Inhibition of human liver phenol sulfotransferase by nonsteroidal anti-inflammatory drugs

Objective: The aim of this investigation was to study the inhibition of 11 nonsteroidal anti-inflammatory drugs (NSAIDs) on the human liver phenol sulfotransferases (HL-PST) and catechol sulfotransferase (HL-CST). Methods: The activities of HL-PST and HL-CST were measured with 4 μM 4-nitrophenol and 60 μM dopamine (the sulfate acceptors) and 0.4 μM 3′-phosphoadenosine-5′-phosphosulfate [³⁵S] (the sulfate donor). Samples of liver were obtained from five patients, aged 55–79 years, undergoing clinically indicated hepatectomy. The inhibition curves were constructed with at least five concentrations of the inhibitor. Results: With the exception of piroxicam, NSAIDs inhibited HL-PST, and the estimates of the inhibitory concentration for 50% of responses (IC₅₀; μM) were: 0.02 (mefenamic acid), 3.7 (diflunisal), 5.4 (nimesulide), 9.5 (diclofenac), 30 (salicylic acid), 41 (ketoprofen), 74 (indomethacin), 159 (ibuprofen), 245 (ketoralac) and 473 (naproxen). With 4-nitrophenol as the variable substrate, the inhibition of salicylic acid on HL-PST was non-competitive and the K_i and K_ies were 18 μM and 21 μM (n = 5; P = 0.548), respectively. HL-CST was less susceptible than HL-PST to inhibition by NSAIDs, with only five drugs inhibiting this enzyme. The IC₅₀ estimates for these drugs (μM) were 76 (mefenamic acid), 79 (diflunisal), 103 (indomethacin), 609 (salicylic acid) and 753 (diclofenac). Conclusion: The comparison of the IC₅₀ estimates of HL-PST with the therapeutic plasma concentrations of NSAIDs corrected for the plasma unbound fraction was consistent with the view that mefenamic acid and salicylic acid, when administered at therapeutic doses, should impair the hepatic sulfation of those compounds that are substrates of phenol sulfotransferase. Received: 7 June 1999 / Accepted in revised form: 13 January 2000     

Effects of fluvastatin therapy on lipids, antioxidants, oxidation of low density lipoproteins and trace metals

Objective: This study was performed to investigate whether it is possible to use saliva instead of blood usually used for therapeutic drug monitoring (TDM) of disopyramide. Methods: Six healthy male volunteers ingested 200 mg of disopyramide base, and the disopyramide concentrations in saliva and plasma (total and unbound) were determined by the HPLC. Results: Disopyramide concentration-time profiles for the saliva were nearly equal to those for the plasma unbound concentrations. A large variation for absorption time of the drug was observed among the subjects. Disopyramide concentrations (C_s) in saliva did not correlated well with plasma total concentrations (C_p), r = 0.799, but did well with unbound concentrations (C_pu), r = 0.969, for the 3–12 h period on the elimination phase. The mean ratio of disopyramide concentrations in the saliva against the plasma unbound concentrations was almost constant (1.02(0.10), CV = 9.7%) for the period. The pharmacokinetic parameters (t_max, t_1/2, AUC, AUMC and MRT values) for disopyramide calculated from the saliva data were nearly equal to those from the unbound data. Conclusion: Disopyramide concentrations in saliva correlated well with plasma unbound concentrations on the elimination phase. Received: 3 June 1996 / Accepted: 12 November 1996     

Lack of enantiomeric influence on the brain cytoprotective effect of ibuprofen and flurbiprofen

R(−) enantiomers of the 2-arylpropionic acid derivatives ibuprofen and flurbiprofen weakly inhibit cyclooxygenase (COX) activity. However, a possible cytoprotective effect has been proposed. The aim of the study is to investigate the possible mechanism of this effect. An in vitro hypoxia–reoxygenation model in rat brain slices was used (n = 6 rats per group). After reoxygenation, we measured LDH efflux (neuronal death), brain prostaglandin E₂ (PGE₂) concentration, interleukins (IL)-1β and 10, oxidative and nitrosative stress (lipid peroxides, glutathione, 3-nitrotyrosine, and nitrites/nitrates). Anti-COX activity was measured in human whole blood. Racemic, R(−), and S(+) enantiomers of ibuprofen and flurbiprofen were tested. All compounds had a cytoprotective effect with IC₅₀ values in the range of 10⁻⁵ M. R(−) enantiomers did not significantly inhibit brain PGE₂. The concentration of IL-1β was reduced by 53.1% by the racemic form, 30.6% by the S(+) and 43.2% by the R(−) enantiomer of ibuprofen. The IL-10 concentration increased significantly only with S(+)-flurbiprofen (33.1%) and R(−)-flurbiprofen (26.1%). Lipid peroxidation was significantly reduced by all three forms of flurbiprofen. Nitrite + nitrate concentrations were reduced by racemic, S(+), and R(−)-flurbiprofen. Peroxynitrite formation (3-nitrotyrosine) was significantly reduced by racemic and S(+)-ibuprofen. COX inhibition is not the main mechanism of cytoprotection for these compounds. Their influence on inflammatory mediators and oxidative and nitrosative stress could account for the potential cytoprotective effect of R(−) enantiomers.     

Estimation of the area under the concentration-time curve of racemic lansoprazole by using limited plasma concentration of lansoprazole enantiomers

Objective The purpose of this study was to identify the common time point that gives plasma concentrations of lansoprazole enantiomers that adequately reflect the AUC of racemic lansoprazole. Methods A randomized, double-blind, placebo-controlled, crossover study in three phases was conducted at intervals of 2 weeks. Eighteen healthy Japanese volunteers, including three CYP2C19 genotype groups, took a single 60-mg oral dose of lansoprazole after 6 days of pretreatment, with either clarithromycin (800 mg/day), fluvoxamine (50 mg/day), or a placebo. Multiple linear regression analysis was used to identify the most informative sampling times of (R)- and (S)-lansoprazole, using one to three samples to estimate the AUC_0−∞ of racemic lansoprazole. Results The best R ² in each prediction formula for the AUC of racemic lansoprazole using one, two, and three sampling points of (R)- and (S)-lansoprazole based on the data sets from all three pretreatment groups (n = 54) were 0.897, 0.930, and 0.929, respectively. The best prediction formula for the AUC of racemic lansoprazole, using the fewest sampling points of (R)- and (S)-lansoprazole, was (P < 0.001), where C_3h is the plasma concentration 3 h after administration, G1 = 1 for the homozygous extensive metabolizer (EM) and 0 for the other genotypes, G2 = 1 for the heterozygous EM and 0 for the other genotypes. Conclusions C_3h monitoring of (R)- and (S)-lansoprazole is a useful time point to estimate the AUC of racemic lansoprazole. This method of plasma concentration monitoring at a few time points within 3 h might be more suitable for AUC estimation than CYP2C19 genotyping, particularly when lansoprazole is co-administered with CYP inhibitors.     

Pharmacokinetics of oral entacapone after frequent multiple dosing and effects on levodopa disposition

Objective: Entacapone is a peripherally acting catechol O-methyltransferase (COMT) inhibitor used as an adjunct to each daily levodopa/dopa decarboxylase (DDC) inhibitor dose in the treatment of Parkinson's disease. Parkinsonian patients with advanced disease and motor fluctuations take several doses of levodopa daily, due to the short action of levodopa in this patient population. The present study was conducted in order to evaluate the pharmacokinetics of entacapone after multiple dosing and the pattern of COMT inhibition in erythrocytes during the first day of dosing as well as during steady state. Furthermore, the disposition of plasma levodopa and carbidopa was studied after a single dose of levodopa/carbidopa during the same conditions. Methods: Twelve healthy male volunteers received 200 mg entacapone eight times daily during study day 1 and day 6 at 2-h intervals from 0800 hours to 2200 hours. During days 3, 4 and 5, 200 mg of entacapone was taken ten times daily, from 0800 hours to 0200 hours on the following day. One levodopa/carbidopa tablet (100/25 mg) was taken on study day 1 and day 6 at 1000 hours. Plasma entacapone concentrations and erythrocyte COMT activities were measured frequently on study days 1–2 and 6–7, and twice daily on study days 3–5. Pharmacokinetic parameters calculated from plasma drug concentrations on days 1–2 and 6–7 were compared with each other. Results: There were no differences in maximal plasma concentration (C_max), time to maximal drug concentration in plasma (t_max), elimination half-life (t_1/2) and area under the plasma concentration–time curve (AUC) of entacapone between day 1 and day 6. The mean t_1/2 values of entacapone were 1.3 h and 1.8 h during the first and sixth days, respectively; the difference was not significant. No signs of accumulation of entacapone were noted after the first day. Entacapone reduced erythrocyte COMT activity after the first dose, and this effect was quite stable during frequent dosing. There were no indications of accumulation of COMT inhibition during frequent dosing of entacapone. There were no between-day differences in C_max, t_1/2 (2.4 h on days 1–2 and 2.3 h on days 6–7) or AUC of levodopa, whereas t_max occurred at 0.8 h on day 1 and at 1.2 h on day 6 (P = 0.03). There were no between-day differences in the pharmacokinetic parameters (C_max, t_max and AUC) of carbidopa. Conclusion: Even when dosed frequently, there are neither indications of accumulation of entacapone nor of its COMT inhibiting activity. Received: 28 December 1998 / Accepted in revised form: 29 March 1999     

Clinical efficacy, safety and pharmacokinetics of a newly developed controlled release morphine sulphate suppository in patients with cancer pain

Objective: To compare the efficacy, safety and pharmacokinetics of a newly developed controlled- release suppository (MSR) with MS Contin tablets (MSC) in cancer patients with pain. Methods: In a double-blind, randomised, two-way cross-over trial, 25 patients with cancer pain were selected with a morphine (M) demand of 30 mg every 12 h. Patients were divided into two groups. Group 1 received active MSC (30 mg) and placebo MSR, followed by placebo MSC and active MSR (30 mg) each for a period of 5 days. Group 2 started with active MSR and placebo MSC, followed by active MSC and placebo MSR, each for a period of 5 days. Blood for determination of plasma concentration of morphine (M) and its 3- and 6-glucuronides (M3G, M6G) was collected, and area under the plasma concentration–time curve (AUC)_0–12 h, peak plasma concentration (C_max), time to reach C_max (t_max), and C0 and C12 of M, M6G and M3G were determined on day 5 and day 10. Intensity of pain experienced by each patient was assessed every 2 h on a 0–10 scale, while side effects and rescue medication were recorded. Results: Twenty patients (ten patients in each group) completed the study. A pronounced inter-patient variability in plasma concentrations of M, M3G and M6G was observed after administration of both forms. Apart from the C0 and C12, no significant differences in AUC_0–12 h, t_max and C_max of morphine between the rectal and oral route of administration were found. In the case of the metabolites, it was found that AUC_0–12 h and C_max of M6G, and AUC_0–12 h, C_max, C0 and C12 of M3G after rectal administration were significantly lower than after oral administration. However, apart from the t_max of M6G, none of the pharmacokinetic parameters of M, M6G or M3G met the criteria for bioequivalence. There were no significant (P=0.44) differences in pain intensity score between the oral and rectal forms within the two groups, regardless of the treatment sequence. No treatment differences in nausea, sedation or the demand on escape medication (acetaminophen tablets) between the rectal and oral forms were observed. Conclusion: The newly developed controlled-release M suppository is safe and effective and may be a useful alternative for oral morphine administration in patients with cancer pain. Received: 3 September 1999 / Accepted: 15 March 2000     

Pharmacokinetics of (deaminohydroxy)toremifene in humans: a new, selective estrogen-receptor modulator

Purpose: New selective estrogen-receptor modulators for the treatment and prevention of osteoporosis, cardiovascular disease and breast cancer are currently the focus of intense research. (Deaminohydroxy)toremifene (Z-2-[4-(4-chloro-1,2-diphenyl-but-1-enyl)phenoxy]ethanol; FC-1271a) has been shown to prevent bone resorption in rats while having no or weak estrogen-like effects on the uterus, which makes it a good candidate drug for osteoporosis prevention. Our purpose here was to examine the pharmacokinetics of (deaminohydroxy)toremifene in humans included in two phase-I studies. Methods: The first was a single-dose, dose-escalation study with 28 healthy male volunteers. Doses ranged from 10 mg to 800 mg. The second study was conducted during a 12-week period with 40 healthy, post-menopausal women, who received repeated oral doses of 25–200 mg. Standard pharmacokinetic parameters were assessed. Results: In the single-dose study, time to reach peak concentration (t_max) ranged from 1.3 h to 4.0 h; peak concentration (C_max) ranged from 15 ng/ml to 445 ng/ml; and the estimated terminal elimination half-life (mean ± SD; t_1/2) was 24.8 ± 7.0 h. In the repeated-dose study, t_max ranged from 1.9 h to 2.6 h at 6 weeks and from 2.5 h to 2.9 h at 12 weeks. C_max ranged from 295 ng/ml to 1043 ng/ml at 6 weeks and from 25 ng/ml to 1211 ng/ml at 12 weeks. The average t_1/2 at all dose levels was 29.7 ± 1.5 h (overall mean ± SD). Strong linear correlations between the dose and C_max and between the dose and the area under the curve were observed in both studies. Conclusion: Our results indicate that (deaminohydroxy)toremifene has pharmacokinetics suitable for single daily dosing. The prophylactic use of this agent in women susceptible to development of osteoporosis, cardiovascular disease and breast cancer could, therefore, be tested using a once-daily dosing schedule similar to those of other hormone-replacement therapy regimens. Received: 12 July 1999 / Accepted in revised form: 18 May 2000     

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     

Pharmacokinetics and tolerability of formoterol in healthy volunteers after a single high dose of Foradil dry powder Inhalation via aerolizerTM

Objective: The pharmacokinetics of the long-acting β₂-agonist formoterol fumarate, which is a racemate of the (S,S)- and (R,R)-enantiomers were evaluated in 12 healthy (eight male, four female) volunteers after a single inhaled high dose of 120 μg of formoterol fumarate. The tolerability and safety were also assessed. Methods: Each volunteer inhaled the single 120-μg dose through the Aerolizer device within 2–5 min, using ten 12-μg dry powder capsules for inhalation. Formoterol, i.e., the sum of both enantiomers, was determined in plasma over 24 h, whereas the separate enantiomers were determined in urine over 48 h. Incidence, seriousness and severity of adverse experiences, electrocardiogram (ECG), including the corrected QT interval (QTc) calculation, systolic blood pressure, heart rate, and plasma potassium levels were recorded. Results: In nine of the 12 volunteers, the peak plasma concentration of formoterol was observed already at 5 min after inhalation. The absorption kinetics were complex, as depicted by multiple peaks or shoulders within 0.5–6 h after inhalation. Mean with (SD; n = 12) of maximum concentration (C_max) and area under the curve (AUC) of formoterol in plasma were 266 (108) pmol · l⁻¹ and 1330 (398) pmol · h · l⁻¹, respectively. The moderate inter-individual variability in systemic exposure of formoterol reflects the homogeneous pharmacokinetics of the drug. A predominant slow elimination of formoterol from plasma with a mean half-life (t_1/2) of 10 h was demonstrated. Assuming linear kinetics in plasma suggested by urinary data, the steady-state trough plasma levels of formoterol for a b.i.d. dosing regimen are predicted to amount to 20% of C_max. In urine, mean with (SD; n = 10) of the amount excreted over 48 h was 3.61 (0.89)% of dose for the pharmacologically active (R,R)-enantiomer and 4.80 (1.33)% of dose for the (S,S)-enantiomer. The terminal half-lives calculated from the excretion rate-time curves, i.e., 13.9 h and 12.3 h for the (R,R)- and (S,S)-enantiomer, respectively, confirm the slow elimination of formoterol from plasma. The dose inhaled was 10 times the most frequently recommended dose (12 μg) and 5 times the highest recommended dose (24 μg). Ten of 12 subjects experienced mild and transient nervousness. Pulse readings demonstrated the maximum mean increase of 25.8 beats · min⁻¹ at 6 h. The mean maximum QTc increase was 25 msec at 6 h. Pulse and QTc values returned to baseline or close to baseline values at 24 h or before. Potassium levels in plasma decreased in eight out of 12 subjects; the lowest mean value was 3.53 mmol · l⁻¹ at 2 h post-dose. The lowest individual potassium measurement was 2.95 mmol · l⁻¹ between 15 min and 6 h. By 8 h post-dose all values had returned to within the normal ranges. Conclusions: The extremely fast appearance of formoterol in plasma shows the predominance of airways absorption shortly after inhalation. Due to a terminal elimination half-life of about 10 h, sustained systemic concentrations of formoterol are predicted for a twice daily treatment regimen without noteworthy accumulation. The excreted amounts in percent of dose of the enantiomers in urine and the enantiomer ratio are similar to data reported previously after lower doses and suggest linear kinetics for doses between 12 μg and 120 μg of formoterol fumarate. The expected side effects on heart rate, QTc interval, and plasma potassium were small and had no clinical consequences in spite of the very high dose of 120 μg (5 to 10 times the recommended therapeutic dose of Foradil). It should be noted that the impact of high doses may be greater in patients. Nevertheless these findings provide reassurance on the safety margin of formoterol after accidental and intentional overdosing. Received: 22 June 1998 / Accepted in revised form: 2 December 1998     

Bioavailability of intranasal formulations of dihydroergotamine

Objective: A comparison of the pharmacokinetic properties of two novel intranasal preparations of dihydroergotamine mesilate (DHEM) with a commercially available intranasal preparation. Methods: Two intranasal formulations of DHEM in combination with randomly methylated β-cyclodextrin (RAMEB) were prepared. Subsequently, in an open, randomised, crossover study in nine healthy volunteers, the following medication was administered: 2 mg DHEM/2% RAMEB nasal spray ( =two puffs of 100 μl); 2 mg DHEM/4 mg RAMEB nasal powder; 2 mg Diergo nasal spray ( =four puffs of 125 μl); 0.5 mg DHEM i.m., and 2 mg DHEM solution p.o. Results: No statistically significant differences were found in maximum plasma concentration (C_max), time to reach C_max (t_max), area under plasma concentration–time curve (AUC_0–8 h), Frel_(t=8 h) and C_max/ AUC_(t=8 h) for the three intranasal preparations. The relative bioavailabilities of the DHEM/RAMEB nasal spray, the DHEM/RAMEB nasal powder and the commercially available DHEM nasal spray were 25%, 19% and 21%, respectively, in comparison with i.m. administration. The relative bioavailability after oral administration was 8%. Conclusion: The pharmacokinetic properties of the novel intranasal preparations are not significantly different from the commercially available nasal spray. Advantages of the DHEM/RAMEB nasal spray are (1) less complicated handling, (2) reduction of the number of puffs and (3) a preference by the volunteers. Received: 12 February 1999 / Accepted in revised form: 23 August 1999