**4.2 Therapeutic drug monitoring (TDM)**

Despite their impactful role in improving transplant outcome and graft survival, immunosuppressive medicines exhibit narrow therapeutic range between levels that inhibit rejection and toxic levels hence TDM is often required. Establishing a patient's dose requirements in the immediate post – surgery period and avoiding over immunosuppression remains a challenge. Calcineurin inhibitors have variable pharmacokinetics [86–89]. While ethnic differences have not been demonstrated in pharmacokinetics of MMF and AZA, African Americans have been shown to have 20–50% lower oral bioavailability for TAC, CYP, sirolimus and everolimus and as such require higher drug doses than Caucasians [90, 91]. This has been attributed to genetic polymorphism of key enzymes in the metabolism of these medications [90]. Genetic profiling is not readily done in SSA hence, TDM is essential. This attracts huge costs for the health system and for patients who pay OOP. It is imperative to tailor medications to patient's need. Some countries do not have the capacity to analyze drug levels, so patient's blood samples are sent overseas for analysis. Within the first-year post-transplant, TDM is done at least twice during timed follow-up visit for patients coming from rural and urban areas. However, more frequent monitoring is done when indicated. During emergency presentation for allograft dysfunction, patients are admitted, samples for TDM sent out and other possible causes of allograft dysfunction are excluded or managed if present. Decision to increase drug dosage is often delayed till TDM result is available but dose reduction or withdrawal can be done in the presence of overt signs and symptoms suggestive of toxicity. For subsequent years, TDM is done as indicated.
