Atropine serum concentrations after multiple inhaled doses of atropine sulfate

Studies on retinal mechanisms possibly related to myopia inhibition by atropine in the chicken

PURPOSE

While low-dose atropine eye drops are currently widely used to inhibit myopia development in children, the underlying mechanisms are poorly understood. Therefore, we studied possible retinal mechanisms and receptors that are potentially involved in myopia inhibition by atropine.

METHODS

A total of 250 μg atropine were intravitreally injected into one eye of 19 chickens, while the fellow eyes received saline and served as controls. After 1 h, 1.5 h, 2 h, 3 h, and 4 h, eyes were prepared for vitreal dopamine (DA) measurements, using high-pressure liquid chromatography with electrochemical detection. Twenty-four animals were kept either in bright light (8500 lx) or standard light (500 lx) after atropine injection for 1.5 h before DA was measured. In 10 chickens, the α_2A-adrenoreceptor (α_2A-ADR) agonists brimonidine and clonidine were intravitreally injected into one eye, the fellow eye served as control, and vitreal DA content was measured after 1.5 h. In 6 chickens, immunohistochemical analyses were performed 1.5 h after atropine injection.

RESULTS

Vitreal DA levels increased after a single intravitreal atropine injection, with a peak difference between both eyes after 1.97 h. DA was also enhanced in fellow eyes, suggesting a systemic action of intravitreally administered atropine. Bright light and atropine (which both inhibit myopia) had additive effects on DA release. Quantitative immunolabelling showed that atropine heavily stimulated retinal activity markers ZENK and c-Fos in cells of the inner nuclear layer. Since atropine was recently found to also bind to α_2A-ADRs at doses where it can inhibit myopia, their retinal localization was studied. In amacrine cells, α_2A-ADRs were colocalized with tyrosine hydroxylase (TH), glucagon, and nitric oxide synthase, peptides known to play a role in myopia development in chickens. Intravitreal atropine injection reduced the number of neurons that were double-labelled for TH and α_2A-ADR. α_2A-ADR agonists clonidine and brimonidine (which were also found by other authors to inhibit myopia) severely reduced vitreal DA content in both injected and fellow eyes, compared to eyes of untreated chicks.

CONCLUSIONS

Merging our results with published data, it can be concluded that both muscarinic and α_2A-adrenergic receptors are expressed on dopaminergic neurons and both atropine and α_2A-ADR antagonists stimulate DA release whereas α_2A-ADR agonists strongly suppress its release. Stimulation of DA by atropine was enhanced by bright light. Results are in line with the hypothesis that inhibition of deprivation myopia is correlated with DA stimulation, as long as no toxicity is involved.

Myopia-Inhibiting Concentrations of Muscarinic Receptor Antagonists Block Activation of Alpha2A-Adrenoceptors In Vitro

Purpose

Myopia is a refractive disorder that degrades vision. It can be treated with atropine, a muscarinic acetylcholine receptor (mAChR) antagonist, but the mechanism is unknown. Atropine may block α-adrenoceptors at concentrations ≥0.1 mM, and another potent myopia-inhibiting ligand, mamba toxin-3 (MT3), binds equally well to human mAChR M4 and α1A- and α2A-adrenoceptors. We hypothesized that mAChR antagonists could inhibit myopia via α2A-adrenoceptors, rather than mAChR M4.

Methods

Human mAChR M4 (M4), chicken mAChR M4 (cM4), or human α2A-adrenergic receptor (hADRA2A) clones were cotransfected with CRE/promoter-luciferase (CRE-Luc; agonist-induced luminescence) and Renilla luciferase (RLuc; normalizing control) into human cells. Inhibition of normalized agonist-induced luminescence by antagonists (ATR: atropine; MT3; HIM: himbacine; PRZ: pirenzepine; TRP: tropicamide; OXY: oxyphenonium; QNB: 3-quinuclidinyl benzilate; DIC: dicyclomine; MEP: mepenzolate) was measured using the Dual-Glo Luciferase Assay System.

Results

Relative inhibitory potencies of mAChR antagonists at mAChR M4/cM4, from most to least potent, were QNB > OXY ≥ ATR > MEP > HIM > DIC > PRZ > TRP. MT3 was 56× less potent at cM4 than at M4. Relative potencies of mAChR antagonists at hADRA2A, from most to least potent, were MT3 > HIM > ATR > OXY > PRZ > TRP > QNB > MEP; DIC did not antagonize.

Conclusions

Muscarinic antagonists block hADRA2A signaling at concentrations comparable to those used to inhibit chick myopia (≥0.1 mM) in vivo. Relative potencies at hADRA2A, but not M4/cM4, correlate with reported abilities to inhibit chick form-deprivation myopia. mAChR antagonists might inhibit myopia via α2-adrenoceptors, instead of through the mAChR M4/cM4 receptor subtype.

Development and validation of an LC/MS/MS method for the determination of L-hyoscyamine in human plasma

A sensitive and specific LC/MS/MS method for the determination of L-hyoscyamine was developed and validated over the linearity range 20-500 pg ml-1 with 1.0 ml of plasma using scopolamine as the internal standard. The API III-Plus LC/MS/MS was operated under the multiple reaction monitoring mode using the atmospheric pressure chemical ionization technique. The instrument parameters were optimized to obtain 1.8 min run time with baseline separation of the internal standard from L-hyoscyamine. The between-run precision and accuracy of the calibration standards were 1.2 to 5.0% RSD and -4.5 to +2.5% relative error (RE). The within-run precision and accuracy of quality controls (60, 150 and 350 pg ml-1) were 1.9-3.4% RSD and -3.3 to +5.1% RE. Stability of L-hyoscyamine in human plasma and processed samples has been established.

The Pharmacological Treatment of Ambulatory Chronic Obstructive Pulmonary Disease Patients

Because of the widespread prevalence of chronic obstructive pulmonary disease (COPD) and the important role of drug therapy in its management, there is significant opportunity for the pharmacist to interact with COPD patients. Whether educating patients or other health care providers about COPD, a knowledge of the treatment options and their correct application in these patients is essential for pharmacists today. This article reviews the pharmacological management of ambulatory COPD patients, including the roles of β-agonists, anticholinergics, theophylline, steroids, oxygen, and other treatment modalities. Copyright © 1992 by W.B. Saunders Company

Should anticholinergics be used in acute severe asthma?

Anticholinergic drugs have been used in Western medicine for the treatment of asthma since the early 19th century. Studies evaluating drug efficacy in acute severe asthma over the last decade have renewed interest in the optimal use of anticholinergics in this condition. Unlike other bronchodilators (i.e., beta 2-agonists and methylxanthines), the anticholinergics produce bronchodilation only by inhibiting cholinergic-mediated bronchospasm. Therefore, anticholinergic drugs are more dependent on the mechanism of bronchospasm than other bronchodilators. The 18 clinical trials of anticholinergics in acute severe asthma are critically reviewed for design and endpoint measurements. Anticholinergics alone produce a modest bronchodilation in acute severe asthma but are not as consistently effective as beta 2-agonists. Anticholinergics consistently produce an added bronchodilation to aerosolized beta 2-agonists in single- and multiple-dose studies. This bronchodilation appears to be greater in the more severely obstructed patients. This bronchodilation is generally modest (10-20 percent), has not yet been shown to produce greater overall outcome, and has not been evaluated against high-dose frequent administration of aerosolized beta 2-agonists. Currently, only the quaternary amine derivatives are recommended for use in acute asthma. These agents should be reserved as second-line agents for acute severe asthma except possibly for those patients presenting with more severe obstruction (peak expiratory flow rate less than 35 percent of predicted).

Pharmacokinetic implications for the clinical use of atropine, scopolamine and glycopyrrolate

Several specific and sensitive new methods for determining atropine and its metabolites in biological fluids have increased the possibility to characterise the pharmacokinetic properties of this antimuscarinic agent. Following i.v. injection, atropine disappears very quickly from the circulation, resembling its fast onset of action. Age, but not sex, appears to have a clear effect on its kinetics, explaining at least partly the higher sensitivity of very young and very old patients to this anticholinergic agent. Following i.m. or oral atropine administration, typical anticholinergic effects coincide quite well with the absorption rate of the drug, indicating that the premedication should be given about 1 and 2 h before induction of anaesthesia. A sufficient absorption after rectal administration offers an alternative treatment, especially in children. Differing from its placental transfer, atropine has a delayed and incomplete lumbar cerebrospinal fluid penetration, indicating a fundamental difference between these two biological membranes. Oropharyngeally administered atropine has a very variable absorption, but inhaled or intratracheally given drug has produced interesting new results, e.g. pulmonary atropine administration appears to have clinical significance in special situations, such as cardiac arrest and organophosphate poisoning (military personnel). Depending on the method used, different data on the metabolism and excretion for atropine have been reported and therefore further studies are needed in this respect. The pharmacokinetics of scopolamine and glycopyrrolate and their relation to clinical response are poorly understood.