Nitrofurantoin dosage

Nitrofurantoin Dosage in Children Based on Body Weight... 

The effect of particle size reduction on the bioavailability of nitrofurantoin was shown in Fig. 4. The microcrystalline form (< 10 pm) is more rapidly and completely absorbed from the tablet dosage form than is the macrocrystalline form (74-177 pm) from the capsule dosage form. This is not a completely satisfactory illustration of the effect of particle size on the rate and extent of availability, since other manufacturing variables have not been held constant. Nevertheless, it does suggest some correlation between particle size, dissolution rate, and rate of availability. 

Table 3 Effect of pH on the Dissolution Half-Life of Nitrofurantoin from Commercial Dosage Forms at 37°C...

Groning R, Heun G. Dosage forms with controlled gastrointestinal passage—Studies on the absorption of nitrofurantoin. Int J Pharm 1989 56 111-116. 

The dosage for urinary tract infection in adults is 100 mg orally taken four times daily. The drug should not be used to treat upper urinary tract infection. Oral nitrofurantoin can be given for months for the suppression of chronic urinary tract infection. It is desirable to keep urinary pH below 5.5, which greatly enhances drug activity. A single daily dose of nitrofurantoin, 100 mg, can prevent recurrent urinary tract infections in some women. 

Nitrofurantoin has been used as an urinary antiseptic in calves and horses at an oral dosage of 10 mg/kg bw/day. It is absorbed rapidly and completely from the gastrointestinal tract. About 40% of the drug is eliminated in the urine, while the remainder is catabolized. 

Drugs that meet one or more of the criteria given above and have been shown to exhibit significant differences in the bioavailability of marketed dosage forms include digoxin, quinidine, furosemide, nitrofurantoin, prednisone, chloramphenicol, theophylline, chlorpromazine, phenytoin, amitriptyline, and phenylbutazone. 

Nelson WO, Bunge RG. The effect of therapeutic dosages of nitrofurantoin (Furadantin) upon spermatogenesis in man. J Urol 1957 77(2) 275-81. 

The achievement of adequate serum concentrations and high urinary excretion is an important factor in evaluating the merits of antibacterial compounds. This is particularly true for nitrofurantoin since it is administered most frequently by the oral route. Results of studies in this connection proved to be very favourable 30 to 40 per cent of the administered dosages of nitrofurantoin were excreted in the urine of rats and men [Table 6.20). 

Another compound used in Italy is a hydroxymethyl-nitrofurantoin which produces higher urinary concentrations than nitrofurantoin and is also excreted more rapidly . When 200 to 300 mg were given orally in divided dosages daily for two to ten days, good results were obtained in 73-5 per cent of the cases . Comparative studies with nitrofurantoin yielded good results in 75 per cent of cases. This compound is also known as Z-56. 

The oral dosage of nitrofurantoin for adults is 50-100 mg four times a day with meals and at bedtime. A single 50- to 100-mg dose at bedtime may be sufficient to prevent recurrences. A course of therapy should not exceed 14 days. Pregnant women, individuals with impaired renal function (creatinine clearance <40 mUmin), and children <1 month of age should not receive nitrofurantoin. 

Liver toxicity after nitrofurantoin is especially serious in women. It is often connected with the appearance of autoantibodies (antinucleic factors) and hyperglo-bulinemia and shows no relation to the daily dosage. 

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