Lack of information: some suggestions

Last updated: Thursday, September 24, 2015

Theoretical predictions

If there is no published evidence to guide you, then there are a couple of strategies to consider. The first might be to try to make a theoretical prediction about how trihexyphenidyl would be handled in a patient on HD. You can read a little about the factors that affect drug removal by Renal Replacement Therapy here.

So in this scenario you might try to find out about the pharmacokinetics of the drug such as how it is normally eliminated from the body, whether it is metabolised, whether any metabolites are pharmacologically active, the degree of protein-binding and its volume of distribution (Vd).  However making theoretical predictions is not without risk, especially in a complex situation such as this when multiple factors could influence how the drug is handled by the body.

Asking the experts

Think about who might have experience of managing such patients. You may have a team of practitioners at your hospital with renal expertise, or if not you will have a regional renal unit that may be able to help. Consider whether any expert bodies may have issued consensus guidelines in the area, or whether there may be relevant specialist discussion groups that you may be able to search. You might be able to contact a colleague in the Renal Pharmacists' Group for assistance.

Explore the alternatives

If you really can’t find any evidence upon which to base a decision, then is there an alternative drug that may be suitable? In this case you could check to see if there were data for e.g. procyclidine in patients receiving HD.

Courtesy of Simon Wills

Achieving a decision 

If there is no, or very limited information, remind yourself that the decision to use any medicine should be based upon a careful consideration of the perceived benefit to the patient versus the potential harm. This will differ between patients according to their individual preference, the severity of their disease, and their risk of developing side effects. It's also important to think about where the patient is based (e.g. in the community or an inpatient), as this will affect how closely they can be monitored for treatment benefits and for adverse events.

In this kind of situation, you should always check your proposed solution with a senior colleague first before getting back to the consultant. You also need to be up-front with the consultant that there are no published data on which to make a decision and, wherever possible, the lack of information should be discussed with the patient too.

The rule of thumb of ‘starting low: going slow’, which means starting at a low dose and building it up gradually, could be helpful in this situation. You may want to discuss this with the consultant to determine between you a sensible starting dose and speed of dose increase. This is the kind of ward-based intervention that you would want to document carefully for future reference.