Parasympathomimetic Drugs

Cholinomimetic drugs may be broadly classified rmder the following two categories. They are (a) Directly Acting 

A few typical examples of medicinal compormds bleonging to this category are discussed below acetylcholine chloride bethanechol chloride carbachol methacholine chloride pilocarpine nitrate, etc. 

Choline chloride acetate (2-Acetoxyethyl) trimethyl-ammonium chloride (2-Hydroxyethyl) trimethylammonium chloride, acetate Ethanaminium, 2-(acetyloxy)-N, N, N-trimethyl-, chloride USP. 

Acetylcholine chloride may be prepared by the interaction of trimethylamine and 2-ehloroethyl acetate. 

It is a potent quaternary ammonium parasympathomimetie agent. Its transient action is due to its destruetion by cholinesterase. It is a vasodilator and cardiac depressant. The vasodilator aetion eaused by aeetyleholine is found to be most prominent in the peripheral vaseular areas. It has been used in a wide range of conditions such as cataract surgery, iridectomy, trophic ulcers, paroxysmal tachycardia, gangrene and Raynaud s disease. 

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Giolinergic drugs mimic the activity of the parasympathetic nervous system (PNS). They also are called parasympathomimetic drugs. An understanding of the PNS is useful in understanding the cholinergic dni. ... 

The muscle fibres of the ciliary bodies are innervated by the mrd or oculomotor nerve. As explained above, when these fibres contract they allow the lens to take up its natural shape. Direct stimulation of the Illrd nerve therefore produces accommodation for near objects. Parasympathomimetic drugs have a similar action, whereas atropine paralyses this effect and so accommodates the lens for seeing distant objects. 

Drugs that mimic the actions of acetylcholine are termed cholinomimetic, and those that mimic epinephrine and/or norepinephrine are adrenomimetic. The cholinomimetic drugs are also called parasympathomimetic drugs. The adrenomimetic drugs are often called sympathomimetic. 

Basic Pharmacology of the Directly Acting Parasympathomimetic Drugs... 

From the influence of the autonomic nervous system it follows that all sympatholytic or sympathomimetic and parasympatholytic or parasympathomimetic drugs can produce corresponding effects on cardiac performance. These possibilities are exploited therapeutically for instance, p-blockers for suppressing excessive sympathetic drive (p. 96) ipratropium for treating sinus bradycardia (p. 108). An unwanted activation of the sympathetic system can result from anxiety, pain, and other emotional stress. In these cases, the heart can be protected from harmful stimulation by psychopharmaceuticals such as benzodiazepines (diazepam and others important in myocardial infarction). 

PARASYMPATHOMIMETICS DRUG DEPENDENCE THERAPIES-BUPROPION t risk of seizures. This risk is marked in elderly people, in patients with a history of seizures, with addiction to opiates/cocaine/stimulants, and in diabetics treated with oral hypoglycaemics or insulin Bupropion is associated with a dose-related risk of seizures. These drugs, which lower seizure threshold, are individually epileptogenic. Additive effects occur when combined Extreme caution. The dose of bupropion should not exceed 450 mg/day (or 150 mg/day in patients with severe hepatic cirrhosis)... 

PARASYMPATHOMIMETICS >- Drugs Acting on the Nervous System, Drugs used to treat neuromuscular diseases and movement disorders ... 

The situation is complex in smooth muscles. Both acetylcholine and the phosphodiesterase inhibitor, l-methyl-3-iso-butylxanthine, elevate cyclic GMP levels, but acetylcholine causes contraction of the muscle preparation whereas the phosphodiesterase inhibitor produces relaxation [69]. In the guinea-pig ileum, the increase in cyclic GMP brought about by a parasympathomimetic drug can be prevented by the inclusion of isoprenaline in the incubation medium however, isoprenaline causes an increase in the concentration of cyclic AMP that can be inhibited by a parasympathomimetic drug [70]. In guinea-pig lung slices, acetylcholine and bradykinin increase both cyclic GMP and cyclic AMP yet indometha-cin and aspirin inhibit the effect on cyclic AMP but not that on cyclic GMP [71]. 

Parasympathomimetic drugs, e.g. bethanechol, car-bachol and distigmine, may be used to stimulate the detrusor when the bladder is h5 otonic, e.g. due to an upper motor neuron lesion. Distigmine, which is an anticholinesterase, is preferred but, as its effect is not sustained, intermittent catheterisation is also needed when the hypotonia is chronic. 

The action of muscarine (16) and acetylcholine on smooth muscle is very similar muscarine is a potent parasympathomimetic drug (Antkowiak and Antkowiak, 1991). The term muscarinic activity is used to describe the direct peripheral action on cholinergic receptors in smooth muscles of the gastrointestinal tract, eye, exocrine glands, and heart (Wang and Joullie, 1984). Much early experimental work with muscarine is unreliable, as many of the materials used were impure. 

From the time of Langley s early experiments, physiologists knew that pilocarpine stimulates secretion of saliva rich in mucus. Stimulation of the parasympathetic nerves to the salivary glands does so as well, and to that extent pilocarpine is a parasympathomimetic drug. When Franklin Hollander reviewed the effect of pilocarpine upon secretion of mucus by the stomach in 1947, he found that reported experiments on human subjects had given rampantly inconsistent results. The same. 

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