What dose of ivermectin is recommended for a 195-pound patient suspected of having scabies?

Ivermectin Dosing for Scabies in a 195-Pound Patient

For this 195-pound (88.6 kg) patient with suspected scabies, order ivermectin 200 μg/kg orally, which equals approximately 17.7 mg (typically rounded to 18 mg using available tablet strengths), with a mandatory second dose in 2 weeks. 1, 2

Dose Calculation and Administration

• The standard dose is 200 μg/kg body weight 1, 2, 3
• For 195 lbs (88.6 kg): 88.6 kg × 200 μg/kg = 17,720 μg = 17.7 mg 1
• Ivermectin must be taken with food to increase bioavailability and enhance penetration into the epidermis 1, 2
• A second dose after 14 days is essential because ivermectin has limited ovicidal activity and may not kill eggs present at initial treatment 1, 2, 4

Why Two Doses Are Critical

• Single-dose regimens show suboptimal cure rates; studies demonstrate that 80% of patients required at least two doses for complete resolution 5
• The two-week interval allows newly hatched mites from surviving eggs to mature before the second treatment eliminates them 1, 4
• Failure to administer the second dose is a common treatment pitfall that leads to persistent infection 2

Important Patient Counseling Points

• Pruritus and rash may persist for up to 2 weeks after successful treatment due to ongoing hypersensitivity reaction to dead mites 2
• Approximately 48% of patients may develop new eczematous eruptions within 72 hours of ivermectin administration, which should be treated with topical corticosteroids and emollients 5
• All close contacts, household members, and sexual partners from the preceding month must be treated simultaneously, even if asymptomatic, to prevent reinfection 1, 2

Environmental Decontamination

• Machine wash and dry all bedding and clothing using hot cycles, or remove from body contact for at least 72 hours 1, 2
• Fumigation of living areas is unnecessary 1, 2

Special Considerations and Contraindications

• No dosage adjustment needed for renal impairment 1, 2
• Safety in severe liver disease is not established; use with caution 1, 6
• If crusted (Norwegian) scabies is present (heavily crusted lesions suggesting high mite burden), combination therapy is required: ivermectin 200 μg/kg on days 1,2,8,9, and 15 PLUS daily permethrin 5% cream for 7 days, then twice weekly 2

When to Reassess

• Evaluate after 2 weeks; if live mites are observed or symptoms worsen (rather than just persist), consider treatment failure or reinfection 2
• Persistent symptoms beyond 2 weeks warrant investigation for untreated contacts, inadequate environmental decontamination, or alternative diagnoses 2