Neomycin and polymyxin B sulfates are antibiotics frequently used in combination to treat or prevent various bacterial infections. This dual-action approach targets a broader spectrum of bacteria, with neomycin being an aminoglycoside and polymyxin B being a polypeptide. While effective, they are associated with a range of side effects, from common local irritations to rare but serious systemic toxicities, particularly with prolonged use, high dosage, or systemic absorption. The specific side effects can vary depending on the route of administration, such as topical creams, ear drops (otic), or eye drops (ophthalmic).
Allergic and Skin-Related Side Effects
Topical preparations containing neomycin and polymyxin B are a common cause of skin-related side effects. The most significant concern is allergic sensitization, particularly due to neomycin. Allergic contact dermatitis may manifest as itching, redness, swelling, and rash at the application site, sometimes presenting with a follicular pattern. For some individuals, this can complicate the healing process of the underlying condition.
- Common Reactions: Burning, itching, redness, or a rash at the application site.
- Severe Allergic Reactions: Hives, swelling of the face, lips, tongue, or throat, and difficulty breathing, which requires immediate medical attention.
- Systemic Contact Dermatitis: In individuals sensitized to topical neomycin, taking it orally may trigger a systemic skin reaction, though this is rare.
Serious Systemic Toxicities
While typically used topically, systemic absorption of these antibiotics can occur, especially with large-area application, prolonged use, or on damaged skin. This can lead to serious toxicities, including:
Ototoxicity (Ear Toxicity)
Both neomycin and polymyxin B have ototoxic potential, meaning they can harm the inner ear, with neomycin being especially cochleotoxic (affecting hearing). The risk is significantly higher with systemic absorption or when used as ear drops, particularly if there is a perforated eardrum.
- Symptoms include: Hearing loss (which can be permanent), a ringing or buzzing sound in the ears (tinnitus), feeling of fullness in the ears, and loss of balance or dizziness.
- Risk Factors: Prolonged use (over 10 days), pre-existing hearing or kidney problems, and concurrent use of other ototoxic drugs increase the risk.
Nephrotoxicity (Kidney Toxicity)
Kidney damage can occur if the antibiotics are absorbed systemically. Neomycin and polymyxin B are both nephrotoxic, and their effects can be additive. Signs of nephrotoxicity include changes in urination frequency or volume, and blood in the urine.
Neuromuscular Blockade
In rare cases of significant systemic absorption, these antibiotics can cause neuromuscular paralysis, which may lead to respiratory arrest. This risk is heightened when used alongside other neuromuscular-blocking agents, such as during anesthesia.
Superinfection
Similar to other antibiotic treatments, prolonged use of neomycin and polymyxin B can disrupt the normal balance of microorganisms, leading to an overgrowth of non-susceptible organisms, such as fungi. If the infection does not improve or worsens after a few days, a healthcare provider should be consulted to rule out superinfection.
Side Effects by Administration Route
The manifestation of side effects is dependent on where the medication is applied.
Ophthalmic (Eye Drops/Ointment)
- Common: Eye irritation, itching, burning, stinging, or redness.
- Serious: Eye pain, changes in vision (including blurred vision or blindness), increased intraocular pressure, glaucoma, or cataracts with prolonged use (especially if combined with corticosteroids).
Otic (Ear Drops)
- Common: Burning or stinging, dryness, or scaling of the skin.
- Serious: Hearing loss and balance issues are significant concerns, especially if the eardrum is perforated.
Topical (Creams/Ointments)
- Common: Allergic contact dermatitis (rash, itching, redness), burning, or stinging.
- Other: Skin thinning, unwanted hair growth, or changes in skin color, particularly when combined with corticosteroids.
Neomycin and Polymyxin B Side Effect Comparison
| Side Effect Category | Topical Use (Skin) | Otic Use (Ear) | Ophthalmic Use (Eye) |
|---|---|---|---|
| Common Irritation | Itching, burning, rash, redness, swelling | Burning, stinging, itching, dryness | Burning, itching, redness, irritation, discharge |
| Allergic Reaction | Frequent. Allergic contact dermatitis, hives | Itching, swelling, rash | Itching, swelling, rash |
| Toxicity Risk | Moderate. Systemic absorption can occur if applied to large, broken areas | High. Risk of ototoxicity (hearing loss, dizziness) if eardrum is perforated | Low. Primarily local eye irritation |
| Serious Complications | Systemic allergic reactions, superinfection | Ototoxicity (potentially permanent hearing loss) | Eye pain, change in vision, glaucoma (with steroids), delayed wound healing |
Precautions for Using Neomycin and Polymyxin B Sulfates
To minimize risks, follow these precautions and consult your doctor:
- Limited Duration: Do not use for more than 10 days unless directed by a doctor.
- Renal Impairment: Patients with kidney problems are at higher risk for systemic toxicity due to impaired drug clearance.
- Perforated Eardrum: Avoid using otic preparations if a perforated eardrum is present to prevent potential inner ear damage.
- Superinfection: If symptoms do not improve or worsen, consult a healthcare provider. An overgrowth of non-susceptible organisms, like fungi, may be the cause.
- Allergy History: Individuals with a known hypersensitivity to neomycin, polymyxins, or other aminoglycosides should avoid these medications.
Conclusion
Neomycin and polymyxin B sulfates are effective antibiotic agents for targeted bacterial infections when used correctly. However, their use is not without risks, particularly concerning the potential for allergic reactions and severe systemic toxicities like ototoxicity and nephrotoxicity, especially with systemic absorption. Adherence to proper administration, duration limits, and careful patient monitoring are critical for preventing adverse events. If you experience any severe side effects, worsening symptoms, or signs of allergic reaction, seek immediate medical attention. Always discuss potential risks and benefits with your healthcare provider before use.
For more detailed prescribing information, refer to official drug resources such as the FDA DailyMed website.
