disease: effects on the cardiovascular risk factor plasminogen activator inhibitor type-1

Objectives: Iloprost, an analogue of prostacyclin, is often utilised in subjects with diabetes mellitus complicated by macroangiopathy. Methods: The effects of iloprost infusion on plasminogen activator inhibitor type-1 (PAI-1), glucometabolic control and cardiovascular equilibrium in patients with type-2 diabetes mellitus and peripheral arterial occlusive disease were investigated. Thirteen (7 men/6 women) normal-weight, normotensive and non-smoker type-2 diabetic patients (63.8 ± 3.4 years, mean ± SD) with peripheral arterial occlusive disease, stage-II according to Fontaine classification, were enrolled. Eight (four men/four women) patients underwent three study designs, each separated by a 1-week interval: study I, infusion of iloprost (3 ng kg⁻¹ min⁻¹ for 5 h) for 1 day alone (short-term treatment); study II, infusion of saline (for 5 h) for 1 day (control treatment); study III, infusion of iloprost (3 ng kg⁻¹ min⁻¹ for 5 h) over a period of 28 days (long-term treatment). The remaining five (three men/two women) patients underwent study IV only, infusion of saline over a period of 28 days (placebo treatment). Plasma levels of glucose, plasminogen, PAI-1 activity and fibrinogen, blood pressure and heart rate were determined in all studies, while plasma insulin levels, blood HbA_1c, walking distance and Winsor index only in studies III and IV. Results: Both short- and long-term treatments with iloprost significantly reduced PAI-1 activity (baseline vs end: 17.4 ± 1.9 AU/ml vs 15.0 ± 1.6 AU/ml, P < 0.02; 20.5 ± 7.6 AU/ml vs 7.9 ± 2.1 AU/ml, P < 0.002, respectively). Long-term treatment with iloprost significantly increased walking distance (baseline vs end: 325 ± 41 m vs 496 ± 52 m, P < 0.0001), but not Winsor index. Neither glucometabolic control nor cardiovascular equilibrium were affected by short- and long-term treatments with iloprost. Control and placebo treatments did not cause any significant modifications in the parameters evaluated. Conclusion: If confirmed by further investigations, the results of this pilot study suggest that iloprost, infused for both brief and long periods, is able to reduce the cardiovascular risk factor PAI-1, increases free walking capacity and does not affect glucometabolic control and blood pressure in type-2 diabetic patients complicated by macroangiopathy. Received: 25 August 1998 / Accepted in revised form: 8 June 1999     

Effects of gender and moderate smoking on the pharmacokinetics and effects of the CYP1A2 substrate tizanidine

Objective We studied the effects of gender and smoking on the pharmacokinetics and effects of the cytochrome P450 (CYP) 1A2 substrate tizanidine. Methods Seventy-one healthy young volunteers (male and female nonsmokers, male smokers) ingested 4 mg tizanidine. Plasma concentrations and pharmacodynamics of tizanidine were measured, and a caffeine test was performed. Results Among nonsmokers, the peak concentration (C_max) and area under concentration-time curve from 0 to infinity [AUC(0-∞)] of tizanidine did not differ significantly between females and males. However, the half-life (t_1/2) was 9% shorter in female nonsmokers than in male nonsmokers (P < 0.05). In male smokers, the t_1/2 was 10% shorter and the weight-adjusted AUC(0-∞) 33% smaller than in male nonsmokers (P < 0.05). The caffeine/paraxanthine ratio was 35–40% smaller (P = 0.001) in male smokers than in nonsmoking males or females, but did not differ between males and females. Tizanidine lowered blood pressure and caused drowsiness significantly (P < 0.05) more in females than in either male groups. The effects on blood pressure were smallest in male smokers (P < 0.05). Conclusions Gender by itself seems to have no clinically significant effect on the pharmacokinetics of tizanidine, whereas smoking reduces plasma concentrations and effects of tizanidine. Any possible effect of gender and smoking is largely outweighed by individual variability in CYP1A2 activity due to genetic and environmental factors and in body weight. Careful dosing of tizanidine is warranted in small females, whereas male smokers can require higher than average doses. This study was supported by grants from the Helsinki University Central Hospital Research Fund, the National Technology Agency, and the Sigrid Jusélius Foundation, Finland.     

The effect of cimetidine on the steady-state pharmacokinetics and pharmacodynamics of warfarin in humans

Objective: The interaction of multiple oral doses of cimetidine on the steady-state pharmacokinetics and pharmacodynamics of warfarin was investigated in six healthy male volunteers. Methods: The subjects were given individually adjusted doses of warfarin to achieve therapeutic levels of prothrombin activity. The established daily maintenance oral dose of warfarin was kept stable throughout the trial and, on study days 8–14, each volunteer received a 800-mg daily dose of cimetidine. The degree of anticoagulant response produced by warfarin was quantified by the determination of both the prothrombin time and factor-VII clotting activity. Results: Cimetidine co-administration had no significant effect on the pharmacokinetics of the more potent S-warfarin but significantly increased by 28% (P < 0.05) mean R-warfarin trough plasma concentrations and decreased by 23% (P < 0.05) mean R-warfarin apparent clearance. Both prothrombin time and factor-VII clotting activity displayed considerable inter-subject variability and were not significantly affected by concurrent cimetidine treatment. The reduction of apparent clearance of R-warfarin by cimetidine was found to be the effect of inhibition of the formation of warfarin metabolites as determined by apparent formation clearance values (±SD) of R-6-hydroxywarfarin (31.1 ± 7.4 ml/h baseline; 18.5 ± 4.5 ml/h at end of cimetidine treatment; P < 0.01), and R-7-hydroxywarfarin (6.9 ± 1.3 ml/h baseline; 4.3 ± 1.1 ml/h at end of cimetidine treatment; P < 0.01). Conclusion: Cimetidine stereoselectively affects the steady-state pharmacokinetics of warfarin by inhibiting the disposition of the less potent R-warfarin in humans. However, this interaction is likely to be of minimal clinical significance in most patients. Received: 11 December 1998 / Accepted in revised form: 17 March 1999     

Measurement of furancarboxylic acid, a candidate for uremic toxin, in human serum, hair, and sweat, and analysis of pharmacological actions in vitro

3-Carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF), a candidate for uremic toxin, was measured in human hair for examining a possible utility as indicator of renal dysfunction. The serum concentration of CMPF was much higher (32.3 ± 2.7 μg/ml, n=17; mean ± SEM) in uremic patients aged 40–55 years receiving hemodialysis treatment than in healthy younger subjects (3.61 ± 0.19 μg/ml, n=22), aged 18–23 years. However, the hair concentration of CMPF tended to be lower in the patients (6.8 ± 1.7 ng/10 mg hair) than in the healthy younger subjects (15.8 ± 4.5 ng/10 mg) and was significantly lower than that in the healthy age-matched subjects (22.4 ± 5.3 ng/10 mg, n=12), aged 40–47 years. Since CMPF was measurable in the sweat (4.4 ± 3.7 ng/mg) collected from six out of seven healthy subjects examined, it was suggested that the contribution of sweat to the measurement of CMPF in hair was considerable. The fact that the uremic patients undergoing hemodialysis therapy had less sweat than healthy subjects may explain the lower concentration of CMPF in the patients' hair. The pathophysiological roles of CMPF in the body were attempted to be explored by using excised guinea pig organs, and human platelets and neutrophils. CMPF showed no remarkable effects in the concentration range of ≤10⁻⁴ M except for only slight suppression of spontaneous contracture of guinea pig tenia coli at 10⁻⁴ M. As far as the organs and tissues examined in the present study are concerned, the biological activity of CMPF itself, if any, may be very weak. Precaution should be taken against the delivery of a substance through sweat to hair when a small amount of substance is attempted to be measured in hair by employing a sensitive analytical method. Received: 14 September 1999 / Accepted: 3 November 1999     

Detection of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage, in white blood cells of workers occupationally exposed to styrene

Styrene-7,8-oxide (SO), the major in vivo metabolite of styrene, is a genotoxic compound and a potential carcinogenic hazard to occupationally exposed workers. The aim of the present work was to investigate the ability of styrene exposure to induce formation of 8-hydroxy-2′-deoxyguanosine (8-OHdG) in white blood cells (WBC) of boatbuilders occupationally exposed to styrene. The study of these adducts was conducted to see if styrene exposure can cause oxidative damage of DNA. The 8-OHdG/10⁵ dG ratio from 17 styrene-exposed workers showed significant increases (mean ± SD, 2.23 ± 0.54, median 2.35, P < 0.001) in comparison to the controls (1.52 ± 0.45, median 1.50). However, 11 out of 17 workers who were between the ages of 32 and 60 years and had been occupationally exposed to styrene for >10 years showed higher 8-OHdG/10⁵ dG ratios (2.31 ± 0.62, median 2.37) in comparison to 6 workers with <6 years of occupational styrene-exposure (2.11 ± 0.36, median 2.05; P > 0.05, no significant difference between the two groups of workers). The studies presented here provide an indication that styrene exposure can result in oxidative DNA damage. Received: 13 January 1997 / Accepted: 24 March 1997     

Abnormal pain response in pain-sensitive opiate addicts after prolonged abstinence predicts increased drug craving

Rationale  Craving is a primary feature of opiate addiction and is clinically significant because of its potential to trigger opiate use and relapse. Opiate use can also produce abnormal pain perception. We predicted that for opiate addicts (OAs), there may be an association between these two major features of addiction (drug craving and abnormal pain responses). Objectives  To examine pain responses in abstinent opiate addicts in comparison with healthy controls using a cold-pressor test (CPT) and investigate the correlations of cue-induced drug craving with pain responses. Material and methods  Fifty-four abstinent OAs and 46 healthy subjects participated in the CPT, and the OAs were also exposed to heroin-related cues the day before the pain test. Outcome measures included pain-tolerance time, VAS ratings of pain intensity and distress, and (in the cue-exposure procedure) VAS ratings of heroin craving and anxiety. Results  In the CPT, abstinent addicts showed shorter pain-tolerance time (85.1 ± 14.1 s vs. 133.7 ± 16.7 s, p < 0.05) and higher ratings of pain distress (61 ± 3.2 vs. 45.6 ± 3.2, p < 0.01) compared to healthy controls. When we divided the addicts and controls into pain-sensitive (PS) and pain-tolerant (PT) groups by dichotomizing each group in terms of pain-tolerance time, we again found differences between the two PS groups (37.3 ± 3.5 s vs. 57.4 ± 5.1 s, p < 0.01 for pain-tolerance time; 66.7 ± 3.2 vs. 52.4 ± 3.3, p < 0.01 for distress ratings). For all participants, pain-tolerance time was negatively correlated with VAS ratings for pain intensity and distress. More importantly, the PS addicts reported greater cue-induced craving than the PT addicts (17.8 ± 2.2 vs. 4.5 ± 4.2, p < 0.05). For the addict group as a whole, pain distress (the affective aspect of pain) was positively correlated with intensity of cue-induced craving measured on a different day (r = 0.33, p = 0.01). Conclusions  A hyperalgesic state persists for at least 5 months in abstinent OAs and is predictive of cue-induced craving. Longitudinal research is needed to clarify the direction of causation between hyperalgesia and opiate addiction.     

The pharmacokinetics of caffeine in Nigerian children suffering from malaria and kwashiorkor

Objectives: Caffeine-containing beverages are generally consumed by Nigerians suffering from malaria and kwashiorkor in the belief that caffeine aids early recovery from these illnesses, which are common in the tropics. However, there are no studies on the influence of these diseases on the absorption and pharmacokinetics of caffeine in Africans. Materials and methods: A single oral dose of caffeine was given to five healthy children and to five and seven children suffering from malaria and kwashiorkor, respectively. Caffeine and its dimethylxanthine metabolites were measured in plasma using high-performance liquid chromatography. Results: The maximum plasma concentration (C_max) of caffeine and the time of C_max were similar (P > 0.05) in the three groups. However, the elimination half-life of caffeine was significantly longer in children with malaria (9.2 ± 3.5 h) (P < 0.01) and kwashiorkor (13.1 ± 7.9 h) (P < 0.05) than in the healthy controls (3.7 ± 1.8 h). The total plasma oral clearance of caffeine of 4.4 ± 1.9 ml/min/kg in healthy children was significantly higher (P < 0.01) than in those with kwashiorkor (2.0 ± 0.9 ml/min/kg) and malaria (1.6 ± 1.0 ml/min/kg) (P < 0.05). Paraxanthine was the principal metabolite in all the three groups with C_max significantly higher in healthy children (1.3 ± 0.3 μg/ml) than in children with malaria (0.8 ± 0.4 μg/ml) (P < 0.05) and kwashiorkor (0.3 ± 0.1 μg/ml) (P < 0.0001). CYP1A2 activity, measured by the plasma ratios of paraxanthine: caffeine, was significantly lower in kwashiorkor and malaria. Conclusions: This study showed that the plasma kinetics of caffeine are significantly altered in malaria and kwashiorkor, and CYP1A2 activity was lower in these two disease groups. Received: 12 April 1999 / Accepted in revised form: 30 November 1999     

Higher serotonin transporter occupancy after multiple dose administration of escitalopram compared to citalopram: an [123I]ADAM SPECT study

Objectives Previous studies have investigated the occupancy of the serotonin reuptake transporter (SERT) after clinical doses of citalopram and other selective serotonin reuptake inhibitors. In the present study, the occupancies of SERT after multiple doses of escitalopram and citalopram were compared using the radioligand [¹²³I]ADAM and single photon emission computed tomography (SPECT). Methods Fifteen healthy subjects received escitalopram 10 mg/day (n = 6) or citalopram 20 mg/day (n = 9) for a total of 10 days. SERT occupancies in midbrain were determined with SPECT and [¹²³I]ADAM at three different time points: at baseline (no medication) and at 6 and 54 h after last drug intake. Results At 6 h after the last dose, mean SERT occupancies were 81.5 ± 5.4% (mean±SD) for escitalopram and 64.0 ± 12.7% for citalopram (p < 0.01). At 54 h after the last dose, mean SERT occupancies were 63.3 ± 12.1% for escitalopram and 49.0 ± 11.7% for citalopram (p < 0.05). The plasma concentrations of the S-enantiomer were of the same magnitude in both substances. For both drugs, the elimination rate of the S-enantiomer in plasma was markedly higher than the occupancy decline rate in the midbrain. Conclusion The significantly higher occupancy of SERT after multiple doses of escitalopram compared to citalopram indicates an increased inhibition of SERT by escitalopram. The results can also be explained by an attenuating effect of R-citalopram on the occupancy of S-citalopram at the SERT.     

Impact of CYP2D6*10 on H1-antihistamine-induced hypersomnia

Objective This study investigated the relevance of the cytochrome P450 (CYP) 2D6 genotype to the adverse drug reactions (ADRs) of H1-antihistamines and the level of sedation.Methods Japanese participants in a health screening program were asked to describe any past history of ADRs. Any subjects reporting ADRs induced by H1-antihistamines were then individually interviewed and defined as cases. Excessive daytime sleepiness, which had occurred in the cases as an H1-antihistamine-induced ADR, was assessed by the Epworth sleepiness scale (ESS), and an ESS score ≥12 was considered hypersomnia. CYP2D6*4, *5, *14, and *10 were genotyped by a panel of polymerase chain reaction techniques.Results Out of 2,074 participants, 100 cases (M:F = 37:63, mean age 51.9 ± 9.2 years) were eligible for analysis. The most common etiological drug was chlorpheniramine, which is the most frequently used H1-antihistamine in Japan. CYP2D6*10 allele and genotypes were more frequently found in the cases than in the healthy Japanese population in a large study (P < 0.005 and P = 0.039, respectively), but no difference was observed in the null alleles and genotypes. The ESS scores in 75 cases (M:F=25:50) who had experienced excessive daytime sleepiness were 9.5 ± 5.5 in men and 12.9 ± 6.1 in women (P < 0.001, cases vs. 34 subjects without symptoms; P = 0.001 men vs. women). The occurrence of hypersomnia increased as the number of CYP2D6 mutant alleles increased (P = 0.045).Conclusion The results suggest that the presence of the CYP2D6*10 allele is a risk factor for development of H1-antihistamine-induced ADRs in Japanese.     

Grapefruit juice has no effect on quinine pharmacokinetics

Objective: As quinine is mainly metabolised by human liver CYP3A4 and grapefruit juice inhibits CYP3A4, the effect of grapefruit juice on the pharmacokinetics of quinine following a single oral dose of 600 mg quinine sulphate was investigated. Methods: The study was carried out in ten healthy volunteers using a randomised cross-over design. Subjects were studied on three occasions, with a washout period of 2 weeks. During each period, subjects received a pretreatment of 200 ml orange juice (control), full-strength grapefruit juice or half-strength grapefruit juice twice daily for 5 days. On day 6, the subjects were given a single oral dose of 600 mg quinine sulphate with 200 ml of one of the juices. Plasma and urine samples for measurement of quinine and its major metabolite, 3-hydroxyquinine, were collected over a 48-h period and analysed by means of a high-performance liquid chromatography method. Results: The intake of grapefruit juice did not significantly alter the oral pharmacokinetics of quinine. There were no significant differences among the three treatment periods with regard to pharmacokinetic parameters of quinine, including the peak plasma drug concentration (C_max), the time to reach C_max (t_max), the terminal elimination half-life (t_1/2), the area under the concentration–time curve and the apparent oral clearance. The pharmacokinetics of the 3-hydroxyquinine metabolite were slightly changed when volunteers received grapefruit juice. The mean C_max of the metabolite (0.25 ± 0.09 mg l⁻¹, mean ± SD) while subjects received full-strength grapefruit juice was significantly less than during the control period (0.31 ± 0.06 mg l⁻¹, P < 0.05) and during the intake of half-strength grapefruit juice (0.31 ± 0.07 mg l⁻¹, P < 0.05). Conclusion: These results suggest that there is no significant interaction between the parent compound quinine and grapefruit juice, so it is not necessary to advise patients against ingesting grapefruit juice at the same time that they take quinine. Since quinine is a low clearance drug with a relatively high oral bioavailability, and is primarily metabolised by human liver CYP3A4, the lack of effect of grapefruit juice on quinine pharmacokinetics supports the view that the site of CYP inhibition by grapefruit juice is mainly in the gut. Received: 2 November 1998 / Accepted in revised form: 18 February 1999     

Restricted brain penetration of the tyrosine kinase inhibitor erlotinib due to the drug transporters P-gp and BCRP

Purpose Erlotinib (Tarceva?, OSI-774) is a small molecule inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase. As high-grade gliomas frequently show amplification, overexpression and/or mutation of EGFR, this drug has been tested in several clinical trials with glioblastoma patients, but unfortunately, with little success. As erlotinib is a known substrate of P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) we have investigated the effect of these ABC-transporters on the brain penetration of erlotinib. Study design Erlotinib (50 mg/kg) was given by i.p. administration to wild-type (WT), Mdr1ab^-/- (single P-gp knockout), Bcrp1^-/- (single Bcrp1 knockout) and Mdr1ab^-/-Bcrp1^-/- (compound P-gp and Bcrp1 knockout) mice. Drug levels in plasma and tissues were determined by reversed-phase high-performance liquid chromatography. Results Relative to Mdr1ab^-/-Bcrp1^-/- mice that are deficient for both drug transporters, the area under the concentration time curve in brain tissue (AUC)_brain of erlotinib decreased significantly by 1.6-fold in Mdr1ab^-/- mice where Bcrp1 is present (49.6 ± 3.95 versus 31.1 ± 1.7, μg/g*h; P < 0.01). In Bcrp1^-/- mice, were P-gp is present, a more pronounced 3.8-fold decrease to 13.0 ± 0.70, μg/g*h (P < 0.01) was observed, which is close to the 4.5-fold decrease in the AUC_brain of erlotinib found in WT mice where both drug transporters are present (11.0 ± 1.35, P < 0.01). The plasma clearance of erlotinib was similar in mice deficient for P-gp and/or Bcrp1 compared with wild-type mice. In all other tissues the differences between the genotypes were negligible. Conclusions Both P-gp and Bcrp1 reduce the brain penetration of erlotinib. Although P-gp appears to be the most effective factor limiting the brain penetration of erlotinib, the highest brain accumulation was observed when Bcrp1 was also absent. Strategies to inhibit P-gp/BCRP in patients to improve delivery of (novel molecular-targeted) substrate agents, such as erlotinib, to the brain may be required for treatment of intracranial malignancies.     

Effects of carbenoxolone on syncytial electrical properties and junction potentials of guinea-pig vas deferens

The effects of the putative gap junction blocker carbenoxolone on smooth muscle syncytial properties and junction potentials were studied in guinea pig vas deferens (GPVD). Treatment with 50 μM carbenoxolone reversibly and significantly increased input resistance (R _in) (by 682.5 ± 326.0 %, P < 0.05) and abolished cable potentials within 6–7 mins of incubation, without disturbing resting membrane potential. Carbenoxolone reversibly and significantly increased the amplitude of spontaneous excitatory junction potentials (sEJPs) by 96.9 ± 35.45% (P < 0.05), shifted their amplitude distribution rightwards, and reduced their frequency of occurrence by 58.17 ± 17.7% (P < 0.05), without altering their time courses. Similarly, carbenoxolone increased the amplitude of evoked excitatory junction potentials (eEJPs) by 17.7 ± 5.88% and τ _decay by 19.43 ± 8.29% (P < 0.05). Our results indicate that carbenoxolone alters the electrical properties and junctional potentials of the GPVD by a mechanism consistent with a relatively specific block of gap junctions. These results suggest that gap junction mediated cell-to-cell communication may significantly modulate the electrical properties and junctional potentials of the GPVD and consequently the physiological functioning of this tissue.     

Contribution of age,body weight,and CYP2C9 and VKORC1 genotype to the anticoagulant response to warfarin: proposal for a new dosing regimen in Chinese patients

Objective The objective of this study was to assess the contribution of the VKORC1 and CYP2C9 genotypes and age, body size, and weight of the patients to the warfarin dose requirement in a Chinese population. Methods Blood samples were collected from 178 Chinese patients with stable warfarin dose requirements and an international normalized ratio (INR) of the prothrombin time within the target range (1.5–3.0). The polymorphisms for the VKORC1 (-1639GA) and CYP2C9*3 genotypes, venous INR, and plasma concentration and unbound concentration of warfarin were then analyzed. Results VKORC1 (-1639G>A) genotyping showed that 149 patients were homozygous AA, 28 were heterozygous GA, and one was homozygous for the GG genotype. CYP2C9*3 genotyping showed that 162 patients were *1/*1, and 16 patients were heterozygous *1/*3. Patients with the VKORC1(-1639 GG+GA) (3.32 ± 1.02 mg/day) and CYP2C9*1/*1 (2.06 ± 0.82 mg/day) genotypes required a significantly higher warfarin dose than those with the -1639 AA (1.76 ± 0.57 mg/day; P < 0.001) or CYP2C9*1/*3 (1.60 ± 1.29 mg/day; P < 0.001), genotype. The multiple linear regression model for warfarin dose indicated significant contributions from age (r ² = 0.084; P < 0.001), weight (r ² = 0.063; P < 0.001), VKORC1 genotype (r ² = 0.494; P < 0.001), and age, weight, and CYP2C9 and VKORC1 genotype together (r ² = 0.628; P < 0.001). Conclusion This study shows that age, weight and the VKORC1 and CYP2C9 polymorphism affect warfarin dose requirements in our sample of Chinese patients receiving long-term therapy and showing stable control of anticoagulation. It is anticipated that the use of dosing regimens modified by taking into account the contribution of age, weight, and the CYP2C9 and VKORC1 genotypes has the potential to improve the safety of warfarin therapy.     

Prolactin response to nemonapride, a selective antagonist for D2 like dopamine receptors, in schizophrenic patients in relation to Taq1A polymorphism of DRD2 gene

The dopamine D₂ receptor (DRD2) gene has a Taq1A restriction fragment length polymorphism yielding two alleles, A1 and A2. It has been shown that the subjects with less frequent allele, the A1 allele, have lower density and diminished function of DRD2 in the striatum, compared to those with no A1 allele. In the present study, the relationship between this polymorphism and prolactin response to nemonapride, an antipsychotic drug with selective and potent DRD2 antagonistic property, was investigated in 25 Japanese schizophrenic inpatients (13 males, 12 females). The daily dose of nemonapride was fixed at 18 mg, and the duration of treatment was 3 weeks. Taq1A genotypes were determined by the polymerase chain reaction method. Plasma prolactin concentrations were measured by enzyme immunoassay. The subjects were divided into four subgroups by gender and Taq1A genotypes, i.e., six males and eight females with the A1 allele, seven males and four females with no A1 allele. The Δprolactin (change from the pretreatment concentration) at 1 week was significantly (P<0.05) higher in females with the A1 allele (78.0±47.1 ng/ml) than in males with the A1 allele (33.4±14.0 ng/ml) or with no A1 allele (29.5±24.8 ng/ml). In addition, Δprolactin at 3 weeks was significantly (P<0.05) higher in females with the A1 allele (98.1±67.9 ng/ml) than in females with no A1 allele (33.4±24.6 ng/ml), males with the A1 allele (29.1±17.3 ng/ml) or males with no A1 allele (28.6±22.0 ng/ml). The present study thus suggests that female patients with the A1 allele show a greater prolactin response to nemonapride, who may have a high risk for adverse effects associated with neuroleptic-induced hyperprolactinemia. Received: 27 July 1999 / Final version: 9 December 1999