8-Hydroxyquinolines

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Chapter: Essential pharmacology : Antiamoebic And Other Antiprotozoal Drugs

The 8-hydroxyquinolines were widely employed in the past: have similar properties; are active against Entamoeba, Giardia, Trichomonas, some fungi (dermatophytes, Candida) and some bacteria.


8-HYDROXYQUINOLINES

 

The 8-hydroxyquinolines were widely employed in the past: have similar properties; are active against Entamoeba, Giardia, Trichomonas, some fungi (dermatophytes, Candida) and some bacteria. They kill the cyst forming trophozoites in the intestine, but do not have tissue amoebicidal action. Like diloxanide furoate, they are not very effective in acute amoebic dysentery but afford relief in chronic intestinal amoebiasis. Their efficacy in eradicating cysts from asymptomatic carriers is rated lower than that of diloxanide furoate. They are totally valueless in extraintestinal amoebiasis.

 

Absorption of 8hydroxyquinolines from the intestine is variable. Least absorbed (10–30%) and probably safer drug is di-iodohydroxyquin. The absorbed fraction is conjugated in liver with glucuronic acid and sulfate and excreted in urine; t½ ~12 hours. Therapeutic concentrations are not attained in the intestinal wall or in liver. The unabsorbed part reaches lower bowel and acts on luminal cycle of amoebae.

 

These drugs have been widely and injudiciously used for the prophylaxis and treatment of nonspecific diarrhoeas, traveller’s diarrhoea, dietary indiscretion, etc. An apparent therapeutic effect is frequently noted in mild cases, probably because most such conditions are self-limiting any way. This has fostered repeated and prolonged usage, which is irrational and may be harmful.

 

8-Hydroxyquinolines are well tolerated: produce few side effects—nausea, transient loose and green stools, pruritus, etc. Goiter has been reported after prolonged medication.

 

Iodism (furunculosis, inflammation of mucous membranes) may occur due to chronic iodine overload. Individuals sensitive to iodine may experience acute reaction with chills, fever, angioedema and cutaneous haemorrhages.

 

Prolonged/repeated use of relatively high doses of quiniodochlor caused a neuropathic syndrome called ‘subacute myelooptic neuropathy’ (SMON) in Japan in an epidemic form, affecting several thousand people in 1970. Other 8hydroxyquinolines have also produced neuropathy and visual impairment. However, despite widespread use in the past, only sporadic and unconfirmed cases have been reported from India. These drugs have been banned in Japan and few other countries, but in India they are banned only for pediatric patients, because their use for chronic diarrhoeas in children has caused blindness. Their fixed dose combinations, except those used for diarrhoea, dysentery and for external application are banned in India, and a cautionary note is inserted that use of high doses for more than 14 days can cause neuritis and optic damage.

 

8-Hydroxyquinolines are cheap and have good patient acceptability. They may be employed in intestinal amoebiasis as alternative to diloxanide furoate.

 

Other uses are—giardiasis; local treatment of monilial and trichomonas vaginitis, fungal and bacterial skin infections.

 

Quniodochlor (Iodochlorohydroxyquin, Clioquinol): 250– 500 mg TDS;

 

ENTEROQUINOL, QUINOFORM, DEQUINOL 250 mg tab.

 

Diiodohydroxyquin (Iodoquinol): 650 mg TDS; DIODOQUIN 650 mg tab, 210 mg/5 ml susp.

 

Tetracyclines

 

They directly inhibit amoebae only at higher concentrations. The older tetracyclines are incompletely absorbed in the small intestine, reach the colon in large amounts and inhibit the bacterial flora with which Entamoebae live symbiotically. Thus, they indirectly reduce proliferation of entamoebae in the colon and are especially valuable in chronic, difficult to treat cases with only the luminal cycle and little mucosal invasion. Tetracyclines have an adjuvant role in the management of such cases, in conjunction with a more efficacious luminal amoebicide. They are not good for acute dysentery and for hepatic amoebiasis.

 

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