Antibiotics have become a dominant component of our prescription in an era of instant results. But while doing so seldom do we pause to see if we have given the proper dosage or have crossed the limit? While, inadequate dosages give sub optimal result, create resistance and call for the need to change to a higher drug, which is unnecessary most often, the over dosage have their own side effects. Let us look at some commonly prescribed antibiotics just to draw the line between the recommended dosage and a rational prescription.

Amoxicillin, the commonest one among the time tested antibiotics, which should be given at a dosage of 20-50mg/kg/day BID/TID, has been proved rational with its dose raised considerably without any risk of toxicity e.g. dose of 200mg/kg/day to treat meningitis. The recent studies have shown even better cure rates of otitis with dosage of 90mg/kg/day of amoxicillin. At times for synergistic effect, we use combination of amoxicillin and clavulanate. Amoxicillin- clavulanate can be given even to a neonate orally in dose of 30mg/kg/day BID without any risk and to children at 20-45mg/kg/dayBID/TID and a dose of 80-90mg/kg /day is needed for otitis media.

Of late, the market is flooded with a number of oral cephalosporins, which are claimed to be safer. Cefadroxil is a commonly used oral cephalosporin with long half-life and can be given at a dose of 30mg/kg/dayBID. Cefaclor is used less often and can be given at 20-40mg/kg/dayBID/TID but the maximum daily dose should be2gm. Cefixime is a newer molecule & can be given at 8mg/kg /day OD/ BID.It is an excellent choice for starting therapy in case of shigellosis, enteric fever, selected cases of UTI. Cefpodoxime is usually used as a second line drug at a dose of 10mg/kg/dayBID. Cefuroxime is a costlier drug and hence should be prescribed at a proper recommended dose to avail maximum benefit. The dose is 20-30mg/kg/dayTID. Last but not the least among cephalosporins, cephalexin is given at 25mg/kg/day. Maximum dose allowed for this drug is 100mg/kg/day TID/QID.

However, macrolides, by and large tissue antibiotics which exert their efficacy in tissue at the cost of that in the blood hence making them poor choice in cases of bacteremia. Erythromycin is another drug, which can be safely given to even in neonates orally. The dose is 20mg/kg/dayfor those weighing below 1200 gm and 30 mg/kg/day for above 1200 gm. For children maximum dose allowed is 2gm/day. However the dose is different for treatment of pertussis where it needs to be given at 40mg/kg/day for 14 days. Regular prescribed dose is 30-50mg/kg/day TID/QID. Azithromycin is also a potent drug and can be given at10mg/kg on 1st day (max500mg) followed by 5mg/kg for 4 days. In suspected streptococcal infection 12mg/kg/day with a maximum of 500mg/day should be given for 5 days. Clarithromycin is similarly given at a dose of 15mg/kg/dayBID. Cotrimoxazole is still a very chosen drug in spite of the risk of sulpha allergy. The safe prescription ranges as 6-20mg TMP/kg/day BID. However for pneumocystis carinii15-20mg/kg/dayBID is given and for prophylaxis of P.carinii 5 mg/kg/day of TMP or 3 times /week is recommended. Among quinolones only Nalidixic acid is allowed in children, which is given at 50-55mg/kg/dayQDS. The suppressive dose of nalidixic acid is 25-33mg/kg/dayTDS/QDS. There are only few studies, which tell that ofloxacin that to short course therapy is superior to cefixime in treating enteric fever. Metronidazole is used for amoebiasis at 30mg/kg/dayTDS. It is given at15mg/kg/day TDS while treating Giardiasis. This is another antibiotic, which can be given to even a neonate at 7.5-30mg/kg/day depending on the weight of the child. Lastly, we must know about Nitrofurantoin, which is still a common drug .It, is to be given at 5-7 mg/kg/day QDS .The maximum dose is 400 mg/day. When used for suppressive therapy, it is to be given at 1-2.5 mg/kg/day BD/OD (maximum100mg/day).

Now lets look at some probable reasons behind making an error while prescribing. Firstly we must realize that some companies have products, which contain double the strength of drug per 5ml compared to other brands of the same drug. For example, Syrup Cefspan of GSK contains 100 mg of cefixime, whereas most others have 50 mg per 5ml. Another reason for not administering a correct dose could be human factor, which can be minimized by giving a dispersible tablet rather than syrup. For instance, pentads (Sarabhai) is still a very well chosen drug. But the availability of penicillin in syrup form is difficult Similarly we get only capsule form of clindamycin, which is a second line drug for tonsillitis. Cost puts a hurdle most often for completing a desired duration of antibiotics and hence we land up giving shorter course.

The diseases demanding a longer course are Enteric fever, chronic tonsillitis, urinary tract infection, deep tissue infection, pertussis. Another reason for not availing optimal dose is that we do not bother to explain the amount to be given showing an actual measuring cup. We must always discourage using home spoon which most patients still use in preference to the measure provided with the bottle. It is always a better policy to explain the parents about the common anticipated side effects of the drug they are taking to avoid getting panic. It is a common trend to see an antibiotic with lactobacill combination, which is claimed to be superior. However most often the antibiotics used are not of the duration to neither cause any harm nor can lactobacilli help avoiding diarrhea in any regard. Such combinations should not be actually claimed superior and hence should not be made costlier. These are some of the tips provided on basis of practically encountered problem in an outpatient setup, which in our view should help a general practitioner in practicing in a more rational way.

-- The author is a leading Mumbai-based paediatrician