Limited evidence of effectiveness of physostigmine for the symptomatic treatment of Alzheimer's disease

Physostigmine is an acetylcholinesterase inhibitor; it works by obstructing the enzyme responsible for ACh destruction in the synaptic cleft. Studies conducted more than 20 years ago suggested that physostigmine could improve memory in people with or without dementia. Investigation of this property has been limited by the very short half-life of physostigmine. Various forms of administering the drug have been tried to overcome this problem, most recently a controlled-release (CR) oral formulation, and a skin patch. An additional limiting factor has been a high incidence of adverse effects, including nausea, vomiting and diarrhoea. Physostigmine appears to have no advantage over some newer anticholinesterase drugs. The short half-life remains a serious disadvantage and requires complex forms of administration. There is no reason to recommend further research into this drug.

Authors' conclusions: 

The evidence of effectiveness of physostigmine for the symptomatic treatment of Alzheimer's disease is limited. Even in a controlled release formulation designed to overcome the short half-life, physostigmine showed no convincing benefit and adverse effects remained common leading to a high rate of withdrawal.

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Background: 

The main pharmacological approach for the treatment of Alzheimer's disease (AD) has been based on the use of agents potentiating cholinergic transmission, particularly by inhibiting acetylcholinesterase (AChE), the enzyme that destroys acetylcholine after it has been secreted into the synaptic clefts. Physostigmine is an AChE inhibitor originally extracted from calabar beans. It is licensed in many countries as an agent for reversing the effect of drugs and poisons causing the anticholinergic syndrome. Studies conducted more than 20 years ago suggested that physostigmine could improve memory in people with or without dementia. Investigation of this property has been limited by the very short half-life of physostigmine. Various forms of administering the drug have been tried to overcome this problem, most recently a controlled-release (CR) oral formulation, and a skin patch.

Objectives: 

To determine the clinical efficacy and safety of physostigmine in Alzheimer's disease.

Search strategy: 

The Specialized Register of the Cochrane Dementia and Cognitive Improvement Group (CDCIG), The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL and LILACS were searched on 10 January 2008 using the terms: physostigmine OR syrapton OR antilirium. The CDCIG Specialized Register contains records from all major health care databases (CENTRAL, MEDLINE, EMBASE, PsycINFO, CINAHL, LILACS) as well as from many trials databases and grey literature sources.

We asked Forest Laboratories and Pharmax, owners of the rights to market physostigmine for Alzheimer's disease, for additional data and reports of clinical trials but we did not receive any information.

Selection criteria: 

All relevant unconfounded, double-blind, randomized, placebo-controlled trials in which physostigmine was administered for more than one day to patients with dementia of Alzheimer type.

Data collection and analysis: 

Data were extracted independently by two reviewers (JMC and JB), pooled where appropriate and possible, and the weighted or standardized mean differences or Peto odds ratios (95% CI) were estimated. Where possible, intention-to-treat analysis was used.

Main results: 

Fifteen studies were included using four different methods of administration of physostigmine. Four studies, 29 people, used intravenous infusion; seven, 131 people, used a conventional oral form; four, 1456 people, used a controlled-release oral form, and one study of 181 people used a verum skin patch.

Intravenous infusion
There are no usable results from the intravenous infusion trials,

Oral form
The few results from the trials of the conventional oral form showed no benefit of physostigmine compared with placebo.

Controlled release

The results from two of the four studies of the controlled-release physostigmine apply only to a group of patients identified as responders in a pre-randomization titration period. The best dose physostigmine was associated with improvement on the ADAS-Cog score compared with placebo at 6, 12 weeks. There were statistically significantly higher numbers of patients from the physostigmine group withdrawing from the trial (22/183 vs 2/183)(OR 5.92, 95% confidence limits 2.59 to 13.54, p<0.0001) and suffering at least one event of nausea, vomiting, diarrhoea, anorexia, dizziness, stomach pain, flatulence or sweating compared with placebo at 6 weeks. There were statistically significantly higher numbers of patients from the physostigmine group withdrawing from the trial due to adverse events (13/83 vs 5/93)(OR 3.05, 95% CI 1.15 to 8.07, p=0.02) and suffering at least one event of nausea, vomiting, diarrhoea, anorexia, dizziness, stomach pain, tremor, asthenia or sweating compared with placebo at 12 weeks. When no attempt was made to identify responders and all relevant patients with Alzheimer's disease were randomized, fixed dose physostigmine (mean 33 mg/day) was associated with a statistically significantly higher number withdrawing (234/358 vs 31/117)(OR 4.82, 95% CI 3.17 to 7.33, p<0.00001), withdrawing due to adverse events (196/358 vs 10/117) (OR 6.54, 95%CI 4.29 to 9.95, p<0.00001) and suffering at least one event of nausea, vomiting, diarrhoea, anorexia, dizziness, stomach pain, dyspepsia, sweating, asthenia, dyspnoea or abnormal dreaming, but with no benefit on cognition compared with placebo at 24 weeks.

Verum patch
The double dose (delivering mean dose 12 mg/day) was associated with statistically significantly higher numbers suffering at least one adverse event of vomiting, nausea, or abdominal cramps, and the lower dose (delivering mean dose 5.7mg/day) was associated with statistically significantly higher numbers suffering gastrointestinal complaints compared with placebo at 24 weeks. There was no difference between physostigmine (higher and lower dose) and placebo for numbers improved (CGIC) at 24 weeks.

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