Therapeutic drug monitoring is advised in all except
Metformin Therapeutic drug monitoring is paicularly useful in the following situation (i) As a guide to the effectiveness of the therapy Plasma gentamycin and other antimicrobials against sensitive bacteria. Plasma theophylline for asthma. Blood cyclosporine to avoid transplant rejection. (ii) When the desired effect is suppression of infrequent sporodic events such as: Epileptic seizures (anticonvulsants) Episodes of cardiac arrythmia (antiarryhthmics) (iii) To reduce the risk of adverse drug effect (therapeutic index low) Digoxin Anticonvulsants Antiarrythmics Theophylline TCA Aminoglycoside Lithium (iv) When lack of therapeutic effect and toxicity may be difficult to distinguish Digoxin is both a treatment for and sometime the cause for supraventricular tachycardia, therefore a plasma digoxin measurement will help to distinguish whether an arryhthmia is due to too little or too much digoxin. (v) When there is no quick and reliable assessment of effect Lithium for mood disorder. (vi) To check patient compliance on a drug regimen, when there is a failure of threrpaeutic effect at a dose that is expected to be effective. Antiepilepsy drug (vii) Poisoning and overdose Monitoring of plasma concentration is of no value for (i) Cases where dose can be titrated against a quickly and easily measured effect such as Antihypeensive -9 Blood pressure (B.P. can be easily monitored) Diuretics ---> Body weight Hypoglycemics --4 Blood sugar (blood glucose level can be easily monitored) Oral anticoagutants --> INR (ii) Plasma concentration has no correlation with effect This is the case with drugs that act irreversibly and these have been named hit and rundrugs" because their effect persits long after the drug has left the plasma Such drugs destroy or inactivate target tissue (enzyme, receptor and restoration of effect occurs only after days or weeks).
Metformin
Phenytoin
Tacrolimus
Cyclosporine