,It is possible to have a sputum
negative result but still prescribed anti tubercular medicines. Fever,cough,loss of weight, or any other finding in blood test
may indicate active tuberculosis or even some time therapeutic trial may be given in endemic areas.
knows best .As far as side effects are concerned watch for any development of nausea vomiting and Yellow colour in eyes that is Jaundice which may occur in minority of cases where some drugs needs to be stopped. All the best.