Novobiocin：An aminocoumarin antibiotic

DESCRIPTION 

Novobiocin (Albamycin, Cathamycin, Spheromycin) is an aminocoumarin antibiotic originally isolated from Streptomyces niveus in the Upjohn Research Laboratories and initially was given the generic name of ‘streptonivicin’ . It was also isolated almost simultaneously in other laboratories, and was given several other names.  Novobiocin inhibits the GyrB subunit of DNA gyrase and is primarily active against Gram-positive microorganisms. It was used under the trade name Albamycin and was withdrawn from the market in the US. Its latest use included eradication of methicillin-resistant Staphylococcus aureus (MRSA) and other resistant microorganisms. In addition, it has been applied in cancer therapy.

ANTIMICROBIAL ACTIVITY

Novobiocin is active against some of these bacteria, such as S. aureus (including beta-lactamase-producing strains) and the pneumococcus. Its MIC against strains of MRSA is r 0.25 mg/L, and against such strains when combined with rifampicin it shows neither synergy nor antagonism, but emergence of resistance to either agent seems to be prevented. Streptococcus pyogenes is much less susceptible and Streptococcus viridans strains vary in their sensitivity. Enterococcus faecalis is usually moderately resistant, but E. faecium, including multiresistant strains, is susceptible. Gram-positive bacilli, such as Bacillus anthracis, Clostridium tetani, C. perfringens, and Corynebacterium diphtheriae, are novobiocin susceptible. S. saprophyticus is intrinsically resistant due to alteration in the GyrB gene.

MECHANISM OF DRUG ACTION

Novobiocin inhibits DNA and bacterial protein synthesis by binding to the GyrB subunit of DNA topoisomerase II (gyrase), an enzyme which is associated with the supercoiling of DNA. Although quinolones also target DNA gyrase, the binding site for quinolones is different. Like other aminocoumarin antibiotics, novobiocin acts as a competitive inhibitor of the ATPase reaction catalyzed by GyrB. There is also activity against topoisomerase IV .

PHARMACOKINETICS

Novobiocin is well absorbed from the alimentary tract. After a single oral dose of 0.5 g to adults, a peak serum level of 10–20 mg/l levels may persist for 24 h or longer. Doubling the dose doubles the serum concentrations. If a dose of 0.5 g is administered orally every 6 h, there is often some accumulation, and after four doses the peak serum level may reach 100 mg/l. When an oral dose of 0.5 g novobiocin was given orally twice daily to adult volunteers for 27 doses, the mean serum concentration prior to dose 27 was 21.6 mg/l; this rose to a mean peak serum level 2 h after the dose of 55.5 mg/l. When oral rifampicin (300 mg 12-hourly) was given concomitantly, the comparative values before and after the last dose were 6.9 and 49.2 mg/l, respectively. Similarly, novobiocin levels were lower when rifampicin was co-administered than when novobiocin was given alone at 8 h (7.9 versus 21.6 mg/l) and at 12 h after the 27th dose (3.0 versus 16.0 mg/l). The half-life of novobiocin (5.85 h) was reduced to 2.66 h when administered in combination with rifampicin. 

CLINICAL USES

Novobiocin formerly had a role in the treatment of staphylococcal infections. With the advent of the penicillinase-resistant penicillins and other anti-staphylococcal agents, novobiocin is no longer used for this indication, except perhaps as an adjunct to other drugs for the treatment of methicillin-resistant staphylococcal infections. For instance, novobiocin/sodium fusidate and novobiocin/rifampicin combinations have been used successfully to treat staphylococcal infections of this nature. These combinations have only been used to prevent the emergence of further drug resistance among such strains, and there is no evidence that they act synergistically. With the emergence of more resistant staphylococci there is an increased interest in the drug. It has been used as a prophylactic agent in the prevention of catheter infections in cancer patients. 

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