Pharmacokinetics of 6-hydroxybuspirone and its enantiomers administered individually or following buspirone administration in humans

Concordance of Direct and Indirect Measures of Medication Adherence in A Treatment Trial for Cannabis Dependence

The current study compared adherence rates as measured by two indirect measurement methods (pill count and daily medication diary) to two direct measurement methods (urine riboflavin and serum 6-OH-buspirone level measurement) among participants (n = 109) in a medication treatment trial for cannabis dependence. Pill count and diary data showed high levels of percent agreement and strong kappa coefficients throughout the study. Riboflavin levels indicated lower level of percent in adherence during the study as compared to both pill count and self-report. In the subset of participants with 6-OH-buspirone levels (n = 58), the kappa coefficient also showed low to moderate agreement between the pill count and medication diaries with 6-OH-buspirone levels. In contrast to pill count and medication diaries, adherence as measured by riboflavin and 6-OH-buspirone significantly decreased over time. The findings from this study support previous work demonstrating that pill count and patient self-report of medication taking likely overestimate rates of medication adherence, and may become less reliable as the duration of a clinical trial increases.

Effects of chronic buspirone treatment on nicotine and concurrent nicotine+cocaine self-administration

Nicotine dependence and cocaine abuse are major public health problems, and most cocaine abusers also smoke cigarettes. An ideal pharmacotherapy would reduce both cigarette smoking and cocaine abuse. Buspirone (Buspar) is a clinically available, non-benzodiazepine anxiolytic medication that acts on serotonin and dopamine systems. In preclinical studies, it reduced cocaine self-administration following both acute and chronic treatment in rhesus monkeys. The present study evaluated the effectiveness of chronic buspirone treatment on self-administration of intravenous (IV) nicotine and IV nicotine+cocaine combinations. Five cocaine-experienced adult rhesus monkeys (Macaca mulatta) were trained to self-administer nicotine or nicotine+cocaine combinations, and food pellets (1 g) during four 1-h daily sessions under a second-order schedule of reinforcement (FR 2 (VR16:S)). Each nicotine+cocaine combination maintained significantly higher levels of drug self-administration than nicotine or cocaine alone (P<0.05-0.001). Buspirone (0.032-0.56 mg/kg/h) was administered IV through one lumen of a double-lumen catheter every 20 min for 23 h each day, for 7-10 consecutive days. Each 7-10-day sequence of buspirone treatment was followed by saline-control treatment for at least 3 days until food- and drug-maintained responding returned to baseline. Buspirone dose-dependently reduced responding maintained by nicotine alone (0.001-0.1 mg/kg/inj; P<0.01) and by nicotine (0.001 or 0.0032 mg/kg/inj)+cocaine combinations (0.0032 mg/kg/inj; P<0.05-0.001) with no significant effects on food-maintained responding. We conclude that buspirone selectively attenuates the reinforcing effects of nicotine alone and nicotine+cocaine polydrug combinations in a nonhuman primate model of drug self-administration.

Modification of cocaine self-administration by buspirone (buspar®): potential involvement of D3 and D4 dopamine receptors

Converging lines of evidence indicate that elevations in synaptic dopamine levels play a pivotal role in the reinforcing effects of cocaine, which are associated with its abuse liability. This evidence has led to the exploration of dopamine receptor blockers as pharmacotherapy for cocaine addiction. While neither D1 nor D2 receptor antagonists have proven effective, medications acting at two other potential targets, D3 and D4 receptors, have yet to be explored for this indication in the clinic. Buspirone, a 5-HT1A partial agonist approved for the treatment of anxiety, has been reported to also bind with high affinity to D3 and D4 receptors. In view of this biochemical profile, the present research was conducted to examine both the functional effects of buspirone on these receptors and, in non-human primates, its ability to modify the reinforcing effects of i.v. cocaine in a behaviourally selective manner. Radioligand binding studies confirmed that buspirone binds with high affinity to recombinant human D3 and D4 receptors (∼98 and ∼29 nm respectively). Live cell functional assays also revealed that buspirone, and its metabolites, function as antagonists at both D3 and D4 receptors. In behavioural studies, doses of buspirone that had inconsistent effects on food-maintained responding (0.1 or 0.3 mg/kg i.m.) produced a marked downward shift in the dose-effect function for cocaine-maintained behaviour, reflecting substantial decreases in self-administration of one or more unit doses of i.v. cocaine in each subject. These results support the further evaluation of buspirone as a candidate medication for the management of cocaine addiction.

Medication discovery for addiction: translating the dopamine D3 receptor hypothesis

The dopamine D3 receptor (D3R) has been investigated as a potential target for medication development to treat substance use disorders (SUDs) with a particular focus on cocaine and methamphetamine. Currently, there are no approved medications to treat cocaine and methamphetamine addiction and thus developing pharmacotherapeutics to complement existing behavioral strategies is a fundamental goal. Novel compounds with high affinity and D3R selectivity have been evaluated in numerous animal models of drug abuse and favorable outcomes in nonhuman primate models of self-administration and relapse have provided compelling evidence to advance these agents into the clinic. One approach is to repurpose drugs that share the D3R mechanism and already have clinical utility, and to this end buspirone has been identified as a viable candidate for clinical trials. A second, but substantially more resource intensive and risky approach involves the development of compounds that exclusively target D3R, such as GSK598809 and PG 619. Clinical investigation of these drugs or other novel D3R-selective agents will provide a better understanding of the role D3R plays in addiction and whether or not antagonists or partial agonists that are D3R selective are effective in achieving abstinence in this patient population.