New York: If you are overweight, the chances are your doctor is prescribing you half the necessary dosage of any medicine when you are ill, a new study contends.

The study, by researchers at the Oregon State University, noted that the effectiveness of a medicine depends to an extent on the body mass index (BMI) of the patient.

And as most medicines, especially antibiotics, are produced in a "one size fits all" dosage, obese patients are probably getting less than the necessary dosage in their prescriptions.

Findings of the study have been published in the forthcoming issue of the journal Pharmacotherapy.

The study said many doctors are still not attuned to this issue and may be prescribing less than the required dosage to the obese.

The problem assumes importance as "the number of ... very obese people is up 600 percent between 1986 and 2000", said David Bearden, who participated in the study.

"Very obese individuals in some cases, even those with severe infections, may be getting only half the necessary dose of a prescription drug such as an antibiotic," Bearden said.

"That's a problem. It could lead not only to antibiotic failure but also an increase in antibiotic resistance, another serious issue."

The problem is somewhat less of a concern with dosages of medications that patients take for extended periods, such as blood pressure or cholesterol medications, because the results of taking those medications are more routinely monitored and dosages can be increased as necessary.

It's a particular concern with antibiotics, Bearden said, because they are often used to treat severe or even life-threatening infections, and "bad things can happen quickly if the drug is ineffective".

Drug companies are just now becoming more aware of this issue and beginning to test and recommend dosages more appropriate for adults of varying weights, Bearden said.

But there often is little or no data for adjusting dosages with older drugs that are commonly used. IANS