Contraindications

Cholinergic agonists, such as pilocarpine and carbachol, should be avoided in conditions where pupillary constriction and intraocular vascular congestion are undesirable, such as in acute iritis or visually significant lens changes. These agents should also be avoided where there is a history of, or predisposition to, retinal detachment, or a proven sensitivity to these agents, or, for the membrane delivery dosage form, the presence of acute infectious conjunctivitis or keratitis. Patients with severe asthma, bronchial obstruction, acute cardiac failure, active peptic ulcer, hyper-thyroidism, gastrointestinal spasm, urinary tract obstruction, Parkinsonism, recent myocardial infarction, and, perhaps, poorly controlled blood pressure disorders are at risk for having these conditions exacerbated by cholinergic agonists.3

Schlemm's Scleral Tendon

Schlemm's Scleral Tendon

Trabecular Ciliary lamellae muscle

Figure 5.3. Architecture of cribriform region and ciliary muscle tendon attachments in humans and higher monkeys. One type of tendon connects the anterior muscle tips to the scleral spur. A second type of tendon traverses the entire meshwork to insert into the corneal stroma. A third tendon type fans out in brushlike endings within the mesh and, via an elastic network and connecting fibrils, attaches to the juxtacanalicular and innerwall region. Redrawn with permission from Rohen JW. The evolution of the primate eye in relation to the problem of glaucoma. In: Lutjen-Drecoll E, ed. Basic Aspects of Glaucoma Research. Stuttgart: Schattauer Verlag; 1982:3-33.

Trabecular Ciliary lamellae muscle

Figure 5.3. Architecture of cribriform region and ciliary muscle tendon attachments in humans and higher monkeys. One type of tendon connects the anterior muscle tips to the scleral spur. A second type of tendon traverses the entire meshwork to insert into the corneal stroma. A third tendon type fans out in brushlike endings within the mesh and, via an elastic network and connecting fibrils, attaches to the juxtacanalicular and innerwall region. Redrawn with permission from Rohen JW. The evolution of the primate eye in relation to the problem of glaucoma. In: Lutjen-Drecoll E, ed. Basic Aspects of Glaucoma Research. Stuttgart: Schattauer Verlag; 1982:3-33.

Caution should be exercised in children because of lower body weight and greater likelihood of accidental systemic overdosage. Carbachol, which is a more complete agonist than pilocarpine, is more likely to produce systemic effects, although these are still extremely rare.

These risks are all increased when the powerful indirect-acting cholinergics, such as echothiophate and demecarium, are used. Some of these drugs are no longer available in the United States. Additional problems may arise in patients with the following conditions:

1. Down's syndrome: echothiophate may cause hyperactivity

2. Epilepsy

3. Gastrointestinal disturbances

4. Narrow anterior chamber angle: precipitation of acute angle closure by pupillary block secondary to the strong miosis and iridial congestion, which can also occur with high concentrations of direct-acting cholinomimetics; indeed, two drops of pilocarpine 2% will induce adequate miosis in most instances, to help reverse acute angle-closure glaucoma

Figure 5.4. Outflow facility and facility responses to intravenous (IV) and intracameral (IC) pilocarpine hydrochloride (Pilo) before and after unilateral ciliary muscle disinsertion in a typical bilaterally iridectomized cynomolgus monkey. Intramuscular (IM) atropine sulfate (Atr) was given before each perfusion to minimize systemic effects of intravenous pilocarpine. Note the absence of facility increase following intravenous and intracameral pilocarpine in the iridectomized and disinserted eye (orange circles), as opposed to large facility increases in opposite iridectomized-only eye (blue circles). Redrawn with permission from Kaufman PL, Barany EH. Loss of acute pilocarpine effect on outflow facility following surgical disinsertion and retrodisplacement of the ciliary muscle from the scleral spur in the cynomolgus monkey. Invest Ophthalmol. 1976;15:793-807. Copyright 1976 Association for Research in Vision and Ophthalmology.

Figure 5.4. Outflow facility and facility responses to intravenous (IV) and intracameral (IC) pilocarpine hydrochloride (Pilo) before and after unilateral ciliary muscle disinsertion in a typical bilaterally iridectomized cynomolgus monkey. Intramuscular (IM) atropine sulfate (Atr) was given before each perfusion to minimize systemic effects of intravenous pilocarpine. Note the absence of facility increase following intravenous and intracameral pilocarpine in the iridectomized and disinserted eye (orange circles), as opposed to large facility increases in opposite iridectomized-only eye (blue circles). Redrawn with permission from Kaufman PL, Barany EH. Loss of acute pilocarpine effect on outflow facility following surgical disinsertion and retrodisplacement of the ciliary muscle from the scleral spur in the cynomolgus monkey. Invest Ophthalmol. 1976;15:793-807. Copyright 1976 Association for Research in Vision and Ophthalmology.

5. Intraocular surgery: may be complicated by severe uveitis

6. Marked vagotonia

Echothiophate and demecarium may decrease plasma concentrations or activity of pseudocholinesterase, the enzyme that metabolizes succinylcholine, thereby enhancing the neuromuscular blockade effect of depolarizing muscle relaxants, such as succinylcholine, when they are used concurrently. In this case, cardiovascular collapse, increased or prolonged respiratory depression, or paralysis may occur. The effects of this interaction may persist for weeks or months after echothiophate has been discontinued.

Caution is recommended in administering edrophonium to patients with symptoms of myasthenic weakness who are also using echothiophate. Symptoms of cholinergic overdosage crisis—sweating, salivation, nausea, tremors, slowing of the pulse, and decrease in blood pressure—may be similar to those occurring with myasthenic crisis (underdosage), and the patient's condition may be worsened by use of edrophonium.

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