Doxycycline Antacids

Adverse effects with the tetracyclines include gastrointestinal upset drug interactions with dairy products, antacids, and iron and phototoxicity. Minocycline can also cause vestibular complications (headache and dizziness) and skin discoloration that is not typical with tetracycline and doxycycline.16... 

Doxycycline 100 mg twice daily Avoid in children under 8 years Can cause photosensitivity, gastrointestinal problems, tooth staining in young children many drug-drug interactions (antacids, iron, calcium)... 

Absorption from the gastrointestinal tract can be affected by other drugs and by food. Aluminum, calcium, and magnesium ions in antacids or dairy products form insoluble chelates with all tetracyclines and inhibit their absorption. Food inhibits tetracycline absorption but enhances doxycycline absorption food delays but does not diminish metronidazole absorption fatty food enhances griseofulvin absorption. 

These antibiotics are partially absorbed from the stomach and upper gastrointestinal tract. Food impairs absorption of all tetracyclines except doxycycline and minocycline. Absorption of doxycycline and minocy-cbne is improved with food. Since the tetracyclines form insoluble chelates with calcium (such as are found in many antacids), magnesium, and other metal ions, their simultaneous administration with milk (calcium), magnesium hydroxide, aluminum hydroxide, or iron will interfere with absorption. Because some of the tetracyclines are not completely absorbed, any drug remaining in the intestine may inhibit sensitive intestinal microorganisms and alter the normal intestinal flora. 

The absorption of tetracycline administered orally is variable and depend upon the type of tetracycline used. The tetracycline form insoluble complexes i.e. chelation with calcium, magnesium, milk and antacids reduce their absorption. Administration of iron also interferes with the absorption of tetracycline. Doxycycline is rapidly and virtually completely absorbed after oral administration and its absorption is not affected by presence of food or milk. 

The oral dosage for rapidly excreted tetracyclines, equivalent to tetracycline hydrochloride, is 0.25-0.5 g four times daily for adults and 20-40 mg/kg/d for children (8 years of age and older). For severe systemic infections, the higher dosage is indicated, at least for the first few days. The daily dose is 600 mg for demeclocycline or methacycline, 100 mg once or twice daily for doxycycline, and 100 mg twice daily for minocycline. Doxycycline is the oral tetracycline of choice because it can be given as a once-daily dose and its absorption is not significantly affected by food. All tetracyclines chelate with metals, and none should be orally administered with milk, antacids, or ferrous sulfate. To avoid deposition in growing bones or teeth, tetracyclines should be avoided in pregnant women and children less than 8 years of age. 

Tetracyclines mainly differ in their absorption after oral administration and their elimination. Absorption after oral administration is approximately 30% for chiortetracycline 60-70% for tetracycline, oxytetracycline, demeclocycline, and methacycline and 95-100% for doxycycline and minocycline. A portion of an orally administered dose of tetracycline remains in the gut lumen, modifies intestinal flora, and is excreted in the feces. Absorption occurs mainly in the upper small intestine and is impaired by food (except doxycycline and minocycline) by divalent cations (Ca2+, Mg2+, Fe2+) or Al3+ by dairy products and antacids, which contain multivalent cations and by alkaline pH. Specially buffered tetracycline solutions are formulated for intravenous administration. 

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. 

The administration of tetracycline with food can ameliorate its irritative effects, bnt food can adversely affect the drug s absorption. In contrast, the absorption of doxycycline is only slightly affected by the presence of food, including dairy prodncts. Becanse all tetracyclines can form complexes with divalent cations, the absorption of any tetracycline is markedly decreased when administered with iron-containing tonics or antacids containing calcium, magnesium, or aluminum. Sodium bicarbonate also adversely affects tetracycline absorption. 

Case Condasion VD. prolonged exposure to sunlight and to avoid concomitant dosing wi antacids or any othw medications that may contain muitivalem cations. 

Drug interactions The bioavailability of tetracyclines is significantly deaeased when administered with antacids containing aluminum, calcium, or magnesium, with iron-containing products, or with food. Food or dairy products do not affect the bioavailability of doxycycline or minocycyline. 

As tetracyclines have moderate to high lipophilic properties, the poor bioavailability associated with oral administration is somewhat surprising. Papich and Riviere suggest that causes may be multifactorial. As zwitterions, they are mainly ionized at pHs within GIT liquor. Moreover, feed reduces bioavailability, and tetracyclines chelate with polyvalent cations. Oxytetracycline absorption has been shown, experimentally, to be reduced by feed, dairy products, Ca +, Mg +, Al +, and Fe + ions and antacids. Even though doxycycline has a similar structure, affinity for metals is different from that of oxytetracycline with greater affinity for zinc and less for calcium. 

Taking your antibiotic with food may help reduce this sick feeling. Ciprofloxacin and doxycycline should not be taken within 2 hours ol taking antacids. Ciprofloxacin and doxycycline should not be taken with dairy or calcium-fortified products (such as ice cream or calcium-fortified orange juice). 

Nguyen VX, Nix DE, Gillikin S, Schentag JJ. Effect of oral antacid administration on the pharmacokinetics of intravenous doxycycline. Antimicrob Agents Chemother (1989) 33, 434-6. 

Because of their chelating action, tetracycline drugs are inactivated in the patient s bowel by any dietary calcium or magnesium ions, whether from milk or from antacid medication. Through such mishaps, many patients have lost the potential benefit of these antibiotics. Tetracyclines are usually given orally. Tetracycline, itself, is still much prescribed, but there are also lower-dose forms available demeclocycline and methacycline, and a sub-class of these which require less frequent dosing doxycycline and minocycline. 

An active substance, although initially released from its dosage form (and dissolved), may become unavailable for absorption due to reactimis with other medicines or food components [4]. An example is the formation of insoluble complexes of tetracycline with calcium or aluminium ions from antacids or milk products. Interaction (chelation or binding) with iron ions leads to a reduced absorption for a variety of active substances such as doxycycline, penicillamine, methyldopa and ciprofloxacin. The absorption of active substances showing pH-dependent dissolution behaviour may be influenced by medicines that influence the gastric pH, such as H2-antagonists, proton pump inhibitors and antacids. Antimycotic active substances such as ketoconazole or itraconazole dissolve better in acidic fluids. Therefore their bioavailability may be increased by the concomitant use of an acidic drink like cola, whereas the concomitant use of antacids or proton pump inhibitors is likely to reduce the bioavailability. Concomitant use of milk may increase the dissolution of acidic active substances, whereas fats from food may increase the bioavailability of lipophilic active substances like albendazole and griseofulvin. 

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