TDM (Therapeutic Drug Monitoring)
These tests check whether you are getting adequate blood levels of a protease inhibitor, NNRTI or T-20. Tests for maraviroc and raltegravir are also available.
Doses for HIV drugs are worked out for an average person. However, individual differences in absorption can vary.
TDM can check doses in many situations. These include:
- When using unstudied combinations where they may be a drug interaction. This is important with new drugs.
- To individualise dosing when there are no dosing recommendations.
- If you have pre-existing liver or kidney damage, or have haemophilia or other medical conditions that require careful monitoring. For example, drug levels of both amprenavir and abacavir can be too high if your liver is damaged. Using TDM you can safely reduce the dose when recommended.
This may be true for some other drugs. If your liver is not working to clear then they can take longer to leave your body. Dosing is easier to individualise in this situation. - For children. Differences in growth rates and the way children process drugs at different ages are not always accounted for. Even when doses are calculated by body weight or body surface area they often need altering.
- If you may not be absorbing drugs properly. For example, if you have severe diarrhoea.
TDM is recommended in UK guidelines and your doctor should be able to order this for you. If you have been taking all your drugs at the right time, this may be why your combination did not work so well.
Using TDM and resistance tests together produces better results than either test alone.
TDM costs around £70 per drug from Delphic: