Phenylephrine
Mechanism :
It is a selective alpha 1 agonist that causes vasoconstriction. It also vasoconstriction in the eye and thus reduces intra-ocular tension. It is used as eyedrops to cause mydriasis for ophthalmic examinations. It is also used as a nasal decongestant. It is also used in the treatment of hypotension.
Indication :
- Decongestant for reducing nasal/sinus stuffiness
- Hypotension
- Ocular procedures
Contraindications :
MAO inhibitor use w/in 14 days, Urinary retention, CAD, Uncontrolled or severe HTN.
Caution if HTN, arrhythmias, cardiovascular disease, diabetes mellitus, angle-closure glaucoma, hyperthyroidism, renal impairment, PKU (phenylalanine-containing forms), in pts <6 yo.
Dosing :
Mild-Moderate Hypotension:
0.1-0.5 mg IV every 10-15 mins; maximum dose: 0.5 mg/dose IV or 2-5 mg SC/IM every 1-2 hours as and when required initially; followed by 1-10 mg maintenance dose.
Severe hypotension:
100-150 mcg/dose (IV bolus) every 5-10 mins as and when required; maximum dose: 500 mcg or 100-180 mcg/min (IV infusion); titrate to achieve desired response or 0.5 mcg/kg/min and titrate to achieve desired response.
Ocular procedures:
<1 year:
1 drop of 2.5% solution 15-20 mins before procedure for mydriasis
≥1 year:
Ophthalmoscopy: 1-2 drops of 2.5% or 10% solution, may be repeated after 10-60 mins, No cyclopegia; mydriasis persists for >3 hours.
Ocular surgery: 1-2 drops of 2.5-10% solution 30-60 mins before operation.
Irrigation:
1-2 drops of 0.12% solution into the affected eye four times daily; can be given for 72 hour (Maximum).
Nasal Congestion:
4 to 5 years: 2.5 mg PO every 4 to 6 hours as needed. Max: 15 mg/day PO.
6 to 11 years: 5 mg PO every 4 to 6 hours as needed. Max: 30 mg/day PO.
>12 years: 10 mg PO every 4 hours. Max: 60 mg/24 hours.
Intranasal drops (1% nasal drops or 0.5% and 1% nasal spray):
2-5 years: Apply 2 to 3 drops (0.125% nasal drops) to each nostril every 4 hours.
>6 years: Apply 0.25% nasal spray: 2 to 3 sprays to each nostril every 4 hours.
>12 years: Apply 2 to 3 sprays or drops to each nostril every 4 hours.
Use beyond 3 days is not recommended.
Adverse Effect :
As eye drops may cause blurring of near vision. As nasal decongestant may cause sneezing, itching and burning. Systemically can cause hypertension, angina, bradycardia, myocardial infarction, subarachnoid haemorrhage, IV extravasation and necrosis. Hypersensitivity and photosensitivity.
Interaction :
Contraindicated:
Isocarboxazid, phenelzine, procarbazine, selegiline transdermal, tranylcypromine.
Hepatic Dose :
Dose adjustment guidelines are not available, there may be decreased responsiveness to the drug due to hepatic impairment, so higher dose may be required to be given, however begin therapy in the recommended dosage range.