Clinical validation of the dried blood spot analysis for antituberculosis drugs

Tuberculosis (TB) is caused by Mycobacterium tuberculosis and is a chronic
infectious disease. TB is one of the top three (with malaria and HIV/AIDS)
leading causes of death from a single infectious agent disease. Worldwide,
approximately 1.7 million deaths are attributed to TB annually. World Health
Organization (WHO) estimates that annually 9.2 millions new TB cases to occur.
The threat of TB is aggravated by co-infection with HIV (synergistic pandemic)
and multidrug-resistant TB (MDR-TB). These facts emphasise the importance of
new efforts for development of new TB diagnostic tests, new anti-tuberculosis
drugs and new effective anti-tuberculosis drug combination regimens. These aims
are however accessible just by a good treatment management strategies. Fully
supervised treatment (directly observed treatment * DOT) has been adopted by
WHO and the IUTLD as well as Stop-TB, and the Green-Light-Committee as an
essential element to secure appropriate adherence to therapy, but good
adherence to an inappropriate, or inappropriately dosed regimen is bound to
fail. Therefore, Therapeutic Drug Monitoring (TDM) is an important and powerful
element to safeguard management of TB, especially with MDR-TB (resistance
against the two most powerful drugs - isoniazide and rifampicin). Measurement
of the drug concentrations and its metabolites over time is the best way to
guide a treatment regimen. The classical way of measuring drug concentrations
is by venous blood sampling. However, venous blood sampling has disadvantages
which restrict TDM. A alternative for venous blood sampling as has been used
for an array of indications, with blood glucose measurements the most widely
used, is capillary (finger prick) blood sampling. If applied to measurements of
blood drug concentrations this would greatly simplify TDM, and it would
conceivably improve the applicability of TDM as well as pharmacokinetic
research in important areas like MDR-TB.
Assays based on finger prick blood sampling, which is named Dried Blood Spot
(DBS) analysis, seems to solve some of issues of conventional blood sampling.
In this method, a small amount of capillary blood from the finger tip of a
patient is taken (by creating a prick by sterile lancet, or automatic
disposable lancet) and collected onto special filter paper. This method is more
patient friendly than a vena puncture. The blood drop will be absorbed onto
paper and dried under room condition creating DBS which is more suitable for
storage, transportation than conventional liquids like plasma because of its
stability.

The objective of this study is to validate drug concentration measurement using
DBS by comparing the results of blood samples routinely withdrawn from venous
blood versus withdrawn by finger prick and transferred to filter paper to make
dried blood spots.
TB drugs that are of interest for this study are: isoniazide, rifampicin,
ethambutol, pyrazinamide, amikacin, kanamycin, moxifloxacin, clarithromycin and
linezolid.

This is a prospective observational study to compare DBS with routine sampling.
The venous blood samples are collected from patients who have routinely TDM of
ATB drugs. Parallel with the sampling of venous blood (max. 4 ml) a finger
prink blood (0.1 ml) will be taken to make a DBS. At the same time with venous
blood sampling, DBS sample will be taken from patient's finger prick by medical
staff. A DBS will be produced from venous samples (about 0.05 ml) to evaluate
the differences between the drug concentration in venous blood and capillary
blood. These samples will be stored at -80C with a QC sample and analyzed by a
validate method. The results from the two methods will be compared to evaluate
whether DBS method is reliable for routine TDM and clinical pharmacokinetics
studies.

Patients may experience some discomfort from the finger prick. But as this
method is widely applied for glucose monitoring in diabetic patients and INR
control in patients using anticoagulants, discomfort is estimated to be mild.
There are no advantages for the participant in this study.