Usage
Lidocaine + Phenylephrine + Tropicamide is prescribed for inducing mydriasis (pupil dilation) and providing intraocular anesthesia during cataract surgery in adults. It is administered intracamerally (directly into the anterior chamber of the eye).
Pharmacological Classification:
This combination drug includes three components with distinct classifications:
* Lidocaine: Local anesthetic (amide type)
* Phenylephrine: Mydriatic, sympathomimetic (alpha-adrenergic agonist)
* Tropicamide: Mydriatic, anticholinergic (muscarinic antagonist)
Mechanism of Action:
- Phenylephrine: Stimulates alpha-1 adrenergic receptors on the iris dilator muscle, causing pupil dilation (mydriasis). It also constricts blood vessels, reducing eye redness.
- Tropicamide: Blocks acetylcholine receptors on the iris sphincter and ciliary muscle, further enhancing pupil dilation and inducing cycloplegia (paralysis of accommodation).
- Lidocaine: Inhibits sodium channels in nerve fibers, blocking nerve impulse transmission and providing local anesthesia.
Alternate Names
Mydrane is one of the known brand names for this specific fixed-dose combination for intracameral injection. T+Ultra is another brand name.
How It Works
Pharmacodynamics:
The combination of phenylephrine and tropicamide works synergistically to achieve significant mydriasis. Phenylephrine acts directly on alpha-1 adrenergic receptors of the iris dilator muscle, while tropicamide blocks the opposing action of the iris sphincter muscle by antagonizing muscarinic receptors. Lidocaine stabilizes the neuronal membrane by blocking sodium channels, preventing nerve signal propagation and leading to local anesthesia.
Pharmacokinetics:
The intracameral route of administration results in minimal systemic absorption of all three drugs. Systemic exposure is expected to be negligible, thereby minimizing the risk of systemic side effects.
Mode of Action:
- Receptor Binding: Phenylephrine binds to alpha-1 adrenergic receptors, and tropicamide binds to muscarinic receptors.
- Enzyme Inhibition/Neurotransmitter Modulation: Lidocaine inhibits sodium channels, and tropicamide modulates cholinergic neurotransmission.
- Elimination Pathways: Given the minimal systemic absorption, elimination pathways are not a primary concern with intracameral administration. Some minimal systemic absorption is expected for lidocaine, being eliminated by hepatic metabolism.
Dosage
Standard Dosage
Adults:
A single intracameral injection of 0.2 ml Mydrane at the start of cataract surgery is recommended. No additional doses are recommended due to the risk of increased endothelial cell loss and limited evidence of additional benefit. T+Ultra also recommends 0.2 ml intracamerally per eye.
Children:
The safety and efficacy in children have not been fully established. However, there is growing evidence of safety and efficacy for intracameral use in pediatric cataract surgery.
Special Cases:
- Elderly Patients: No dose adjustment is typically necessary. However, close monitoring for potential systemic effects, particularly cardiovascular effects, is advisable.
- Patients with Renal Impairment: No dose adjustment is necessary due to low systemic exposure.
- Patients with Hepatic Dysfunction: No dose adjustment is necessary due to low systemic exposure of phenylephrine and tropicamide. Lidocaine is primarily metabolized by the liver; however, given its low systemic absorption from intracameral application, dose adjustments should not be necessary.
- Patients with Comorbid Conditions: Caution is warranted in patients with hypertension, cardiovascular disease, hyperthyroidism, or other conditions that might be exacerbated by phenylephrine’s systemic effects (even though these are expected to be minimal).
Clinical Use Cases
The primary clinical use case is cataract surgery to achieve mydriasis and intraocular anesthesia.
Dosage Adjustments
No dose adjustments are typically required based on renal or hepatic impairment. However, patient-specific factors like shallow anterior chamber, history of acute narrow-angle glaucoma, or insufficient pupil dilation should be considered, as these conditions may increase the risk of complications.
Side Effects
Common Side Effects:
- Ocular: Corneal edema, increased intraocular pressure, ocular hyperemia (eye redness), headache.
Rare but Serious Side Effects:
- Ocular: Posterior capsule rupture, cystoid macular edema.
- Systemic effects due to phenylephrine and tropicamide are not expected because of their minimal systemic absorption after intracameral injection. However, some minor side effects such as transient increases in blood pressure, heart rate, and headache can be experienced, particularly in elderly or susceptible patients.
Long-Term Effects:
Long-term side effects are not typically associated with the intracameral administration of this drug combination, given the single dose used during surgery and the minimal systemic absorption.
Adverse Drug Reactions (ADR):
Severe adverse reactions are rare with intracameral use. However, any signs of posterior capsule rupture or cystoid macular edema require urgent medical attention.
Contraindications
- Hypersensitivity to any of the active substances or excipients.
- Hypersensitivity to amide-type local anesthetics.
- Hypersensitivity to atropine derivatives.
Drug Interactions
Due to minimal systemic absorption, drug interactions are unlikely. However, caution should be exercised if monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants (TCAs) or other sympathomimetics are being used concurrently.
Pregnancy and Breastfeeding
This combination should be avoided during pregnancy and breastfeeding due to the lack of safety data for phenylephrine and tropicamide and the potential for lidocaine to be excreted in breast milk.
Drug Profile Summary
- Mechanism of Action: Synergistic mydriasis from phenylephrine (alpha-1 agonist) and tropicamide (anticholinergic), and local anesthesia from lidocaine (sodium channel blocker).
- Side Effects: Primarily ocular: corneal edema, increased IOP, ocular hyperemia. Rare but serious: posterior capsule rupture, cystoid macular edema.
- Contraindications: Hypersensitivity to components, amide-type anesthetics, or atropine derivatives.
- Drug Interactions: Unlikely due to minimal systemic absorption. Caution with MAOIs, TCAs and other sympathomimetics.
- Pregnancy & Breastfeeding: Avoid.
- Dosage: 0.2 ml single intracameral injection for adults. Not established for children.
- Monitoring Parameters: Pupil size, intraocular pressure, corneal clarity, vital signs (especially in elderly or patients with comorbidities).
Popular Combinations
The fixed combination of lidocaine, phenylephrine, and tropicamide is itself a popular combination for cataract surgery. The synergy between phenylephrine and tropicamide is exploited to ensure adequate pupil dilation.
Precautions
- General Precautions: Ensure proper aseptic technique during administration. Pre-operative assessment of pupil dilation with topical mydriatics is recommended.
- Specific Populations:
- Pregnant Women: Avoid.
- Breastfeeding Mothers: Avoid.
- Children & Elderly: Limited safety data for children. Monitor elderly patients for potential systemic effects.
- Lifestyle Considerations: Transient blurred vision may affect driving ability.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Lidocaine + Phenylephrine + Tropicamide in cataract surgery?
A: The standard dose is a single 0.2 ml intracameral injection for adults.
Q2: Can Lidocaine + Phenylephrine + Tropicamide be used in children undergoing cataract surgery?
A: Although safety and efficacy are not fully established, there is increasing evidence to support its use in this population.
Q3: What are the contraindications to using this drug combination?
A: Hypersensitivity to any component, hypersensitivity to amide-type local anesthetics, and hypersensitivity to atropine derivatives are contraindications.
Q4: Are there any significant drug interactions to be aware of?
A: Due to low systemic absorption, drug interactions are unlikely. Caution is still advised with MAOIs, TCAs, and other sympathomimetics.
Q5: Can this combination be used in pregnant or breastfeeding women?
A: No, it is contraindicated during pregnancy and breastfeeding.
Q6: What are the common side effects associated with this drug combination?
A: Common side effects are primarily ocular and include corneal edema, increased IOP, and ocular hyperemia.
Q7: What should be done if the pupil dilation is insufficient after the injection?
A: Additional mydriatics may be necessary, but further injection of this particular fixed combination isn’t typically recommended.
Q8: How long does the anesthetic effect of lidocaine last after intracameral injection?
A: The anesthetic effect typically lasts for the duration of the cataract procedure.
Q9: Are there any specific monitoring parameters for patients receiving this injection?
A: Monitor pupil size, IOP, corneal clarity, and vital signs, particularly in elderly patients and those with comorbidities.
