Didanosine Quinolones

DIDANOSINE QUINOLONES 1 efficacy of ciprofloxacin and possibly levofloxacin, moxifloxacin, norfloxacin and ofloxacin with buffered didanosine Cations in the buffer of didanosine preparation chelate and adsorb ciprofloxacin. Absorption of the other quinolones may be i by the buffered didanosine formulation, which raises gastric pH Give the antibiotic 2 hours before or 6 hours after didanosine. Alternatively, consider using the enteric-coated formulation of didanosine, which does not have to be given separately... 

Multivalent cations (antacids, iron, sucralfate, zinc, vitamins, dairy, citric acid) didanosine Decreased absorption of quinolone Separate by 2 hours... 

Ciprofloxacin (Cipro, Cipro XR, Proquin XR) [Antibiotic/ Fluoroquinolone] Uses Rx lower resp tract, sinuses, skin skin structure, bone/joints, urinary tract Infxns including prostatitis Action Quinolone antibiotic DNA gyrase Dose Adults. 250-750 mg PO ql2h XR 500-1000 mg PO q24h or 200-400 mg IV ql2h in renal impair Caution [C, /-] Children <18 y Contra Component sensitivity Disp Tabs, susp, inj SE Restlessness, N/V/D, rash, ruptured tendons, T LFTs Interactions T Effects Wf probenecid T effects OF diazepam, theophylline, caffeine, metoprolol, propranolol, phenytoin, warfarin effects W/ antacids, didanosine, Fe salts. Mg, sucralfate, Na bicarbonate,... 

Foscarnet (Foscavir) [Antiviral] Uses CMV retinitis acyclovir-resistant hCTpes Infxns Action -1- Viral DNA polym ase RT Dose CMV retinitis Induction 60 mg/kg IV qSh or 100 mg/kg ql2h X 14—21 d Meant 90-120 mg/kg/dIV (Moo.-Fiti ) Acyclovir-resistant HSV Induction 40 mg/kg IV q8-12h x 14—21 d use central line -1- w/ renal impair Caution [C, —] T Sz potential w/ fluoroquinolones avoid n hrotoxic Rx (cyclosporine, aminoglycosides, ampho B, protease inhibitors) Contra CrCl <0.4 mL/min/kg Disp Inj SE Nephrotox, electrolyte abnormalities Interactions T Risks of Sz W/ quinolones t risks of n hrotox W/ aminoglycosides, amphotCTicin B, didanosine, pentamidine, vancomycin EMS Known to cause electrolyte disturbances (extremity numbness paresthesia indicates electrol5rte unbalance) monitor ECG OD May cause extremity numbing, and Szs hydrate w/ IV fluids... 

All quinolones interact with multivalent cations, forming chelation complexes resulting in reduced absorption. Major offenders are antacids vitamins containing calcium and iron can also be problematic. All fluoroquinolones interact with warfarin, didanosine (ddi), and phenytoin, resulting in decreased absorption or metabolism. Ciprofloxacin and other second-generation drugs interact with theophylline by decreasing its clearance, which leads to theophylline toxicity. 

An extremely marked reduction in the serum levels of ciprofloxacin occurs if it is given at the same time as didanosine tablets, because of an interaction with the antacid buffers in the didanosine formulation. Taking the ciprofloxacin 2 hours before or 6 hours after didanosine tablets minimises this interaction. Other quinolones are expected to interact similarly. Didanosine enteric-coated capsules do not interact with ciprofloxacin. 

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. 

Direct information is limited to these reports but the interaction between buffered didanosine and ciprofloxacin appears to be clinically important. Such drastic reductions in serum ciprofloxacin levels mean that minimal inhibitory concentrations are unlikely to be achieved. Ciprofloxacin should be given at least 2 hours before or 6 hours after didanosine tablets (see Quinolones + Antacids or Calcium compounds , p.328). Other qui-nolone antibacterials that interact with antacids are also expected to interact with didanosine tablets, but so far reports are lacking. Didanosine enteric-coated capsules do not interact. 

Some of the didanosine preparations (e.g. chewable tablets) are formulated with antacid buffers that are intended to facilitate didanosine absorption by minimising acid-induced hydrolysis in the stomach. These preparations can therefore alter the absorption of other drugs that are affected by antacids (e.g. azole antifungals, quinolone antibacterials, tetracyclines). This interaction may be minimised by separating administration by at least 2 hours. Alternatively, the enteric-coated preparation of didanosine (gastro-resistant capsules) may be used. 

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