Transdermal physostigmine in the treatment of Alzheimer's disease

Current advances in transdermal delivery of drugs for Alzheimer's disease

Alzheimer's disease (AD) is a common, progressive, fatal neurodegenerative disorder, which will play an increasingly important role both socially and financially in the aging populations. Treatments for AD show modest improvements in cognition and global functioning among patients. Furthermore, the oral administration of treating AD has had some drawbacks that decrease the medication adherence and efficacy of the therapy. Transdermal drugs are proposed as an alternative remedy to overcome the disadvantages of current pharmaceutical dosage options for this chronic disorder. They could have different strengths, such as offering a stable diffusion of active substance, avoiding the first pass metabolism, and reducing system adverse reactions. This article reviews the technical principles, novel techniques of transdermal delivery drug, and prospects for future development for the management of cognitive and behavioral dysfunctions in AD patients.

Abnormalities of resting-state functional cortical connectivity in patients with dementia due to Alzheimer's and Lewy body diseases: an EEG study

Previous evidence showed abnormal posterior sources of resting-state delta (<4 Hz) and alpha (8-12 Hz) rhythms in patients with Alzheimer's disease with dementia (ADD), Parkinson's disease with dementia (PDD), and Lewy body dementia (DLB), as cortical neural synchronization markers in quiet wakefulness. Here, we tested the hypothesis of additional abnormalities in functional cortical connectivity computed in those sources, in ADD, considered as a "disconnection cortical syndrome", in comparison with PDD and DLB. Resting-state eyes-closed electroencephalographic (rsEEG) rhythms had been collected in 42 ADD, 42 PDD, 34 DLB, and 40 normal healthy older (Nold) participants. Exact low-resolution brain electromagnetic tomography (eLORETA) freeware estimated the functional lagged linear connectivity (LLC) from rsEEG cortical sources in delta, theta, alpha, beta, and gamma bands. The area under receiver operating characteristic (AUROC) curve indexed the classification accuracy between Nold and diseased individuals (only values >0.7 were considered). Interhemispheric and intrahemispheric LLCs in widespread delta sources were abnormally higher in the ADD group and, unexpectedly, normal in DLB and PDD groups. Intrahemispheric LLC was reduced in widespread alpha sources dramatically in ADD, markedly in DLB, and moderately in PDD group. Furthermore, the interhemispheric LLC in widespread alpha sources showed lower values in ADD and DLB than PDD groups. At the individual level, AUROC curves of LLC in alpha sources exhibited better classification accuracies for the discrimination of ADD versus Nold individuals (0.84) than for DLB versus Nold participants (0.78) and PDD versus Nold participants (0.75). Functional cortical connectivity markers in delta and alpha sources suggest a more compromised neurophysiological reserve in ADD than DLB, at both group and individual levels.

Differential effects of scopolamine and lorazepam on working memory maintenance versus manipulation processes

Between-study comparisons of benzodiazepine and anticholinergic drugs on working memory suggest that anticholinergics may produce greater impairment in maintenance processes, whereas benzodiazepines may produce greater impairment in manipulation processes. This study directly compared acute effects ofthe benzodiazepine lorazepam (1.0 and 2.0 mg/70 kg, orally administered) and the anticholinergic scopolamine (0.25 and 0.50 mg/70 kg, subcutaneously administered) on working memory maintenance (storage and rehearsal) and manipulation processes in a placebo-controlled, double-dummy, double-blind, crossover design in 20 healthy volunteers. Using a modified Sternberg paradigm, storage, rehearsal, and manipulation processes were parametrically manipulated by varying memory load, delay between stimulus presentation and test, and number of operations performed on the letter strings, respectively, while controlling for drug effects on nonmemory processes. As predicted, the results suggested greater impairment in maintenance processes (rehearsal) with scopolamine than with lorazepam and greater impairment in manipulation processes with lorazepam than with scopolamine. In addition, the results suggested greater overall slowing of working memory processes with lorazepam.

Ghrelin degradation by serum and tissue homogenates: identification of the cleavage sites

The endogenous ligand for the GH secretagogue receptor is ghrelin, a peptide recently purified from the stomach. Ghrelin is n-octanoylated on the Ser(3) residue, and this modification is essential for its interaction with the receptor. The degradation of ghrelin by rat and human serum, purified commercial enzymes, and tissues homogenates was analyzed by combining HPLC and mass spectrometry. In serum, ghrelin was desoctanoylated, without proteolysis. The desoctanoylation was significantly reduced by phenylmethylsulfonyl fluoride, a serine proteases and esterases inhibitor. In rat serum, the carboxylesterase inhibitor bis-p-nitrophenyl-phosphate totally inhibited ghrelin desoctanoylation, and a correlation was found between ghrelin desoctanoylation and carboxylesterase activity. Moreover, purified carboxylesterase degraded ghrelin. Thus, carboxylesterase could be responsible for ghrelin desoctanoylation in that species. In human serum, ghrelin desoctanoylation was partially inhibited by eserine salicylate and sodium fluoride, two butyrylcholinesterase inhibitors, but not by bis-p-nitrophenyl-phosphate and EDTA. Purified butyrylcholinesterase was able to degrade ghrelin, and there was a correlation between the butyrylcholinesterase and ghrelin desoctanoylation activities in human sera. This suggested that several esterases, including butyrylcholinesterase, contributed to ghrelin desoctanoylation in human serum. In contact with tissues homogenates, ghrelin was degraded by both desoctanoylation and N-terminal proteolysis. We identified five cleavage sites in ghrelin between residues -Ser(2)-(acyl)Ser(3)- (stomach and liver), -(acyl?)Ser(3)-Phe(4)- (stomach, liver, and kidney), -Phe(4)-Leu(5)- (stomach and kidney), -Leu(5)-Ser(6)- and -Pro(7)-Glu(8)- (kidney). In all cases, the resulting fragments were biologically inactive.

Galantamine facilitates acquisition of hippocampus-dependent trace eyeblink conditioning in aged rabbits

Cholinergic systems are critical to the neural mechanisms mediating learning. Reduced nicotinic cholinergic receptor (nAChR) binding is a hallmark of normal aging. These reductions are markedly more severe in some dementias, such as Alzheimer's disease. Pharmacological central nervous system therapies are a means to ameliorate the cognitive deficits associated with normal aging and aging-related dementias. Trace eyeblink conditioning (EBC), a hippocampus- and forebrain-dependent learning paradigm, is impaired in both aged rabbits and aged humans, attributable in part to cholinergic dysfunction. In the present study, we examined the effects of galantamine (3 mg/kg), a cholinesterase inhibitor and nAChR allosteric potentiating ligand, on the acquisition of trace EBC in aged (30-33 months) and young (2-3 months) female rabbits. Trace EBC involves the association of a conditioned stimulus (CS) with an unconditioned stimulus (US), separated by a stimulus-free trace interval. Repeated CS-US pairings results in the development of the conditioned eyeblink response (CR) prior to US onset. Aged rabbits receiving daily injections of galantamine (Aged/Gal) exhibited significant improvements compared with age-matched controls in trials to eight CRs in 10 trial block criterion (P = 0.0402) as well as performance across 20 d of training [F(1,21) = 5.114, P = 0.0345]. Mean onset and peak latency of CRs exhibited by Aged/Gal rabbits also differed significantly [F(1,21) = 6.120/6.582, P = 0.0220/0.0180, respectively] compared with age-matched controls, resembling more closely CR timing of young drug and control rabbits. Galantamine did not improve acquisition rates in young rabbits compared with age-matched controls. These data indicate that by enhancing nicotinic and muscarinic transmission, galantamine is effective in offsetting the learning deficits associated with decreased cholinergic transmission in the aging brain.

Transdermal delivery of physostigmine: effects of enhancers and pressure-sensitive adhesives

The purpose of this study was to investigate the effects of various pressure-sensitive adhesives (PSA) on the percutaneous absorption of physostigmine across hairless mouse skin. In addition, the influences of various vehicles and polyvinylpyrrolidone (PVP) on the percutaneous absorption of physostigmine from PSA matrix across hairless mouse skin were evaluated using a flow-through diffusion cell system at 37 degrees C. Physostigmine showed the highest permeability from silicone adhesive matrix, followed by polyisobutylene (PIB), styrene-isoprene-styrene (SIS), acrylic, and styrene-butadiene-styrene (SBS) matrix. Among acrylic adhesives, the permeability of physostigmine was the highest from grafted acrylic adhesive. Polyvinyl pyrrolidone inhibited the crystallization of physostigmine in the PIB adhesive matrix and enhanced the permeability of physostigmine from the PIB adhesive matrix. When esters of sorbitol and fatty acid, polyethylene glycol (PEG) alkyl esters, and caprylic/capric triglycerides were tested, the more lipophilic was a surfactant, the higher the permeation rate within the same group of surfactants. The enhancement effect of PEG derivatives was lower than that of non-PEG derivatives. Among non-linear fatty acid derivatives, linoleate derivatives showed higher permeability of physostigmine than oleate derivatives. This study showed that several non-ionic surfactants, including PEG-20 evening primrose glyceride, enhanced the permeation of physostigmine across hairless mouse skin better than oleic acid.

Physostigmine for Alzheimer's disease

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. It has been proposed as a potential drug for the symptomatic treatment of AD.

OBJECTIVES

To determine whether there is evidence of beneficial effects for the use of physostigmine in Alzheimer's disease. To assess the incidence and severity of adverse effects.

SEARCH STRATEGY

The Cochrane Controlled Trials Register was searched using the following terms: 'physostigmine', 'physostigmine salicylate', 'Synapton' and 'Antilirium' in accordance with the Cochrane Dementia and Cognitive Improvement Group's search strategy. The pharmaceutical company was contacted.

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. Trials in which the allocation to the treatment was not randomized, or in which the allocation to the treatment was not concealed were excluded.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two reviewers (JMC & 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, involving 29 people in total, used intravenous infusion; seven, involving 131 people, used a conventional oral form; four, involving 1456 participants, used a controlled-release oral form, and one study of 181 people used a verum skin patch. There are no usable results from the intravenous infusion trials, and the few results from the conventional oral form showed no benefit of physostigmine compared with placebo. 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 (mean 25mg/day) was associated with a 1.75 point improvement on ADAS-Cog score (mean difference -1.75, 95% confidence interval -2.90, -0.60 on an intention-to-treat basis) and a 0.26 point improvement on the CGIC score (treated as a continuous scale) (mean difference -0.26, 95% confidence interval 0.06, 0.46 on an intention-to-treat basis) compared with placebo at 6 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, 13.54) and suffering at least one event of nausea, vomiting, diarhoea, anorexia, dizziness, stomach pain, flatulence or sweating compared with placebo at 6 weeks. The best dose physostigmine (mean 27mg/day) was associated with a 2.0 point improvement on ADAS-Cog score (mean difference -2.02, 95% confidence interval -3.59, -0.45 on an intention to treat basis) compared with placebo at 12 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% confidence limits 1.15, 8.07) and suffering at least one event of nausea, vomiting, diarhoea, 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% confidence limits 3.17, 7.33), withdrawing due to adverse events (196/358 vs 10/117) (OR 6.54, 95%confidence limits 4.29, 9.95) and suffering at least one event of nausea, vomiting, diarhoea, anorexia, dizziness, stomach pain, dyspepsia, sweating, asthenia, dyspnoea or abnormal dreaming compared with placebo at 24 weeks. The results from the study of the verum patch physostigmine show that the double dose (delivering mean dose 12mg/day) was associated with statistically significantly higher numbers suffering at least one adverse event of vomiting, nausea or abdominal cramps compared with placebo at 24 weeks, but placebo was associated with statistically significantly greater numbers of gastrointestinal complaints at 24 weeks compared with single-dose physostigmine.

REVIEWERS' 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.

Time course of pharmacodynamic and pharmacokinetic effects of physostigmine assessed by functional brain imaging in humans

In imaging studies of brain functions using pharmacological probes, identification of the time point at which central effects of intravenously infused drugs become stable is crucial to separate the effects of experimental variables from the concomitant changes in drug effects over time. We evaluated the time courses of the pharmacokinetics and pharmacodynamics, including butyrylcholinesterase inhibition and central neural responses, of physostigmine in healthy young subjects. Ten positron emission tomography (PET) scans that alternated between a rest condition (eyes open, ears unplugged) and a working memory for faces (WM) task were acquired in healthy subjects. Subjects in the drug group received a saline infusion for the first two scans, providing a baseline measure, then received an infusion of physostigmine for all subsequent scans. Subjects in the control group received a placebo infusion of saline for all scans. Physostigmine plasma levels and percent butyrylcholinesterase inhibition increased over time (p < 0. 0001), and both became stable by 40 min. Physostigmine decreased reaction time (RT) (p = 0.0005), and this effect was detected after 20 min of infusion and stable thereafter. Physostigmine also decreased regional cerebral blood flow (rCBF) in right prefrontal cortex during task (p = 0.0002), and this effect was detected after 40 min of infusion and stable thereafter. No change in RT or rCBF was observed in the control group. These results indicate that a 40-min infusion of physostigmine was necessary to obtain stable central effects. More generally, we have demonstrated that experimental effects can vary with time, especially during the initial phases of a drug infusion, indicating that it is critical that these changes are controlled.

Cholinergic enhancement improves performance on working memory by modulating the functional activity in distinct brain regions: a positron emission tomography regional cerebral blood flow study in healthy humans

Previously, we have shown that physostigmine, an acetylcholinesterase inhibitor, improved performance on a working memory for faces task, as reflected by reduced reaction time (RT), and reduced task-specific regional cerebral blood flow (rCBF) in right prefrontal cortex and, further, that these reductions in RT and right frontal rCBF were significantly correlated. Here we investigated the relation between the effects of physostigmine on task performance and task-specific functional brain response throughout the cortex by examining correlations between physostigmine-related changes in rCBF in all brain areas and changes in RT. In subjects who received an infusion of physostigmine, reduced RT correlated (p<0.001) positively with reduced rCBF in right frontal cortex, left temporal cortex, anterior cingulate, and left hippocampus; and correlated with increased rCBF in medial occipital visual cortex. In subjects who received a placebo infusion of saline, no significant correlations between changes in RT and cortical rCBF were observed. The results show that cholinergically induced improvements in working memory performance are related to alterations in neural activity in multiple cortical regions, including increased neural activity in regions associated with early perceptual processing and decreased neural activity in regions associated with attention, memory encoding, and memory maintenance.

Recent developments in the drug treatment of Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder with an impact on public health which continues to increase with the increasing longevity of the population. The disease is characterised clinically by a progressive loss of cognitive and behavioural function. These deficits are thought to result from decreased cholinergic transmission; therefore, restoring cholinergic function has been the main focus in the development of drugs for AD. Several pharmacological approaches to enhancing cholinergic function have been developed for symptomatic or palliative therapy of AD. Although these strategies have resulted in modest cognitive and behavioural improvements in patients with AD, they do not address the underlying progression of the disease. New strategies will be required to slow, stop or reverse the effects of neurodegeneration in AD. A number of potential therapies are currently under investigation, including estrogen replacement, anti-inflammatory agents, free radical scavengers and antioxidants, and monoamine oxidase-B (MAO-B) inhibitors. The evidence for a protective effect of estrogens or nonsteroidal anti-inflammatory drugs (NSAIDs) is controversial, and largely based on retrospective studies. More controlled prospective studies are needed to definitively demonstrate the benefits of long term estrogen or NSAID use in the prevention of AD. Free radical scavengers/antioxidants such as idebenone, and selective prevention MAO-B inhibitors such as lazabemide are well tolerated, but require additional studies in order to demonstrate preventative effects. In addition, other approaches, such as anti-amyloid treatments that affect beta-amylase secretion, aggregation and toxicity, appear promising; treatments that hinder neurofibrillary tangle construction and nerve growth factor (NGF) induction are in the very early stages of development.

Reappraising neurotransmitter-based strategies

A number of observations support the hypothesis that a central deficit in acetylcholine (ACh) may be responsible for the initiation of Alzheimer's disease (AD). For example, cholinergic innervation in AD is reduced in areas of the brain important for processing information. Further, reduced concentrations of choline acetyltransferase (ChAT), the enzyme responsible for the synthesis of ACh, correlate with the number of beta-amyloid senile plaques and cognitive dysfunction in AD patients. Consequently, several strategies to increase cholinergic neurotransmission have been developed, including ACh precursors, ACh release enhancers, cholinesterase (ChE) inhibitors and receptor agonists. Although ChE inhibitors appear to be the most promising, tacrine, the first ChE inhibitor to be registered and approved for the treatment of AD, has significant tolerability problems. Thus, ChE inhibitors with improved side-effect profiles have been developed and subsequently awarded marketing approval. However, in addition to the cholinergic system that is the most severely affected neurotransmitter system in AD, other neurotransmitter systems may be involved (e.g. serotonergic, noradrenergic and glutamatergic). Therefore, bifunctional compounds or combinations of drugs may provide additional therapeutic value.

Functional imaging of the brain in the evaluation of drug response and its application to the study of aging

Functional neuroimaging techniques including single photon emission computerised tomography (SPECT), positron emission tomography (PET) and functional magnetic resonance imaging (FMRI) can provide insight into the functional connectivity of the human brain in both health and disease, including the effects of aging and drugs on brain function. Neuroimaging measurement techniques can either be direct, using radio-specific ligands, or indirect, using the neurophysiological consequences of pharmacological interventions. Both approaches can be combined with sensorimotor or cognitive activation to examine the interaction between the targeted receptor function and the sensorimotor or cognitive process implicit in the study design. Using radionuclides, PET can provide absolute measurement of cerebral blood flow to regions of interest and can measure changes in cerebral metabolism using labelled fluorodeoxyglucose. PET offered the first opportunity to image brain activation caused by a variety of stimuli and hence to measure the effect of drugs on brain activation. PET also enables the study of drug disposition within the brain. SPECT has been used to study relative changes in cerebral blood flow associated with disease processes and also receptor occupancy. FMRI, by contrast, does not involve ionising radiation and has better spatial and temporal resolution. It is still a relatively new technique and limited by its ability to only measure haemodynamic changes through the blood oxygen level-dependent (BOLD) signal. The effects of aging on drug responsiveness and the effects of drug treatment of diseases associated with old age are relatively unexplored areas of functional neuroimaging research.

Effects of metrifonate on radial arm maze acquisition in middle-aged rats

The efficacy of metrifonate, a well-tolerated cholinesterase (ChE) inhibitor, in attenuating the normal aging- and corticosterone-induced impairments of radial maze performance of rats was compared. Middle-aged Fischer 344 rats were screened for their spatial orientation performance in the Morris water escape task. Good and bad performers were selected: good performers (N= 22) were treated with subcutaneous sustained-release corticosterone pellets, resulting in hippocampal cell damage and impaired spatial orientation in the radial maze; age-induced bad performers (N = 20) were tested without additional pharmacological intervention. Metrifonate (MFT), administered daily during radial maze testing, 30 min before training, at a dose of 15 mg/kg p.o., facilitated the acquisition of the task in age-impaired rats, but not in corticosterone-impaired rats.

Cholinergic stimulation alters performance and task-specific regional cerebral blood flow during working memory

Modulation of the cholinergic neurotransmitter system results in changes in memory performance, including working memory (WM), in animals and in patients with Alzheimer disease. To identify associated changes in the functional brain response, we studied performance measures and regional cerebral blood flow (rCBF) using positron emission tomography (PET) in healthy subjects during performance of a WM task. Eight control subjects received an infusion of saline throughout the study and 13 experimental subjects received a saline infusion for the first 2 scans followed by a continuous infusion of physostigmine, an acetylcholinesterase inhibitor, for the subsequent 8 scans. rCBF was measured using H215O and PET in a sequence of 10 PET scans that alternated between rest and task scans. During task scans, subjects performed the WM task for faces. Physostigmine both improved WM efficiency, as indicated by faster reaction times, and reduced WM task-related activity in anterior and posterior regions of right midfrontal gyrus, a region shown previously to be associated with WM. Furthermore, the magnitudes of physostigmine-induced change in reaction time and right midfrontal rCBF correlated. These results suggest that enhancement of cholinergic function can improve processing efficiency and thus reduce the effort required to perform a WM task, and that activation of right prefrontal cortex is associated with task effort.

Metrifonate treatment enhances acquisition of eyeblink conditioning in aging rabbits

The cholinergic system is known to show deterioration during aging and Alzheimer's disease. In response, a therapeutic approach to Alzheimer's disease has been to attempt to compensate for the decrease in central cholinergic function by potentiating the activity of the remaining intact cholinergic cells with cholinesterase inhibitors. In this study treatment with the long-lasting cholinesterase inhibitor metrifonate enhanced acquisition of eyeblink conditioning in aging rabbits without producing interfering side effects. The effects of metrifonate on central and peripheral cholinesterase activity were evaluated, as was the involvement of plasma atropine esterase activity on the central and peripheral response to metrifonate. Results demonstrate that metrifonate can produce predictable, dose-dependent ChE inhibition. Associative learning in the aging rabbit was improved by metrifonate-induced steady state ChE inhibition within a range of 30-80%. Metrifonate was behaviorally effective in the absence of the severe side effects which typically plague cholinesterase inhibitors, suggesting that metrifonate is a possible treatment for the cognitive deficits resulting from normal aging and Alzheimer's disease.

Cognitive effects of scopolamine in dementia

Cholinergic deficiency was postulated to play an important role in the mental decline observed in Alzheimer's (AD), Parkinson's (PD) and multiinfarct (MID) dementia. In the present study, 11 AD, 8 MID and 7 PD patients (DSM III-R diagnostic criteria for dementia) and 9 healthy age-matched controls (CTRL) were given IV 0.5 mg scopolamine (SCO) or placebo (PLA) in random order (double blind) within one week. The Hebrew Short Mental Test (SMT) and Wechsler Memory Scale (WMS) were administered before and after SCO and PLA in each patient. A comparison of SCO vs. PLA utilizing MANCOVA (the covariate being the basal mental performance [BAS] with SMT or WMS) showed that SCO affected all the groups similarly, except for the Wechsler subtest of logic memory which showed larger deterioration in CTRL compared to demented patients. ANOVA and MANCOVA analyses did not distinguish between the three demented groups. SCO administration does not differentiate between demented patients and CTRL and does not enable discrimination between patients with AD, MID and PD. Moreover, some CTRL with still normal cognitive performance, but lower BAS may be more vulnerable to SCO than others. The integrity of the cholinergic system may be responsible for the different sensitivity to SCO challenge.

Treatment of Alzheimer's disease: future directions

Following the introduction of tacrine hydrochloride (Cognex) in the United States and several other countries, researchers are pursuing two broad therapeutic strategies for Alzheimer's disease (AD). The first involves identifying agents or combinations of agents whose actions can compensate for the considerable cerebral damage that has typically occurred by the time the diagnosis of AD is made. Such therapeutic approaches include the development of additional cholinesterase inhibitors, agents that work on the receptors of other systems damaged by the disease process, and anti-inflammatory and immunomodulatory agents. The second and ultimately more promising strategy involves the development of approaches to retard, halt, or even prevent disease progression. Such protective approaches, which depend on the development of more effective methods for predicting and diagnosing AD, include the administration of nerve growth factor and other neurotrophins and the use of pharmacologic or genetic interventions to limit amyloid deposition and the formation of neurofibrillary tangles.

Effects of M2 antagonists on in vivo hippocampal acetylcholine levels

There is evidence that muscarinic receptors of the M2 subtype are presynaptic autoreceptors that modify the release of acetylcholine (ACh) through a negative feedback mechanism. Blocking these receptors by selective antagonists may therefore lead to increased ACh release. This in vivo microdialysis study examined the effects of three M2 antagonists, AF-DX 116, AF-DX 384, and AQ-RA 741, on hippocampal cholinergic neurotransmission. Drug (2, 4, 8, or 16 microM) or vehicle (Ringer's solution) was perfused via a microdialysis probe into the CA1 hippocampal region of conscious male Fischer 344 rats. Levels of ACh and choline were assessed by HPLC-EC. When the dose was expressed in K1 multiples, all drugs (except AQ-RA 741 at the two highest concentrations) were found to be on the same linear dose-response curve. Choline levels were not affected by drug administration. All three compounds elevated ACh levels in a similar K1-normalized dose-response fashion, strongly supporting the concept that the proposed presynaptic mechanism of action is indeed based on the same M2 receptor. Such elevations of ACh may not only improve performance on memory tasks, but may also have therapeutic advantages in conditions of cholinergic hypofunction, such as Alzheimer's disease.

Prophylactic transdermal treatment with physostigmine and scopolamine against soman intoxication in guinea-pigs

This study was designed to evaluate the prophylactic efficacy of transdermally administered physostigmine (PHY) against soman exposure using guinea-pigs. Transdermal PHY pad (3 cm2 kg-1; 60 micrograms cm-2), containing a vehicle based on propionic acid, was applied onto the dorsal back of the animals, 24 h before exposure to the organophosphate. At the time of exposure, PHY concentrations in brain and plasma were ca. 3.6 ng g-1 and 4.1 ng ml-1, respectively. Brain and whole blood cholinesterase (ChE) activity was inhibited to 70% and 47% of the original activity, respectively. Transdermal PHY by itself protected up to 70% of the animals exposed to 1.5 LD50 of soman (100% mortality was recorded in the control group). Combining transdermal PHY with Scopoderm provided full protection against 1.5 LD50 of soman (protection of 70% against 3 LD50). When the prophylactic treatment was combined with post-exposure therapy (atropine, 10 mg kg-1; toxogonin, 10 mg kg-1) 1 min after 5 LD50 of soman, protection of 90% of the animals was achieved.

Transcutaneous drug delivery: a practical review

OBJECTIVE

To describe the advantages, disadvantages, practical considerations, and future developments of transcutaneous drug delivery.

MATERIALS AND METHODS

The physiochemical properties of the drug preparation that are factors in the effectiveness of transcutaneous transport are drug stability or volatility, use of a solvent carrier or vehicle, use of a penetration enhancer, and type of delivery device. Because a drug should remain on the skin without evaporating or becoming otherwise inactive, it is suspended in a vehicle--any gel, lotion, or paste used to apply the drug to the skin. Penetration enhancers include several compounds that are mixed into vehicles to alter the molecular environment of the epidermis and facilitate absorption. The delivery system itself occasionally proves to be the ultimate determinant of transdermal drug flow.

RESULTS

The advantages of transcutaneous drug delivery are avoidance of the gastrointestinal tract and hepatic first-pass biotransformation and metabolism, control of absorption, availability of multiple skin sites to avoid local irritation and toxicity, and improved patient compliance. The disadvantages include the potential for localized irritant and allergic cutaneous reactions, systemic toxicity, and difficulties associated with the time necessary for a drug to diffuse through the skin.

CONCLUSION

Transdermal drug regimens are safe and effective. They provide clinicians the opportunity to offer more therapeutic options to their patients to optimize their care.