Urine and Plasma Pharmacokinetics of Lofexidine after Oral Delivery in Opiate-Dependent Patients
ABSTRACT The objective of this study was to investigate lofexidine urine and plasma pharmacokinetics using three different dosing regimens in opioid dependent subjects. To date, there have been no published studies on lofexidine appearance and excretion in urine of opioid dependent subjects.
Subjects were stabilized with 100 mg morphine sulphate on days 3-8 of the study. The dosing regimens of lofexidine hydrochloride were .8 mg twice a day (BID), 1.2 mg BID, or .8 mg three times a day (TID) on days 9 through 16 of the study. Plasma and urine samples were collected at appropriate time points. Area under the concentration-time curve (AUC), maximum concentration in plasma (C(max)), time when maximum concentration was reached (T(max)) and fraction excreted unchanged in urine (Fe) were calculated.
The average half-life obtained from all profiles was 12.1 +/- 6.3 hr. Steady-state (SS) was reached by study day 15. The plasma pharmacokinetic parameters for 1.2 mg BID and .8 mg TID dosing regimens did not seem to be different at steady state (day 15). T(max) was not statistically significantly different across dosing regimens. Fe values ranged between .01% and 34% with high variability within the same dosing regimen. For the total dose of 2.4 mg/day the two dosing regimens that were evaluated, namely 1.2 mg BID and .8 mg TID, did not show a significant statistical difference in plasma and urine pharmacokinetic parameters.
Although preliminary due to the limited number of subjects, these findings are the first to document lofexidine urine pharmacokinetics in opiate addicts using a highly sensitive liquid chromatography tandem mass spectrometric analysis.
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ABSTRACT: To review the pharmacology, toxicology, pharmacokinetics, efficacy, adverse effects, drug interactions, and dosage guidelines for lofexidine, an alpha(2)-agonist, for opioid detoxification. Primary literature was identified through a MEDLINE search (1950-September 2009), EMBASE (1988-July 2009), International Pharmaceutical Abstracts (1970-September 2009), and the Cochrane Library (1996-September 2009) using the key words lofexidine and opioid withdrawal. Abstracts were included in the absence of published results of studies. Studies published in English-language literature reporting on animal and human pharmacology, toxicology, and pharmacokinetics were included in addition to clinical trials using lofexidine for opioid detoxification in comparison to placebo or active controls. Lofexidine is an alpha(2)-agonist structurally related to clonidine. It is not an effective antihypertensive agent; however, it decreases the sympathetic outflow responsible for many opioid withdrawal symptoms. Nine clinical studies were reviewed representing 354 patients receiving lofexidine including a recent Phase 3 clinical trial. Eight studies involved comparisons of lofexidine to an opioid receptor agonist or clonidine for opioid detoxification. In these trials, lofexidine dosing was titrated to a maximum of 1.6-3.2 mg/day in divided doses for a total of 5-18 days. The data suggest that lofexidine has positive efficacy in reducing opioid withdrawal symptoms and is at least as effective as the opioid receptor agonists utilized for detoxification. Not all withdrawal symptoms are alleviated by alpha(2)-agonists, with many patients complaining of insomnia and aching. The most common adverse event with lofexidine in the Phase 3 trial was insomnia. Hypotension was also reported; however, the studies comparing clonidine with lofexidine suggest decreased incidence and severity of adverse events with lofexidine. Lofexidine appears to be a promising agent for opioid detoxification. If approved, it would be the first nonopioid agent approved for this indication. Further large-scale controlled studies are needed to identify the safest, most effective dosage regimen required to achieve opioid detoxification.Annals of Pharmacotherapy 02/2010; 44(2):343-51. DOI:10.1345/aph.1M347 · 2.92 Impact Factor