Usage
Phenylephrine + Tropicamide is prescribed to induce mydriasis (pupil dilation) and cycloplegia (paralysis of accommodation) for ophthalmic examinations and procedures. This allows for better visualization of the internal eye structures. It is also used in some pre- and postoperative states and as an adjunct in treating anterior uveitis. It may also be used to temporarily lower intraocular pressure in glaucoma.
Its pharmacological classifications include:
- Mydriatic: Dilates the pupil.
- Cycloplegic: Paralyzes the ciliary muscle, inhibiting accommodation.
- Sympathomimetic (Phenylephrine): Mimics the effects of the sympathetic nervous system.
- Anticholinergic/Antimuscarinic (Tropicamide): Blocks the action of acetylcholine at muscarinic receptors.
Alternate Names
This combination is often referred to as Tropicamide/Phenylephrine ophthalmic.
Brand Names: Mydcombi, Phenyltrope, Tropigen Plus, Mydrephrine-P
How It Works
Pharmacodynamics:
- Phenylephrine: Stimulates alpha-1 adrenergic receptors in the iris dilator muscle, causing pupillary dilation. It also constricts conjunctival arterioles.
- Tropicamide: Blocks muscarinic receptors in the iris sphincter muscle and ciliary muscle, causing pupillary dilation and paralysis of accommodation.
Pharmacokinetics:
- Absorption: Topically applied, with limited systemic absorption. Systemic absorption can be minimized by applying pressure to the lacrimal sac for 60 seconds after instillation.
- Metabolism: Limited information is available on the metabolism of the ophthalmic formulation.
- Elimination: Primarily through renal excretion (Phenylephrine), though the elimination pathway of Tropicamide in ophthalmic form is not well established.
Mode of Action:
- Phenylephrine: Acts as an alpha-1 adrenergic receptor agonist, leading to contraction of the iris dilator muscle.
- Tropicamide: Acts as a competitive antagonist at muscarinic receptors, preventing acetylcholine from binding and causing contraction of the sphincter pupillae and ciliary muscle.
Receptor Binding, Enzyme Inhibition or Neurotransmitter Modulation:
- Phenylephrine: Binds to alpha-1 adrenergic receptors.
- Tropicamide: Blocks muscarinic cholinergic receptors.
Dosage
Standard Dosage
Adults:
One to two drops instilled into the affected eye(s). May repeat after 5 minutes if needed. For prolonged effect, an additional drop may be instilled after 20-30 minutes.
Children:
One drop instilled into each eye to be dilated; repeat after 5 minutes if necessary. Not to exceed 3 sprays/eye per day. Use with caution in children as CNS and cardiovascular side effects are possible. Not recommended for children under 1 year of age.
Special Cases:
- Elderly Patients: Use with caution, monitoring for cardiovascular effects.
- Patients with Renal Impairment: No dosage adjustment is generally recommended.
- Patients with Hepatic Dysfunction: No dosage adjustment is generally recommended.
- Patients with Comorbid Conditions: Use with caution in patients with glaucoma, cardiovascular disease, hypertension, diabetes, hyperthyroidism.
Clinical Use Cases
Dosage is generally the same across clinical settings involving ophthalmic examinations:
- Intubation: Not applicable (used for ophthalmic procedures).
- Surgical Procedures (Ophthalmic): As directed by the surgeon, usually preoperatively.
- Mechanical Ventilation: Not applicable.
- Intensive Care Unit (ICU) Use: Not applicable.
- Emergency Situations: Not applicable.
Side Effects
Common Side Effects:
Transient stinging, blurred vision, increased sensitivity to light (photophobia), eye pain, eye irritation, burning or stinging sensation in the eye, dry mouth, increased intraocular pressure.
Rare but Serious Side Effects:
Allergic reactions (rash, hives, itching, swelling), angle-closure glaucoma (sudden rise in eye pressure), cardiovascular effects (arrhythmias, hypertension, coronary artery spasm), CNS effects (hallucinations, mood changes, unusual behavior, especially in children).
Long-Term Effects:
With appropriate use for diagnostic purposes, long-term effects are unlikely. Prolonged administration can lead to local irritation, hyperemia, edema, and conjunctivitis.
Contraindications
Hypersensitivity to tropicamide, phenylephrine, or any component of the formulation. Narrow-angle glaucoma. Use of 10% Phenylephrine is contraindicated in patients with hypertension, thyrotoxicosis and in children less than 1 year.
Drug Interactions
- Atropine-like drugs: May enhance pressor effects and induce tachycardia.
- Cholinergic agonists and ophthalmic cholinesterase inhibitors (e.g., carbachol, pilocarpine): Tropicamide may interfere with their antihypertensive action.
- Potent inhalation anesthetic agents: Phenylephrine may potentiate cardiovascular depressant effects.
- MAO inhibitors (e.g., isocarboxazid, linezolid): May increase effects of phenylephrine.
- Antihypertensives, antidepressants (e.g., tricyclics), antiarrhythmics (e.g., quinidine): Potential for interactions with phenylephrine.
Pregnancy and Breastfeeding
Pregnancy Safety: Limited data available. Use only if clearly needed and the benefits outweigh the risks. May cause vasoconstriction which can be detrimental.
Breastfeeding: Not known if excreted in human milk. Exercise caution if administering to a nursing woman.
Drug Profile Summary
- Mechanism of Action: Phenylephrine: Alpha-1 adrenergic agonist causing mydriasis. Tropicamide: Muscarinic antagonist causing mydriasis and cycloplegia.
- Side Effects: Stinging, blurred vision, photophobia, dry mouth, increased intraocular pressure; rarely allergic reactions, angle-closure glaucoma, cardiovascular effects, CNS effects.
- Contraindications: Hypersensitivity, narrow-angle glaucoma; 10% phenylephrine contraindicated in hypertension, thyrotoxicosis, and children <1 year.
- Drug Interactions: Atropine-like drugs, cholinergic agonists, inhalation anesthetics, MAO inhibitors, antihypertensives.
- Pregnancy & Breastfeeding: Limited data; use with caution if benefits outweigh risks.
- Dosage: Adults and children >1 year: 1-2 drops, repeat after 5 minutes if needed.
- Monitoring Parameters: Pupil size, intraocular pressure, heart rate, blood pressure (especially in patients with cardiovascular disease).
Popular Combinations
Often used in combination with cyclopentolate for enhanced mydriasis and cycloplegia, especially in pediatric patients.
Precautions
Screen for allergies, glaucoma, cardiovascular disease, and other relevant conditions. Use caution in children, pregnant/breastfeeding women, and elderly patients. Advise patients to avoid tasks requiring clear vision until the effects wear off.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Phenylephrine + Tropicamide?
A: Adults and children >1 year: 1-2 drops in the affected eye(s), repeated after 5 minutes if needed. For prolonged effect, an additional drop may be instilled after 20-30 minutes. Not recommended for children under 1 year.
Q2: How long does the effect of Phenylephrine + Tropicamide last?
A: The mydriatic and cycloplegic effects typically last for 3-8 hours, although this can vary depending on individual factors like eye pigmentation.
Q3: What are the common side effects?
A: Transient stinging, blurred vision, increased sensitivity to light, dry mouth, and increased intraocular pressure are common.
Q4: Are there any serious side effects I should be aware of?
A: Rarely, allergic reactions, angle-closure glaucoma, cardiovascular effects (arrhythmias, hypertension), and CNS effects (especially in children) can occur.
Q5: Can this medication be used during pregnancy or breastfeeding?
A: Data are limited. Use with caution only if the benefits clearly outweigh potential risks. Discuss with the patient and consider alternative approaches if possible.
Q6: What are the contraindications for using this medication?
A: Contraindications include hypersensitivity to the components and narrow-angle glaucoma. The 10% Phenylephrine solution is contraindicated in patients with hypertension, thyrotoxicosis and children under 1 year.
Q7: Are there any drug interactions I should be aware of?
A: Yes, interactions can occur with atropine-like drugs, cholinergic agonists, inhalation anesthetics, and certain antidepressants and antihypertensives.
Q8: How should I advise patients after administering this medication?
A: Advise patients to avoid tasks requiring clear vision until the effects wear off, protect their eyes from bright light by wearing sunglasses, and report any severe or persistent side effects.
Q9: Can Phenylephrine + Tropicamide be used in infants?
A: Use with caution in infants and children, as they may be more susceptible to systemic side effects, particularly CNS disturbances. Not recommended for use in children less than 1 year of age.
Q10: What precautions should be taken when administering this drug?
A: Apply pressure to the lacrimal sac for 60 seconds after instillation to minimize systemic absorption. Monitor for changes in pupil size, intraocular pressure, heart rate, and blood pressure.
