Neuromuscular transmission and its pharmacological blockade. Part 1: Neuromuscular transmission and general aspects of its blockade

Neurotoxicity in snakebite--the limits of our knowledge

Snakebite is classified by the WHO as a neglected tropical disease. Envenoming is a significant public health problem in tropical and subtropical regions. Neurotoxicity is a key feature of some envenomings, and there are many unanswered questions regarding this manifestation. Acute neuromuscular weakness with respiratory involvement is the most clinically important neurotoxic effect. Data is limited on the many other acute neurotoxic manifestations, and especially delayed neurotoxicity. Symptom evolution and recovery, patterns of weakness, respiratory involvement, and response to antivenom and acetyl cholinesterase inhibitors are variable, and seem to depend on the snake species, type of neurotoxicity, and geographical variations. Recent data have challenged the traditional concepts of neurotoxicity in snake envenoming, and highlight the rich diversity of snake neurotoxins. A uniform system of classification of the pattern of neuromuscular weakness and models for predicting type of toxicity and development of respiratory weakness are still lacking, and would greatly aid clinical decision making and future research. This review attempts to update the reader on the current state of knowledge regarding this important issue.

The role of sugammadex in the development and modification of an allergic response to rocuronium: evidence from a cutaneous model

The availability of sugammadex as a selective encapsulating agent for rocuronium has led to speculation that it may be useful in mitigating rocuronium-induced anaphylaxis. Off-label use of sugammadex for this indication has already been documented in case reports although there are theoretical objections to the likelihood of an allergen-binding agent's being able to attenuate the immunological cascade of anaphylaxis. Using a cutaneous model of anaphylaxis in rocuronium-sensitised patients, we were unable to demonstrate that sugammadex was effective in attenuating the type-1 hypersensitivity reaction after it has been triggered by rocuronium, but we were able to demonstrate that these patients are anergic to sugammadex-bound rocuronium. These findings demonstrate that a cyclodextrin can bind an allergen and exclude it from interacting with the immune system, and may potentially lead to novel applications in other allergic diseases. However, there is no evidence that sugammadex should be used for the treatment of rocuronium-induced anaphylaxis, and clinical management should follow established protocols.

Muscarinic effects of the Caribbean ciguatoxin C-CTX-1 on frog atrial heart muscle

The effects of Caribbean ciguatoxin (C-CTX-1) isolated from horse-eye jack (Caranx latus) on the electrical and mechanical activities of frog auricle were studied. C-CTX-1 (1 pM-50 nM) dose-dependently shortened the duration of the plateau and the repolarizing phase of the action potential (AP). The AP shortening induced by C-CTX-1 (50 nM) was suppressed or prevented either by tetrodotoxin (TTX; 0.6 nM) or by atropine (0.1mM). C-CTX-1 (50 nM) prolonged the TTX (0.6 nM)-sensitive electrical response of the vagus nerve branches, which innervate the auricle. The C-CTX-1 (50 nM)-induced shortening of the plateau and of the repolarization phase were prevented or reversed by gallamine (20 microM) and pirenzepine (0.5 microM), respectively. C-CTX-1 (50 nM) decreased the amplitude of the peak contraction and shortened its duration. In the presence of gallamine (20 microM), C-CTX-1 decreased the amplitude of the peak contraction and shortened its duration in the presence of pirenzepine (0.5 microM). C-CTX-1 (50 nM) decreased the time constant of the relaxation phase of the peak contraction suggesting that it increased the Na(+)/Ca(2+) exchange activity. Acetylcholine (ACh; 1 pM) shortened APD, decreased the peak contraction and mimics the effects of C-CTX-1. In conclusion, the presented data show that C-CTX-1 released ACh from atrial cholinergic nerve terminals which activated M(1) and M(2) muscarinic receptors subtype (mAChR). Our findings suggest that M(1) and M(2) mAChR are present in frog atrial tissue and play a previously unrecognized role in the modulation of the AP duration and of the mechanical activity of cardiac tissue.

Pharmacology of botulinum toxin

BACKGROUND

Botulinum toxin has a well-defined role among dermatologists for the treatment of facial wrinkling, brow position, and palmar and axillary hyperhidrosis.

OBJECTIVE

The purpose of this study is to educate dermatologists on the pharmacology of botulinum toxin.

METHODS

A retrospective review of the literature on botulinum toxin from 1962 to the present was conducted. We examined the clinical applications of botulinum toxin, cholinergic neuromuscular transmission, the toxin's structure and molecular actions, drug and disease interactions at the neuromuscular junction, toxin assays, determinants of clinical response, and adverse side effects.

RESULTS

Botulinum toxin blocks the release of acetylcholine from the presynaptic terminal of the neuromuscular junction. Several drugs and diseases interfere with the neuromuscular junction and the effects of botulinum toxin. The mouse bioassay, the most sensitive and specific measurement of toxin activity, is the gold standard for botulinum toxin detection and standardization. The major determinants of clinical response to treatment are the toxin preparation, individual patient's anatomy, dose and response relationships, length of toxin storage after reconstitution, and immunogenicity. To minimize potential antibody resistance, one should use the smallest effective dose, utilize treatment intervals of more than 3 months, and avoid booster injections. Uncommon adverse effects include ptosis, ectropion, diplopia, bruising, eyelid drooping, hematoma formation, and temporary headaches.

CONCLUSION

Botulinum toxin is a safe and effective treatment. Knowledge of the pharmacologic basis of therapy will be useful for standardizing techniques and achieving consistent therapeutic results in the future.

Succinylcholine-associated postoperative myalgia

The subject of postoperative myalgia associated with the use of succinylcholine is reviewed. We discuss the mechanisms of succinylcholine-induced myalgia and the techniques available to prevent and treat the myalgia. In situations where patients are at risk of developing myalgia and succinylcholine is the neuromuscular blocker of choice, the use of a combination of techniques may prove to be a useful strategy.