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RENAL AND HEPATIC DOSE CHECKING (User's Manual, pgs. 885-886)

In last month's newsletter, we saw how version 4.8 can automatically estimate the patient's creatinine clearance based on the serum creatinine stored in the Lab Book. Version 4.8 can use this information to adjust its dosage warnings based on the patient's estimated renal function. It also adjusts its dosage warnings based on whether or not the patient has liver disease. If the patient has both renal and liver disease, it adjusts the dosage to whichever of the two doses is most conservative. However, you should always use your own best clinical judgment of the situation, based upon the indication for the drug, the severity of the patient's illness, and how significant you feel the patient's liver and renal disease are. (For example, a muscular young man might have a slightly high serum creatinine due to his high muscle mass, resulting in a lower than normal estimated creatinine clearance, and yet have normal actual creatinine clearance, and therefore should receive the full dose of a drug).

Let's see how this dose checking works:

1. If you haven't already done so, do last month's Newsletter, adding Fred Uremia as a patient, with an estimated creatinine clearance of 40 ml/min using the MDRD formula.

2. Press System\Medication Options. Select Estimate renal function using Modification of Diet in Renal Disease and press Ok. This causes the Dose Checker to use this method when estimating the proper dose to use.

3. First, let's look up dosing information for lamivudine in general. Press Libraries\Dose Checker.

4. For Drug Name, type in LAMIVUDINE.

5. Notice that the dosing recommendations vary depending upon the indication (HIV vs. Hepatitis B) and the patient's estimated creatinine clearance. If you know Fred's estimated creatinine clearance is 40 ml/min, you can see that the recommended dose for HIV would be 150 mg po qd, and for hepatitis B would be 100 mg first dose, then 50 mg qd.

Now, let's see what happens when we add lamivudine as a drug specifically for Fred:

1. Press Write\Medications.

2. Enter Fred Uremia as the name of the patient.

3. Press Add.

4. For Drug, enter "lamivudine".

5. If you now press the Dose button, you see dosing recommendations tailored to Fred's renal function. You also see what his estimated creatinine clearance is that the Dose Checker is basing this on, and how fresh that creatinine clearance estimate is. (If it is too out of date, you should enter the latest serum creatinine into his Lab Book first).

6. Press Cancel or <ESC> to close this window. Now, let's see what happens if we enter an inappropriate dose for Fred.

7. In the Instruction field, type in "300 mg po qd". (Note that this would be the correct dose for someone with normal renal function).

8. Note that the Dose Alert for lamivudine is triggered. Press Ok to read more about why it was triggered.

9. This brings up the same tailored dose information that we saw on step 5.

10. Press Cancel, and go back to the Instruction field and type in the proper dose (e.g. 150 mg po qd assuming the indication is HIV).

The Dose Checker considers the patient to have "liver disease" by looking at the active diagnoses listed in the patient's Diagnosis Editor, not based on any particular Lab Book result. If the patient has an active diagnosis whose Kind in the Vocabulary Editor is HEPATOBILIARY DISORDERS, then the Dose Checker considers the patient to have liver disease.

Note that, for many drugs, the Dose Checker only says something like "a lower dose may be needed. No specific dosage guidelines available". This is because, for many drugs, the manufacturers have never tested the drugs in sufficient numbers of patients with renal or liver disease in order to come up with specific recommended doses, but based on the pharmacokinetic data on the drug, they expect that the drug level might rise in such patients and thus a lower dose may be needed. In these cases, the Dose Checker can't know what doses to consider too high, and can only give you these general statements. You still must monitor the patient and use your best clinical judgment as to what dose is appropriate.

By using the new capabilities of the Dose Checker, you can reduce your chances of making dosing errors and provide better care for your patients.

Version 4.9 will include a database of indications for medications, with associated warnings. If you have any suggestions for new features, please let us know. We love the feedback!