Understanding Natroba and Its Use
Natroba is a prescription topical suspension with the active ingredient spinosad [1.2.2]. Spinosad is derived from a soil bacterium and works by causing neuronal excitation in insects like lice and scabies mites, leading to their paralysis and death [1.5.2, 1.5.5]. It is approved for treating head lice (pediculosis capitis) in adults and children six months of age and older, and for scabies in adults and children four years of age and older [1.7.3, 1.7.2]. The treatment typically involves applying the suspension to dry hair and scalp for 10 minutes before rinsing for lice, or to the entire body for at least six hours for scabies [1.4.2].
Common Side Effects of Natroba
The most frequently reported side effects of Natroba are localized to the area of application. These reactions are generally mild and may resolve as your body adjusts to the medication. According to clinical trials and prescribing information, these include:
- Application Site Redness (Erythema): This is one of the most common side effects, occurring in about 3% of users during head lice trials [1.6.5].
- Ocular Redness (Eye Redness): If the medication gets near the eyes during scalp application, it can cause redness. This was observed in 2% of trial participants [1.6.5]. It's crucial to avoid contact with the eyes [1.4.2].
- Application Site Irritation: This includes sensations like burning, stinging, or pain at the application site and was reported in about 1% to 3% of users for lice and scabies, respectively [1.2.2].
- Dry Skin: When used for scabies, about 2% of users experienced dry skin [1.2.2]. Less common occurrences of dry scalp or skin have also been reported [1.2.1].
Less Common and Rare Side Effects
While most reactions are mild, some less common side effects have been observed in under 1% of users. These can include:
- Application site exfoliation (peeling skin) [1.8.6]
- Hair loss (alopecia) or thinning of the hair [1.2.1]
- Flaking, itching, swelling, or soreness at the application site [1.2.1]
Serious Side Effects and Important Warnings
Serious side effects from Natroba are rare, but it's important to be aware of them.
Benzyl Alcohol Toxicity: Natroba contains benzyl alcohol as a preservative [1.3.1]. This ingredient can cause serious, life-threatening side effects known as "gasping syndrome" in neonates and low-birth-weight infants if absorbed systemically [1.7.1]. For this reason, Natroba is not recommended for treating head lice in infants below the age of 6 months or for scabies in children under 4 years old [1.7.3, 1.7.2].
Allergic Reaction: Though very rare, a severe allergic reaction (anaphylaxis) is possible. Seek immediate emergency medical help if you experience hives, difficulty breathing, or swelling of the face, lips, tongue, or throat after using Natroba [1.3.2, 1.8.4]. If you experience severe burning, stinging, or irritation, you should rinse the medication off and contact your doctor [1.3.2].
Comparison with Other Lice Treatments
Natroba's side effect profile compares favorably to other common lice treatments. For instance, in clinical trials comparing Natroba to permethrin 1%, application site redness was less frequent with Natroba (3%) than with permethrin (7%) [1.6.5]. Furthermore, unlike some older treatments like lindane, spinosad has not been associated with neurotoxicity such as seizures [1.6.1].
| Feature | Natroba (Spinosad 0.9%) | Permethrin 1% |
|---|---|---|
| Mechanism | Causes neuronal hyperexcitation, paralysis, and death in lice [1.5.2]. | Acts as a neurotoxin to lice [1.6.6]. |
| Application | 10-minute application to dry hair; re-treat in 7 days only if live lice are seen [1.4.2]. | Often requires two applications, 7-10 days apart. |
| Common Side Effects | Application site redness (3%), ocular redness (2%) [1.6.5]. | Application site redness (7%), itching, swelling [1.6.5, 1.3.3]. |
| Age Limit (Lice) | 6 months and older [1.7.3]. | Varies by product, often 2 months and older. |
Conclusion
Natroba (spinosad) is an effective treatment for head lice and scabies with a generally well-tolerated safety profile. The most common side effects are mild and localized skin or eye irritation. The primary safety concern involves the inactive ingredient benzyl alcohol, which restricts its use in very young infants. As with any prescription medication, it is crucial to use Natroba exactly as directed by a healthcare provider and to be aware of the signs of both common and serious potential side effects.
For more information, you can visit the FDA's drug information portal.
