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Drug interactions

Adrenergic Antagonist: Epinephrine compounds produce additional IOP reduction when combined with pilocarpine. However, the effect of either combination is less than the additive effect of the two drugs.
Available as E-Pi101 - E-Pi106 concentration from 1 to 6%. This is also true for the alpha 2 agonists apraclonidine and brimonidine.

Adrenergic Antagonists: Timolol has also shown to have a partially additive effect with pilocarpine, which is also true for all the other topical β blockers.
Prostaglandin Agonists: Even though pilocarpine reduces and prostaglandin increases the uvea scleral outflow, there is an additive IOP lowering effect.
Pilocarpine and Physostigmine combination: Available in pilocarpine 2% and 0.25% physostigmine salicylate.
Carbonic Anhydrase Inhibitors: Pilocarpine in combination with CAI reduces the IOP effectively.
Antibiotic and Corticosteroids Ointments: It is supposedly to bring down the efficacy of the drug. However, whether it is due to the drug or the ointment not very sure. But it is advisable to use the drug after 5 minutes.
Other Miotics: Have no adding effect, but may interact with them to bring down the potency.

Side effects

1. Ocular:
1. Periorbital and Conjunctiva.
2. Periocular Pain.
3. Orbicularis muscle spasm and lid twitching Allergic Blepharoconjunctivitis.
4. Ocular Pseudopemphegoid.
5. Irritation.
6. Lacrimation.
7. Punctal stenosis.
8. Vascular Dilatation and conjunctival hyperemia.
2. Cornea:
1. Corneal epithelial staining and vascularisation atypical band keratopathy.
3. Iris and ciliary body:
1. Iris hyperemia.
2. Pigment epithelial cyst formation.
3. Ciliary muscle spasm.
4. Post operative iritis and synechae formation.
4. Lens:
1. Cataract
2. Increase lens thickness - myopia
5. Posterior segment:
1. Retinal hole, detachment and vitreous hemorrhage.
6. Miscellaneous:
1. Inverse glaucoma in a few cases.

Systemic Side Effects: Sweating, salivation and lacrimation, nausea, vomiting and abdominal cramps, weakness, fatigue and muscle spasm, paraesthesia, night mare, depression & delusion, prolonged respiratory paralysis after GA, bronchial spasm, asthma and pulmonary edema.

Other Cholinergic Agents
Carbachol:

1. It is a synthetic derivative of choline.
2. It is dual action parasympathomimetic which produces direct motor end plates stimulation and at pre synaptic receptors to release acetylcholine. They are longer acting than pilocarpine. Thus greater stabilizing effect on diurnal pressure and myopia fluctuations.
3. Comes in 0.75% to 3% concentration administered 3 to 4 times a day.
4. Can be used in patients who are allergic to pilocarpine.

Methacholine:

1. It is also a synthetic derivative rarely used because it is unstable.
2. It was used in 2% to 10% concentration.

Aceclidine:

1. A synthetic agent directly inhibits cholinesterase.
2. Acts directly on the muscarinic end plates.
3. It is weaker than pilocarpine and induces less miosis and accommodation than pilocarpine.

Miotics are avoided in:

1. Eyes with ocular inflammation.
2. Patients who are younger than 40.
3. Patients with central corneal opacities.
4. Moderate to severe myopia.
5. Presence of peripheral retinal degenerations.
6. Eyes with extensive synechial angle closure.
7. Malignant glaucoma.
8. Angle recession glaucoma (miotics causes a paradoxical IOP raise by decreasing uveoscleral outflow).
9. Acute pressure elevation in which the angle closure due to forward displacement of iris lens diaphragm.

Anticholinesterase Agents:
Originally anticholinesterase agents were classified into reversible and irreversible enzyme inhibitors. Now it is better to classify them as weak/short acting and strong/long acting inhibitors.
Physostigmine:

Physostigmine (Eserine) is a short acting inhibitor of cholinesterase. It comes in aqueous solution in the concentration of 0.25% to 1% and is administered every 4 to 6 hours. (Preparation of salicylate & sulfate).
Physostigmine solutions are unstable decompose with Ph changes or after exposure to light.
It reduces IOP by increasing out flow.
Indications are in primary glaucoma's especially aphakia, chronic synechial angle closure glaucoma and following cyclodialysis surgery.

Demacarium Bromide:

1. It is a potent, stable long acting cholinesterase inhibitor.
2. The mechanism of action is similar to that of physostigmine.
3. In addition to the indication already mentioned it is also used in accommodative esotropia.
4. It is available in concentration of 0.125% and 0.25%. It is to be used twice daily because of its prolonged effect.

Ecothiophate Iodide:

1. It is a potent inhibitor of both true cholinesterase and pseudo cholinesterase.
2. It depresses both plasma and erythrocyte cholinesterase.
3. It has a much longer duration of action than pilocarpine and controls IOP in some eyes which are resistant to pilocarpine. (Irreversible)
4. It is available in the concentration of 0.03% to 0.25% and administered every 12 to 48 hours.
5. It is unstable in room temperature and therefore it has to be refrigerated.

Isoflurophate:

1. It is a potent cholinesterase inhibitor and like Ecothiophate it depresses both plasma and erythrocyte cholinesterase.
2. It is usually administered in ointment form in concentration of 0.025% in a polyetheylene mineral gel. It also has a prolonged action so has to be used once or twice daily.
3. Wash hands immediately after administering as in the presence of water it will turn to form hydrofluric acid.
4. Keep ointment tightly closed. It causes allergic reactions and it has to be refrigerated.

Alpha Adrenergic Agonists:

1. Clonidine Apraclonidine
2. Brimonidine Tartrate (Alphagan)
3. Dapiprazole

Clonidine: The first such α2 adrenergic agonist, an imidazole derivative, it is used as an anti hypertensive agent. The drug acts principally on the centrally and peripheral α2 agonist, thereby inhibiting norepinephrine release and suppressing sympathetic outflow to the cardiovascular system.

Applied topically to normal and glaucomatous eye in concentration of 0.125% and 0.5% it lowers IOP for 6 to 8 hours. When it is applied to the eye it is partially absorbed in to the system causing hypotension. Therefore not used alone.

Apraclonidine:It is a relatively selective α2 adrenergic agonist. When installed in the eye it reduces the IOP and has minimal systemic effects.
The mechanism of action is not clearly understood but it is thought to be that β2 receptors stimulation that results in decrease aqueous humor formation.
Dosage: It is available as topical 0.5% ophthalmic solution (5 ml packs) and 1% in a single dose 0.25% pack. Usually dosage is 1 drop before and after laser procedure.
Indications:

1. It is used to control increase of IOP after anterior segment surgery.
2. Acute raise in IOP.
3. And now most recently as adjuvant to other antiglaucoma drugs.

Contra indications: It includes hypersensitivity to the drug and also cardiac disease with untreated arteriovenous block or bradycardia.
Adverse Reactions:  On topical use after laser surgery-­

1. Upper lid elevation.
2. Conjunctival blanching.
3. Burning or itching sensation.
4. Subconjunctival hemorrhage.

Systemic effects: Gastrointestinal reactions, Bradycardia, Vasovagal attack, Palpitation, Orthostatic hypotension, CNS disturbances, Irritability and decrease libido, which are all transient.

 

 

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