Original ArticlesEffect of Halving the Dose of Venlafaxine to Adjust for Putative Pharmacokinetic and Pharmacodynamic Changes in an Animal Model of Chronic Hepatic EncephalopathyWikell, Cecilia*†; Kugelberg, Fredrik C.†‡; Hjorth, Stephan§; Apelqvist, Gustav*; Bengtsson, Finn*†Author Information *Department of Clinical Pharmacology, Lund University, Lund; Departments of †Psychiatry and ‡Clinical Pharmacology, Linköping University, Linköping; and §Department of Pharmacology and Clinical Neuroscience, Umeå, Sweden Address correspondence and reprint requests to Cecilia Wikell, Department of Clinical Pharmacology, Lund University Hospital, S-221 85 Lund, Sweden. Clinical Neuropharmacology: November-December 2001 - Volume 24 - Issue 6 - p 324-333 Buy Abstract Patients with chronic hepatic encephalopathy display monoaminergic perturbations together with affective symptoms. Thus, these patients belong to a group with a probability of receiving antidepressant drug treatment. The liver impairment may result in pharmacokinetic alterations of the antidepressant drug, which in turn may affect the already perturbed monoaminergic function. Venlafaxine (VEN) was administered as a single subcutaneous challenge to portacaval shunted (experimental hepatic encephalopathy model) rats (5 mg/kg) and sham-operated rats (5 and 10 mg/kg). The aims were to investigate whether a reduced dose in portacaval shunted rats resulted in higher concentrations of VEN and serotonin as compared to control rats, which had been demonstrated earlier when the rats received the same dose (10 mg/kg). A 50% reduction of the dose of VEN administered to portacaval shunted rats resulted in elevated levels of VEN in serum, brain parenchyma, and brain dialysate about 300 minutes after the injection. The VEN challenge increased the serotonin and noradrenaline concentrations in dialysate in portacaval shunted rats and both sham groups, but the three VEN groups did not differ in any major way in serotonin and noradrenaline output. Therefore, when the dose of VEN administered to experimental hepatic encephalopathy was reduced 50% as compared to control rats, mainly pharmacokinetic, and possibly also monoaminergic, alterations were observed. © 2001 Lippincott Williams & Wilkins, Inc.