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Ectoparasiticides

The document discusses ectoparasiticides used to treat infestations of lice and scabies, detailing various available drugs such as permethrin, lindane, and ivermectin. It outlines their mechanisms of action, recommended preparations, efficacy, side effects, and usage guidelines. Additionally, it highlights issues related to resistance and systemic toxicity for certain treatments.

Health & Medicine◦
Ectoparasiticides Dr. D. K. Brahma Associate Professor Department of Pharmacology NEIGRIHMS, Shillong
Introduction •Drugs used to kill parasites that live on body surface • Lice – Pediculosis sp. – wingless insects •Mites – Sarcoptes/Acarus scabiei – Arachnids – minute arthropods infesting human hair and skin
Scabies • Highly contagious mite •Burrows through the epidermis, laying eggs – form papules – immenseitching • Secondary infection – antibiotics • Finger webs • Forearm, trunks, genitals and lower legs • Family members • Cross infection andre-infection
Source: Google Images
Pediculosis •The lice thrive on head - P. capitis • Body – P. corporis • Pubic region – P. pubis •Cause itching, suck blood and produce typhus and relapsing fever •The eggs are called nits – attached to hair and clothes by chitin like content
Source: Google Images
Available drugs •Permethrin • Lindane • Benzyl benzoate • Crotamiton • Sulfur • Dicophane (DDT) • Ivermectin
Sulfur ointment • Oldest scabicide – weak pediculocide, antiseptic, fungicide an keratolytic • MOA: Slowly reduced to H2S and SO2on skin and pentathionic acid • pentathionic acid – dissolve the cuticle of mice and kill it • Reactions are carried out by epidermal cells and arthropod themselves • Used as 10% ointment – After a warm scrubbing bath (to open up burrows) – messaged over the entire body (below neck) – 3 consecutive nights – soap water bath on 4th day • Disadvantages: •Messy treatment •Socially unacceptable – interfere with person`s vocation •Repeated applicationneeded
Permethrin • Broad spectrum • Most efficacious and most convenient for both scabies and lice • MOA: Neurological paralysis of insects – delayed depolarization • Toxicity lower in human than lindane • Persists over skin for days but systemic absorption low • 100% cure rate and resistance rare • Effective in lindane non-responsivecases • ADRs: Transient burning, itching, tingling, erythema and rash • Preparations: For scabies – 5% cream, 1$ soap and 5% lotion For head lice: 1% lotion and 5% cream • First choice drug now for scabies and lice
Source: Google Images
Lindane •Gamma benzene hexachloride • broad spectrum – lice and mites •MOA: Penetrates to insects through their chitinous cover and affects nervous system • Head lice – 67% to 92%cure rate and scabies – 84 t0 92% • Lower efficacy than permethrin andresistance • Combines with Benzyl benzoate –100% • Preparations: 1% lotion and cream •Pediculosis: apply over scalp, 12 – 24 hours, shower cap – repeat after one week if needed, avoideyes •For Scabies: Rubbed over body below neck and scrub bath after 12 -24 hours – repeat after one week if needed •Disadvantages: Lipid soluble, gets absorbed, systemic toxicity – CN stimulation, vertigo, convulsion (Children) and cardiac arrhythmia
Lindane •Widely distributed in the body – fats •Metabolized and eliminated and half-life 24 hours • Microsomal enzyme inducer • Less favoured for treatment of scabies • Whole body application – systemic toxicity •Avoid in infants, young children and pregnancy Source: Google Images
Benzyl benzoate • Oily liquid with faint aromatic smell • The emulsion is applied all over the body and 2nd coat on next day – except face and neck • Wash off after 24 hours • Convenient and does not interfere normal works •70 – 100% cure rate in scabies – no systemic toxicity • Contraindicated in children - Neurological symptoms • Preparatin – 25% lotion
Other drugs Crotamiton • Scabicidal, pediculocide and antipruritic • Low cure rate • Lesser systemictoxicity • Preferred in children •10% cream andlotion Dicophane (DDT) • Popular insecticide fpor mosquitoes, flies and pests • Scabies and pediculosis 1 – 2% lotion or cresam • Washed off after 24 hours •Absorbed through skin and – enzyme induction, rashes, tremor etc. • Acts as neurotoxin forarthropods
Ivermectin • Source: Streptomyces avermitilis •Anthelmintic drug – also useful in scabies and pediculosis • SARS Cov 2 ??? •Only orally effective drug – 12 mg single dose – 100% cure rate • AIDS with scabies and head lice also • Replaced DEC – in River blindness • DOC in Strongyloidosis • Bancroftian and brugian filaria Source: Google Images
Ivermectin – contd. MOA: •Nematodes develop tonic paralysis • Acts through special type of Cl- channel present only in invertebrates •No such channel in flukes and tapeworm – ineffective • Potentiation of GABAergic receptors • p-glycoprotein related efflux from brain in human – no action
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