Background:
We have recently shown that pretreatment with certain cholinesterase inhibitors can produce large reductions in cocaine-reinforced behavior in rats (drug self-administration is decreased by more than 70% over a period of three days during which no additional cholinesterase inhibitor is administered). Because the reductions persist over a period two or more weeks, they have been described as persistent attenuation. Similar reductions have been observed after rats receive pretreatment with the cholinesterase inhibitors donepezil or tacrine, but not rivastigmine. The key difference leading to persistent attenuation may be effects of donepezil or tacrine on catecholamine neurotransmitters. Specifically, our hypothesis is that persistent attenuation is caused by a combination of 1.) Cholinesterase inhibition, which increases brain levels of acetylcholine (ACh); and 2.) Increased brain levels of dopamine and serotonin. Although well-tolerated, pretreatment with low doses of the cholinesterase inhibitor donepezil have not modified either the positive subjective effects of cocaine in humans, or cocaine use in outpatients. This may reflect the relatively low doses of donepezil administered (up to 10 mg daily). Transdermal selegiline is a well-tolerated, nonselective monoamine oxidase inhibitor that potentiates actions of dopamine and serotonin in the central nervous system.
Rationale Persistent attenuation may be achieved in humans by administering donepezil at higher doses, or in combination with a centrally-acting inhibitor of monoamine oxidase (MAO). Inhibition of MAO increases brain levels of dopamine and serotonin. If persistent attenuation can be accomplished in humans, this would lead to an important paradigm shift for substance abuse treatment, in that large reductions in cocaine-reinforced behavior could be produced without the need for continuous dosing with a medication. This scenario could remove the requirement for continued compliance with oral dosing in some patients with its associated potential for toxicity.
Specific Aims:
1. Determine whether donepezil can be safely advanced over a 17-day period to an individualized dose of up to 22.5 mg daily (or the highest dose tolerated by each participant).
2. Evaluate whether high-dose donepezil attenuates cocaine-reinforced behavior in humans.
3. Determine whether combined donepezil and selegiline produces greater reductions in cocaine-reinforced behavior than observed for donepezil alone.
Methods This is a randomized, single-blind, placebo-controlled, research-unit, single-center evaluation of the potential for oral donepezil, with or without transdermal selegiline to modify cocaine self-administration in a laboratory setting. Up to 32 non-treatment-seeking, regular cocaine users will be assigned to receive one of four treatments: 1.) Oral placebo; 2.) High-Dose Donepezil \[titrated to 22.5 mg daily\]; and 3.) Low-Dose Donepezil \[titrated to 10 mg daily\] and transdermal selegiline \[6 mg daily\]; and 4.) High-Dose Donepezil \[titrated to 22.5 mg daily\] and transdermal selegiline \[6 mg daily\]. For participants who receive donepezil, it will be advanced to either a target dose (low or high), or a lower dose that is tolerated by individual participants. To evaluate the occurrence of persistent attenuation, cocaine use will be measured over a nine-day follow-up period, through urine drug screens and the timeline-follow-back method. As noncontingent infusions of cocaine are administered, the pharmacokinetics of cocaine and donepezil will be determined.
