KWELL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for KWELL (KWELL).
Gamma benzene hexachloride (lindane) is an ectoparasiticide and scabicide that acts by penetrating the exoskeleton and disrupting the nervous system of parasites, leading to paralysis and death. It also has toxic effects on the central nervous system of humans.
| Metabolism | Lindane is highly lipophilic and is metabolized in the liver via cytochrome P450 enzymes, primarily CYP2B6 and CYP3A4, to various metabolites including hexachlorocyclohexane isomers. It accumulates in adipose tissue and is slowly released. |
| Excretion | Renal: ~80% (50% as unchanged drug, 30% as inactive metabolites). Biliary/fecal: ~20% (primarily as metabolites). |
| Half-life | Terminal elimination half-life: 11-17 hours (mean 14 hours) in adults; prolonged in hepatic impairment (up to 30 hours) or severe renal impairment (up to 24 hours). |
| Protein binding | 99.5% bound primarily to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Vd: 7-20 L/kg (mean 13 L/kg); indicates extensive tissue distribution (e.g., CNS, adipose). |
| Bioavailability | Oral: 95-100% (due to extensive absorption and low first-pass metabolism). Topical: Systemic absorption is minimal (<10%) with intact skin, but increases with abraded skin or prolonged use. |
| Onset of Action | Oral: 1-2 hours; Topical (cream/lotion): 2-4 hours (pruritus relief); Parenteral (IM/SC): 1-2 hours. |
| Duration of Action | Oral: 8-12 hours (clinical effect); Topical: 8-12 hours (single application), residual antipruritic effect up to 24 hours; Parenteral: 12-24 hours. |
Adults: Apply 1% permethrin cream (Kwell) topically to all skin areas from neck to toes, leave on for 8-14 hours, then wash off. Single application is usually sufficient; repeat in 7 days if live lice persist.
| Dosage form | SHAMPOO |
| Renal impairment | No dose adjustment required for renal impairment; systemic absorption is minimal (<2%). |
| Liver impairment | No dose adjustment required for hepatic impairment as drug is metabolized rapidly in skin and has low systemic bioavailability. |
| Pediatric use | Infants ≥2 months and children: Apply 1% permethrin cream to all skin areas (including scalp for infants), leave on for 8-14 hours, then wash off. Single application; repeat in 7 days if needed. For infants <2 months: use only under physician guidance; no established dose. |
| Geriatric use | Same as adult dosing. No specific geriatric adjustments; use caution with extensive skin breakdown due to potential increased absorption. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for KWELL (KWELL).
| Breastfeeding | M/P ratio approximately 1.2; carbamazepine excreted into breast milk at levels ~25% of maternal serum. Infant serum concentrations can reach 6-12% of maternal levels. AAP considers compatible with breastfeeding but monitor infant for drowsiness, poor suck, and hepatic effects. Avoid in premature neonates or infants with hepatic disease. |
| Teratogenic Risk | FDA Pregnancy Category C. In first trimester, risk of neural tube defects and congenital anomalies based on animal studies; human data limited but suggests low teratogenic risk at standard doses. Second and third trimesters: no increased risk of major malformations; potential for fetal growth restriction and preterm birth with high doses (≥800 mg/day). Carbamazepine crosses placenta; fetal antiepileptic drug exposure associated with reduced IQ at age 3. |
■ FDA Black Box Warning
Lindane is contraindicated in premature infants and individuals with known uncontrolled seizure disorders. It should be used with caution in infants, children, elderly, and patients with other skin conditions (e.g., atopic dermatitis, psoriasis) as it may increase systemic absorption and risk of neurotoxicity. Seizures and deaths have been reported with lindane use. Second-line therapy for scabies and lice when other treatments have failed or cannot be tolerated.
| Serious Effects |
Hypersensitivity to lindane or any component of the formulation; premature infants; uncontrolled seizure disorders; pregnant women (category C; may cause fetal harm); nursing mothers (use with caution); patients with known seizure disorders; application to face, mucous membranes, or urethral meatus
| Precautions | Neurotoxicity (seizures, dizziness, headache), especially in patients with low body weight, infants, children, elderly, and those with a history of seizures. Avoid contact with eyes and mucous membranes. Do not apply to open wounds or broken skin. Use only as a second-line treatment. Do not use in patients with crusted scabies or extensive dermatitis due to increased absorption. |
Loading safety data…
| Fetal Monitoring | Maternal: serum drug levels (therapeutic range 4-12 mcg/mL), LFTs, CBC with platelets, electrolytes, and thyroid function at baseline and periodically. Fetal/neonatal: ultrasound for structural anomalies (first trimester), serial growth scans in third trimester if high-dose therapy; neonatal monitoring for withdrawal syndrome (tremors, hypertonia, feeding difficulties) and coagulopathy (vitamin K supplementation at delivery). |
| Fertility Effects | Limited data; possible reduction in fertility due to hormonal alterations (increases SHBG, reduces free testosterone). Menstrual irregularities and anovulation reported in women; reversible upon discontinuation. No evidence of permanent effect on spermatogenesis in males. |