Olanzapine: an updated review of its use in the management of schizophrenia

Olanzapine, a thienobenzodiazepine derivative, is a second generation (atypical) antipsychotic agent which has proven efficacy against the positive and negative symptoms of schizophrenia. Compared with conventional antipsychotics, it has greater affinity for serotonin 5-HT2A than for dopamine D2 receptors. In large, well controlled trials in patients with schizophrenia or related psychoses, olanzapine 5 to 20 mg/day was significantly superior to haloperidol 5 to 20 mg/day in overall improvements in psychopathology rating scales and in the treatment of depressive and negative symptoms, and was comparable in effects on positive psychotic symptoms. The 1-year risk of relapse (rehospitalisation) was significantly lower with olanzapine than with haloperidol treatment. In the first double-blind comparative study (28-week) of olanzapine and risperidone, olanzapine 10 to 20 mg/day proved to be significantly more effective than risperidone 4 to 12 mg/day in the treatment of negative and depressive symptoms but not on overall psychopathology symptoms. In contrast, preliminary results from an 8-week controlled study suggested risperidone 2 to 6 mg/day was superior to olanzapine 5 to 20 mg/day against positive and anxiety/depressive symptoms (p < 0.05), although consistent with the first study, both agents demonstrated similar efficacy on measures of overall psychopathology. Improvements in general cognitive function seen with olanzapine treatment in a 1-year controlled study of patients with early-phase schizophrenia, were significantly greater than changes seen with either risperidone or haloperidol. However, preliminary results from an 8-week trial showed comparable cognitive enhancing effects of olanzapine and risperidone treatment in patients with schizophrenia or schizoaffective disorder. Several studies indicate that olanzapine has benefits against symptoms of aggression and agitation, while other studies strongly support the effectiveness of olanzapine in the treatment of depressive symptomatology. Olanzapine is associated with significantly fewer extrapyramidal symptoms than haloperidol and risperidone. In addition, olanzapine is not associated with a risk of agranulocytosis as seen with clozapine or clinically significant hyperprolactinaemia as seen with risperidone or prolongation of the QT interval. The most common adverse effects reported with olanzapine are bodyweight gain, somnolence, dizziness, anticholinergic effects (constipation and dry mouth) and transient asymptomatic liver enzyme elevations. In comparison with haloperidol, the adverse events reported significantly more frequently with olanzapine in > or = 3.5% of patients were dry mouth, bodyweight gain and increased appetite and compared with risperidone, only bodyweight gain occurred significantly more frequently with olanzapine. The high acquisition cost of olanzapine is offset by reductions in other treatment costs (inpatient and/or outpatient services) of schizophrenia. Pharmacoeconomic analyses indicate that olanzapine does not significantly increase, and may even decrease, the overall direct treatment costs of schizophrenia, compared with haloperidol. Compared with risperidone, olanzapine has also been reported to decrease overall treatment costs, despite the several-fold higher daily acquisition cost of the drug. Olanzapine treatment improves quality of life in patients with schizophrenia and related psychoses to a greater extent than haloperidol, and to broadly the same extent as risperidone.

CONCLUSIONS

Olanzapine demonstrated superior antipsychotic efficacy compared with haloperidol in the treatment of acute phase schizophrenia, and in the treatment of some patients with first-episode or treatment-resistant schizophrenia. The reduced risk of adverse events and therapeutic superiority compared with haloperidol and risperidone in the treatment of negative and depressive symptoms support the choice of olanzapine as a first-line option in the management of schizophrenia in the acute phase and for the maintenance of treatment response.

Glipizide. A review of the pharmacoeconomic implications of the extended-release formulation in type 2 diabetes mellitus

Glipizide is a second generation sulphonylurea agent that is available in a Gastrointestinal Therapeutic System (GITS) extended-release formulation. Glipizide GITS provides more stable plasma drug concentrations than the immediate-release formulation and the once-daily regimen may optimise patient compliance. In patients with type 2 diabetes mellitus, glipizide GITS is at least as effective as the immediate-release formulation of glipizide in providing glycaemic control, and may have a greater effect on fasting plasma glucose levels. Any therapeutic advantage over other antidiabetic agents remains to be established, but in a preliminary report (n = 40) glipizide GITS provided better glycaemic control and produced less fasting insulinaemia than glibenclamide (glyburide). The incidence of hypoglycaemic symptoms with glipizide GITS is low (< or = 3%). Quality of life was improved compared with baseline after 12 weeks' treatment with glipizide GITS 5 to 20 mg/day plus diet in a US double-blind, placebo-controlled trial in 569 patients with type 2 diabetes mellitus. Hyperglycaemic symptom-related distress decreased with glipizide GITS treatment, while hypoglycaemic symptom-related distress was not significantly increased compared with placebo plus diet. Quality of life during glipizide GITS treatment has not been compared with that during treatment with other antidiabetic agents. Monthly productivity losses related to absenteeism were $US91 (1995 values) per patient lower in the glipizide GITS group compared with the placebo group in the latter prospective study. Productivity parameters improved slightly or did not change significantly in the glipizide GITS group, but deteriorated in the placebo group. Differences in direct healthcare costs between groups were small and not comprehensively reported. Glipizide GITS was the least costly strategy for first-line therapy in a US cost-of-treatment model of the first 3 years after diagnosis of type 2 diabetes mellitus. The total per-patient cost was $US4867 with glipizide GITS, $US5196 with metformin and $US5249 with acarbose (1996/1997 values). Monthly drug acquisition costs were lower, and glycosylated haemoglobin levels and patient compliance were improved, after formulary conversion from the immediate-release to the GITS formulation of glipizide in a US single-hospital retrospective analysis.

CONCLUSIONS

Glipizide GITS produced better cost outcomes than metformin and acarbose in a model of 3 years' treatment of type 2 diabetes mellitus. Glipizide GITS had pharmacoeconomic and quality of life advantages over diet alone in the short term, but more clinically relevant comparisons with other antidiabetic agents are needed. There are limitations to the present data, but the available pharmacoeconomic data have been favourable for glipizide GITS.

Alitretinoin

Alitretinoin is a retinoid receptor pan-agonist, which has been investigated in the treatment of Kaposi's sarcoma (KS). Binding with high affinity to all known retinoid receptors, alitretinoin is thought to regulate proliferation, differentiation, and apoptosis of KS cells. Significantly more patients experienced complete or partial responses [according to the AIDS Clinical Trials Group (ACTG) criteria for topical treatment of cutaneous KS] with alitretinoin 0.1% gel 2 to 4 times daily than with vehicle gel in 2 phase III, multicenter, 12-week, randomized, double-blind clinical trials of patients with AIDS-related KS (35 vs 18%, p = 0.002 and 37 vs 7%, p = 0.00003, respectively). Responses were also observed in patients refractory to prior systemic or topical anti-KS therapies. In an intent-to-treat analysis in a phase II trial, 37% of patients with AIDS-related KS receiving alitretinoin capsules 60 to 100 mg/m2/day demonstrated either complete or partial responses (determined by ACTG criteria). The majority of adverse events associated with alitretinoin 0.1% gel were classified as either mild or moderate, occurred at the site of application and were reversible. In both phase III trials, rash was the most common adverse event. The most common adverse events in patients taking alitretinoin capsules included headache, dry skin, rash, alopecia, exfoliative dermatitis, and hyperlipidemia.

Eprosartan: a review of its use in the management of hypertension

Eprosartan is a potent and selective angiotensin II subtype 1 receptor antagonist. Results of large (n > 100) randomised double-blind studies in patients with mild, moderate or severe hypertension demonstrated that the antihypertensive efficacy of eprosartan (usually 400 to 800 mg/day as a single daily dose or in 2 divided doses) is significantly greater than that of placebo and at least as good as that of enalapril. In placebo-controlled trials, eprosartan achieved mean reductions from baseline in trough sitting systolic blood pressure of 6.3 to 15 mm Hg and in diastolic blood pressure of 4.1 to 9.7 mm Hg. Response rates associated with once daily administration of eprosartan 400 to 800 mg were approximately double those with placebo. Overall, eprosartan was well tolerated with a similar tolerability profile to that of placebo. In comparative trials, in which the incidence of persistent dry cough was evaluated as the primary end-point, enalapril was several-fold more likely to induce this adverse event than eprosartan (the difference being statistically significant regardless of study population and definition of cough). In conclusion, the angiotensin II receptor antagonist eprosartan is a well tolerated and effective antihypertensive agent that is administered once or twice daily without regard to meals. Eprosartan has a low potential for serious adverse events, and the drug has not been associated with clinically significant drug interactions. Unlike ACE inhibitors such as enalapril, eprosartan does not have a high propensity to cause persistent nonproductive cough. Thus, eprosartan represents a useful therapeutic option in the management of patients with hypertension.

Mirtazapine. A pharmacoeconomic review of its use in depression

Mirtazapine is a noradrenergic and specific serotonergic antidepressant (NaSSA). The antidepressant efficacy of mirtazapine has been established in randomised, double-blind comparative studies. Mirtazapine has generally shown similar efficacy to other antidepressants. There is evidence for a faster onset of action with mirtazapine than with the selective serotonin (5-hydroxytryptamine; 5-HT) re-uptake inhibitors (SSRIs) on the basis of mean depression rating scale scores. Data from a long term (mean 240 days) clinical trial that was subsequently used in pharmacoeconomic analyses showed that mirtazapine was associated with significantly higher sustained remission rates and rates of discontinuation because of improvement than amitriptyline and placebo. Although differences were not statistically significant, mirtazapine had higher response rates at 6 weeks than the SSRI fluoxetine in an analysis that was also used as the basis of pharmacoeconomic studies. Mirtazapine improved quality of life to a similar extent to fluoxetine, citalopram and paroxetine in unpublished studies of 6 and 8 weeks' duration. Pooled analyses suggest that mirtazapine may be associated with greater improvement than fluoxetine and citalopram in quality of life after 2 and 4 weeks, although confirmation is required. In a decision analytical model of approximately 6 months' duration, mirtazapine was associated with a higher proportion of successfully treated patients and lower total direct costs than amitriptyline. The direct cost per successfully treated patient with mirtazapine was lower than that with amitriptyline by 33,112 Austrian schillings (S; year of costing not stated), 24,212 French francs (FF; 1995/1996 values), 13,851 Swedish kronor (SEK; 1997 values) and 553 Pounds (1997/1998 values) in Austrian, French, Swedish and UK analyses, respectively. Compared with fluoxetine, mirtazapine was associated with higher per-patient costs in all 4 countries but a higher proportion of successfully treated patients. Mirtazapine was more cost effective than fluoxetine: the direct cost per successfully treated patient was lower by S32,046 in Austria, FF25,914 in France, SEK9796 in Sweden and 327 Pounds in the UK. The additional cost of mirtazapine versus fluoxetine for each additional successfully treated patient at 6 months was S11,732, SEK17,229, 750 Pounds and FF3342 in the Austrian, Swedish, UK and French analyses, respectively. Mirtazapine was generally associated with lower indirect costs (for lost productivity of employed patients) than amitriptyline and similar indirect costs to fluoxetine in the analyses.

CONCLUSIONS

Available data suggest that mirtazapine is a cost-effective alternative to amitriptyline and fluoxetine for the treatment of depression. Mirtazapine also has similar effects to SSRIs on quality of life with possibly a shorter time to onset of action, although published trial results are required to confirm these preliminary data.

Levobupivacaine: a review of its pharmacology and use as a local anaesthetic

Based on findings that the cardiotoxicity infrequently observed with racemic bupivacaine shows enantioselectivity, i.e. it is more pronounced with the R(+)-enantiomer, the S(-)-enantiomer (levobupivacaine) has been developed for clinical use as a long acting local anaesthetic. The majority of in vitro, in vivo and human pharmacodynamic studies of nerve block indicate that levobupivacaine has similar potency to bupivacaine. However, levobupivacaine had a lower risk of cardiovascular and CNS toxicity than bupivacaine in animal studies. In human volunteers, levobupivacaine had less of a negative inotropic effect and, at intravenous doses >75 mg, produced less prolongation of the QTc interval than bupivacaine. Fewer changes indicative of CNS depression on EEG were evident with levobupivacaine. Levobupivacaine is long acting with a dose-dependent duration of anaesthesia. The onset of action is < or = 15 minutes with various anaesthetic techniques. In studies of surgical anaesthesia in adults, levobupivacaine provided sensory block for up to 9 hours after epidural administration of < or = 202.5 mg, 6.5 hours after intrathecal 15 mg, and 17 hours after brachial plexus block with 2 mg/kg. Randomised, double-blind clinical studies established that the anaesthetic and/or analgesic effects of levobupivacaine were largely similar to those of bupivacaine at the same dose. Sensory block tended to be longer with levobupivacaine than bupivacaine, amounting to a difference of 23 to 45 minutes with epidural administration and approximately 2 hours with peripheral nerve block. With epidural administration, levobupivacaine produced less prolonged motor block than sensory block. This differential was not seen with peripheral nerve block. Conditions satisfactory for surgery and good pain management were achieved by use of local infiltration or peribulbar administration of levobupivacaine. Levobupivacaine was generally as effective as bupivacaine for pain management during labour, and was effective for the management of postoperative pain, especially when combined with clonidine, morphine or fentanyl. The tolerability profiles of levobupivacaine and bupivacaine were very similar in clinical trials. No clinically significant ECG abnormalities or serious CNS events occurred with the doses used. The most common adverse event associated with levobupivacaine treatment was hypotension (31%).

CONCLUSIONS

Levobupivacaine is a long acting local anaesthetic with a clinical profile closely resembling that of bupivacaine. However, current preclinical safety and toxicity data show an advantage for levobupivacaine over bupivacaine. Clinical data comparing levobupivacaine with ropivacaine are needed before the role of the drug can be fully established. Excluding pharmacoeconomic considerations, levobupivacaine is an appropriate choice for use in place of bupivacaine.

Tacrolimus: a further update of its pharmacology and therapeutic use in the management of organ transplantation

Tacrolimus (FK-506) is an immunosuppressant agent that acts by a variety of different mechanisms which include inhibition of calcineurin. It is used as a therapeutic alternative to cyclosporin, and therefore represents a cornerstone of immunosuppressive therapy in organ transplant recipients. Tacrolimus is now well established for primary immunosuppression in liver and kidney transplantation, and experience with its use in other types of solid organ transplantation, including heart, lung, pancreas and intestinal, as well as its use for the prevention of graft-versus-host disease in allogeneic bone marrow transplantation (BMT), is rapidly accumulating. Large randomised nonblind multicentre studies conducted in the US and Europe in both liver and kidney transplantation showed similar patient and graft survival rates between treatment groups (although rates were numerically higher with tacrolimus- versus cyclosporin-based immunosuppression in adults with liver transplants), and a consistent statistically significant advantage for tacrolimus with respect to acute rejection rate. Chronic rejection rates were also significantly lower with tacrolimus in a large randomised liver transplantation trial, and a trend towards a lower rate of chronic rejection was noted with tacrolimus in a large multicentre renal transplantation study. In general, a similar trend in overall efficacy has been demonstrated in a number of additional clinical trials comparing tacrolimus- with cyclosporin-based immunosuppression in various types of transplantation. One notable exception is in BMT, where a large randomised trial showed significantly better 2-year patient survival with cyclosporin over tacrolimus, which was primarily attributed to patients with advanced haematological malignancies at the time of (matched sibling donor) BMT. These survival results in BMT require further elucidation. Tacrolimus has also demonstrated efficacy in various types of transplantation as rescue therapy in patients who experience persistent acute rejection (or significant adverse effect's) with cyclosporin-based therapy, whereas cyclosporin has not demonstrated a similar capacity to reverse refractory acute rejection. A corticosteroid-sparing effect has been demonstrated in several studies with tacrolimus, which may be a particularly useful consideration in children receiving transplants. The differences in the tolerability profiles of tacrolimus and cyclosporin may well be an influential factor in selecting the optimal treatment for patients undergoing organ transplantation. Although both drugs have a similar degree of nephrotoxicity, cyclosporin has a higher incidence of significant hypertension, hypercholesterolaemia, hirsutism and gingival hyperplasia, while tacrolimus has a higher incidence of diabetes mellitus, some types of neurotoxicity (e.g. tremor, paraesthesia), diarrhoea and alopecia.

CONCLUSION

Tacrolimus is an important therapeutic option for the optimal individualisation of immunosuppressive therapy in transplant recipients.

Abciximab. A pharmacoeconomic review of its use in percutaneous coronary revascularisation

Abciximab is a monoclonal antibody fragment that inhibits platelet aggregation through antagonism of glycoprotein IIb/IIIa. The drug is used in conjunction with heparin and aspirin to prevent ischaemic complications associated with percutaneous coronary revascularisation in patients with coronary heart disease. Large and well designed clinical studies have shown abciximab, as an adjunct to aspirin and heparin, to reduce by around one-third to one-half the incidence of ischaemic complications within 30 days of percutaneous coronary revascularisation. Use of the drug appears advantageous in patients at high risk, and abciximab also reduces complications in patients undergoing coronary stenting, although the drug does not appear to inhibit restenotic tissue volume within stents. Longer term benefit has also been reported, with emerging 1-year data from a study in patients at all levels of risk showing reductions in a composite end-point of death, myocardial infarction (MI) or urgent repeat revascularisation. Three-year benefit has been reported in high risk patients. Meta-analysis results, and 1-year data from patients receiving stents, have shown reduced mortality with abciximab. Abciximab therapy had an incremental cost over standard therapy from a hospital perspective of $US293 per patient (1991/1992 values) over 6 months in a prospective economic substudy from a major US clinical trial of the drug in high risk patients. Abciximab was cost saving in patients with unstable angina. A mean net cost of hospitalisation of $US476 per patients (1995 costs) has been shown in a further study in patients with a broad range of levels of risk, and observational data indicate reduced duration of hospitalisation with abciximab. Cost-effectiveness data favoured abciximab with aspirin and heparin over a 6-month period in Spanish and Dutch analyses in which data from the above trial were combined with local cost data, but not in an Australian analysis. Subgroup analyses have indicated enhanced cost effectiveness in high risk patients. Available data also show clinical benefit and cost effectiveness of abciximab therapy in conjunction with coronary stent placement.

CONCLUSIONS

Data indicate intravenous bolus plus 12-hour infusion regimens of abciximab to be economically viable in patients at high or low risk of ischaemic complications after percutaneous coronary revascularisation. The drug has been shown to be cost effective in patients receiving the drug in conjunction with coronary stents, and subgroup analyses indicate additional cost effectiveness in certain groups of patients at high risk of ischaemic complications (notably those with acute MI and unstable angina).

Acamprosate. Pharmacoeconomic implications of therapy

Acamprosate is thought to reduce the craving for alcohol. The drug helps to maintain abstinence in alcohol-dependent patients who have successfully undergone detoxification. Abstinence rates during 3 to 12 months' treatment with acamprosate were approximately double those with placebo in most clinical trials, although abstinence rates were generally still < 50% in patients assigned to receive acamprosate. The drug is generally well tolerated, with the most common adverse effect being diarrhoea. In a German cost-effectiveness model, a treatment programme including acamprosate was the dominant strategy, producing a lifetime cost saving of 2602 Deutschmarks (1992 to 1995 values) per additional abstinent patient compared with treatment without acamprosate. In a Belgian pharmacoeconomic model, total direct medical costs over 2 years were 21,301 Belgian francs (1997 values) per patient lower with a treatment programme including acamprosate than treatment without acamprosate in alcohol-dependent patients. The main factors in the cost savings with acamprosate in these models were reduced costs for acute hospitalisation and rehabilitation/follow-up. The results of a cost-benefit analysis that considered both direct and indirect costs for the total alcohol-dependent population in Spain were consistently in favour of acamprosate. The lifetime net benefit for acamprosate over placebo (the incremental benefit) ranged between 61,642 million and 99,069 million pesetas (1996 values) in various scenarios with 40 to 60% of patients receiving treatment.

Rapacuronium bromide: a review of its use in anaesthetic practice

Rapacuronium bromide (rapacuronium) is an aminosteroid, nondepolarising neuromuscular blocking agent (NMBA). At the recommended dose for endotracheal intubation (1.5 mg/kg), an intravenous bolus of rapacuronium has a rapid onset (approximately 1.2 to 1.8 minutes) and short duration of action (10.2 to 16.5 minutes) in adults undergoing elective surgery. Rapacuronium 1.5 mg/kg produced clinically acceptable intubating conditions in 68 to 89% of these patients at about 1 minute after administration. The onset, extent and duration of action and clinical efficacy of an intubating dose of rapacuronium appeared to be similar in the general adult population, adult patients with renal or hepatic dysfunction, patients undergoing Caesarean section, and elderly, paediatric or obese adult patients. Onset time with rapacuronium 1.3 to 2.5 mg/kg (0.9 to 1.8 minutes) was similar to or slower than that with a 1 mg/kg dose of the depolarising NMBA suxamethonium chloride (0.8 to 1.2 minutes). Intubating conditions were clinically acceptable about I minute after administration in 86 to 100% of patients with rapacuronium 1.3 to 2.5 mg/kg compared with in 88 to 97% of patients with suxamethonium chloride 1 or 1.5 mg/kg. Spontaneous recovery was slower with rapacuronium than with suxamethonium chloride, but neostigmine 0.04 or 0.05 mg/kg administered 2 or 5 minutes after rapacuronium 1.3 or 1.5 mg/kg accelerated recovery. In the few available comparative clinical trials, rapacuronium 1.5 mg/kg appeared to have a more rapid onset of action than the nondepolarising NMBAs mivacurium chloride 0.25 mg/kg, rocuronium bromide 0.45 or 0.6 mg/kg or vecuronium bromide 0.07 mg/kg, and a shorter duration of action than rocuronium bromide 0.45 or 0.6 mg/kg or vecuronium bromide 0.07 mg/kg. Additional boluses (< or =3) of rapacuronium 0.5 or 0.55 mg/kg after an intubating bolus of 1.5 mg/kg provided continued skeletal muscle relaxation during short surgical procedures in adult patients. However, these patients may recover more slowly than those who receive a single bolus of the drug. Bronchospasm was the most common treatment-related adverse event with rapacuronium 0.3 to 3 mg/kg (3.4% of adult patients). Tachycardia, injection site reaction and hypotension were also reported in small proportions of patients (1.6, 1.1 and 0.9%). The overall incidence of drug-related adverse events was similar with rapacuronium 1.5 or 2.5 mg/kg or suxamethonium chloride 1 mg/kg (8 vs. 6%) but bronchospasm, tachycardia and injection site reaction tended to occur more often with rapacuronium.

CONCLUSIONS

At the recommended dose of 1.5 mg/kg, the nondepolarising NMBA rapacuronium has a rapid onset and short duration of action. It may provide a nondepolarising alternative to suxamethonium chloride for endotracheal intubation. Rapacuronium may be preferred over rocuronium bromide, vecuronium bromide or mivacurium chloride in this indication.

Deferiprone: a review of its clinical potential in iron overload in beta-thalassaemia major and other transfusion-dependent diseases

Patients with beta-thalassaemia and other transfusion-dependent diseases develop iron overload from chronic blood transfusions and require regular iron chelation to prevent potentially fatal iron-related complications. The only iron chelator currently widely available is deferoxamine, which is expensive and requires prolonged subcutaneous infusion 3 to 7 times per week or daily intramuscular injections. Moreover, some patients are unable to tolerate deferoxamine and compliance with the drug is poor in many patients. Deferiprone is the most extensively studied oral iron chelator to date. Non-comparative clinical studies mostly in patients with beta-thalassaemia have demonstrated that deferiprone 75 to 100 mg/kg/day can reduce iron burden in regularly transfused iron-overloaded patients. Serum ferritin levels are generally reduced in patients with very high pretreatment levels and are frequently maintained within an acceptable range in those who are already adequately chelated. Deferiprone is not effective in all patients (some of whom show increases in serum ferritin and/or liver iron content, particularly during long term therapy). This may reflect factors such as suboptimal dosage and/or severe degree of iron overload at baseline in some instances. Although few long term comparative data are available, deferiprone at the recommended dosage of 75 mg/kg/day appears to be less effective than deferoxamine; however, compliance is superior with deferiprone, which may partly compensate for this. Deferiprone has additive, or possibly synergistic, effects on iron excretion when combined with deferoxamine. The optimum dosage and long term efficacy of deferiprone, and its effects on survival and progression of iron-related organ damage, remain to be established. The most important adverse effects in deferiprone-treated patients are arthropathy and neutropenia/agranulocytosis. Other adverse events include gastrointestinal disturbances, ALT elevation, development of antinuclear antibodies and zinc deficiency. With deferiprone, adverse effects occur mostly in heavily iron-loaded patients, whereas with deferoxamine adverse effects occur predominantly when body iron burden is lower.

CONCLUSION

Deferiprone is the most promising oral iron chelator under development at present. Further studies are required to determine the best way to use this new drug. Although it appears to be less effective than deferoxamine at the recommended dosage and there are concerns regarding its tolerability, it may nevertheless offer a therapeutic alternative in the management of patients unable or unwilling to receive the latter drug. Deferipone also shows promise as an adjunct to deferoxamine therapy in patients with insufficient response and may prove useful as a maintenance treatment to interpose between treatments.

Bivalent cholera and typhoid vaccine

The live attenuated vaccine strains Vibrio cholerae CVD 103-HgR and Salmonella typhi Ty21a can be combined into an oral bivalent vaccine without compromising the immunogenicity of the individual vaccine strains. Seroconversion rates of 87 to 94% for Inaba vibriocidal antibodies and 72 to 91% for anti-S. typhi lipopolysaccharide antibodies (IgG or IgA) were reported in healthy European volunteers receiving a bivalent CVD 103-HgR/Ty21a vaccine-based schedule (bivalent vaccine on day 1 and monovalent Ty21a vaccine on days 3 and 5). The immunogenicity of bivalent CVD 103-HgR/Ty21a vaccine is not adversely affected by concomitant administration of mefloquine, yellow fever vaccine or oral polio vaccine. Chloroquine may reduce the immunogenicity of the CVD 103-HgR component and proguanil may reduce the immunogenicity of the Ty21a component. Bivalent CVD 103-HgR/Ty21a vaccine does not adversely affect the immunogenicity of the yellow fever YF 17D vaccine. The type, incidence and severity of adverse events seen in individuals receiving bivalent CVD 103-HgR/Ty21a vaccine-based schedules are similar to those that occur with the monovalent vaccines.

Donepezil. Pharmacoeconomic implications of therapy

Donepezil is a specific acetylcholinesterase inhibitor that can improve symptoms in patients with mild-to-moderate Alzheimer's disease; cognitive function is maintained above baseline levels for up to 1 year and normal decline of cognitive function is slowed. The ability of the patient to perform daily activities and neuropsychiatric symptoms may also be improved by donepezil, but data are limited. Donepezil is not expected to alter the underlying neurodegenerative process, and the response to the drug varies between individuals. In the absence of validated instruments to measure quality of life, it is not clear how donepezil affects this parameter. In a US survey of caregivers of patients with Alzheimer's disease who were being cared for at home at the start of the 6-month study period, treatment with donepezil did not increase overall direct medical costs. The acquisition cost of the drug was balanced by reduced institutionalisation costs. Economic analyses using Markov models from the US, UK and Canada suggest that donepezil initiated in the early stages of disease may be effectively cost neutral as a result of patients remaining in a nonsevere state of disease for a longer time.

Olanzapine. A pharmacoeconomic review of its use in schizophrenia

Olanzapine is an atypical antipsychotic agent which is at least as effective as the conventional agent haloperidol and the atypical agent risperidone. Olanzapine may be superior to haloperidol in some respects, including treatment of negative symptoms. A major advantage of olanzapine over haloperidol is its lower risk of extrapyramidal symptoms. Olanzapine improves quality of life and other aspects of functioning to a greater extent than haloperidol, and improves quality of life to at least the same extent as risperidone. However, olanzapine has a high acquisition cost compared with conventional antipsychotics. Despite this, most pharmacoeconomic analyses indicate that treatment with olanzapine does not significantly increase, and may even decrease, the overall direct treatment costs of schizophrenia, compared with haloperidol. Total direct medical costs calculated from prospective resource utilisation data were lower with olanzapine than with haloperidol by $US388 (1995 values) per patient over 6 weeks and by $US55 per patient per month during 46 weeks extended treatment. In a mixed effects linear model of the same data, total costs over 1 year were $US10,301 (1996 values) per patient lower with olanzapine than haloperidol, and olanzapine was associated with 18.3 more symptom-free days per patient. Compared with risperidone, mean total direct medical costs over 28 weeks were $US493 (1995 values) per patient lower with olanzapine. In a Markov model of 5 years' treatment, olanzapine was associated with more time in a disability-free state than haloperidol at a total cost per patient that was lower by $US1539 (1995 values), 816 Pounds (1995/1996 values), 977 Dutch guilders (NLG; 1995 values) and 2296 Deutschmarks in US, UK, Dutch and German analyses, respectively. In a similar Spanish analysis, the overall total cost was higher with olanzapine, giving an incremental cost effectiveness for olanzapine of 32,516 pesetas (1995 values) per month of disability-free time gained. When risperidone was a comparator, the total cost per patient was $US1875 and NLG202 lower with olanzapine in US and Dutch analyses, respectively.

CONCLUSIONS

The high acquisition cost of olanzapine is offset by reductions in other treatment costs in patients with schizophrenia. Compared with haloperidol, the drug improved patient outcome and quality of life, while overall direct treatment costs were generally not increased, or even decreased. Olanzapine has also been reported to decrease overall treatment costs compared with risperidone, but confirmation is required. Olanzapine is a cost-effective alternative to conventional agents for the treatment of moderately to severely ill patients with longstanding schizophrenia.

Diclofenac/hyaluronic acid

Topical gel containing 3% diclofenac in 2.5% hyaluronic acid (HYAL CT1101) is used for the treatment of actinic keratosis. In animal models, diclofenac in hyaluronic acid inhibited angiogenesis and induced neovascular regression in inflammatory tissue, and depleted substance P content in snout tissue. Diclofenac delivered in hyaluronic acid appears to accumulate in the epidermis of human skin in vitro and mice in vivo. Results of clinical trials indicate that topical HYAL CT1101 is effective in the treatment of actinic keratosis. A clinical cure (all lesions fully resolved) was seen in 47% of 108 patients using HYAL CT1101 compared with 19% of patients using placebo after 3 months in 1 randomised, double-blind study. Mild to moderate skin irritation has been reported in up to 72% of patients treated with HYAL CT1101 in clinical studies.

Evidence suggesting that the angiotensin II-sensitive intracellular Ca2+ pool is reloaded from the external space in adrenal glomerulosa cells

Adrenal glomerulosa cells prelabeled with 45Ca2+ and perifused for 10 min with 10 nM angiotensin II (AII) in a dynamic perifusion system show a biphasic response with an initial transient increase in 45Ca2+ efflux, followed by a sustained phase of increased 45Ca2+ efflux. When labeled adrenal golmerulosa cells were treated with 10 nM AII for three consecutive periods of 5 min, the transient increase in 45Ca2+ efflux was observed only in the first period. However, when 40Ca2+ was measured in the perifusate using a Ca2+-sensitive electrode coupled to the perifusion system, a transient increase in 40Ca2+ efflux was observed in each period of AII treatment. Exposing the cells to AII for 1 min, the amount of 40Ca2+ effluxed out of the cells was 58.3 +/- 8.4 nmol/10(8) cells. In contrast, when the cells were exposed to an increase in the external potassium (K+) concentration of 4 to 12 mM during 1 min of perifusion, the amount of 40Ca2+ effluxed was 16 +/- 5 nmol/10(8) cells. These results indicate that AII induces an increase in the Ca2+ concentration in a local domain outside of the plasma membrane. This Ca2+ comes from AII-induced intracellular Ca2+ depletion and may play a role in refilling intracellular Ca2+ stores.

Dienogest

The progestogen dienogest exhibits highly selective binding to the progesterone receptor. It has high progestational and significant antiandrogenic activity, but only moderate antigonadotrophic activity. Dienogest inhibits ovulation, produces secretory transformation of the endometrium and has antiproliferative effects. Oral dienogest 2 mg/day plus ethinylestradiol 30 micrograms/day provides effective contraception (Pearl Index approximately 0.2). Cycle stability is good during long term use of this combination; irregular vaginal bleeding was evident in 6% of women after 12 months' use. Androgenic symptoms (including hirsutism, seborrhoea, alopecia, acne vulgaris and hair and skin greasiness) improved in women treated with dienogest plus ethinylestradiol. The adverse events associated with dienogest are typical of those expected of a progestogen. The drug does not produce androgenic adverse effects and has little clinically significant effect on metabolic, lipid and haemostatic parameters.

Abciximab. An updated review of its use in ischaemic heart disease

Abciximab is a glycoprotein IIb/IIIa receptor antagonist that has proven to be of significant clinical value in improving patient outcome after percutaneous coronary revascularisation. Primarily, the drug inhibits platelet aggregation, but it may also have anticoagulant activity and other beneficial effects, such as inhibiting migration and promoting apoptosis of smooth muscle cells. Large well designed studies have found administration of abciximab (as an adjunct to heparin and aspirin) during percutaneous coronary revascularisation to significantly reduce the incidence of ischaemic complications occurring in the 30 days after the procedure. Significant benefit, particularly on the incidence of myocardial infarction, was still evident after 6 months in 2 of 4 major trials. Abciximab provides particular benefit in patients with unstable angina or myocardial infarction who are undergoing percutaneous coronary revascularisation. The benefits of the drug are additive to those achieved with coronary stenting. Very preliminary data suggest that abciximab may improve coronary blood flow after myocardial infarction and allow reperfusion to be achieved with reduced thrombolytic doses. Caution is required to minimise the risk of bleeding complications with the use of abciximab in combination with heparin and aspirin. Careful patient selection, use of an appropriate heparin regimen, early vascular sheath removal and meticulous femoral artery access site care are recommended. Thrombocytopenia can occur with abciximab treatment, but severe cases are uncommon (< 2% of patients) and can be treated with platelet transfusions. The high acquisition cost of abciximab may be partly or fully offset by the costs averted by the reduced incidence of ischaemic complications and need for urgent and/or repeat revascularisation in high risk patients who receive the drug. However, if bleeding complications occur, this adds to treatment costs. Cost effectiveness analyses generally support the use of abciximab in high risk patients.

CONCLUSIONS

Abciximab can be recommended for the prevention of acute ischaemic events in most patients undergoing percutaneous coronary revascularisation, but careful patient selection and strict adherence to the recommended treatment protocol are required to reduce the risk of bleeding complications and thrombocytopenia. Its use in high risk patients is largely supported by pharmacoeconomic data. Further pharmacoeconomic information is needed to establish the drug as a standard of care for all patient groups. The indications for abciximab are likely to expand as more data on its use in acute coronary syndromes become available.

Is ouabain produced by the adrenal gland?

1. Ouabain or a related stereoisomer, termed endogenous ouabain, has been identified in adrenal cortex tissue and culture medium from adrenocortical cells. 2. Angiotensin II and adrenocorticotropin, the main activators of aldosterone secretion from adrenal glomerulosa cells appear to increase the production of this compound. 3. The purpose of this review is to briefly discuss recent available experimental evidence suggesting that endogenous ouabain is secreted by the zona glomerulosa of the adrenal gland.

Risperidone. A pharmacoeconomic review of its use in schizophrenia

The availability of new atypical antipsychotics, such as risperidone, that have higher acquisition costs than conventional treatments has promoted pharmacoeconomic evaluation of their costs and benefits. Risperidone is reported to have superior efficacy to haloperidol and similar efficacy to other atypical antipsychotics. At dosages < or = 8 mg/day, risperidone is generally associated with a lower risk of extrapyramidal symptoms than conventional antipsychotics and may have a more favourable effect on cognitive function and quality of life. Overall treatment costs during the first year of risperidone treatment were lower than in the previous year in a number of studies in patients with schizophrenia, reflecting a reduction in hospitalisation, although costs slightly increased after risperidone initiation in 2 studies. Total treatment costs were not significantly different with risperidone or conventional antipsychotics in a large, prospective naturalistic study. The use of risperidone in preference to conventional antipsychotics in patients with chronic schizophrenia has been supported by several modelled studies, including a cost-effectiveness analysis that compared risperidone and haloperidol in chronic schizophrenia and a cost-utility study that compared the drug with oral haloperidol, depot haloperidol decanoate and depot fluphenazine decanoate for 1 year's treatment of an initially hospitalised chronic schizophrenic patient with moderate symptoms. In another study, the cost-utility ratio for risperidone versus haloperidol was 24,250 Canadian dollars per quality-adjusted life year (year of costing not stated), but only drug costs were considered. Risperidone had favourable cost-benefit ratios relative to conventional antipsychotic treatment in a study that investigated a scenario in which all patients hospitalised with newly diagnosed schizophrenia received conventional antipsychotic therapy for 6 months, and then those who did not respond received a 6-month trial of risperidone or clozapine. The results of 2 limited decision-analytical models did not favour risperidone. One study compared risperidone with oral haloperidol or depot haloperidol decanoate for the outpatient treatment of a schizophrenic patient with a history of relapse and rehospitalisation. The other compared risperidone, olanzapine and oral haloperidol for the treatment of schizophrenia.

CONCLUSIONS

Despite its high acquisition cost, risperidone does not increase, and may even reduce, overall treatment costs of schizophrenia by reducing hospitalisation compared with standard treatment regimens. While further pharmacoeconomic evaluation of risperidone as a first-line agent is required, pharmacoeconomic data overall support its use in patients with chronic schizophrenia.

Tazarotene

Tazarotene is a topical retinoid that appears to exert its effects via retinoic acid receptors. It normalises differentiation and proliferation of keratinocytes and has an anti-inflammatory effect. Topical tazarotene 0.05% or 0.1% gel was effective in the treatment of plaque psoriasis in clinical trials and its therapeutic effect was maintained for at least 12 weeks after treatment discontinuation in some patients. In one study in patients with psoriasis, tazarotene had similar efficacy to fluocinonide in reducing plaque elevation, but not erythema. In another study, tazarotene was reported to be less effective than fluocinonide. Combination treatment with tazarotene plus a mid- or high-potency corticosteroid was more effective in the treatment of psoriasis than tazarotene alone. Topical tazarotene 0.1% gel significantly reduced lesion counts in patients with mild to moderate facial acne vulgaris. Skin irritation is a common adverse event with topical tazarotene, but it is mainly of mild to moderate severity. Tazarotene is not recommended for use in women who are, or may become, pregnant.

Abacavir

Abacavir is a nucleoside analogue reverse transcriptase inhibitor that inhibits clinical isolates of HIV in vitro with a potency similar to that of zidovudine. Resistance to abacavir develops relatively slowly. Cross-resistance between abacavir and didanosine, zalcitabine or lamivudine, but not zidovudine or stavudine, has been reported in vitro. Abacavir has good oral bioavailability, as demonstrated in animals, and penetrates the CNS. Treatment with abacavir, alone or in combination with other anti-HIV agents (zidovudine, lamivudine, nevirapine, amprenavir and/or other protease inhibitors), decreased viral load and increased CD4+ cell count in patients with HIV infection. Effectiveness was maintained for at least 48 weeks. In early phase I/II trials, headache, gastrointestinal disturbances, rash, malaise, fatigue and/or asthenia were the most common adverse events reported with abacavir alone or in combination with other anti-HIV agents. Hypersensitivity reactions lead to discontinuation of therapy in 2 to 3% of patients.

Cefotaxime. A pharmacoeconomic review of its use in the treatment of infections

Cefotaxime is a parenterally administered third generation cephalosporin with a broad spectrum of antimicrobial activity. After more than a decade of use, cefotaxime continues to play an important role in the treatment of patients with serious infections, particularly those caused by Gram-negative bacteria. Clinical trials of cefotaxime have demonstrated clinical and/or bacteriological success rates usually between 75 and 100% in hospitalised patients with infections such as pneumonia, complicated urinary tract infections and bacteraemia. In general, comparative trials have shown that cefotaxime has equivalent clinical efficacy to ceftriaxone. Although cefotaxime was traditionally administered at 6- or 8-hourly intervals, evaluations of twice daily regimens have demonstrated the feasibility of using this extended dosage interval in selected patients. Like other parenterally administered cephalosporins, cefotaxime is well tolerated. Cefotaxime does not cause a significant incidence of coagulopathies, as observed with some cephalosporins (e.g., cefamandole and cefoperazone), nor is it associated with the development of pseudocholelithiasis as seen with ceftriaxone. Some hospitals have achieved significant cost savings by implementing programmes or policies involving replacement of prescriptions for ceftriaxone with those for cefotaxime; however, other institutions have shown cost savings when cefotaxime is replaced by ceftriaxone. Similarly, conflicting results were seen in studies that assessed only the drug acquisition and administration supply costs (with or without inclusion of labour costs), highlighting the difficulty in applying pharmacoeconomic data from one clinical setting to another. A limited number of detailed pharmacoeconomic analyses of cefotaxime have been conducted. One analysis, in patients with pneumonia or other serious infections, incorporated published clinical trial data as well as published or estimated cost data (from 1992 or earlier) for the US healthcare setting. Total treatment costs per patient-day were $US25.21 for cefotaxime 1 g twice daily and $US37.23 for cefotaxime 1 g 3 times daily, compared with $US69.97 for ceftriaxone 2 g once daily and $US74.57 for ceftriaxone 1 g twice daily. Costs included those associated with drug acquisition, administration and preparation, laboratory monitoring and adverse events. A large retrospective analysis was conducted between 1989 and 1993 in a US hospital. Patients treated with cefotaxime twice daily had similar clinical outcomes, including duration of hospital stay (7.21 vs 7.24 days), to those receiving antimicrobials other than cefotaxime. However, when a model was applied to determine attributable differences, a trend was demonstrated towards reduced length of hospitalisation (mean reduction 0.5 days) and total cost of hospitalisation (mean reduction $US623 per patient) with cefotaxime. In a Canadian clinical decision-analysis model of initial empirical monotherapy for an average infectious disease state (costs for serious lower respiratory tract infection, urinary tract infection, sepsis, skin/soft tissue infection and febrile neutropenia were weighted according to the incidence of each infection and combined to give a single value), the average total cost per patient for cefotaxime was $Can4099 (1994 dollars). This was lower than that for ceftriaxone ($Can4257) but higher than that for cefepime ($Can3945), ciprofloxacin ($Can4008) and ceftazidime ($Can4086). Costs included those related to drug acquisition, preparation and administration, bacterial culture and sensitivity testing, hospitalisation and adverse events. An analysis conducted in France demonstrated that cefotaxime 1 g 3 times daily was associated with total treatment costs equal to or lower than those for ceftriaxone 2 g once daily. The study also evaluated total costs of cefotaxime 1 g twice daily and ceftazidime 1 g 3 times daily; treatment costs associated with cefotaxime were less than on

Estradiol and dydrogesterone. A review of their combined use as hormone replacement therapy in postmenopausal women

The focus of this review is hormone replacement therapy (HRT) with continuous oral 17 beta-estradiol (herein referred to as estradiol) 2 mg/day plus sequential oral dydrogesterone 10 or 20 mg/day for 14 days of each 28-day cycle. According to data from nonblind trials, this regimen relieves climacteric symptoms, preserves bone mineral density (BMD) and improves the cardiovascular risk profile in postmenopausal women. Increases in mean BMD in the lumbar spine of 2.4 to 6.4% have been reported after 2 years' treatment. The effect on BMD of oral estradiol plus sequential dydrogesterone was similar to that achieved with transdermal estradiol plus sequential oral dydrogesterone or with oral tibolone. Good protection against endometrial hyperplasia and cancer is provided by the dydrogesterone component. Cyclical vaginal bleeding occurs in most treatment cycles, but is generally light to moderate and the time of onset is highly predictable. Noncyclical bleeding occurs in < 10% of cycles. Mean serum high density lipoprotein-cholesterol levels are increased and low density lipoprotein-cholesterol levels are decreased during treatment with oral estradiol plus sequential dydrogesterone. Insulin resistance appears to be improved. Blood pressure and bodyweight are not generally affected to any clinically important extent. Serum homocysteine levels were reported to decrease in postmenopausal women with high pretreatment levels. No data are available on the general tolerability profile of this regimen. However, the adverse events that most commonly led to discontinuation of treatment in clinical trials were typical of those associated with HRT, including vaginal bleeding headache, bloating and breast tenderness. Although the risk of breast cancer has not been specifically assessed for this regimen, it is unlikely to carry a greater risk than that of other HRT regimens. In summary available data indicate that treatment with continuous oral estradiol plus sequential dydrogesterone is effective in relieving climacteric symptoms and preserving BMD in postmenopausal women. The dydrogesterone component provides good endometrial protection and cycle control without negating the cardiovascular benefits of estradiol. Comparisons with other standard HRT regimens and long term data (including clinical end-points) are needed. In the meantime, this regimen can be regarded as an acceptable HRT option.

Ibutilide. A review of its pharmacological properties and clinical potential in the acute management of atrial flutter and fibrillation

Ibutilide is the first 'pure' class III antiarrhythmic drug to become available. Its predominant action is prolongation of the myocardial action potential duration. This appears to be achieved by a unique ionic mechanism of action that involves activation of a late inward sodium current and possibly blockade of the rapidly activating component of the cardiac delayed rectifier potassium current. Intravenous ibutilide 0.01 to 0.025 mg/kg or 1 to 2 mg successfully converted atrial flutter or fibrillation to sinus rhythm in 33 to 49% of patients in 2 placebo-controlled trials involving 439 patients with sustained arrhythmia. In a third trial in 300 patients who developed atrial flutter or fibrillation after cardiac surgery, ibutilide 2 mg successfully converted the arrhythmia in 57% of patients. The mean times to conversion were < or = 30 minutes in these trials. In 3 comparative trials, ibutilide was significantly more effective than racemic sotalol or procainamide in terminating atrial flutter or fibrillation. The pretreatment duration of the arrhythmia is an important predictor of the success of ibutilide treatment; the greatest conversion rates are achieved when the arrhythmia is of recent onset (i.e. < or = 30 days' duration). Ibutilide is more effective in terminating atrial flutter than atrial fibrillation. Adverse events associated with ibutilide are predominantly cardiovascular. Sustained polymorphic ventricular tachycardia developed in 1.7%, and non-sustained polymorphic ventricular tachycardia in 2.7%, of 586 patients treated with ibutilide in clinical trials. However, no proarrhythmia-related deaths have been reported with the use of ibutilide. The drug has minimal haemodynamic effects and is associated with few noncardiovascular adverse events. Thus, ibutilide is a useful agent for the pharmacological cardioversion of recent-onset atrial fibrillation or flutter, provided that adequate steps are taken to monitor for proarrhythmic events. The drug causes few noncardiovascular adverse events and has minimal haemodynamic effects. Furthermore, it appears to be more effective than procainamide (especially in patients with atrial flutter) and racemic sotalol.

Paroxetine : a review of its pharmacology and therapeutic potential in the management of panic disorder

SYNOPSIS

Paroxetine is the first selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor (SSRI) to be approved for the treatment of patients with panic disorder with or without agoraphobia. It is a highly selective inhibitor of presynaptic serotonin reuptake and does not interact with adrenergic, dopaminergic, histaminergic or serotonergic receptors to any significant extent. Oral paroxetine 10 to 60 mg/day is significantly more effective than placebo in reducing the frequency of panic attacks and improving associated symptoms, as shown in short term trials in patients with panic disorder with or without agoraphobia. The efficacy of the drug was maintained during up to 6 months'; treatment, and continued therapy reduced the risk of relapse. Oral paroxetine 10 to 60 mg/day was at least as effective as clomipramine 10 to 150 mg/day, but appeared to have a more rapid onset of effect, in a placebo-controlled trial. The tolerability profile of paroxetine is similar to that established for other SSRIs and is characterised by adverse events such as nausea, headache, somnolence, dry mouth, tremor, insomnia, asthenia, sweating, constipation, dizziness and sexual dysfunction. Paroxetine was better tolerated overall than clomipramine and was associated with a lower incidence of certain anticholinergic events (such as dry mouth and constipation) in a comparative trial. It is not associated with the type of dependence seen with benzodiazepines, and it appears to be safer in overdose than the tricyclic antidepressants. Paroxetine 20 or 30mg does not significantly impair psychomotor function or interact with alcohol (ethanol). In conclusion, the good tolerability profile of paroxetine, including lack of dependence potential and relative safety in overdose, makes it attractive for the treatment of patients with panic disorder. It appears to be at least as effective as clomipramine in reducing panic attacks and associated symptoms. Although further trials to compare the efficacy and tolerability of paroxetine with that of other tricyclic agents (especially Imipramine), high-potency benzodiazepines and monoamine oxidase inhibitors are needed, the drug appears to have the potential to become a first-line treatment for panic disorder.

PHARMACODYNAMIC PROPERTIES

Paroxetine increases serotonergic neurotransmission by inhibiting presynaptic reuptake of serotonin (5-hydroxytryptamine; 5-HT) and thereby increasing the level of the neurotransmitter at the synaptic cleft. In vitro, it is a more potent inhibitor of serotonin uptake than the selective serotonin reuptake inhibitors (SSRIs) Citalopram, fluvoxamine and fluoxetine. Paroxetine was more potent than sertraline in one study that compared mean inhibition constants for serotonin uptake, but not in another study that compared the concentrations required to inhibit serotonin uptake by 50%. In contrast to the tricyclic antidepressants, paroxetine has little effect on the uptake of dopamine or noradrenaline (norepinephrine) in vitro. It has negligible affinity for αr(1-), αr(2-) and βr-adrenoceptors, dopamine D(1) and D(2) receptors, hi starnine H(1) receptors and serotonin 5-HT(1A), 5-HT(2A) and 5-HT(2C) receptors. However, paroxetine does have weak affinity for muscarinic cholinergic receptors. As shown in rats, paroxetine appears to indirectly activate somatodendritic 5-HT(1A) autoreceptors when initially administered, thereby inhibiting firing of 5-HT neurons and release of serotonin. This may explain why the onset of therapeutic effect of paroxetine is delayed. However, repeated administration of paroxetine causes adaptive changes in synaptic serotonergic receptors, including a decrease in the responsiveness of somatodendritic and terminal serotonin autoreceptors. Central βr-adrenoceptors are not down-regulated by administration of paroxetine to rats. Various studies in healthy volunteers without sleep disorders or volunteers reporting poor sleep have indicated that paroxetine disturbs normal sleep patterns by reducing rapid eye movement (REM) sleep time and lengthening REM latency. The effect of paroxetine on sleep in patients with panic disorder has not been determined, but in patients with depression the drug improves subjective quality of sleep. In electroencephalographic studies in healthy volunteers, administration of a single dose of paroxetine 30mg produced changes indicative of a sedative profile, whereas administration of 70mg produced changes indicative of activating properties. No significant impairment of psychomotor function was observed after administration of single or multiple doses of paroxetine 20 or 30mg to healthy volunteers or patients with depression. The sedation and impairment of psychomotor function caused by haloperidol, amobarbital, oxazepam or alcohol (ethanol) were not potentiated by the administration of paroxetine 30mg. In contrast to amitriptyline 150 mg/day or doxepin 150 mg/day, 2 to 6 weeks' treatment with paroxetine 20 or 30 mg/day did not produce clinically significant haemodynamic or electrophysiological effects on cardiac function in healthy volunteers or patients with depression. Fewer adverse cardiac effects were reported by paroxetine than nortriptyline recipients in a study in patients with depression and ischaemic heart disease. The anxiolytic activity of paroxetine has been demonstrated after 7 or 21 days' administration in several rodent models.

PHARMACOKINETIC PROPERTIES

Paroxetine is well absorbed after oral administration. It undergoes extensive first-pass metabolism and is rapidly distributed into tissue. Only about 1% of the paroxetine dose remains in the systemic circulation. Approximately 95% of paroxetine is protein bound in the plasma. Steady-state concentrations are reached after 7 to 14 days of oral administration and the terminal elimination half-life (t1/2βr) is approximately 24 hours. However, there is a great deal of interindividual variation in the pharmacokinetics of paroxetine. Paroxetine is metabolised by at least 2 enzymes of the cytochrome P450 (CYP) system, one of which is CYP2D6. This enzyme is subject to genetic polymorphism, and thus the pharmacokinetics of paroxetine differ between individuals who have the enzyme (extensive metabolisers) and those who do not (poor metabolisers). The metabolites of paroxetine are essentially inactive. Metabolism of paroxetine by CYP2D6 is saturable. Consequently, with repeated administration, bioavailability of paroxetine increases and pharmacokinetics may become nonlinear in some patients, especially when the dosage of paroxetine is increased. Approximately two-thirds of a paroxetine dose is eliminated in the urine and the remainder is excreted in faeces. Almost all of the dose is eliminated as metabolites; lt3% is excreted as unchanged drug. The plasma concentration and area under the plasma concentration-time curve of paroxetine are greater, and the t1/2βr prolonged, in elderly patients and those with hepatic or severe renal impairment compared with the general population. Paroxetine distributes into breast milk to produce concentrations similar to those in plasma.

THERAPEUTIC POTENTIAL

As shown in 3 short term placebo-controlled trials in patients with panic disorder with or without agoraphobia, oral paroxetine 10 to 60 mg/day is significantly more effective than placebo for most variables measuring reduction in panic attack frequency. The drug also produced significantly greater improvements in various anxiety and depression scales than placebo. An extension phase of one of the placebo-controlled studies showed that the efficacy of paroxetine in reducing panic attack frequency is maintained during up to 6 months' treatment and that the drug reduces the risk of relapse. Oral paroxetine 10 to 60 mg/day was at least as effective as clomipramine 10 to 150 mg/day in a comparative study. During weeks 7 to 9 of treatment, 51% of paroxetine recipients had no full panic attacks, compared with 37% of clomipramine recipients. The onset of action appeared to be more rapid for paroxetine than for clomipramine. The 2 drugs were equally effective in improving generalised anxiety, phobic avoidance and social, family and work interactions. In patients who elected to continue treatment for a further 36 weeks in an extension phase of the above study, response rates increased further in all groups, including the placebo group. During weeks 34 to 36 of extended treatment, 85% of paroxetine recipients, 72% of clomipramine recipients and 59% of placebo recipients had no panic attacks. The difference between paroxetine and placebo was statistically significant at this time point; however, there was no significant difference between groups at the primary efficacy endpoint (weeks 22 to 24).

TOLERABILITY

Paroxetine is generally well tolerated by both younger and older individuals and its adverse event profile is consistent with that expected for an SSRI. The tolerability profile of paroxetine in patients with panic disorder appears to resemble that in patients with depression. Headache, nausea, somnolence, dry mouth and insomnia were the most common adverse events among 469 patients with panic disorder who received paroxetine 10 to 60 mg/day in short term clinical trials. The individual incidences for these events ranged from 18 to 25%; however, the incidence of headache in paroxetine-treated patients was the same as that in placebo recipients. (ABSTRACT TRUNCATED)

Recent progress in understanding aldosterone secretion

1. The synthesis and secretion of aldosterone in the adrenal zona glomerulosa in physiologic conditions is controlled by adrenocorticotropin (ACTH), angiotensin II (AII), and extracellular (K+). 2. ACTH effects on aldosterone output are explained by cyclic AMP-(cAMP)- and Ca(2+)-dependent mechanisms. 3. All effects on aldosterone secretion are initiated by an increase in Ca2+ influx through hormone-operated Ca2+ channels and G-protein- and phospholipase C-(PLC) dependent hydrolysis of phosphoinositides leading to the generation of inositol 1,4,5 trisphosphate (IP3) and DAG that induce intracellular Ca2+ release and PKC activation, respectively. 4. ACTH increases DAG formation with marginal or undetectable IP3 generation. The effect of ACTH on DAG levels is discussed. 5. The requirement of external Ca2+ in PLC activation and aldosterone secretion also is discussed.

Adrenocorticotropin activates glycerol-3-phosphate acyltransferase in bovine adrenal glomerulosa cells

1. The mechanism whereby ACTH activates the synthesis of diacylglycerol (DAG) in isolated adrenal glomerulosa cells was investigated. 2. ACTH activates glycerol-3-phosphate acyltransferase (G3PAT) in intact and cell-free preparations of adrenal glomerulosa cells. Whereas activation of G3PAT by ACTH was observed in homogenates and membrane fractions, no activation was observed by angiotensin II (AII) at the same concentration. 3. ACTH effects were mimicked by nonspecific phospholipase C (PLC). 4. Our preliminary results suggest that ACTH activation of G3PAT may account for ACTH-induced increases in DAG via de novo synthesis of phosphatidic acid (PA).

External calcium is required for activation of phospholipase C by angiotensin II in adrenal glomerulosa cells

Previous studies have shown that external calcium (Ca2+) is required for the effects of angiotensin II (AII) on aldosterone secretion in adrenal glomerulosa zone. Using bovine adrenal glomerulosa cells prepared by collagenase dispersion, we examined whether external Ca2+ is required for the activation of phospholipase C by AII. Adrenal glomerulosa cells were exposed to Ca-EGTA buffered media to provide accurate estimates of external free Ca2+ concentrations. Phospholipase C activation was evaluated by measurement of inositol phosphates production. At 0.1 microM Ca2+ and less, sustained AII effects on inositol monophosphate (IP), inositol bisphosphate (IP2) and inositol trisphosphate (IP3) were markedly inhibited. Increasing the Ca2+ concentration to 50 microM or greater fully restored AII-induced inositol phosphates production. AII-induced increases in cytosolic Ca2+ measured by Quin-2 fluorescence, were diminished at lower external Ca2+ concentrations. Treating adrenal glomerulosa cells with Chelex-100, a strong Ca2+ binding resin, blocked early activation of phospholipase C by AII. Inhibition of IP3 production was also observed when inhibitors of Ca2+ movement across the plasma membrane were used, viz., La2+, TMB-8 and nifedipine. The requirement for Ca2+ during AII-induced activation of phospholipase C may be explained, at least partly by a requirement for Ca2+ at a site between the AII receptor and Phospholipase C.

Angiotensin II increases diacylglycerol in calf adrenal glomerulosa cells by activating de novo phospholipid synthesis

Effects of angiotensin II (AII) on diacylglycerol (DAG) synthesis were examined in calf adrenal glomerulosa cells. AII provoked rapid increases in [3H]glycerol-labeling and content of DAG. Effects on [3H]glycerol-labeling of DAG were observed both in cells prelabeled with [3H]glycerol for 60 minutes, and when AII and [3H]glycerol were added simultaneously. Increases in [3H] DAG labeling were associated with increases in total glycerolipid labeling, and in simultaneous addition experiments, were preceded by increased [3H] phosphatidic acid (PA) labeling. Labeling of glycerol-3-PO4, on the other hand, was not increased by AII, suggesting that increases in lipid labeling were not due to prior increases in precursor specific activity. ACTH, which does not increase the hydrolysis of inositol-phospholipids appreciably in this tissue, provoked increases in content and [3H]glycerol-labeling of DAG, which were only slightly less than those provoked by AII. Thus, part of the AII-induced increase in DAG may also be derived from sources other than inositol-phospholipids. Moreover, AII-induced increases in DAG appear to be at least partly derived from increased de novo synthesis of PA.

A rapid decline in external Ca2+ induces Ca2+ mobilization in bovine adrenal glomerulosa cells

Bovine adrenal glomerulosa cells perifused with M 199 containing 1 mM Ca2+ showed a transient increase in 45Ca2+ when the external Ca2+ was decreased. The efflux observed in the presence of 100 nM angiotensin II was similar to that observed when the external Ca2+ was changed from 1 mM to 50 microM. This efflux is the result of the transient activation of the PIP2 hydrolysis with the subsequent production of inositol-trisphosphate.