Nefazodone. A review of its pharmacology and clinical efficacy in the management of major depression

Nefazodone hydrochloride is a phenylpiperazine antidepressant with a mechanism of action that is distinct from those of other currently available drugs. It potently and selectively blocks postsynaptic serotonin (5-hydroxytryptamine; 5-HT) 5-HT2A receptors and moderately inhibits serotonin and noradrenaline (norepinephrine) reuptake. In short term clinical trials of 6 or 8 weeks' duration, nefazodone produced clinical improvements that were significantly greater than those with placebo and similar to those achieved with imipramine, and the selective serotonin reuptake inhibitors (SSRIs) fluoxetine, paroxetine and sertraline. The optimum therapeutic dosage of nefazodone appears to be between 300 and 600 mg/day. Limited long term data suggest that nefazodone is effective in preventing relapse of depression in patients treated for up to 1 year. Analyses of pooled clinical trial results indicate that nefazodone and imipramine produces similar and significant improvements on anxiety- and agitation-related rating scales compared with placebo in patients with major depression. Short term tolerability data indicate that nefazodone has a lower incidence of adverse anticholinergic, antihistaminergic and adrenergic effects than imipramine. Compared with SSRIs, nefazodone causes fewer activating symptoms, adverse gastrointestinal effects (nausea, diarrhoea, anorexia) and adverse effects on sexual function, but is associated with more dizziness, dry mouth, constipation, visual disturbances and confusion. Available data also suggest that nefazodone is not associated with abnormal weight gain, seizures, priapism or significant sleep disruption, and appears to be relatively safe in overdosage. Nefazodone inhibits the cytochrome P450 3A4 isoenzyme and thus has the potential to interact with a number of drugs. Further long term and comparative studies will provide a more accurate assessment of the relative place of nefazodone in the management of major depression. Nonetheless, available data suggest that nefazodone is a worthwhile treatment alternative to tricyclic antidepressants and SSRIs in patients with major depression.

Interaction between fluoxetine and haloperidol: pharmacokinetic and clinical implications

The extent and clinical significance of the pharmacokinetic interaction between fluoxetine and haloperidol was studied in 13 schizophrenic patients with prominent negative symptoms. Patients stabilized on chronic low-dose haloperidol (3-8 mg day-1) received additional fluoxetine (20 mg day-1) for 12 consecutive weeks. Mean plasma concentrations of haloperidol increased significantly from 6.5 +/- 2.4 nmol l-1 at baseline to 8.8 +/- 3.6 nmol l-1 (P < 0.01) at week 12 of fluoxetine treatment, but this effect was not associated with an increase in mean extrapyramidal side effects score on the Simpson and Angus Scale. The improvement in negative symptomatology, as measured by the Scale for Assessment of Negative Symptoms, did not correlate significantly with the increase in plasma haloperidol levels. Though our findings confirm that fluoxetine impairs haloperidol clearance, this interaction is unlikely to have adverse clinical consequences, at least in patients chronically stabilized on a low dosage of haloperidol. As fluoxetine is a potent inhibitor of cytochrome P450 (CYP) 2D6, these results also provide indirect evidence for an involvement of CYP2D6 in the metabolism of haloperidol.

The effect of nefazodone on the single-dose pharmacokinetics of phenytoin in healthy male subjects

The effect of nefazodone on the pharmacokinetics of a single dose of phenytoin was evaluated in 18 healthy male subjects. The subjects received a single oral dose of phenytoin, 300 mg, on day 1 of the study and the pharmacokinetic profile of the drug was determined. After a washout period followed by oral administration of nefazodone, 200 mg twice daily for 7 days, subjects received a single dose of phenytoin, 300 mg concomitantly with the morning dose of nefazodone on day 12, and the pharmacokinetic profile of phenytoin was determined again. Minimum plasma concentrations of nefazodone and its main metabolites indicated that steady state had been achieved for nefazodone when phenytoin and nefazodone were administered concomitantly. No significant differences were demonstrated between mean single-dose pharmacokinetic parameters of phenytoin when administered alone on day 1 and concomitantly with nefazodone on day 12. Assessment of adverse events, clinical laboratory parameters, electrocardiograms, vital signs, and physical examinations indicated that concomitant administration of nefazodone and phenytoin was safe and well tolerated. These data demonstrate that nefazodone does not affect the single-dose pharmacokinetics of phenytoin, but do not preclude the possibility of such an interaction when phenytoin is administered on a long-term basis. A clinically significant interaction between nefazodone and phenytoin through a pharmacokinetic mechanism is unlikely.

Relationship between fluvoxamine pharmacokinetics and CYP2D6/CYP2C19 phenotype polymorphisms

OBJECTIVE

The purpose of this study was to investigate whether the disposition of fluvoxamine is associated with the CYP2D6 and CYP2C19 phenotype polymorphisms.

METHODS

The serum concentration of fluvoxamine was followed for 48 h after oral administration of a single dose of 50 mg fluvoxamine to five poor metabolizers of the CYP2D6 test drug dextromethorphan, five poor metabolizers of the CYP2C19 test drug mephenytoin, and five extensive metabolizers of both test drugs.

RESULTS

Poor metabolizers of dextromethorphan had significantly higher areas under the serum concentration-time curve than extensive metabolizers of dextromethorphan (mean 1.31 vs 1.00 mumol.h.l-1). There were no differences between poor and extensive metabolizers of mephenytoin (mean, 1.00 vs 1.15 mumol.h.l-1).

CONCLUSION

The results are consistent with a possible minor to moderate role of CYP2D6, but not CYP2C19, in fluvoxamine metabolism.

[Serious drug interaction between clozapine-Leponex and fluvoxamine-Fevarin]

A 67 year-old woman in steady-state treatment with clozapine 150 mg/24 h was co-medicated with 100 mg/24 h of fluvoxamine. During the next months the patient suffered from nausea and occasionally vomited, but these symptoms were ascribed to fluvoxamine, and as she mentally improved, both treatments were continued. Two months after the start of fluvoxamine her serum clozapine concentration was 7570 nmol/l or 7.5 fold higher than before fluvoxamine was added. The woman was admitted to hospital, suffering from abdominal pain, dehydration and fever (38.5 degrees C). Serum creatinine concentration was increased, but normalized during hydration. After 18 days care the woman felt well and was discharged from hospital. The case report shows that certain combinations of selective serotonin reuptake inhibitors and neuroleptic drugs should either be avoided or the serum concentrations of the drugs closely followed.

Single and multiple dose pharmacokinetics of nefazodone in subjects classified as extensive and poor metabolizers of dextromethorphan

1. The single and multiple dose pharmacokinetics of nefazodone (NEF) and its active metabolites hydroxynefazodone (HO-NEF) and m-chlorophenyl-piperazine (mCPP) were evaluated in subjects classified as extensive metabolizers (EM) or poor metabolizers (PM) of dextromethorphan. 2. In a parallel design study, 10 subjects from each phenotype received either 50 mg or 200 mg oral doses of NEF as single doses on Day 1 and multiple (twice daily) doses on Days 12-22. 3. Serial plasma and urine samples were collected at specified time intervals after dosing on Days 1, 16, 18, 20 and 22. Plasma samples were analyzed for NEF, HO-NEF and mCPP. Urine samples were analyzed for mCPP and its metabolite p-hydroxy-mCPP (p-HO-mCPP) before and after hydrolyzing the samples with beta-glucuronidase. 4. For the 200 mg dose group, the single dose plasma results showed no significant differences in pharmacokinetic parameters for NEF and HO-NEF in EM compared with PM subjects. However, for mCPP, Cmax was 89 ng ml-1 in the PM subjects compared with 44 ng ml-1 in the EM subjects, AUC was higher in the PM than EM subjects (1642 ng ml-1 h and 412 ng ml-1 h, respectively), and mCPP elimination half-life increased from 6.1 h in the EM subjects to 16.4 h in the PM subjects. Upon multiple dosing, plasma levels for NEF and all metabolites reached steady state within 3 days of dosing in both groups of subjects. Steady state pharmacokinetic parameters for NEF and HO-NEF in EM and PM subjects were not significantly different. The steady state Cmax and AUC values for mCPP in the PM subjects were 182 ng ml-1 and 1706 ng ml-1 h, respectively, compared with 49.6 ng ml-1 and 182 ng ml-1 h in the EM subjects. 5. The cumulative urinary excretion of mCPP and p-HO-mCPP was different for EM and PM subjects. Excretion of total mCPP and total p-HO-mCPP was approximately four-fold lower and five-fold higher, respectively, in the EM subjects than PM subjects. 6. These results indicate that the conversion of mCPP to p-HO-mCPP is attributable to metabolism by cytochrome P450 2D6. The differences in mCPP pharmacokinetic parameters in PM subjects did not affect the time required for NEF and its metabolites to attain steady state or the number of adverse experiences in either group of subjects. Based on the results of this study, NEF may be dosed to EM and PM patients without regard to their cytochrome P450 2D6 phenotype.

The effect of activated charcoal on the absorption of fluoxetine, with special reference to delayed charcoal administration

The effect of activated charcoal on fluoxetine (40 mg) absorption, with special reference to delayed charcoal administration, was investigated in a randomized study with four parallel groups of eight Healthy volunteers. The first group ingested fluoxetine on an empty stomach with water only (control). The second group received 25 g of activated charcoal as a suspension immediately after fluoxetine. The third and fourth groups took fluoxetine with water and received 25 g of charcoal 2 or 4 hr after fluoxetine. Timed blood samples were taken and plasma fluoxetine and norfluoxetine concentrations were measured by GC for 96 hr. When charcoal was administered immediately after fluoxetine, the AUC (0-96 hr) of fluoxetine was reduced by more than 96% (P < 0.0005) and the Cmax by more than 98% (P < 0.0005). The reduction in the AUC (0-96 hr) and Cmax of norfluoxetine was similar to that of fluoxetine. When the administration of charcoal was delayed 2 or 4 hr, there was a non-significant mean reduction of 16% and 23% in the AUC (0-96 hr) of fluoxetine. Similarly, the Cmax was not significantly reduced by charcoal given 2 or 4 hr later. Also, the half-life of fluoxetine was not significantly reduced (by 25%) by the late administration of charcoal. We conclude that activated charcoal, ingested immediately after fluoxetine, practically completely prevents the gastrointestinal absorption of fluoxetine. However, regardless of the relatively slow absorption of fluoxetine, delaying charcoal administration 2-4 hr greatly reduces its antidotal efficacy.

Fluoxetine addition to methadone in addicts: pharmacokinetic aspects

We report nine cases where fluoxetine (FX) (20 mg/day) was added to maintenance treatment with methadone (MTD) (dose range: 30-100 mg) in addicts with affective disorders. MTD plasma levels were measured before and after treatment with FX under steady-state conditions. Among the nine patients, two also received fluvoxamine (FLVX) at different times. Although it is possible that in some patients a moderate FX-MTD interaction occurs, resulting in increased plasma levels of MTD, this interaction is certainly less marked than that between FLVX and MTD and unlikely to have clinical consequences.

Effects of age and gender on venlafaxine and O-desmethylvenlafaxine pharmacokinetics

This single- and multiple-dose, nonrandomized, inpatient study was conducted to determine the effects of age and gender on the pharmacokinetic profiles of the antidepressant venlafaxine and its equally active metabolite, O-desmethylvenlafaxine. The subjects were 18 elderly (age 60-80 yrs) and 18 young (age 21-44 yrs) subjects, 9 men and 9 women per age group. They received a single 50-mg venlafaxine dose followed by 50-mg doses every 8 hours for 5 days. No significant differences in venlafaxine single-dose pharmacokinetics were seen between age groups, but the steady-state half-life increased 24% in the elderly. For O-desmethylvenlafaxine, single doses had a significantly lower apparent clearance in the elderly (0.29 vs 0.38 L/hr/kg), longer half-life (13.2 vs 10.3 hrs), and 14% greater steady-state half-life. For the composite (venlafaxine+O-desmethylvenlafaxine), there was a nonsignificant 16% increase in elderly steady-state area under the curve (AUC* = AUC+activity factor AUCm), and AUC* was linear between doses and age groups. We conclude that venlafaxine dosage adjustments for age or gender are not necessary based on pharmacokinetics.

Nefazodone: its place among antidepressants

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, adverse effects, and drug interactions of nefazodone as well as to determine its place among currently available antidepressants.

DATA SOURCES

A search of European and American literature using EMBASE and MEDLINE was completed. Nefazodone was the search term.

DATA SYNTHESIS

Nefazodone is an antidepressant that blocks serotonin type 2 (5-HT2) receptors in addition to inhibiting the reuptake of serotonin and norepinephrine. In double-blind, placebo-controlled studies, nefazodone demonstrates antidepressant activity at dosages ranging from 400 to 600 mg/d. Sedation, dry mouth, nausea, and dizziness are the more common adverse effects of nefazodone. Nefazodone, an analog of trazodone, has not been associated with priapism at this time, and may have fewer sexual adverse effects than other antidepressants. More studies are needed to determine the potential role of nefazodone in treating anxiety, pain, and premenstrual syndrome.

STUDY SELECTION

Only double-blind, placebo-controlled studies designed to establish the efficacy of nefazodone as an antidepressant were reviewed.

CONCLUSIONS

Based on placebo-controlled, double-blind, comparative trials, nefazodone demonstrates greater efficacy than placebo, and equivalent efficacy to imipramine. Somnolence, dry mouth, nausea, dizziness, and constipation are the most common adverse effects. Nefazodone appears to have a milder adverse effect profile than the tricyclic antidepressants, causes fewer sexual dysfunctions than the serotonin selective reuptake inhibitors, and may cause less dizziness than trazodone. Nefazodone at dosages of at least 300 mg/d provides another option for the treatment of depression.

Seasonal variation in platelet [3H]paroxetine binding in healthy volunteers. Relationship to climatic variables

Recently, our laboratory has reported significant seasonal differences in [3H]paroxetine binding to platelets in depressed subjects. This study aimed to examine the seasonal variation in [3H]paroxetine binding to platelets and the relationships between [3H]paroxetine binding and climatic variables in healthy volunteers. We took monthly blood samples during one calendar year from 26 healthy volunteers for assay of [3H]paroxetine binding and analyzed the data by means of univariate and multivariate spectral and cosinor analyses. There was a statistically highly significant seasonal pattern in [3H]paroxetine binding to platelets with significant annual, 4-monthly, and bimonthly rhythms, which were expressed as a group phenomenon. [3H]Paroxetine binding to platelets was significantly lower in fall and summer than in winter and spring; lows occurred in summer and peaks in spring. The peak-trough difference in this yearly variation, expressed as a percentage of the mean, was as large as 83.7%. A large part of the variance, that is, 32.5%, in [3H]paroxetine binding could be explained by weather variables, such as ambient temperature, relative humidity, and air pressure. Highly significant common annual rhythms were expressed in [3H]paroxetine binding and ambient temperature or humidity (both inversely related) and changes in temperature the 2 weeks preceding blood samplings (positively related).

Drug-drug interactions involving antidepressants: focus on venlafaxine

Selection of an antidepressant is influenced by many factors, including the patient's current drug regimen and the drug's potential for drug-drug interactions. Many psychotropic agents are known to be involved in drug-drug interactions because they are metabolized by various cytochrome pigment 450 (CYP) isoenzymes. In vitro testing with human hepatic microsomal preparations and monoclonal antibody techniques has allowed for the identification and investigation of many of these isoenzymes. Also, screening of substrates (both drug and probe) at the level of the various enzymes expressed in the human liver has allowed for the development of models that predict the risk for drug-drug interactions in vivo. Antidepressants are metabolized by and are competitive inhibitors of several isoenzymes: CYP1A2, CYP2D6, CYP3A3/4, CYP2C8/9, CYP2C19, and others. Of these, CYP2D6 has been the most thoroughly investigated and is the most extensively characterized, whereas CYP3A3/4 are more abundant and play a major role in the metabolism of many commonly used drugs. CYP2D6, but not CYP3A3/4, is subject to genetic polymorphism, which has been identified through the administration of a probe drug (sparteine, debrisoquin, or dextromethorphan). This analysis allows for the determination of an individual's "metabolizer status." This article discusses the CYP isoenzyme system in general terms and presents selected in vitro information that has been used to determine the likelihood of in vivo drug-drug interactions with various antidepressants. Of the marketed antidepressants, venlafaxine seems to have one of the most favorable drug-interaction profiles, and data specific to it are highlighted. In vitro and in vivo data indicate that venlafaxine either does not significantly inhibit or weakly inhibits the activity of isoenzymes CYP2C9, CYP2D6, CYP1A2, or CYP3A3/4.

Pharmacokinetic fluvoxamine-clomipramine interaction with favorable therapeutic consequences in therapy-resistant depressive patient

We describe the case of a depressive patient who was a rapid metabolizer of CYP2D6 substrates and a heavy smoker, and who did not respond to several courses of treatment with antidepressants, as a result of unusually low drug-plasma levels. During hospitalization, he did not improve after treatment with clomipramine (150-225 mg/day during three weeks), but showed a response within four days after addition of fluvoxamine (100 mg/day). Plasma levels of clomipramine and desmethylclomipramine changed from 58 ng/ml and 87 ng/ml to 223 ng/ml and 49 ng/ml respectively one week after addition of fluvoxamine. Present knowledge of the role of cytochrome P-450 isozymes, such as CYP1A2, CYP2C19, CYP2D6, and CYP3A4, in the metabolism of psychotropic drugs as well as therapeutic drug-plasma level monitoring may thus help to determine individual treatment.

[Fluoxetine and tricyclic antidepressants: clinical tolerance in short-term combined administration]

The tricyclic SSRI antidepressant association is often used in the treatment of resistant depressive illness. The pharmacokinetic interaction existing between these two types of drugs is well known, with as result, an increase of tricyclic antidepressant plasma levels. The aim of this work was to assess the clinical tolerance of the association of fluoxetine and tricyclic antidepressants, prescribed at usual doses. In 10 patients, having a bad response to a tricyclic antidepressant treatment, with in the therapeutic window adjusted plasma levels since 3 weeks, an association of fluoxetine (20 mg/d) to the tricyclic was prescribed. The other associated treatments were unmodified. The clinical evolution was recorded with the MADRS and the UKU scale for side effects, before the tricyclic antidepressant treatment adjustment (D-21) and just before the fluoxetine association (D1) and every 7 days after this association too. The tricyclic plasma levels (amitriptyline and clomipramine) and the patient phenotype CYP 2D6 and 2C19 were determined before and 7 days after the fluoxetine addition. A good clinical evolution was noted since the 7th day after the fluoxetine association to tricyclic (mean MADRS scores on D-21, D1, D7 and D14; 35.4, 33.1, 23.9, 16.8 respectively). In 3 patients, an anxiety increase on day 6, 14 and 16 respectively, after fluoxetine addition, induces a stop of the serotonergic antidepressant. In one patient all the treatment was stopped due to the appearance of a mood inversion. In another patient, after 14 days of antidepressant association, EC were prescribed as asked by the patient, due to an insufficient mood improvement, with a good clinical result and tolerance. The evolution of the side effects was surprising. There was no increase of the UKU score mean during the associated treatment, despite an increase of the tricyclic plasma levels that reached, in three patients, the toxic level (510, 605 and 860 ng/ml of amitriptyline + nortriptyline or clomipramine + demethylclomipramine). The UKU psychic score mean significatively decreased (7.7, 6.8, 5.3, 4 on D-21, D1, D7, D14 respectively). The fluoxetine association did not modify the neurological, neuro-endocrinologic and the skin side effects. None increase of headheck was noted. The increase of anxiety, observed in 3 patients, was not considered as a side effect of the antidepressant association, but an effect of the stimulant potency of fluoxetine in anxious patients. The pharmacogenetic results confirmed the strong inhibition potenty of fluoxetine on the CYP 2D6 isoenzyme. In 5 patients indeed, the extensive metabolizer phenotype was modified in a poor metabolizer phenotype, seven days after the association of fluoxetine. The CYP 2C19 phenotype was unchanged after this association. The patient phenotype did not seem to interfere with the clinical results. In conclusion, in this group of patients, the short-term clinical tolerance of the tricyclic antidepressant and fluoxetine association was very good, despite the pharmacokinetic interaction existing between these two types of drugs.

Therapeutic options for treating major depression, and the role of venlafaxine

Major depression is a debilitating disorder that is often undertreated. Psychotherapy, electroconvulsive therapy, and pharmacotherapy are options for management. Tricyclic antidepressants and selective serotonin reuptake inhibitors are the cornerstones of drug therapy. Venlafaxine, a phenylethylamine antidepressant that primarily inhibits reuptake of norepinephrine and serotonin, is an alternative to those agents. It has been studied in short-term and continuation studies and appears to have efficacy similar to that of imipramine, trazodone, and fluoxetine. Moreover, venlafaxine is effective in approximately one-third of patients with treatment-resistant depression. Venlafaxine is metabolized by the P-450 enzyme system to an active metabolite O-desmethyl-venlafaxine, which is excreted renally. Nausea, somnolence, and dizziness are dose-related adverse effects that often occur with initiation of therapy. Increases in blood pressure, particularly with high dosages, also may occur. Drug-drug interactions appear to be minimal.

Nefazodone pharmacokinetics: assessment of nonlinearity, intra-subject variability and time to attain steady-state plasma concentrations after dose escalation and de-escalation

OBJECTIVE

The time required to reach steady-state plasma levels after an increase and a subsequent decrease in the dose of nefazodone, an antidepressant drug with nonlinear pharmacokinetics, was assessed in 24 healthy, male volunteers.

METHODS

Each subject was administered 100 mg nefazodone hydrochloride b.i.d. (q 12 h) from study day 1 to 7, 200 mg b.i.d. from study day 8 to 14 and 100 mg b.i.d. from study day 15 to 21. Trough (Cmin blood samples were obtained just prior to the morning dose on days 4-7, 11-14 and 16-21 to evaluate the attainment of steady state. Serial blood samples were collected for 12 h after the morning dose on days 7, 14, 16, 18 and 21 for pharmacokinetic analysis of plasma levels of nefazodone (NEF) and its metabolites, hydroxynefazodone (HO-NEF), m-chlorophenylpiperazine (mCPP) and triazoledione (DIONE), which were determined by validated HPLC/UV assay methods. The Cmin results indicated that when nefazodone was administered at a dose of 100 mg b.i.d., steady-state plasma levels of parent compound and its metabolites were attained by the 4th day (i.e., after six doses) and when the dose was increased from 100 mg b.i.d. to 200 mg b.i.d. and then decreased back to 100 mg b.i.d., new steady-state plasma levels were also reached by the beginning of the 3rd or 4th day of each regimen. Consistent with the attainment of steady-state data, there were no statistically significant differences in Cmax or AUC values for nefazodone or its metabolites between study days 7, 18 and 21. Also consistent with the known nonlinear pharmacokinetics of nefazodone, the mean nefazodone steady-state Cmax and AUC values for the 200-mg dose were three fold and four fold greater, respectively, than those at the 100-mg dose level. Intrasubject variability (% cv) for NEF and its metabolites ranged from 13% to 24% for Cmax and AUC after 100 mg b.i.d.. Intersubject variability was considerably greater and ranged from 29% to 131% for Cmax and AUC after the same dose.

The lack effect of food on the bioavailability of nefazodone tablets

The objective of this study was to assess the effect of food on the pharmacokinetics of nefazodone (NEF). A group of 24 healthy adult male volunteers received a single 200 mg dose of NEF under fasting conditions as well as 5 min after a high-fat breakfast. There was a 1 week washout between treatments. Serial blood samples were collected for 48 h after dosing and assayed by a validated HPLC method for NEF and the metabolites hydroxynefazodone (HO-NEF), m-chlorophenylpiperazine (mCPP), and triazoledione (dione). The mean (SD) peak concentration (Cmax) for NEF was not affected by food and was 416 (220) ng mL-1 and 446 (271) ng mL-1 after the fed and fasted treatments, respectively. The median time to reach Cmax (Tmax) was also unaffected by food and was 2 h for both treatments. However, the mean (SD) area under the curve (AUC) was significantly reduced by food from 1815 (1017) ng h mL-1 to 1409 (695) ng h mL-1. Although there was an 18% decrease in NEF AUC when administered with food, food had no effect on Cmax and Tmax values for NEF, HO-NEF, mCPP or dione or AUC values for HO-NEF, mCPP, or dione, indicating that NEF can be administered without regard to meals.

Pharmacokinetic interaction between multiple-dose venlafaxine and single-dose lithium

Venlafaxine is a structurally novel antidepressant. Because lithium and antidepressants may be administered concomitantly, it is important to determine whether the disposition of venlafaxine and lithium is affected by coadministration. An open-label study was conducted to evaluate the effects of multiple-dose, steady-state venlafaxine administration on the pharmacokinetics of a single oral dose of lithium. Analogously, the effects of administration of a single-dose of lithium on the disposition of venlafaxine and its active metabolite, O-desmethylvenlafaxine, after multiple-dose administration of venlafaxine were assessed. Administration of 600 mg lithium carbonate did not affect venlafaxine absorption. Lithium significantly reduced the renal clearance of venlafaxine from 0.053 to 0.027 L/h/kg. However, renal excretion is not a major elimination pathway for venlafaxine; thus, lithium did not affect the total clearance of venlafaxine. Lithium administration had similar effects on elimination of O-desmethylvenlafaxine. Multiple-dose administration of 50 mg of venlafaxine every 8 hours produced a slight increase in the rate of lithium absorption, but did not affect the extent of lithium absorption. Total clearance (0.026 L/h/kg) and steady-state volume of distribution (0.71 L/kg) of lithium were not affected by administration of venlafaxine. Thus, there were no clinically significant pharmacokinetic interactions between venlafaxine and lithium.

A study of the effect of age and gender on the pharmacokinetics of nefazodone after single and multiple doses

The single-dose (S-D) and steady-state (S-S) pharmacokinetics of nefazodone (NEF) and two of its pharmacologically active metabolites, hydroxynefazodone (HO-NEF) and m-chlorophenylpiperazine (mCPP), in healthy elderly (> 65 years) men and women (N = 12 each) were compared with those in healthy younger (18-40 years) men and women (N = 12 each). All subjects were classified as extensive metabolizers of dextromethorphan (cytochrome P4502D6). Subjects were administered a 300-mg dose of nefazodone hydrochloride for the evaluation of S-D pharmacokinetics. For the evaluation of S-S pharmacokinetics, 300-mg doses of NEF were administered twice daily (every 12 hours) for 8 days (single morning dose on day 8). Serial blood samples were collected after the single dose and the morning dose on day 8 of the twice-daily administration; a blood sample for trough level was collected from each subject just before the morning dose on days 2 to 8 of the twice-daily dosing to assess the attainment of steady state. Plasma samples were assayed for NEF, HO-NEF, and mCPP by a specific, validated high-performance liquid chromatography assay. After a single dose of NEF, the mean peak concentrations in plasma and the area under the curves (AUC) for NEF and HO-NEF were about twofold higher in elderly versus young subjects, but mean AUCs for mCPP were similar. Levels in plasma for NEF, HO-NEF, and mCPP reached steady state by day 3 of multiple dosing. At steady state, exposure to NEF and HO-NEF, based on AUC(TAU) values, was quite variable among age/gender groups but on the average was about 50% higher in elderly women compared with the other three groups of subjects; the exposure to mCPP at steady state was similar in elderly and young subjects. Because all subjects were extensive metabolizers, the effect of gender or age on the pharmacokinetics of NEF and its metabolites in poor metabolizers is not known. There were no serious or unexpected adverse experiences observed in this study. Assuming that similar systemic exposure to NEF and its active metabolites will result in similar therapeutic effects in young and elderly individuals, the difference in systematic exposure to NEF and HO-NEF in elderly subjects suggests that NEF treatment should be initiated at half the usual dose with titration upward and that the usual precautions exercised in treating elderly patients should be used.

Assessment of pharmacokinetic and pharmacodynamic drug interactions between nefazodone and digoxin in healthy male volunteers

The effect of nefazodone on pharmacokinetic and pharmacodynamic parameters of digoxin were evaluated in an open, randomized, multiple-dose, three-way crossover study of 18 healthy male volunteers. The volunteers received nefazodone alone (200 mg twice daily), digoxin alone (0.2 mg daily), or nefazodone combined with digoxin during three 8-day treatment periods, with a single dose on the ninth day. There was a 10-day washout period between treatment periods. Coadministration of nefazodone with digoxin had no effect on the frequency and severity of adverse events compared with those observed with either drug alone. Steady-state area under the concentration-time curve (AUC) and peak (Cmax) and trough (Cmin) concentrations of digoxin were significantly higher (15%, 29%, and 27%, respectively) after coadministration of nefazodone/digoxin than after administration of digoxin. Despite these increases, no clinically significant changes in vital signs, heart rate, or PR, QRS, and QT intervals on the electrocardiogram occurred after coadministration from those measured after digoxin monotherapy. Coadministration did not affect the pharmacokinetics of nefazodone or its metabolites (hydroxynefazodone, m-chlorophenylpiperazine, triazole dione). Because digoxin has a narrow therapeutic index, monitoring of plasma digoxin levels and appropriate adjustment of dosage are recommended when nefazodone and digoxin are administered concurrently.

Investigation of pharmacokinetic and pharmacodynamic interactions after coadministration of nefazodone and haloperidol

A double-blind, placebo-controlled study using 12 healthy men was designed to evaluate pharmacokinetic and pharmacodynamic interactions when nefazodone and haloperidol are coadministered. Two groups of six subjects each received a 5-mg oral dose of haloperidol or a placebo on study days 1 and 2. Nefazodone, 200 mg, was administered to all 12 subjects twice daily (every 12 hours) on study days 3 to 9; on study day 10, only the morning dose of nefazodone was administered. On study days 9 and 10, all subjects also received 5 mg of haloperidol or a placebo along with the morning dose of nefazodone. Serial blood samples for pharmacokinetic analysis were collected from each subject over a 12-hour period after the morning dose on study days 1, 2, 9, and 10. Plasma samples were assayed for haloperidol, reduced haloperidol, nefazodone, hydroxynefazodone and m-chlorophenylpiperazine by specific, validated high-performance liquid chromatogoraphy methods. Psychomotor performance tests to evaluate haloperidol pharmacodynamics were also performed on days 1, 2, 9, and 10. Reduced haloperidol in the majority of samples was below the limit of quantitation; therefore, the effect of nefazodone on the pharmacokinetics of reduced haloperidol could not be determined. The administration of 5 mg of haloperidol to subjects dosed with nefazodone to steady state led to a modest pharmacokinetic interaction, as indicated by a 36, 13, and 37% increase in mean area under the curve (AUC0-12), highest concentration, and 12-h concentration values for haloperidol, respectively; only the increase in AUC was statistically significant. In contrast, the steady-state pharmacokinetics of nefazodone, hydroxynefazodone, and m-chlorophenylpiperazine were not affected by the administration of haloperidol. Although there were significant differences observed in some psychomotor performance tests, the effects of nefazodone on the pharmacodynamics of haloperidol could not be consistently demonstrated. The results from this study suggest that nefazodone has only modest pharmacokinetic and pharmacodynamic interactions with haloperidol. Although no specific recommendations can be made, dosage adjustment may be necessary for haloperidol when coadministered with nefazodone.

Excretion of fluoxetine and its metabolite, norfluoxetine, in human breast milk

A study was conducted to measure breast milk concentrations of fluoxetine and its active metabolite, norfluoxetine, excreted in breast milk in a cohort of nursing women using fluoxetine, and to estimate infant dose from nursing. The study included 10 women nursing 11 infants (median age, 185 days). The mean fluoxetine dose was 0.39 mg/kg/day. Each patient manually collected 3 to 6 milk samples throughout a dosing interval. Concentrations of fluoxetine and norfluoxetine in milk were measured by gas-liquid chromatography. Mothers reported whether they observed adverse effects in their infants. The average infant doses of fluoxetine and norfluoxetine, as estimated for an exclusively breast-fed infant ingesting 1000 mL of milk per day, were 0.077 mg (SD = 0.054 mg) and 0.084 mg (SD = 0.043 mg), respectively. The total dose of fluoxetine and norfluoxetine (expressed as fluoxetine equivalents) was 0.165 mg (SD = 0.092 mg), which was equivalent to 10.8% (SD = 2.2%) of the maternal dose, adjusted on a mg/kg basis in a 4-kg infant. No adverse events were reported by mothers in their infants. Approximately one tenth of the adult therapeutic dose of fluoxetine is excreted in breast milk. Although short-term adverse effects in the infant from exposure through nursing were not reported in this cohort, future studies that assess the potential long-term consequences are needed.

Pharmacokinetics, absolute bioavailability, and disposition of [14C]nefazodone in humans

The pharmacokinetics and disposition of nefazodone (NEF) were investigated after administration of intravenous (iv) and oral (po) doses to nine healthy men. All volunteers were administered a 5-mg dose of [14C]NEF by iv infusion on study day 1, and groups of three volunteers each were administered oral solution doses of 50, 100, and 200 mg of [14C]NEF, respectively, on study day 8. Total radioactivity in plasma, urine, and feces collected for 7 days after iv and po dosing was determined. Serial blood samples for pharmacokinetic analysis were also collected over a 48-hr period after iv and po administrations, and plasma samples were assayed for NEF, and the NEF metabolites hydroxynefazodone (HO-NEF) and m-chlorophenylpiperazine (mCPP) by a specific, validated HPLC method. Over the po dose range of 50-200 mg, NEF was rapidly absorbed (tmax values for NEF, HO-NEF and total radioactivity were approximately 0.5 hr). Recovery of total radioactivity in the urine (approximately 50% of dose) was similar after iv and po administrations. Fecal excretion of radioactivity after iv administration of [14C]NEF suggested that biliary excretion also plays a role in drug elimination. The mean (SD) apparent absolute oral bioavailability of NEF was 15(7)%, 18(7)%, and 23(7)% at doses of 50, 100, and 200 mg, respectively. The apparent extent of presystemic metabolism over this dosage range was estimated to be 74-87%. In summary, after po administration, NEF was rapidly and completely absorbed, and extensively metabolized before elimination via urinary and fecal routes.

Fluoxetine in depressed patients with renal failure and in depressed patients with normal kidney function

Nine depressed patients with normal kidney function and seven depressed patients with renal failure undergoing hemodialysis were treated with open-label fluoxetine 20 mg/day in an 8-week study. The study was designed to evaluate the pharmacokinetics of fluoxetine during repeated administration and to acquire preliminary data regarding the effectiveness of this antidepressant in a population undergoing hemodialysis. Six patients in each group completed the study. Of these, five patients undergoing hemodialysis and five patients with normal renal function experienced moderate to marked improvement in their depression. Side effects were equal and minor in both groups, indicating that fluoxetine is safe in patients with renal impairment. The mean +/- standard deviation steady-state plasma concentrations of the sum of fluoxetine plus its metabolite norfluoxetine for patients completing 8 weeks (N = 6, both groups) were comparable for the patients undergoing hemodialysis (253 +/- 61 ng/ml) and those with normal kidney function (218 +/- 122 ng/ml; t = 1.5, df = 70, p > 0.13). These data suggest that the efficacy of fluoxetine in patients with renal failure undergoing hemodialysis is comparable to that in patients with normal kidney function. These data further suggest that renal failure and the process of hemodialysis do not materially alter the pharmacokinetics of fluoxetine or its major metabolite norfluoxetine.

Tolerability and safety: essentials in antidepressant pharmacotherapy

Current antidepressants achieve similar efficacy, with 60% to 80% of patients responding adequately. Clinical response is gradual, and differential response factors are difficult to discern. However, side effect profiles and toxicity vary substantially, so the choice of medication depends primarily on tolerability and safety. Dry mouth is prevalent with tricyclic antidepressants (TCAs), whereas nausea occurs more frequently with a serotonin selective reuptake inhibitor (SSRI). Long-term unwanted effects tend not to be a major problem, with a dropout rate of approximately 5% due to side effects. The relationship between suicidality and antidepressants remains under debate. Many TCAs are highly toxic in overdose whereas the SSRIs appear much safer. Nefazodone is a unique antidepressant with demonstrated efficacy. It is different from other antidepressants because of its two actions in the serotonin system, moderate serotonin selective reuptake blocking properties and direct 5-HT2 antagonism, which also can enhance 5-HT1 neurotransmission. The 5-HT2 antagonist properties may limit serotonin-mediated effects and, as a result, nefazodone may be more anxiolytic than other antidepressants. Nefazodone also moderately inhibits norepinephrine reuptake and blocks alpha 1-adrenergic receptors. The data base on the safety of nefazodone currently comprises approximately 3,500 patients from all research trials, which include controlled trials that allow comparisons of nefazodone treatment with several hundred patients taking TCAs or SSRIs and nearly 900 patients receiving placebo. The most frequent adverse experiences with nefazodone as compared with placebo treatment are nausea (21% vs. 14%), somnolence (19% vs. 13%), dry mouth (19% vs. 13%), dizziness (12% vs. 6%), constipation (11% vs. 7%), asthenia (11% vs. 6%), light-headedness (10% vs. 4%), and amblyopia (blurred vision; 6% vs. 3%). Approximately 12% of nefazodone-treated patients dropped out because of adverse experiences, as compared with 7.4% on placebo, 10.4% on SSRIs, but 21.8% on imipramine after short-term exposure in placebo-controlled trials. Long-term safety data include nearly 1,300 patients; nefazodone was well tolerated. Nefazodone was evaluated in normal subjects by the author and was found to produce less impairment than imipramine and was less likely to interact with alcohol. In summary, nefazodone has a favorable adverse-event profile as compared with the TCAs and a rather different one from the SSRIs. It appears to be safe and well tolerated after both acute and long-term use.

Hostility in heroin abusers subtypes: fluoxetine and naltrexone treatment

1. Substance abusers subtypes have been identified considering underlying psychobiological disorder, familial factors, age of onset, legal problems and drug of choice. 2. In the present study the authors submitted 98 male heroin addicted individuals (age 19-28 y) to the Buss Durkee Hostility Inventory (Italian version) and a structured interview concerning social and clinical history; legal problems, age of onset of drug abuse, drug of choice. 3. Serotonergic system sensitivity was evaluated with fenfluramine challenge for PRL assay. 4. Thirty two patients (group A) showed high score for resentment and guilt at BDHI (hostility in), low rate of legal problems, late age of onset, preference for heroin and alcohol. Twenty nine patients (group B) showed high score for assault and irritability at BDHI (hostility out), high rate of legal problems, early age of onset, preference for heroin and cocaine. The other 37 patients (group C) showed aggression score in the normal range at BDHI, no legal problems, late onset of substance abuse, preference for heroin only. 5. PRL responses was blunted in group A (p < 0.001) and significantly decreased in group B (p < 0.05). PRL plasma levels were inversely correlated with HRSD scores. 6. All the patients were included in a treatment protocol with fluoxetine and naltrexone or placebo and naltrexone for 6 months. 7. The treatment was effective in group A with a significant improvement of BDHI results and decrease of craving score, lower level of drop out, lower level of positive urine controls. No significant differences between fluoxetine and placebo effects have been evidenced in patients of group B and C. The present findings suggest that psychopharmacological approach to addiction needs a diagnostic screening for specific subtypes.

[Toxic tricyclic drug plasma level caused by fluoxetine]

A case study illustrates that even after discontinuation fluoxetine still increases amtitriptyline plasma-levels. This is caused by an inhibition of the metabolism of tricyclics by fluoxetine which was still active due to the long elimination half-life of this substance and its metabolite.

Absorption and presystemic metabolism of nefazodone administered at different regions in the gastrointestinal tract of humans

PURPOSE

The absorption and disposition of nefazodone (NEF) and its metabolites hydroxynefazodone (HO-NEF), m-chlorophenylpiperazine (mCPP) and triazole dione (dione) were assessed in 10 healthy subjects following infusion of NEF solution into the proximal and distal regions of the intestine vs administration of NEF solution orally by mouth.

METHODS

NEF HCl (400 mg) was infused over 5 hours into the proximal or distal intestine through a nasogastric tube, or orally ingested in 10 divided doses over 4.5 hours. The three treatments in the three-period crossover design were separated by one week.

RESULTS

The bioavailability of NEF, based on AUC(INF), from proximal and distal regions relative to that from oral administration was 97% and 106%, respectively. NEF was absorbed equally well from all three treatments with median Tmax of 5.0 hours which coincided with the duration of infusion. Mean Cmax of NEF was not different between proximal and oral administrations, however, mean Cmax after distal instillation was 40% lower than that after oral administration. Exposure to HO-NEF, mCPP and dione, following proximal instillation was also comparable to that after oral administration. AUC(INF) of HO-NEF and dione was significantly lower after distal instillation compared to that after oral administration but AUC(INF) of mCPP was not. Cmax of all metabolites was significantly lower after distal administration in comparison to oral treatment. Terminal half-life for NEF, HO-NEF and mCPP after distal administration was longer than the other two treatments.

CONCLUSIONS

NEF is absorbed throughout the length of the gastro-intestinal tract which supports the development of an extended-release formulation of NEF. The exposure to the metabolites (relative to NEF) was lower from the distal intestinal site compared to the proximal and oral site which may be explained by a reduced first pass of NEF by the cytochrome P450 3A4 in the distal intestine.

Pharmacokinetic and pharmacodynamic evaluation during coadministration of nefazodone and propranolol in healthy men

Potential interactions between nefazodone (200 mg every 12 hours) and propranolol (40 mg every 12 hours) were assessed in 18 healthy male volunteers in an open-label, randomized, three-way crossover study. The nature, frequency, and severity of adverse events during coadministration of nefazodone and propranolol were similar to those observed with either treatment alone. There were no clinically significant effects on vital signs, electrocardiographic results, or laboratory parameters. With coadministration, the maximum peak concentration (Cmax) and area under the concentration-time curve over the dosing interval (AUC tau) of propranolol decreased 29% and 14%, respectively; Cmax and AUC tau of 4-hydroxy-propranolol decreased 15% and 21%, respectively. Despite decreased plasma concentrations of the beta-antagonists, the reduction in exercise-induced tachycardia and post-exercise double product was slightly greater with coadministration than with propranolol alone. Administration of nefazodone alone did not significantly affect either pharmacologic parameter. The pharmacokinetics of nefazodone and its metabolites were largely unaffected during coadministration. Coadministration of propranolol and nefazodone results in modest pharmacokinetic inequivalencies, but no clinically significant alterations of the pharmacodynamics of propranolol.

Effect of cigarette smoking on fluvoxamine pharmacokinetics in humans

OBJECTIVES

Although fluvoxamine inhibits the biotransformation of drugs known to be metabolized by CYP1A2, there are no data available with regard to the importance of CYP1A2 for the metabolism of fluvoxamine itself. Because smoking induces the metabolism of drugs catalyzed by CYP1A2, this study investigated the pharmacokinetics of fluvoxamine in smokers and nonsmokers.

METHODS

The serum concentration of fluvoxamine was determined by high-performance liquid chromatography for 48 hours after oral administration of a single dose of 50 mg fluvoxamine to 12 smokers (> or = 10 cigarettes per day) and 12 nonsmokers.

RESULTS

The smokers had significantly lower areas under the serum concentration-time curve and significantly lower maximal serum concentrations than the nonsmokers (mean +/- SD, 771 +/- 346 versus 1110 +/- 511 nmol.hr.L-1 [p = 0.012] and 39.1 +/- 17.3 versus 57.7 +/- 21.5 nmol.L-1 [p = 0.012], respectively). The terminal elimination half-life did not differ significantly between smokers and nonsmokers (10.1 +/- 1.9 and 10.7 +/- 2.3 hours, respectively). The oral clearance was high among both smokers (4.1 +/- 1.9 L.min-1) and nonsmokers (3.3 +/- 2.7 L.min-1; difference not significant).

CONCLUSION

Smokers had lower serum concentrations of fluvoxamine than nonsmokers after a single oral dose of fluvoxamine. This finding is consistent with a possible role of CYP1A2 in fluvoxamine metabolism.

Safety, tolerance, and preliminary pharmacokinetics of nefazodone after administration of single and multiple oral doses to healthy adult male volunteers: a double-blind, phase I study

Safety, tolerance, and preliminary pharmacokinetics of nefazodone, a new antidepressant, were assessed in a randomized, double-blind, parallel group study carried out in two sequential segments: a single and a multiple daily dose segment. Nine subjects in the single daily dose segment were divided into three treatment groups and received nefazodone doses in a leapfrog fashion. Each day of treatment with nefazodone was followed by 2 days of placebo treatment and then administration of the next higher drug dose. Single doses ranged from 5-500 mg. 8 subjects enrolled in the multiple daily dose segment were divided into two treatment groups. In each group, 3 subjects received nefazodone and one received placebo 3 times a day. Each dosage level was administered for 2 days before proceeding to the next higher dose from 5 mg or 10 mg 3 times a day to a maximum of 500 mg 3 times a day. After the dose-escalation period, the subjects in the multiple daily dose segment underwent a 3-day washout, after which they received a single dose of nefazodone at the maximum tolerated level. Safety and tolerance assessment involved analyses of adverse events, laboratory tests, vital signs, ophthalmic examinations, and ECGs. Blood and urine samples were obtained only in the multiple daily dose segment and analyzed for nefazodone and its two pharmacologically active metabolites, hydroxynefazodone and mCPP. A single blood sample was collected on 8 different days for assessment of trough levels (Cmin) and serial samples were obtained on days 5, 9, and 22 of dosing for pharmacokinetic profiles. Additional serial samples were also obtained after the last single dose of 500 mg after a 3-day washout. Nefazodone was found to be safe and well-tolerated in total daily doses as high as 1350 mg (450 mg 3 times a day). Nefazodone was rapidly absorbed after oral administration and converted to hydroxynefazodone and mCPP. The pharmacokinetics of nefazodone, hydroxynefazodone, and mCPP were found to be dose-dependent, as evidenced by dose normalized values of Cmin, Cmax, and AUC0-8 that progressively increased with dose. Although exposure of normal subjects to nefazodone and its 2 pharmacologically active metabolites was disproportionately higher than the corresponding increase in dose, the safety and tolerance profiles did not show a parallel increase in adverse events. Nefazodone may be well-tolerated by patients receiving expected therapeutic doses from 200-600 mg per day when administered in divided doses every 8 to 12 hours.

Pharmacokinetics of single- and multiple-dose bupropion in elderly patients with depression

A study of a dopaminergic antidepressant that may have an advantageous profile for use in elderly patients, bupropion, was conducted to determine the pharmacokinetics of bupropion in the elderly. Pharmacokinetics of single- and multiple-dose bupropion were examined in six elderly patients (five women and one man) diagnosed with depression. Mean (+/- SD) CL app of bupropion was 1.6 +/- 0.4 L/hr/kg, approximately 80% of the corresponding value reported for younger patients. Mean bupropion t1/2 was 34.2 +/- 8.7 hours, and average apparent Vd (Vd app) was 79.3 +/- 29.4 L/kg. Apparent half-lives (t1/2 app) of the metabolites hydroxybupropion, erythrobupropion, and threohydrobupropion were 34.2 +/- 4.6 hours, 61.4 +/- 21.6 hours, and 38.8 +/- 7.6 hours, respectively. After multiple dosing, the mean t1/2 for bupropion and its metabolites did not change significantly, although in some patients the t1/2 app of the metabolites was substantially prolonged. There was also evidence of inordinate accumulation of metabolites. The elderly are at risk for accumulation of bupropion and its metabolites. Specification of therapeutic drug monitoring parameters for bupropion treatment of the elderly is needed.

Inhibition of trazodone metabolism by thioridazine in humans

To clarify the involvement of cytochrome P4502D6 (CYP2D6) in the metabolism of trazodone, the effects of coadministration of thioridazine, which is an inhibitor of this isozyme, on plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine (m-CPP) were studied. The subjects were 11 depressed patients receiving trazodone at bedtime for 1-18 weeks. The dose was 150 mg in 10 patients and 300 mg in one. Thioridazine 40 mg/day was coadministered for 1 week, and blood samplings were performed before and after the coadministration. Thioridazine significantly (p < 0.001) increased plasma concentrations of both trazodone (713 +/- 252 vs. 969 +/- 370 ng/ml) and m-CPP (61 +/- 22 vs. 94 +/- 34 ng/ml). The present study thus suggests that CYP2D6 is involved in the metabolism of trazodone.

Effects of combined fluoxetine and counseling in the outpatient treatment of cocaine abusers

Three methods of analysis were used to determine the effects of the combination of counseling with fluoxetine (20, 40, or 60 mg) and "active" placebo (diphenhydramine, 12.5 mg) randomly assigned. Forty-five cocaine-only dependent subjects were treated as outpatients with "interpersonal" counseling, medication, and drug use monitoring three times per week for up to 12 weeks. Treatment effects were analyzed: first, by comparing the three original assignments and placebo; second, by comparing the placebo group to fluoxetine subjects with detectable fluoxetine/norfluoxetine blood levels and those with no detectable medication blood level; third, by examining relapse prevention versus use cessation through stratifying the subjects into four groups according to fluoxetine or placebo assignment and initial urine cocaine positivity or negativity. All three analyses showed improvement on some measures over time regardless of group assignment. The 60-mg fluoxetine group showed least effectiveness, the group with detectable blood levels had less cravings, and the fluoxetine subjects who were abstinent at the start of treatment were somewhat less likely to avoid relapse than those on placebo.

Pharmacokinetic interactions between lithium and fluoxetine after single and repeated fluoxetine administration in young healthy volunteers

Pharmacokinetic interactions following coadministration of fluoxetine and lithium were investigated in 10 young healthy subjects. Both drugs were administered orally in a non-blinded design with 3 consecutive treatment periods: single oral dose of lithium (32.4 mmol lithium as acetate, Quilonum; coadministration of single oral doses of lithium (32.4 mmol) and fluoxetine (Fluctin, 60 mg); and single oral dose of lithium after 7-day pretreatment with fluoxetine (20 mg t.i.d.). Periods 1 and 2 were separated by a 1-week washout phase, while period 3 followed on immediately after period 2. Lithium serum concentrations were practically identical in periods 1 and 3 (administration of lithium alone and after chronic fluoxetine dosing). However, in period 2, when the 2 drugs were coadministered as single oral doses, the lithium concentrations were lower in the first 4 hours after medication compared with treatment periods 1 and 3. Cmax was also significantly lower in period 2. The times to peak, however, were not significantly changed by any fluoxetine comedication. The parameters AUC0 --> infinity, t1/2, total clearance (Cltot) and renal clearance (Clren) determined after administration of lithium alone did not differ statistically from values determined after single or after repeated fluoxetine dosing. Coadministration of lithium and fluoxetine did not produce any clinically relevant changes in hemodynamics, ECGs or laboratory parameters. After single doses of both drugs the most frequently reported symptoms were gastrointestinal complaints, while mild sedative symptoms were predominant when lithium was given after repeated fluoxetine medication.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic and pharmacodynamic evaluation of the potential drug interaction between venlafaxine and diazepam

To assess possible pharmacokinetic and pharmacodynamic interactions between the antidepressant venlafaxine and diazepam, a randomized, two-period, crossover study was conducted in 18 men. Multiple-dose venlafaxine (50 mg every 8 hours) or placebo (double-blind) was given for 10 days; on day 4 a single placebo dose (same appearance as diazepam capsule, single-blind) was given; and on day 5 a single dose of diazepam (10 mg) was given. Pharmacokinetic data indicated that diazepam had no significant effect on venlafaxine or O-desmethylvenlafaxine disposition. Diazepam pharmacokinetics were minimally changed in the presence of venlafaxine. Diazepam oral clearance (CL/f) increased slightly (24 +/- 8 versus 26 +/- 6 mL/h/kg; P = .007), volume of distribution (Vz/f) increased (0.85 +/- 0.28 versus 0.99 +/- 0.34 L/kg; P = .02), and AUC decreased (5973 +/- 2304 versus 5008 +/- 1354 ng.h/mL; P = .02). Venlafaxine did not alter desmethyldiazepam pharmacokinetics. Pharmacodynamic data showed a statistically significant diazepam-venlafaxine interaction for only one of the eight psychometric tests given. Critical flicker fusion slightly decreased (P = .01) between placebo-diazepam (37.85 +/- 3.28 Hz) and venlafaxine-diazepam (37.09 +/- 4.13 Hz) treatments. The observed pharmacokinetic and pharmacodynamic interactions between diazepam and venlafaxine were small and probably clinically insignificant.

The pharmacokinetics of venlafaxine when given in a twice-daily regimen

The comparative bioavailability of the novel antidepressant venlafaxine and its pharmacologically active metabolite O-desmethylvenlafaxine was assessed when venlafaxine was given orally twice daily (75 mg bid) or 3 times daily (50 mg tid). Eighteen healthy subjects participated in an open-label, randomized, two-period, crossover study lasting 12 days. Each subject was randomly assigned to take venlafaxine according to a bid or a tid regimen through day 8 and was crossed over to the other regimen on days 9 to 12. The daily dose was titrated up to 150 mg/d and was held constant on days 5 to 12. Plasma samples for quantitation of venlafaxine and O-desmethylvenlafaxine were obtained during a 24-hour steady-state interval on days 8 and 12. Analysis of variance showed no significant differences between the two venlafaxine regimens for peak concentration (Cmax), area under the curve during 24 hours (AUC0-24), trough concentration, or fluctuation ratio for venlafaxine or O-desmethylvenlafaxine in plasma. The bioequivalence ratios for Cmax and AUC0-24 of both compounds were calculated to compare the bid regimen and the tid regimen. The mean value for each of the 4 ratios was between 96 and 100%, and the 90% confidence limits around each ratio were within 90 to 110%. These results indicate that dividing a daily 150-mg venlafaxine dose into 2 or 3 doses provides equivalent total exposure and peak plasma concentrations of venlafaxine and O-desmethylvenlafaxine, its active metabolite. Therefore, based on pharmacokinetic considerations, it appears that the same daily dose of venlafaxine can be given in either two or three divided doses without compromising efficacy.

Venlafaxine: a structurally unique and novel antidepressant

OBJECTIVE

To introduce the new antidepressant venlafaxine. Basic pharmacokinetic data and clinical trials are reviewed, as well as adverse reactions, drug interactions, dosing guidelines, and therapeutic considerations. The article also discusses several pharmacotherapy issues and how venlafaxine compares with other available antidepressants.

DATA SOURCES

A MEDLINE search was used to identify pertinent literature, including reviews.

STUDY SELECTION

As this is a relatively new agent, all available clinical trials were reviewed.

DATA EXTRACTION

All clinical trials that were available prior to submission for publication were reviewed. Preliminary trials and unpublished reports were not reviewed.

DATA SYNTHESIS

Venlafaxine hydrochloride is a structurally novel agent that has recently been approved in the US for the treatment of depression. This unique antidepressant blocks neuronal reuptake of norepinephrine, serotonin, and, to a lesser extent, dopamine. Venlafaxine and its major active metabolite, O-desmethylvenlafaxine, exhibit linear kinetics with an elimination half-life of 5 and 11 hours, respectively. Venlafaxine has been evaluated in 7 clinical trials for the treatment of depression. These have consisted of 2 open trials, 3 double-blind, placebo-controlled trials, and 2 double-blind trials where venlafaxine was compared with trazodone and imipramine. All 7 trials have established efficacy for venlafaxine using standard psychiatric rating scales to measure change of depressive symptoms. The usual daily dosage ranges from 75 to 225 mg/d in 2 to 3 divided doses, with a maximum daily dosage of 375 mg/d. The drug's adverse effect profile differs somewhat from other more specific serotonin reuptake inhibitors in that it appears to cause dry mouth, somnolence, and elevated blood pressure as well as nausea, headache, and dizziness.

CONCLUSIONS

Although venlafaxine has recently become available for use as an antidepressant in the US, few clinical trials have been conducted to help the practitioner evaluate its place in the treatment of depression. There are no comparative trials of venlafaxine with the serotonin specific reuptake inhibitor antidepressants, which are rapidly becoming the newest comparative standard. The clinical place for venlafaxine in the treatment of depression has yet to be determined.

Venlafaxine. A review of its pharmacology and therapeutic potential in depression

Venlafaxine is a phenylethylamine derivative which facilitates neurotransmission in the brain by blocking presynaptic reuptake of serotonin (5-hydroxytryptamine: 5-HT) and noradrenaline (norepinephrine). Clinical data from patients with major depression are consistent with the favourable efficacy and tolerability profile of venlafaxine predicted by pharmacodynamic studies. In patients with major depression, venlafaxine 75 to 375 mg/day administered for 6 weeks was significantly more effective than placebo, and at least as effective as imipramine, clomipramine, trazodone or fluoxetine. Venlafaxine is well tolerated, being associated with fewer anticholinergic and CNS adverse effects than tricyclic antidepressants. Unlike the tricyclic antidepressants, venlafaxine does not appear to significantly affect cardiac conduction, although there have been a few reports of modest increases in blood pressure, particularly after high doses of the drug. In conclusion, wider clinical experience is required to better characterise and confirm potential advantages of venlafaxine compared with other antidepressant agents. These advantages may include a rapid onset of action and reduced propensity to cause anticholinergic effects and cardiotoxicity compared with tricyclic antidepressants. Nevertheless, at this stage venlafaxine offers a more attractive treatment option than tricyclic antidepressants for patients with major depression, primarily because of its good overall tolerability profile.

Overview of the pharmacokinetics of fluvoxamine

The pharmacokinetics of fluvoxamine, a selective serotonin reuptake inhibitor (SSRI) with antidepressant properties, are well established. After oral administration, the drug is almost completely absorbed from the gastrointestinal tract, and the extent of absorption is unaffected by the presence of food. Despite complete absorption, oral bioavailability in man is approximately 50% on account of first-pass hepatic metabolism. Peak plasma fluvoxamine concentrations are reached 4 to 12 hours (enteric-coated tablets) or 2 to 8 hours (capsules, film-coated tablets) after administration. Steady-state plasma concentrations are achieved within 5 to 10 days after initiation of therapy and are 30 to 50% higher than those predicted from single dose data. Fluvoxamine displays nonlinear steady-state pharmacokinetics over the therapeutic dose range, with disproportionally higher plasma concentrations with higher dosages. Plasma fluvoxamine concentrations show no clear relationship with antidepressant response or severity of adverse effects. Fluvoxamine undergoes extensive oxidative metabolism, most probably in the liver. Nine metabolites have been identified, none of which are known to be pharmacologically active. The specific cytochrome P450 (CYP) isoenzymes involved in the metabolism of fluvoxamine are unknown. CYP2D6, which is crucially involved in the metabolism of paroxetine and fluoxetine, appears to play a clinically insignificant role in the metabolism of fluvoxamine. The drug is excreted in the urine, predominantly as metabolites, with only negligible amounts ( < 4%) of the parent compound. Fluvoxamine shows a biphasic pattern of elimination with a mean terminal elimination half-life of 12 to 15 hours after a single oral dose; this is prolonged by 30 to 50% at steady-state. Plasma protein binding of fluvoxamine (77%) is low compared with that of other SSRIs. Fluvoxamine pharmacokinetics are substantially unaltered by increased age or renal impairment. However, its elimination is prolonged in patients with hepatic cirrhosis. Fluvoxamine inhibits oxidative drug metabolising enzymes (particularly CYP1A2, and less potently and much less potently CYP3A4 and CYP2D6, respectively) and has the potential for clinically significant drug interactions. Drugs whose metabolic elimination is impaired by fluvoxamine include tricyclic antidepressants (tertiary, but not secondary, amines), alprazolam, bromazepam, diazepam, theophylline, propranolol, warfarin and, possibly, carbamazepine. Fluvoxamine is a second generation antidepressant that selectively inhibits neuronal reuptake of serotonin (5-hydroxytryptamine; 5-HT). Fluvoxamine exhibits antidepressant activity similar to that of the tricyclic antidepressants, but has a somewhat improved tolerability profile, particularly with respect to a lower incidence of anticholinergic effects and reduced cardiotoxic potential. However, gastrointestinal adverse effects, especially nausea, are seen more frequently with fluvoxamine than with the tricyclic antidepressants. Fluvoxamine does not have an asymmetric carbon in its structure (fig. 1) and therefore does not exist as optical isomers. For this reason, the potentially confounding problem of stereoisomerism does not arise with fluvoxamine.