Preliminary studies of the kinetics of citalopram in man

Pharmacokinetics of CYP2C9, CYP2C19, and CYP2D6 substrates in healthy Chinese and European subjects

PURPOSE

The aim of this analysis is to compare the pharmacokinetics of drug substrates in healthy Chinese and European subjects of aligned CYP2C9, CYP2C19, or CYP2D6 enzyme activity, providing further insight into drivers of interethnic differences in pharmacokinetics.

METHODS

Following identification of appropriate drug substrates, a comprehensive and structured literature search was conducted to identify single-dose pharmacokinetic data in healthy Chinese or European subjects with reported CYP2C9, CYP2C19, or CYP2D6 activity (genotype or phenotype). The ratio of drug AUC in the Chinese and European subjects classified with aligned enzyme activity was calculated (ethnicity ratio (ER)).

RESULTS

For 22/25 drugs identified, the ERs calculated indicated no or only limited interethnic differences in exposure (<twofold) in Chinese and European subjects with aligned polymorphic enzyme activity. The interethnic differences observed can reflect differences across populations in additional determinants of pharmacokinetics, although the notable between study variation and change over time in methods used to assign enzyme activity may also be contributing factors. There was no association between drug substrate fraction metabolized (fm) for CYP2C9, CYP2C19, or CYP2D6 and the ERs calculated.

CONCLUSION

The spectrum of pharmacokinetic determinants for each drug substrate and their differences across ethnic groups must be considered on a case-by-case basis in addition to metabolism by CYP2C9, CYP2C19, or CYP2D6. This analysis has also highlighted the challenges which arise when comparing published datasets if consistent methods to assign polymorphic enzyme activity have not been used.

Measuring citalopram in blood and cerebrospinal fluid: revealing a distribution pattern that differs from other antidepressants

The aim of this study was to measure blood and cerebrospinal fluid concentrations of citalopram and its weakly active N-demethylated metabolite desmethylcitalopram to account for the distribution between the two compartments. The findings are discussed in the context with own preceding studies on the distribution pattern of different antidepressants. Concentrations of citalopram were measured in blood serum and cerebrospinal fluid of 18 patients treated with daily doses of 10-40 mg. Daily doses were correlated with serum and cerebrospinal fluid concentrations, and serum concentrations were correlated with concentrations in cerebrospinal fluid. Serum concentrations of citalopram and desmethylcitalopram showed no significant correlation to the daily dose, r=0.164, P=0.515, and r=0.174, P=0.505, respectively, whereas citalopram concentrations in serum and cerebrospinal fluid were highly correlated (r=0.763, P<0.001). The cerebrospinal fluid/serum ratio for citalopram (total=bound+unbound concentration) varied between 0.14 and 0.86 (mean 0.35, SD 0.16). By correcting the mean cerebrospinal fluid/serum ratio for 80% plasma protein binding, cerebrospinal fluid concentrations of citalopram were on average 77% higher than the calculated unbound serum concentration with a ratio of 1.77 (SD 0.81, range 0.68-4.29). Findings indicate a very good ability of citalopram to cross the blood-brain and cerebrospinal fluid barrier. High concentrations of citalopram in the cerebrospinal fluid are indicative of active transport of citalopram into or missing active transport out of the cerebrospinal fluid. The results suggest a high ability of citalopram to enter the brain with sufficiently high drug concentrations at the target sites within the brain, contributing toward clinical efficacy.

Pharmacokinetics and pharmacodynamics of psychotropic drugs: effect of sex

Data on the specific effects of sex on pharmacokinetics, as well as tolerability, safety, and efficacy of psychotropic medications are still meager, mainly because only recently sex-related issues have attracted a certain degree of interest within the pharmacological domain. Therefore, with the present study, we aimed to provide a comprehensive review of the literature on this topic, through careful MEDLINE and PubMed searches of the years 1990-2012. Generally, data on pharmacokinetics are more consistent and numerous than those on pharmacodynamics. Sex-related differences have been reported for several parameters that influence pharmacokinetics, such as gastric acidity, intestinal motility, body weight and composition, blood volume, liver enzymes (mainly the cytochrome P450), or renal excretion, which may alter plasma drug levels. Sex-related peculiarities may also account for a different sensitivity of men and women to side effects and toxicity of psychotropic drugs. Further, some differences in drug response, mainly to antipsychotics and antidepressants, have been described. Further studies are, however, necessary to explore more thoroughly the impact of sex on the pharmacokinetics and pharmacodynamics of psychotropic drugs, in order to reach the most appropriate and tailored prescription for each patient.

The population pharmacokinetics of citalopram after deliberate self-poisoning: a Bayesian approach

Defining the pharmacokinetics of drugs in overdose is complicated. Deliberate self-poisoning is generally impulsive and associated with poor accuracy in dose history. In addition, early blood samples are rarely collected to characterize the whole plasma-concentration time profile and the effect of decontamination on the pharmacokinetics is uncertain. The aim of this study was to explore a fully Bayesian methodology for population pharmacokinetic analysis of data that arose from deliberate self-poisoning with citalopram. Prior information on the pharmacokinetic parameters was elicited from 14 published studies on citalopram when taken in therapeutic doses. The data set included concentration-time data from 53 patients studied after 63 citalopram overdose events (dose range: 20-1700 mg). Activated charcoal was administered between 0.5 and 4 h after 17 overdose events. The clinical investigator graded the veracity of the patients' dosing history on a 5-point ordinal scale. Inclusion of informative priors stabilised the pharmacokinetic model and the population mean values could be estimated well. There were no indications of non-linear clearance after excessive doses. The final model included an estimated uncertainty of the dose amount which in a simulation study was shown to not affect the model's ability to characterise the effects of activated charcoal. The effect of activated charcoal on clearance and bioavailability was pronounced and resulted in a 72% increase and 22% decrease, respectively. These findings suggest charcoal administration is potentially beneficial after citalopram overdose. The methodology explored seems promising for exploring the dose-exposure relationship in the toxicological settings.

Clinical course and toxicokinetic data following isolated citalopram overdose in an infant

OBJECTIVE

Despite the frequency of use of citalopram, its clinical effects and pharmacokinetics in overdose in the pediatric patient are not well described. We describe the clinical course and drug levels following the ingestion of citalopram by a 10-month-old female.

CASE REPORT

A 10 month-old female ingested an unknown amount of citalopram. Approximately 40 min after ingestion, the child developed horizontal nystagmus, followed by a generalized, tonic-clonic seizure that lasted 2 to 3 min very shortly thereafter. The child received 1 mg of midazolam intramuscularly (IM), followed by 1 mg of midazolam intravenously (IV) for termination of this seizure, and was given a loading dose of 20 mg/kg of fosphenytoin IV. Elective orotracheal intubation was done to protect the airway. Despite the use of midazolam and fosphenytoin, the child had another seizure approximately 85 min following the ingestion. A third seizure was noted at approximately 100 min post-ingestion. In the course of treatment, activated charcoal was administered via nasogastric tube, and IV midazolam and phenobarbital were given. The child was transferred to a nearby facility with pediatric intensive care capabilities in stable condition. The child did not experience any hypotension or dysrhythmia, and the electrocardiographic QTc and QRS complex were normal throughout the clinical course. During the subsequent 48 h, the child awoke and regained normal function. This child's recovery was uneventful, and the child was discharged home without sequelae. Plasma levels of citalopram were 1400 ng/ml, 583 ng/ml, 416 ng/ml, and 296 ng/ml, at one, six, 13, and 23 h post-ingestion, respectively. The first level likely represents a predistributional level with subsequent levels giving an elimination t1/2 of 17.38 h.

CONCLUSION

We report a case of citalopram poisoning in a 10-month-old infant with refractory seizures, and an absence of cardiovascular events with subsequent excellent outcome. The elimination of the parent drug corresponds to an approximate t1/2 of 15-20 h in this single case.

Clinical trials of potential antidepressants: to what extent are the elderly represented: a review

BACKGROUND

There is widespread use of antidepressants in the elderly population. The principle of treatment of depression, however, is derived mostly from studies employing young adults and healthy elderly. This article reviews the literature on the extent to which the elderly are represented in clinical trials of potential antidepressants.

METHOD

Medline search of relevant articles of clinical trials of potential antidepressants.

RESULTS

The maximum age of inclusion for most clinical trials was 65 years. The highest age reported for depressed subjects was 90 years. There was no clear consensus on who were considered to be elderly; clinical trials conducted on the elderly included subjects who were 50, 55, or 60 years and over. Pharmacological studies on healthy subjects were most often done on young adults, age range 18 to 65 years. The period of study was relatively shorter for clinical trials done on elderly subjects. There was however, no difference in the exclusion or inclusion criteria between studies done in young and elderly subjects.

CONCLUSIONS

Elderly subjects aged 75 years and over were clearly underrepresented in the clinical trials of potential antidepressants. For drugs that are used by the elderly, in its pivotal studies for registration, the inclusion of at least 25% of subjects aged 75 years and over is recommended.

Lack of effect of citalopram on the steady-state pharmacokinetics of carbamazepine in healthy male subjects

Carbamazepine, a drug used in the treatment of seizure disorders, and citalopram, a highly selective serotonin reuptake inhibitor used for the treatment of depression and other psychiatric disorders, are both metabolized predominantly by the cytochrome P4503A4 isozyme. In this study, the effect of subchronic administration of citalopram on the steady-state pharmacokinetics of carbamazepine was evaluated in 12 healthy male subjects. Carbamazepine was administered orally twice daily as a 100-mg dose from days 1 to 3, as a 200-mg dose twice a day from days 4 to 6, and as a 400-mg dose once a day from days 7 to 35. Citalopram, 40 mg, administered once daily, was added to the carbamazepine-dosing regimen on days 22 to 35. The steady-state plasma concentration profiles of carbamazepine and its active metabolite, carbamazepine 10,11-epoxide, on day 35 (in the presence of steady-state levels of citalopram) were compared to the corresponding carbamazepine and epoxide metabolite profiles on day 21 (in the absence of citalopram). No significant differences were found between mean steady-state values for maximal drug concentration, area under the curve, or time of maximal concentration values for carbamazepine and its epoxide metabolite before and after the addition of citalopram to the daily carbamazepine dosing regimen (p > 0.05). These results suggest that the use of citalopram in patients stabilized on carbamazepine should not produce clinically significant changes in carbamazepine plasma concentrations.

Metabolism and pharmacokinetics of selective serotonin reuptake inhibitors

1. Five drugs with the predominant pharmacologic effect of inhibiting the neuronal reuptake of serotonin are available worldwide for clinical use. This class of psychoactive drugs, known as selective serotonin reuptake inhibitors (SSRIs), is comprised of fluoxetine, sertraline, paroxetine, fluvoxamine, and citalopram. 2. The SSRIs appear to share similar pharmacodynamic properties which translate to efficacy in the treatment of depression and anxiety syndromes. The drugs are differentiated by their pharmacokinetic properties with regard to stereochemistry, metabolism, inhibition of cytochrome enzymes, and participation in drug-drug interactions. Studies focusing on the relationship of plasma drug concentration to therapeutic and adverse effects have not confirmed the value of plasma concentration monitoring. 3. This review summarizes the metabolism and relevant pharmacokinetic properties of the SSRIs.

Mechanisms of action of selective serotonin reuptake inhibitors in the treatment of psychiatric disorders

Selective serotonin reuptake inhibitors (SSRIs) have demonstrated efficacy in depression and anxiety disorders. This raises the question of how the single action of serotonin reuptake inhibition can improve several psychiatric conditions. In order to understand this apparent paradox it is necessary to consider where SSRIs act in the pathogenic process underlying depression or anxiety disorders. Tryptophan depletion has been used extensively in research into depression and has shown that, in patients receiving an SSRI whose depression is in remission, depleting serotonin leads to recurrence of the disorder. Similar results have been found for panic disorder. This suggests that increased levels of serotonin are necessary in the synapse for the SSRI to be effective in the treatment of depression and panic disorder. In obsessive compulsive disorder, depletion of serotonin in patients recovered on an SSRI does not cause relapse; receptor adaptation may be more important. Variations within the SSRI drug class, such as the selectivity ratios for serotonin versus noradrenaline uptake, elimination half-life, and affinity for the 5-HT2 receptor have been identified and may be important determinants of efficacy, side effects and clinical use.

Citalopram for treatment-resistant obsessive-compulsive disorder

We investigated the comparative efficacy of citalopram vs. citalopram administered with clomipramine, in treatment-resistant obsessive-compulsive disorder (OCD). Sixteen adult outpatients participated in a 90-day, randomized, open-label trial. Eligible patients were aged 18 to 45 years, had moderate to severe DSM-III-R OCD of >/= one year's duration, a baseline Yale-Brown scale (Y-BOCS) score of >/= 25 and no other active axis I diagnosis, and had failed adequate clomipramine and fluoxetine trials. The citalopram-plus-clomipramine group (n = 9) experienced a significantly larger percent decrease in mean Y-BOCS score by day 90 than the citalopram alone group (n = 7). Only one citalopram patient decreased her score by >/= 35%, and two by >/= 25%. All nine citalopram-plus-clomipramine patients experienced decreases of 35%. Side effects were mild to moderate in both groups. We also treated with citalopram six OCD patients who had not tolerated fluoxetine alone and clomipramine alone; three achieved Y-BOCS score decreases of >/= 35% at 90 days. Since citalopram does not significantly affect clomipramine metabolism, the improvement in the combined drug group is unlikely to have resulted from increased plasma clomipramine levels. Double-blind controlled trials are needed of citalopram in OCD, and of combining citalopram with clomipramine in treatment-resistant OCD.

Selective serotonin reuptake inhibitors in affective disorders--I. Basic pharmacology

The selective serotonin reuptake inhibitors (SSRIs), citalopram, fluoxetine, fluvoxamine, paroxetine and sertraline, are the result of rational research to find drugs that were as effective as the tricyclic antidepressants but with fewer safety and tolerability problems. The SSRIs selectively and powerfully inhibit serotonin reuptake and result in a potentiation of serotonergic neurotransmission. The property of potent serotonin reuptake appears to give a broad spectrum of therapeutic activity in depression, anxiety, obsessional and impulse control disorders. However, despite the sharing of the same principal mechanism of action, SSRIs are structurally diverse with clear variations in their pharmacodynamic and pharmacokinetic profiles. The potency for serotonin reuptake inhibition varies amongst this group, as does the selectivity for serotonin relative to noradrenaline and dopamine reuptake inhibition. The relative potency of sertraline for dopamine reuptake inhibition differentiates it pharmacologically from other SSRIs. Affinity for neuroreceptors, such as sigma1, muscarinic and 5-HT2c, also differs widely. Furthermore, the inhibition of nitric oxide synthetase by paroxetine, and possibly other SSRIs, may have significant pharmacodynamic effects. Citalopram and fluoxetine are racemic mixtures of different chiral forms that possess varying pharmacokinetic and pharmacological profiles. Fluoxetine has a long acting and pharmacologically active metabolite. There are important clinical differences among the SSRIs in their pharmacokinetic characteristics. These include differences in their half-lives, linear versus non-linear pharmacokinetics, effect of age on their clearance and their potential to inhibit drug metabolising cytochrome P450 (CYP) isoenzymes. These pharmacological and pharmacokinetic differences underly the increasingly apparent important clinical differences amongst the SSRIs.

Clinically relevant pharmacology of selective serotonin reuptake inhibitors. An overview with emphasis on pharmacokinetics and effects on oxidative drug metabolism

This paper presents an overview of the clinically relevant pharmacology of selective serotonin reuptake inhibitors (SSRIs) with an emphasis on their pharmacokinetics and effects on cytochrome P450 (CYP) enzymes. The SSRIs are potent inhibitors of the neuronal reuptake pump for serotonin (5-hydroxytryptamine; 5-HT) and have minimal effects on a number of other sites of actions (e.g. neuroreceptors and fast sodium channels). For this reason, drugs in this class have remarkable similarity as regards acute and maintenance antidepressant efficacy and tolerability profile. However, individual members of this class differ substantially in their pharmacokinetics and effects on CYP enzymes. Most SSRIs have a half-life (t1/2) of approximately 1 day. Fluoxetine, however, has a longer t1/2 of 2 to 4 days, and its active metabolite, norfluoxetine, has an extended t1/2 of 7 to 15 days. Fluoxetine, paroxetine and, to a lesser extent, fluvoxamine inhibit their own metabolism. That is not the case for citalopram or sertraline. There are nonlinear increases in paroxetine plasma concentrations with dosage increases, but proportional changes with citalopram and sertraline. Indirect data suggest that fluoxetine and fluvoxamine also have nonlinear pharmacokinetics over their usual dosage range. Age-related increases in plasma drug concentrations for citalopram (approximately 130%) and paroxetine (approximately 50 to 100%) have been observed in healthy elderly (65 to 75 years) persons versus those who are younger. There is an age-gender interaction for sertraline, with its plasma concentrations being 35 to 40% lower in young men than in elderly or young females or elderly males. While there is no apparent change in fluvoxamine plasma levels as a function of age, plasma drug concentrations are 40 to 50% lower in males than in females. Limited data from clinical trials suggest that age-related differences with fluoxetine may be comparable to those of citalopram and paroxetine. Marked differences exist between the SSRIs with regard to effects on specific CYP enzymes and, thus, the likelihood of clinically important pharmacokinetic drug-drug interactions. The most extensive in vitro and in vivo research has been done with fluoxetine, fluvoxamine and sertraline; there has been less with paroxetine and citalopram. The available in vivo data at each drug's usually effective antidepressant dose are summarised below. Citalopram produces mild inhibition of CYP2D6. Fluvoxamine produces inhibition (which would be expected to be clinically meaningful) of two CYP enzymes. CYP1A2 and CYP2C19, and probably a third, CYP3A3/4. Fluoxetine substantially inhibits CYP2D6 and probably CYP2C9/10, moderately inhibits CYP2C19 and mildly inhibits CYP3A3/4. Paroxetine substantially inhibits CYP2D6 but doses not appear to inhibit any other CYP enzyme. Sertraline produces mild inhibition of CYP2D6 but has little, if any, effect on CYP1A2, CYP2C9/10, CYP2C19 or CYP3A3/4. Understanding the similarities and differences in the pharmacology of SSRIs can aid the clinician in optimal use of this important class of antidepressants.

Pharmacokinetic-pharmacodynamic relationship of the selective serotonin reuptake inhibitors

The recently introduced antidepressants, the selective serotonin reuptake inhibitors (SSRIs) [citalopram, fluoxetine, fluvoxamine, paroxetine and sertraline], are known for their clinical efficacy, good tolerability and relative safety. They differ from each other in chemical structure, metabolism and pharmacokinetic properties. Therapeutic drug monitoring of these compounds is not widely used, as the plasma concentration ranges within which clinical response with minimal adverse effects appears to be optimal are not clearly defined. Almost all recent assays developed for the quantitative determination of SSRIs and their metabolites in blood are based either on the separation of SSRIs by high performance liquid chromatography (HPLC) or gas chromatography (GC). Citalopram and fluoxetine have been introduced as racemic compounds. There are some differences in the pharmacological profile, metabolism and pharmacokinetics between the enantiomers of the parent compounds and their demethylated metabolites. Stereoselective chromatographic methods for their analysis in blood are now available. With regard to the SSRIs presently available, no clearcut plasma concentration-clinical effectiveness relationship in patients with depression has been shown, nor any threshold which defines toxic concentrations. This may be explained by their low toxicity and use at dosages where serious adverse effects do not appear. SSRIs vary widely in their qualitative and quantitative interaction with cytochrome P450 (CYP) isozymes in the liver. CYP2D6 is inhibited by SSRIs, in order of decreasing potency paroxetine, norfluoxetine, fluoxetine, sertraline, citalopram and fluvoxamine. This may have clinical consequences with some but not all SSRIs, when they are taken with tricyclic antidepressants. Except for citalopram and paroxetine, little is known about the enzymes which control the biotransformation of the SSRIs. There have been many reports on marked pharmacokinetic interactions between fluoxetine and tricyclic antidepressants. Fluoxetine has a stronger effect on their hydroxylation than on their demethylation. Interactions observed between fluoxetine and alprazolam, midazolam and carbamazepine seem to occur on the level of CYP3A. Fluvoxamine strongly inhibits the N-demethylation of some tricyclic antidepressants of the tertiary amine type and of clozapine. This may lead to adverse effects but augmentation with fluvoxamine can also improve response in very rapid metabolisers, as it increases the bioavailability of the comedication. Fluvoxamine inhibits with decreasing potency, CYP1A2, CYP2C19, CYP2D6 and CYP1A1, but it is also an inhibitor of CYP3A. Fluoxetine and fluvoxamine have shown to increase methadone plasma concentrations in dependent patients. Some authors warn about a combination of monoamine oxidase (MAO) inhibitors with SSRIs, as this could lead to a serotonergic syndrome. Studies with healthy volunteers suggest, however, that a combination of moclobemide and SSRIs, such as fluvoxamine, should not present serious risks in promoting a serotonin syndrome. A combination of moclobemide and fluvoxamine has successfully been used in refractory depression, but more studies are needed, including plasma-concentration monitoring, before this combined treatment can be recommended. Paroxetine is a substrate of CYP2D6, but other enzyme(s) could also be involved. Its pharmacokinetics are linear in poor metabolisers of sparteine, and non-linear in extensive metabolisers. Due to its potent CYP2D6 inhibiting properties, comedication with this SSRI can lead to an increase of tricyclic antidepressants in plasma, as shown with amitriptyline and trimipramine. CYP3A has been claimed to be involved in the biotransformation of sertraline to norsertraline. Clinical investigations (with desipramine) confirmed in vitro findings that CYP2D6 inhibition by sertraline is only moderate. (ABSTRACT TRUNCATED)

Analytical methods for the quantitative determination of selective serotonin reuptake inhibitors for therapeutic drug monitoring purposes in patients

Five selective serotonin reuptake inhibitors (SSRIs) have been introduced recently: citalopram, fluoxetine, fluvoxamine, paroxetine and sertraline. Although no therapeutic window has been defined for SSRIs, in contrast to tricyclic antidepressants, analytical methods for therapeutic drug monitoring of SSRIs are useful in several instances. SSRIs differ widely in their chemical structure and in their metabolism. The fact that some of them have N-demethylated metabolites, which are also SSRIs, requires that methods be available which allow therapeutic drug monitoring of the parent compounds and of these active metabolites. most procedures are based on prepurification of the SSRIs by liquid-liquid extraction before they are submitted to separation by chromatographic procedures (high-performance liquid chromatography, gas chromatography, thin layer chromatography) and detection by various detectors (UV, fluorescence, electrochemical detector, nitrogen-phosphorus detector, mass spectrometry). This literature review shows that most methods allow quantitative determination of SSRIs in plasma, in the lower ng/ml range, and that they are, therefore, suitable for therapeutic drug monitoring purposes of this category of drugs.

The SSRIs: advantages, disadvantages and differences

The highly specific mechanism of action of the selective serotonin re-uptake inhibitors (SSRIs) confers advantages on this group, relative to other classes of antidepressant, and thus represents a significant advance in the pharmacotherapy of depression. Whilst their clinical efficacy is equivalent to that of the tricyclic antidepressants (TCAs), the SSRIs have a greatly reduced risk of toxicity in overdose and have been shown to be significantly better tolerated. Specifically, the SSRIs have a low incidence of anticholinergic effects and are essentially devoid of cardiotoxicity. This tolerability advantage may be of significance in improving compliance and hence cost-effectiveness of treatment, particularly in the long term. Despite a lack of sedative effect, there is evidence that SSRIs are more effective than TCAs in the treatment of depression with anxiety. In addition, the SSRIs have been shown to be effective in obsessive-compulsive disorder, panic disorder and social phobia. Although superior efficacy has not been demonstrated for any one of the SSRIs, the structural diversity of this group is reflected in emerging qualitative and quantitative differences in side effects and drug interaction potential. Many of these differential features reflect important variations in pharmacological and pharmacokinetic profiles, including dosage flexibility, washout times, dose-plasma level proportionality and age-related changes in plasma levels. Fluoxetine, for example, has a considerably longer half-life than other SSRIs and side effects and drug interactions may thus occur for an extended period following discontinuation of treatment. Significant differences in the potential for drug interactions in this group are related to their relative potency for inhibition of important liver drug-metabolising enzymes including CYPIID6, CYPIA2 and CYPIIIA4. Large comparative clinical trials of the different SSRIs have yet to be undertaken; however, the differences that have already become apparent provide important information enabling the physician to choose an SSRI appropriate to the individual patient.

Evaluation of S-[11C]citalopram as a radioligand for in vivo labelling of 5-hydroxytryptamine uptake sites

The biologically active S-enantiomer of [N-methyl-11C]citalopram was evaluated as a radioligand for in vivo labelling of the 5-hydroxytryptamine uptake site in brain, using ex vivo tissue counting in rats and positron emission tomography in man. In rats, the maximal signal for total versus non-specific binding was approx. 2 at 60-120 min after radioligand injection. Subsequent studies in man failed to identify a specific signal over a 90 min scanning period, due to prolonged retention of non-specific label.

Citalopram. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in depressive illness

Citalopram is an antidepressant belonging to a new class of drugs which enhance serotoninergic neurotransmission through potent and selective inhibition of serotonin reuptake. Preliminary trials suggest that its short term therapeutic efficacy is significantly greater than that of placebo and mianserin, and comparable to that of amitriptyline, maprotiline and imipramine. It appears to be a weaker antidepressant agent than clomipramine, but better tolerated. Its elimination half-life of 33 hours permits once daily oral administration. Symptomatic improvement obtained with short term treatment has been maintained when therapy has been extended for up to 1 year; in the few patients studied for this extended period, the relapse rate was lower than with fluvoxamine, fluoxetine or imipramine. Compared to standard antidepressant agents, citalopram is well tolerated. It does not appear to be cardiotoxic, has not been associated with seizures in humans, and is relatively nonsedating. Unlike the tricyclic antidepressants, citalopram has minimal anticholinergic effects. Mild and transient nausea, with or without vomiting, is the most frequent adverse effect--occurring in 20% of patients--and increased perspiration, headache, dry mouth, tremor and insomnia are experienced by 15 to 18% of patients. Citalopram thus offers similar therapeutic efficacy and a more favourable tolerability profile than the tricyclic antidepressants. Preliminary data suggest that it may be particularly useful in patients who cannot tolerate the anticholinergic or cardiovascular side effects of tricyclic antidepressants and in those for whom sedation is not indicated.

Citalopram: labelling with carbon-11 and evaluation in rat as a potential radioligand for in vivo PET studies of 5-HT re-uptake sites

In vivo autoradiography of [N-methyl-3H]citalopram in rat brain shows a differential regional localization which correlates with the localization of 5-HT re-uptake binding sites defined in vitro. A comparison of the biodistribution of [N-methyl-3H]citalopram over 2 h after i.v. injection in (1) control rats (2) rats pre-dosed with either citalopram or paroxetine and (3) rats chemically-lesioned with p-chloroamphetamine provides an estimate of specific binding relative to total binding in vivo. The ratio of binding in certain regions (e.g. cingulate) to binding in a reference tissue (e.g. cerebellum) at 30-120 min post injection is c. 1.4. In view of these results a method was developed for labelling citalopram with carbon-11 (t1/2 = 20.3 min, beta + = 99.8%) to provide a potential radioligand for studies using positron emission tomography. Thus, reaction of nca [11C]iodomethane, prepared from cyclotron-produced [11C]carbon dioxide, with norcitalopram in ethanol containing 2,2,6,6-tetramethyl-piperidine for 5 min at 95 degrees C gives crude [N-methyl-11C]citalopram in 60% radiochemical yield, decay-corrected. HPLC on silica gel provides radiochemically and chemically pure [N-methyl-11C]citalopram, as assessed by TLC, HPLC and MS. This product (isolated radiochemical yield, 49%) is easily formulated for i.v. injection. Up to 2 GBq of formulated product with a specific activity of c. 15 GBq/mumol have been prepared within 40 min from the end of radionuclide production. The described radiosynthesis has also been applied to give the single biologically active (+)-enantiomer of [N-methyl-11C]citalopram rather than the racemate. This product gives enhanced specific signal in the rat following i.v. injection, the ratio of uptake in regions of interest relative to cerebellum approaching 2 at 90 min.

The clinical efficacy of citalopram in treatment of emotional disturbances in dementia disorders. A Nordic multicentre study

In this multicenter study, the clinical efficacy of citalopram was investigated in 98 patients with moderate AD/SDAT or VD using a combined double-blind and open technique with placebo and citalopram. Analyses were made for each diagnosis after four weeks of double-blind treatment. Patients with AD/SDAT treated with citalopram showed a significant improvement in emotional bluntness, confusion, irritability, anxiety, fear/panic, depressed mood and restlessness. Those improvements were not found after treatment with placebo. There were no significant improvements in patients with VD. No improvements were recorded in motor or cognitive impairment. Citalopram provoked few and comparatively mild side-effects. None of the changes observed during the double-blind withdrawal period were identified as withdrawal symptoms or rebound phenomena.

Citalopram versus maprotiline: a controlled, clinical multicentre trial in depressed patients

In a double-blind trial, comprising 96 depressed patients, citalopram was compared with maprotiline. The trial period was 6 weeks with ratings (MADRS, CGI) and side effects recordings taking place at Weeks 0, 1, 2, 4, and 6. Both drugs were administered as a single evening dose, 40 or 60 mg for citalopram, and 75 or 150 mg for maprotiline. MADRS total scores and CGI scores showed a highly significant reduction in both groups with no significant difference between them, whether the groups were considered as a whole or whether they were subdivided into endogenously/non-endogenously depressed or melancholic/non-melancholic patients. Side effects were not significantly different, but the maprotiline group showed more anticholinergic side effects, whereas the citalopram group showed more nausea, increased sweating and headache. Two patients on maprotiline were withdrawn because of side effects (hypotension and somnolence in the one case; tremor and insomnia in the other). One patient in each group was withdrawn because of increased transaminases, the citalopram-treated patient having increased values, however, already at baseline. Apart from this, no cardiovascular side effects and no pathological laboratory values related to treatment were observed. The authors conclude that citalopram is a safe antidepressant drug and as effective as maprotiline.

Kinetics of citalopram in elderly patients

The kinetics of the antidepressant drug citalopram, a specific 5-HT uptake inhibitor, has been investigated in 11 elderly patients (age 73-90) and compared to previous data from younger patients and volunteers. The recorded steady state citalopram levels of 140-545 nM after a once-daily 20-mg dose were up to four times higher than expected from data in younger patients and volunteers. The biological half-life (1.5-3.75 days) and estimated systemic clearance (0.08-0.3 1/min) also differed from data in younger individuals (1.5 days and 0.4 1/min, respectively). Clearance values generally decreased with increasing age. Drug/metabolite ratios were higher in patients with the longest half-lives and lowest citalopram clearance, indicating reduced metabolic activity. No reduction in renal clearance was indicated by urine data, obtained for two of the patients. The study suggests that daily doses of 5-20 mg give approximately the same steady state plasma levels in elderly patients as doses of 40 mg in younger, and that this is due to reduced rates of metabolism in the elderly.

Comparative animal studies on cardiovascular toxicity of tri- and tetracyclic antidepressants and citalopram; relation to drug plasma levels

The aim of the present study was to compare cardiovascular and/or cardiotoxic effects of eight anti-depressants (imipramine, chlorimipramine, amitriptyline, nortriptyline , doxepin, maprotiline, mianserin and citalopram) in anaesthetized cats after oral dosing and in conscious rabbits after intravenous infusion. In the cats drug plasma levels were determined as well. When estimated from ECG recordings, citalopram and chlorimipramine in particular, but also mianserin, appeared less cardiotoxic than the other drugs tested. The cardiovascular effects seen in the cats were with few exceptions identical for all the drugs tested but not seen at the same dose (concentration). Safety margins were defined as minimal doses or plasma levels when ECG changes (conduction or rhythm) or cardiovascular effects (+/- 10% change of initial value in a series of parameters) occurred in experimental animals divided by maximal therapeutic dose or mean plasma levels in patients. From comparisons of the safety margins it is concluded that except for citalopram and mianserin (safety margins 80 and 18 respectively in cats and greater than 15 in rabbits) all the other drugs tested (safety margins less than or equal to 9) have a cardiotoxic potential. The probability that cardiovascular side effects may occur is less pronounced for citalopram (safety margins 10-32) than for all the other drugs tested (safety margins ranging from 0.1 to less than 5).

Studies on acute toxicity and drug levels of citalopram in the dog

Electrocardiographic and haemodynamic changes have been studied in conscious dogs after a sublethal oral dose (20 mg . kg-1) of citalopram. Furthermore, the effects of continuous intravenous infusion of citalopram (10 mg . kg-1 per hour) have been studied in conscious and anesthetized dogs. The findings have been related to plasma levels of citalopram. Severe convulsive attacks occurred in conscious dogs after infusion of 21.3 or 26.5 mg . kg-1 and after the oral dose. The convulsions were successfully treated with diazepam. In contrast convulsions were not seen in the anesthetized dogs. They died from respiratory arrest after infusion of 42.2 or 61.3 mg . kg-1. Atrioventricular and intraventricular conduction was unchanged and electrocardiographic changes were negligible. Sinus tachycardia which could be reversed by diazepam and moderate haemodynamic changes were seen. Since no electrocardiographic changes were seen in conscious dogs even during pauses in the convulsive seizure it is concluded that citalopram does not exert cardiotoxic effects in the dog. Good correlation was found between general clinical findings and citalopram levels in plasma. Conscious dogs were exposed to drug levels exceeding those of the average patient by a factor of about 20, while anesthetized dogs had considerable higher concentrations.

Determination of the antidepressant agent citalopram and metabolites in plasma by liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method is described for the determination of citalopram [1-(3-(dimethylaminopropyl)-1-(4-fluorophenyl)-5-phthalancarbonitrile] and its two main metabolites (the methylamino and amino derivatives). The compounds were extracted from alkaline plasma with diethyl ether. The combined ether layers were evaporated after addition of 50 microliter of 0.1 N HCl. The residual extracts were purified with diethyl ether and 20 microliter were injected into a Spherisorb ODS 5-micrometer column with acetonitrile--0.6% phosphate buffer pH 3 (55:45, v/v) as the mobile phase. Using a fluorescence detector the detection limits are 1 ng/ml of plasma for citalopram and the methylamino metabolite and 0.5 ng/ml for the amino metabolite.

Citalopram--pharmacological profile of a specific serotonin uptake inhibitor with antidepressant activity

1. Citalopram (Lu 10-171), a new bicyclic phthalane derivative, is an extremely potent inhibitor of neuronal serotonin (5-HT) uptake but has no effect on the uptake of noradrenaline (NA) and dopamine (DA). 2. Citalopram has no antagonistic activity towards DA, NA, 5-HT, histamine, gamma aminobutyric acid (GABA), acetylcholine, and morphine receptors. In this way it clearly deviates from many old and new antidepressant drugs which have antagonistic effects towards some of these transmitters. 3. In contrast to many tricyclic antidepressants citalopram is devoid of cardiotoxic effects, even when animals are exposed to concentrations far above the therapeutic level. 4. In man citalopram is metabolized to compounds which are also potent 5-HT-uptake inhibitors without effect of NA uptake and which are found in lower concentrations than citalopram itself. 5. In account of its extreme specificity as a 5-HT-uptake inhibitor citalopram should be considered as an experimental tool of the utmost importance. In preliminary clinical experiments citalopram has shown a clear antidepressant effect. This property together with the absence of troublesome anticholinergic adverse effects and cardiotoxic effects also make citalopram a most promising antidepressant drug.

Citalopram, a selective serotonin reuptake inhibitor: clinical antidepressive and long-term effect--a phase II study

In a phase II study the antidepressive effect of citalopram, a selective and potent serotonin reuptake inhibitor, was examined in 20 endogenously and three non-endogenously depressed hospitalized patients. Four endogenously depressed patients dropped out due to deterioration early in the treatment period. The remaining 19 patients completed a 4-6 week treatment schedule. Of 16 endogenously depressed patients 11 responded, one was a partial responder and four did not respond. Of three patients with non-endogenous depressions, two responded and one did not respond. No correlation between plasma citalopram concentration and therapeutic outcome was found. Fourteen patients were given maintenance treatment for 8-113 weeks. One patient developed depression when the dose was reduced from 60 to 40 mg and one patient became manic. After discontinuation of treatment seven patients had a depressive relapse and six of these who again were treated with citalopram responded completely. Side effect rating scores of symptoms usually associated with depression or treatment with tricyclic antidepressants declined during treatment. Three patients complained of increased need of sleep for a period after several weeks of treatment. Apart from an unspecific, transient rise in liver enzymes in two patients, detailed biochemical laboratory tests were all normal. There were no effects on blood pressure, pulse rate, orthostatic reaction, or electrocardiogram. One patient took an overdose of citalopram resulting in plasma levels about six times higher than the average therapeutic level, but there were no signs of severe toxicity. In particular no change in consciousness, electrocardiogram or blood pressure occurred. Pharmacokinetic variables such as dose schedule, steady state kinetics, and metabolism are discussed.

Preliminary studies with citalopram (LU 10-171), a specific 5-HT-reuptake inhibitor, as antidepressant

1. Ten hospitalized, depressive, female patients above the age of 50 have been treated in a 3 week open trial with citalopram, a specific 5-HT-uptake inhibitor. 2. Six full and two partial responders demonstrate a recovery rate within the well known range for tricyclic antidepressant drugs. 3. Early onset of clinical effect and minimal side effects indicate that citalopram is possible a new effective antidepressant.

Kinetics of citalopram in man; plasma levels in patients

1. Citalopram is rapidly absorbed and slowly eliminated in man. The kinetics is linear and characterized by systemic and apparent oral clearance values of 0.4 l/min, a theoretical distribution volume of 14 l/kg and a half-life of 1 1/2 days. 2. The steady state plasma levels in 70 patients range from 95 to 720 nM at doses of 30 to 60 mg and agree well with predicted values. The mean level is 245 nM at the standard dose of 40 mg daily. 3. Inter-individual variation is 7-fold and independent of sex and age (21-65 years). The average intra-individual variation is about 15%. Estimates of apparent oral clearance vary from 0.15 to 1.02 l/min. 4. The average concentration ratio between citalopram and its demethylated metabolite is 2.7. The levels of di-demethylated metabolite are negligible.

Citalopram--a specific 5-HT-reuptake inhibitor--as an antidepressant drug: a phase II multicentre trail

1. Twenty-nine inpatients with a long history of rather severe, affective psychosis were admitted for a 4 weeks treatment with citalopram, a very specific 5-Ht-reuptake inhibitor. 2. Twenty-six patients (15 men and 11 women) completed the study and among these 15 had been depressed for more than 10 years and 19 showed an entry total score of more than 25 points on the Hamilton Rating Scale for Depression (17 items). 3. When treated with a dose of 40-60 mg once daily, approximately one third of the patients showed a marked response and another third a moderate response to treatment. Fifteen of the patients showed a marked or moderate response already within the first two weeks of treatment. 4. Only a few and transient side effects (nausea and increased sweating) were recorded and, in particular, no anticholinergic or cardiovascular side effect were observed. 5. Taking into consideration the severity of illness as well as the long and serious anamneses, these results of treatment with citalopram must be considered most satisfactory.

Kinetics of citalopram in test animals; drug exposure in safety studies

1. Plasma levels of citalopram and its metabolites were assayed after single oral and intravenous doses to baboons (4 mg/kg), dogs (1, 4, 5, and 10 mg/kg), rats (8 mg/kg), and mice (24 mg/kg). Kinetic parameters were estimated. 2. Half-lives were short (estimate for baboon 3, dog 3 1/2-8, rat 3, and mouse 1 1/2 hours) and systemic plasma clearance high (baboon 39, dog 37-14, male rat 82, female rat 103, male mouse 87, and female mouse 116 ml/min/kg body weight). Considerable first-pass metabolism was demonstrated. 3. Drug level data were obtained in long-term safety studies in dogs (1, 3, and 8 mg/kg), rats (32 and 320 mg/kg), and mice (640 mg/kg). The high-dose citalopram level in dogs and rats exceeded that of patients by a factor of 10; the factor for mice was 40.

The kinetics of citalopram: single and multiple dose studies in man

The kinetics of citalopram were studied in a group of volunteers after oral (8 subjects) and intravenous (4 subjects) single doses and repeated oral administration (7 subjects). Inter- and intraindividual variation was limited and linearity of kinetics indicated. Systemic and apparent oral clearance estimates (mean 0.42 l plasma/min.) were similar, indicating roughly complete systemic availability. The presence of unchanged drug in urine, corresponding to 1/7 of the dose, suggests elimination by renal as well as hepatic processes. The data from the intravenous test revealed two compartment kinetics; the total volume of distribution was estimated to about 1150 l and that of the central compartment to 175 l. Upon repeated administration steady-state conditions were generally achieved after one week in agreement with the 33 hrs half-life of elimination. Citalopram peak concentrations were reached within 2-4 hours after the daily dose and maximally two-fold variation was recorded in the 24 hrs dose interval. The levels of a main pharmacodynamically active metabolite were roughly half as high as the drug levels.

Initial, clinical trial of a new, specific 5-HT reuptake inhibitor, citalopram (Lu 10-171)

Ten endogenously depressed inpatients were treated once daily for at least 4 weeks with 40-50 mg citalopram (Lu 10-171) - a specific serotonin reuptake inhibitor. The Hamilton rating scale for depression and global assessment indicated pronounced or moderate response in seven patients and slight or no response in three. Side effects were few, mild and transient and neither anticholinergic nor cardiotoxic effects were observed. No difference was observed between responders and non-responders as regards psychopathology, plasma levels or uptake inhibition. It is concluded, that citalopram seems to possess antidepressant properties and that controlled trials are wanted to evaluate its therapeutic value as well as the underlying hypothesis of serotonin - deficient depressions.