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The hypoalgesic effect of single oral doses of 100 mg imipramine and 125 mg codeine was evaluated in a randomised, placebo-controlled, double-blind, 3-way cross-over experiment including 18 healthy volunteers. Pain tests were performed before and 90, 180, 270, 360 and 450 min after medication. The tests included determination of pain tolerance thresholds to pressure, pain detection/tolerance thresholds to single electrical sural nerve stimulation and pain summation at tolerance threshold to repetitive electrical sural nerve stimulation (temporal summation) and pain experienced during the cold pressor test, rated as peak pain intensity, pain average intensity and discomfort. Compared to placebo, imipramine significantly increased pressure pain tolerance threshold (P = 0.03) and increased pain tolerance threshold (P = 0.05) and pain summation threshold (P = 0.03), but not pain detection threshold to electrical stimulation. Imipramine did not cause significant changes in pain perception during the cold pressor test. Codeine significantly increased pressure pain tolerance threshold (P = 0.02), pain detection (P = 0.04) and pain tolerance threshold (P = 0.01) and pain summation threshold (P = 0.02) to electrical stimulation. In addition, codeine reduced the pain experienced during the cold pressor test (P = 0.04-0.003). It is concluded that both imipramine and codeine inhibit temporal pain summation, whereas only codeine reduces cold pressor pain. Pain summation may be a key mechanism in neuropathic pain. Imipramine has a documented effect on such pain conditions on temporal summation. The present study showed that codeine also inhibits temporal summation, which is in line with the clinical observations indicating that opioids relieve neuropathic pain.

Therapeutic Drug Monitoring (TDM) is based on a series of theoretical assumptions, a clinical pharmacological rationale, scientific documentation and a practical implementation, respecting the theoretical and scientific basis. The clinical pharmacological rationale for TDM; a pharmacokinetic variability exceeding therapeutic index and dose titration on the basis of clinical or paraclinical measurements not being feasible, limits TDM to a minor fraction of all drugs available. The theoretical assumption that blood concentration measurements reflect/predict the tissue/receptor concentration and the clinical endpoints, requires several points to be considered such as concentration fluctuations, protein binding, active metabolites, etc. A relatively constant ratio between blood and tissue/receptor concentration is generally assumed, but the important role of transporter proteins, with inter- and intraindividual variability due to polymorphisms, inducers and inhibitors seriously challenge this basic assumption. Concentration–effect relationships concerns groups of patients and indicate the probability of a given response (therapeutic/toxic) at a given concentration. Dose–effect and concentration–effect studies of drugs like digoxin, lithium and antidepressants have shown that the dose–effect or concentration–effect curves for therapeutic effect and tolerability are flat and overlapping. Dose–effect studies, now standard in drug development, represent a unique possibility to examine dose–concentration–effect relationships of new drugs.

Prescription databases are indispensible in drug safety research and surveillance. For suspected rare serious adverse drug reactions, the confirmation and quantitative risk assesment requires proper epidemiological studies. Often prescription databases provide the information on drug exposure for such studies. Abberant drug utilization in terms of overuse, underuse, polypharmacy etc. may be a threat to the health of the patient, and these aspects can best be studied by prescription databases. In cases of international drug safety alerts, prescription databases may provide information required for rational actions to be taken.

Sumatriptan ranked second in expenditure on drugs for outpatients in Denmark in 1995. The 5% of patients who were heavy users of sumatriptan accounted for nearly 40% of consumption. 1 2 We conducted a population based interview study to evaluate the appropriateness of sumatriptan use. View this table: Characteristics of study subjects and their use of sumatriptan in relation to peak sumatriptan consumption. Values are numbers (percentages) unless indicated otherwise Subjects were recruited through community pharmacies in Funen county, Denmark (population 465 000). Patients who presented prescriptions during two weeks in February 1996 were invited to participate, and relevant data for 1992-6 were retrieved from the county prescription registry.3 Sumatriptan consumption was described as the defined daily dose unit (100 mg for oral sumatriptan and 6 mg for subcutaneous sumatriptan). For each subject, peak dispensing of sumatriptan in any 30 day period was determined from register data. Patients were then classified into three groups: high peak users (≥60 units/30 days), intermediate peak users (30-59 units), and low peak users (

Objective: Codeine O-demethylation to morphine is catalysed by the genetic polymorphic sparteine oxygenase (CYP2D6). The objective of the present study was to assess the analgesic effect of codeine on different types of experimental pain in relation to sparteine phenotype. Methods: Fourteen extensive (EMs) and 14 poor metabolizers (PMs) of sparteine completed a randomized, double-blind, three-way, cross-over study with a single oral dose of codeine (75 or 100 mg) against morphine (20 or 30 mg) and placebo. Pain tests performed before and 1, 2, 3, and 4 h after medication included the cold pressor test and pain thresholds for heat and pressure stimulation. Adverse effects were rated by a structured interview. Results: After morphine, morphine and morphine-6-glucuronide were present in equal amounts in plasma of PMs and EMs. After codeine, neither morphine nor morphine-6-glucuronide could be detected in 13 of the 14 PMs, whereas at least one of the compounds could be detected in all EMs. Peak pain and discomfort rated on a VAS scale during the cold pressor test were significantly reduced by morphine in both EMs and PMs, with a median peak change of 8.5 and 7.0 mm, respectively, for peak pain, and 11.5 and 15.5 mm, respectively, for discomfort. Codeine only reduced these pain measures significantly in EMs, with a median peak change of 5.5 mm for peak pain and 10.5 mm for discomfort. Pain detection and tolerance thresholds to heat and pressure were not consistently altered by either morphine or codeine. In PMs, adverse effects were significantly more pronounced on morphine than on codeine and only showed a slight difference between codeine and placebo. In EMs, there was no difference between codeine and morphine and more pronounced adverse effects on both drugs as compared to placebo. Conclusion: This study confirms that codeine O-demethylation depends on CYP2D6; it shows that the 6-glucuronidation of morphine is independent of CYP2D6; it supports the theory that the analgesic effect of codeine depends on its O-demethylation; and it indicates that this is probably also the case for the adverse effects. The results lend no support to the suggestion of a non-opioid analgesic effect of codeine.

Objectives: The purpose of this pharmacokinetic study was to investigate the dose-dependent inhibition of model substrates for CYP2D6, CYP2C19 and CYP1A2 by four marketed selective serotonin reuptake inhibitors (SSRIs): citalopram, fluoxetine, fluvoxamine and paroxetine. Methods: The study was carried out as an in vivo single-dose study including 24 young, healthy men. All volunteers had been identified as sparteine- and mephenytoin-extensive metabolisers. The volunteers received in randomised order, at weekly intervals, increasing single oral doses of one of the four SSRIs, followed 3 h later by sparteine (CYP2D6), mephenytoin (CYP2C19) and caffeine (CYP1A2) tests. Fluoxetine was given at 3-week intervals because of the long half-life of fluoxetine and its metabolite norfluoxetine. Citalopram, fluoxetine and paroxetine were given in doses of 10, 20, 40 and 80 mg and fluvoxamine was given in doses of 25, 50, 100 and 200 mg. Results: With increasing doses, there was a statistically significant increase in the sparteine metabolic ratio (MR) (P < 0.01, Page's test for trend) for all four SSRIs. The increase was modest after intake of citalopram and fluvoxamine, while the increase was more pronounced after fluoxetine intake, although no volunteers changed phenotype from extensive metabolisers to poor metabolisers. Three of the six volunteers changed phenotype from extensive metabolisers to poor metabolisers after intake of 40 or 80 mg paroxetine. There was a statistically significant increase in the mephenytoin S/R ratio (P < 0.01, Page's test for trend) with increasing doses of fluoxetine and fluvoxamine, but not after citalopram and paroxetine. However, no volunteers changed phenotype from extensive to poor metabolisers of S-mephenytoin. After intake of fluvoxamine, the urinary excretion of the metabolites related to N3 demethylation of caffeine were below the limit of quantification, whereas there were no significant changes in the urinary caffeine metabolic ratios after intake of the other three SSRIs. Conclusion: This investigation confirms that paroxetine and fluoxetine are potent inhibitors of CYP2D6, that fluvoxamine and fluoxetine are moderate inhibitors of CYP2C19 and that fluvoxamine is a potent inhibitor of CYP1A2 in humans in vivo. The clinical prediction of interaction from single-dose experiments may have to take the degree of accumulation during steady-state after multiple doses into account.

1. We conducted a descriptive cross-sectional study of asthma therapy among young adults to assess to what extent the current guidelines for asthma therapy have been implemented. In particular, we examined the use of inhaled corticosteroids in heavy users of inhaled beta-adrenoceptor agonists. 2. Data were retrieved from a population-based prescription database. For each of the years 1991 and 1994, all 20 to 44-year-olds who redeemed anti-asthma medication in the Odense area (210,000 inhabitants) were studied. 3. We identified the number of users and total sales volume for specific anti-asthma medications in defined daily doses (DDD) as well as the number of users and median annual doses of common regimens. Combined use of inhaled corticosteroids and inhaled beta-adrenoceptor agonists was also described. 4. The annual sales volume of anti-asthma drugs increased by 23% to 927,636 DDD from 1991 to 1994. Inhaled corticosteroids were mainly responsible for this with a 52% increase in number of users and an 88% increase in DDD. Inhaled beta-adrenoceptor agonists used in monotherapy remained the most popular regimen in 1994 (1685 users = 39%). Inhaled corticosteroids in combination with inhaled beta-adrenoceptor agonist were the second most popular regimen in 1994 (1308 users = 30%), increasing by 64% as compared with 1991. However, among patients with an annual use of inhaled beta-adrenoceptor agonist of 200 DDD (1600 "puffs') or more the percent of patients not receiving inhaled corticosteroids at all only fell from 37 to 33%. Though the number of patients being treated with inhaled corticosteroids has increased, there is still evidence of a substantial underuse.

S-Mephenytoin and chloroguanide (proguanil) oxidation was studied in 216 Tanzanians. The mephenytoin S/R ratio in urine ranged from 0.9, were arbitrarily defined as poor metabolizers of mephenytoin. The chloroguanide/cycloguanil ratio ranged from 0.82 to 249. There was a significant correlation between the mephenytoin S/R ratio and the chloroguanide/cycloguanil ratios (r(s) = 0.73; p < 0.00001). This indicates that cytochrome P4502C19 or CYP2C19 is a major enzyme that catalyzes the bioactivation of chloroguanide to cycloguanil. Choroguanide is a pro-drug, and hence a low CYP2C19 activity may lead to prophylactic failure caused by inadequate formation of cycloguanil. Fifty-eight women who previously took either 200 mg chloroguanide daily (n = 26) or 200 mg chloroguanide daily plus 300 mg chloroquine weekly (n = 32) in a malaria chemoprophylaxis study showed that there was a significant correlation between the number of earlier breakthrough parasitemia episodes and the chloroguanide/cycloguanil ratio (r(s) = 0.30; p = 0.02). The breakthrough rate did not correlate with the S/R mephenytoin ratio. However, other factors, such as exposure to mosquitoes and sensitivity of the plasmodium to cycloguanil, are probably more important.

1. In order to assess the prevalence of concurrent use of more than one major psychotropic drug (polypsychopharmacy) in out-patients, a prescription database study was conducted in the Odense area for a period of 2 years. 2. During the index period 5.12% of the inhabitants purchased major psychotropic drugs. Of these, 14% had a period of polypsychopharmacy recorded. The age-specific prevalence of users increased with age, the prevalence for over 90 years of age was 18%. Sixty-seven per cent of the psychotropic drug users were women. 3. For neuroleptic and antidepressant users, about 20% were subject to polypsychopharmacy, for lithium 61%. The most prevalent combination was neuroleptics-neuroleptics. In none of the 10 most prevalent combinations were the mean daily doses significantly lower on polypsychopharmacy compared with single drug regimens, in two they were higher. 4. Polypsychopharmacy with psychotropic drugs was frequent in out-patients. In polypsychopharmacy daily doses were not lowered in order to limit side effects.

1 A prescription database study was conducted to describe the out-patient utilization of neuroleptics in the Odense area (207,000 inhabitants) during a period of 1 year. 2 Neuroleptic drug use is widespread, the period prevalence being 2.45% of the population. 3 The prevalence increases with increasing age. Fifteen percent of the population aged 90 years or more received neuroleptic drugs in spite of the many warnings against side effects in the elderly. 4 Estimated daily doses of neuroleptics were considerably lower than the Defined Daily Dose, probably as a reflection of many neuroleptics being prescribed to non-psychotic patients, in whom lower doses are used. 5 For perphenazine, a comparison of estimated daily doses from this study with doses from patients whose treatment had been adjusted by plasma concentration monitoring showed that generally much lower doses were used by patients included in this study.

The effect of the selective serotonin reuptake inhibitor citalopram on diabetic neuropathy symptoms was examined in a double‐blind, placebo‐controlled, crossover study for two 3‐week periods. Citalopram was given as a fixed dose of 40 mg/day. Data from 15 patients could be included in the statistical analysis. Citalopram significantly relieved the symptoms of neuropathy as measured by both observer‐ and self‐rating in comparison with placebo. The steady‐state plasma concentration of citalopram was 10 to 890 nmol/L. There was no significant relationship between the plasma concentration of citalopram and the effect of treatment as measured by observer‐ or self‐rating. Two of 17 patients, both receiving citalopram, left the study because of side effects (nausea and vomiting or gastric upset and diarrhea). Side‐effect ratings were significantly higher during administration of citalopram than during administration of placebo, but citalopram was generally well tolerated. Compared with earlier results obtained with imipramine administered on the basis of plasma level monitoring, citalopram appeared to be less effective, but seemed to be better tolerated. Clinical Pharmacology and Therapeutics (1992) 52, 547–552; doi

Steady‐state plasma concentrations of paroxetine were studied at five or more paroxetine dose levels (10 to 70 mg/day) in each of 13 extensive metabolizers of sparteine and at three or four dose levels (10 to 40 mg/day) in each of three poor metabolizers of sparteine, all treated for diabetic neuropathy symptoms. On a dose of 30 mg/day there was a 25‐fold variation in steady‐state concentrations (25 to 670 nmol/L). The upper extreme of this variation was made up by the poor metabolizers of sparteine and the lower extreme by some fast extensive metabolizers. Further, within the extensive metabolizer group, steady‐state levels showed a significant, positive correlation with sparteine metabolic ratio at all dose levels. On increasing doses, a disproportionate increase in plasma drug levels was observed in the majority of patients. In nearly all extensive metabolizers the concentration‐dose data were best described by a pharmacokinetic model assuming elimination by at least two kinetically distinct processes, one a high‐affinity saturable process and one a low‐affinity linear process. Estimates of clearance at low drug levels of the high‐affinity process showed a significant negative correlation with the sparteine metabolic ratio. Clearance of the low‐affinity process was not related to the metabolic ratio and was of the same magnitude in extensive and poor metabolizers. The data thus confirmed that the metabolism of paroxetine and sparteine cosegregates and indicated that the enzyme responsible for a high‐affinity saturable paroxetine elimination process is identical with CYP2D6, the source of the sparteine oxidation polymorphism. Clinical Pharmacology and Therapeutics (1992) 51, 288–295; doi

The analgesic efficacy and kinetics of a single oral dose of 75 mg codeine was investigated in 12 extensive metabolizers and 12 poor metabolizers of sparteine in a double-blind, placebo-controlled crossover study. The cosegregation of the O-demethylation of codeine to morphine with the sparteine oxidation polymorphism was confirmed. Hence morphine could not be detected in the plasma of any of the poor metabolizers, whereas detectable morphine plasma levels were found in 10 of 12 extensive metabolizers. Pain thresholds to laser stimuli were determined before drug intake and 90, 150, and 210 minutes after drug intake. Codeine significantly increased the pricking pain thresholds in the extensive metabolizers (p < 0.05), whereas there were no significant changes in the poor metabolizers. No change in pain thresholds occurred with placebo in any of the two phenotypes. In the extensive metabolizers there was a significant positive correlation between the increase in pain threshold and plasma concentration of codeine. The study supports the hypothesis that morphine formation is essential for achievement of analgesia during codeine treatment. Clinical Pharmacology and Therapeutics (1990) 48, 686–693; doi:10.1038/clpt.1990.212

The effect of the selective serotonin reuptake inhibitor paroxetine on diabetic neuropathy symptoms was examined in comparison to imipramine and placebo in a randomised, double-blind, cross-over study. Paroxetine was given as a fixed dose of 40 mg/day, while the dose of imipramine was adjusted to yield optimal plasma levels of imipramine plus desipramine of 400-600 nM. Paroxetine significantly reduced the symptoms of neuropathy as measured by both observer- and self-rating, but was somewhat less effective than imipramine. However, patients showing a weaker response to paroxetine than to imipramine had lower plasma concentrations of paroxetine than patients with similar response to the 2 drugs. On imipramine 5 patients dropped out because of intolerable side effects and 4 of 19 patients completing the study reported withdrawal symptoms after discontinuing imipramine. On paroxetine no patients dropped out due to side effects and no withdrawal symptoms were reported. Self-rating showed no depressive symptoms at baseline, and no changes during the study. Neither paroxetine nor imipramine caused changes in objective measures of peripheral nerve function. In conclusion, 40 mg paroxetine/day significantly reduced the symptoms in peripheral diabetic neuropathy and it was suggested that by dose adjustment on the basis of drug level monitoring, paroxetine may become as effective as imipramine. Paroxetine was devoid of the often disturbing autonomic side effects limiting the use of imipramine in several patients.

The kinetics at a single oral dose (400 mg) of quinidine were studied in four extensive metabolizers (EM) and four poor metabolizers (PM) of sparteine. The clearance of quinidine by 3‐hydroxylation was significantly lower in PM than in EM, but the difference was small (25‐ 30%). This finding suggests that 3‐hydroxylation, in part, is catalyzed by the same isoenzyme of cytochrome P450, P450db1 which oxidizes sparteine. Otherwise, no significant phenotypic differences in total or metabolic clearance were found and it is concluded that the metabolism of quinidine is largely carried out by P450 isoenzymes different from P450db1. A biexponential decline in the log plasma quinidine concentration vs time curves was observed in all subjects, and the mean elimination half‐life was 11‐12 h. This is about twice as long as generally reported in the literature. 1990 The British Pharmacological Society

While there is still disagreement on the importance of monitoring the plasma level concentration of tricyclic antidepressants (TCA) to achieve better therapeutic effect (Gram and Kragh-Sorensen, this volume), there is general agreement on the significance of plasma concentration monitoring in achieving greater safety in the treatment of elderly patients. This agreement should be seen in relation to the expected increase in undesired effects, in particular cardiovascular reactions in the elderly who may display higher plasma levels on conventional doses than younger patients do. However, at the present time our knowledge of cardiovascular effects of TCA in the elderly is rather limited, and the practical value of TCA plasma concentration monitoring has not been studied systematically.

The kinetics of dextropropoxyphene (DP) and its main metabolite norpropoxyphene (NP) were studied in 6 healthy male subjects after a single oral dose of 195 mg DP HCl, and during and after 12 daily single oral doses of 195 mg DP HCl. The kinetics varied up to five-fold between individuals after the single dose, the apparent mean elimination half-life (t1/2) was 16 h for DP and 29 h for NP. The mean apparent overall plasma clearance (CL) for DP was 2.61/min. There was no systematic difference in DP clearance between the single and multiple doses, but the accuracy of individual predictions from single to multiple doses was poor, probably because of imprecise determinations of the AUC and t1/2 in the single dose experiments. The individual correlation between single and multiple dose kinetics was good for NP, although the predicted plasma levels during steady state were significantly higher than the observed levels (mean AUCss/AUCsd: 0.81). There was no sign of saturation kinetics on repeated administration. In fact, autoinduction, resulting in significantly lower plasma concentrations after treatment for 1 week was found for NP and was indicated for DP. On discontinuing DP after 12 days of treatment, the apparent mean t1/2 of DP was 23 h and of NP 25 h.

In a randomized double-blind study with flexible dosage, morphine, nicomorphine and pethidine were compared with regard to analgetic effect, dose requirements, dose intervals and adverse reactions. A total of 275 patients were included, and 28 patients were excluded due to adverse reactions (n = 16) and for practical reasons, etc. Acute myocardial infarction (AMI) was diagnosed in about 60% of the patients, and about 30% had ischemic heart disease without AMI. All three analgesics provided equally efficient pain relief in relative doses of morphine 10, nicomorphine 10 and pethidine 75 mg/ml. Severe adverse reactions were few (allergy 3 cases, respiratory insufficiency 4, severe bradycardia 4), whereas nausea was recorded in 20-30%, vomiting in 5-15% and dizziness in 10-30% of the patients, with no difference between the three drugs. Significant blood pressure drop (greater than 30 mmHg) was seen in 3-8% of the patients, with no significant differences between the drugs.

The sparteine/debrisoquine oxidation polymorphism results from differences in the activity of one isozyme of cytochrome P450, the P450db1 (P450 IID1). The oxidation of more than 20 clinically useful drugs has now been shown to be under similar genetic control to that of sparteine/debrisoquine. The clinical significance of this polymorphism may be defined by the value of phenotyping patients before treatment. The clinical significance of such polymorphic elimination of a particular drug can be analyzed in three steps: first, does the kinetics of active principle of a drug depend significantly on P450db1?; second, is the resulting pharmacokinetic variability of any clinical importance?; and third, can the variation in response be assessed by direct clinical or paraclinical measurements? It is concluded from such an analysis that, in general, the sparteine/debrisoquine oxidation polymorphism is of significance in patient management only for those drugs for which plasma concentration measurements are considered useful and for which the elimination of the drug and/or its active metabolite is mainly determined by P450db1. At present, this applies to tricyclic antidepressants and to certain neuroleptics (e.g. perphenazine and thioridazine) and antiarrhythmics (e.g. propafenone and flecainide). Phenotyping should be introduced in to clinical routine under strictly controlled conditions to afford a better understanding of its potentials and limitations. The increasing knowledge of specific substrates and inhibitors of P450db1 allows precise predictions of drug-drug interactions. At present, the strong inhibitory effect of neuroleptics on the metabolism of tricyclic antidepressants represents the best clinically documented and most relevant example of such an interaction.

Four rapid extensive metabolizers (EM), four slow EM, and three poor metabolizers (PM) of sparteine were given single intravenous doses of 50 mg imipramine and desipramine. All subjects had previously taken single oral doses (100 mg) of imipramine and desipramine. The first-pass metabolism of imipramine and desipramine ranged from 23% to 73% and 0% to 48%, respectively, and was more pronounced for both drugs in EM than in poor metabolizers. The study suggested saturable 2-hydroxylation of imipramine and desipramine during the first-pass through the liver, especially in EM.

Total urinary excretion of radioactivity after oral or intravenous administration of a test dose of (14)C-imipramine was measured in eight patients. They were tested before, during, and after treatment with neuroleptics. Excretion diminished while the patients were being treated with perphenazine, haloperidol, or chlorpromazine, though not during flupenthixol treatment.Total urinary excretion of radioactivity and plasma levels of metabolites and unchanged drug were measured in five patients after a test dose of (14)C-nortriptyline. Each patient was tested before and again during perphenazine treatment. In all patients perphenazine treatment caused: (1) decrease of total urinary excretion, (2) decreased plasma level of metabolites, and (3) increased plasma level of unchanged nortriptyline.These results indicate that neuroleptics inhibit the metabolism of tricyclic antidepressants in man.