Friday, January 11, 2008

Blood Work: Tobramycin Peak and Trough

A tobramycin trough, is a blood test that involves drawing blood during the half hour before which the next dose is to be administered. If your results show that the concentration of the drug is <2>2 µg/mL, indicate toxicity. The prescribing doctor and pharmacy are alerted, and your next dose is either delayed, or the concentration of your doses are reformulated.

A tobramycin peak, is another round of bloodwork drawn between 60 and 90 minutes after you have infused the medication. If the concentration is 4-10 µg/mL, nothing needs to be changed. If it's >12 µg/mL, again, the doctor will have you wait with your next dose, or will have the pharmacy reformulate the concentration.

Another thing the doctor might do if your kidneys are in peril, is to switch you to a low protein diet. Proteins are particularly tough for the kidneys to process, so removing or limiting it in the diet gives the kidneys a chance to rest a bit, and possibly regain function. Regaining function is entirely within the realm of possibility, especially if the doctor and patient are diligent to keep an eye on the symptoms of possible renal failure at its earliest signs. Drink plenty of water (more than you think you need) when on antibiotics. If you notice that your urine is staring to darken or smell like your medication, (this happens frequently with ceftazadime, which smells like cat urine) let your doctor know. Also be sure to let your doctor know if, during any time during your course of antibiotic treatment, you experience pain in the middle to lower portion of your back. A dull ache in that area may be indicative of kidney dysfunction.

For people who have exhibited kidney problems in response to tobra before, and you happen to be in the hospital, doctors will most likely start you on a very low dose, and have lots of labs drawn. Your dosage concentration will be ramped up with each new administration of the med until they find a safe and tolerable range for you. In my case, Tobra is one of the few meds I can tolerate, so my doc knows exactly which dose to start me at each time.

In addition to monitoring peak and trough concentrations, many CF centers are now implementing hearing screening exams. The ototoxicity (ear damaging) effect of tobra has been well established; the same was true of gentamycin, which is no longer in wide usage for that very reason.

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