Magnesium hydroxide Ciprofloxacin

Bind to other drugs that are administered within 1 or 2 hours of the antacid, This process results in reduced availability of the co-administered drug for absorption, For example, the chelation of tetracyclines (e.g, tetracycline, doxycycline) will decrease their absorption by up to 90%, Avery similar process - precipitation - occurs with drugs such as quinine with aluminium and magnesium hydroxide preparations, which results in a decreased absorption of quinine, It has to be noted that the absorption of fluoroquinolones (e g. ciprofloxacin, norfloxacin, ofloxacin, enoxacin, perfloxacin i will be decreased by 60-75% if they are co-administered with divalent and trivalent cations. Patients are recommended not to take these divalent and trivalent cationic preparations until fluoroquinolone therapy is discontinued. 

When 12 healthy subjeets were given ciprofloxacin 750 mg with two didanosine plaeebo tablets (i.e. all of the antacid additives but no didanosine), the ciprofloxacin AUC and maximum serum levels were reduced by 98% and 93%, respectively. The antacids in this formulation were dihy-droxyaluminium sodium carbonate and magnesium hydroxide. 

Didanosine is extremely acid labile at pH values below 3, so one ofthe formulations contains buffering agents (dihydroxyaluminium sodium carbonate and magnesium hydroxide) to keep the pH as high as possible to minimise the acid-induced hydrolysis. Ciprofloxacin forms insoluble non-absorbable chelates with these metallic ions in the buffer so that its bioavailability is markedly reduced. See also Quinolones + Antacids or Calcium compounds , p.328. 

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