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caution where there is a history of epilepsy or concurrent use of NSAIDs which potentiate this effect). Reversible arthropathy has developed in weight-bearing joints in immature animals exposed to quinolones. While the significance for humans is uncertain quinolones should be used only for serious infections and then with caution in children and adolescents. Rupture of tendons, notably the Achilles tendon, has occurred, more in the elderly and those taking corticosteroids concurrently.

Some of the quinolones are potent liver enzyme inhibitors and impair the metabolic inactivation of other drugs including warfarin, theophylline and sulphonylureas, increasing their effect. Magnesium-and aluminium-containing antacids impair the absorption of quinolones from the gastrointestinal tract probably through forming a chelate complex; ferrous sulphate and sucralfate also reduce quino-lone absorption.

Individual members of the group include the following:

Ciprofloxacin (tl/2 3 h) is effective against a range of bacteria but particularly the Gram-negative organisms (see above); it has less activity against Gram-positive bacteria such as Streptococcus pneumoniae and Enterococcus faecalis. Chlamydia and mycoplasma are sensitive but anaerobes are not. Ciprofloxacin is indicated for use in infections of the urinary, gastrointestinal and respiratory tracts, tissue infections, gonorrhoea and septicaemia caused by sensitive organisms. It has proven especially useful for oral therapy of chronic Gram-negative infections such as osteomyelitis and recurrent cholangitis, and for acute exacerbations of Pseudomonas infection in cystic fibrosis. The dose is 250-750 mg 12-hourly by mouth, 200-400 mg 12-hourly i.v. but may be halved when the glomerular filtration rate is < 20 ml/min. Ciprofloxacin impairs the metabolism of theophylline and of warfarin, both of which should be monitored carefully when co-administered.

Acrosoxacin (t'/2 7 h) is effective as a single 300 mg oral dose for gonorrhoea; it is usually reserved for patients who are allergic to penicillin or for organisms that are resistant to that drug.

Cinoxacin (t'/2 2 h) is used for cases of urinary tract infection, but not when renal function is impaired.

Norfloxacin (t'/2 3h) is used for acute or chronic recurrent urinary tract infections. Ofloxacin (tV2 4h) has modestly greater Grampositive activity, but less Gram-negative activity than ciprofloxacin. It is indicated for urinary and respiratory tract infections and gonorrhoea. Nalidixic acid (t1/, 6 h) is now used principally for the prevention of urinary tract infection. It may cause haemolysis in glucose-6-phosphate dehydrogenase deficient subjects.

Others. Levofloxacin (t'/2 7h) has greater activity against Streptococcus pneumoniae than ciprofloxacin and is used for respiratory and urinary tract infection. Moxifloxacin (t1/, 12 h) has strong anti-Gram-positive activity, and may prove useful for respiratory tract infections including those caused by 'atypical' pathogens and penicillin-resistant Streptococcus pneumoniae.

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