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Underdosing - a New Clinical Concept in ICD-10 codes T36 – T50

By:  Chris Woolstenhulme, QCC, CMCS, CPC, CMRS
Published:  February 15th, 2015

T36-T50 Poisoning by, adverse effects of and underdosing of drugs, medicaments and biological substances (T36-T50)

Underdosing is a clinical concept new to ICD-10. Underdosing identifies situations referring to the practice of a patient taking less medication as prescribed by a physician, or a physician prescribing less than what is prescribed by the manufacturer, resulting in poor patient outcomes.


Inappropriate prescribing by the physician

  • Physician under prescribing with no justification                             
  • Outdated patient's weight in the medical record can give incorrect weight-based dosage.
  • Prescribing a reduced amount due to adverse affects
  • Antibiotics given at a reduced or “renal dose” and not increased once renal function recovers.  

Patient was prescribed medication to treat a condition and the patient was not compliant

Either deliberately or inadvertently, the patient did not take the medication as prescribed by their physician or took a reduced amount

Coding example:

36 YO Female came in complaining of sharp pains on the right side of her back. Patient was seen previously and treated for a UTI. Patient states she did not finish her medication (tetracycline), which resulted in pyelonephritis (Kidney infection).

Diagnosed as follows:

First Diagnosis

N10Acute tubulo-interstitial nephritis

This event triggered or was prolonged due to this circumstance

Second Diagnosis

T36.4X6AUnderdosing of tetracyclines, initial

underdosing code assigned as secondary

The appropriate 7th character is to be added to each code from category T36

A - initial encounter
D - subsequent encounter
S - sequela



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