2026 ICD-10-CM Diagnosis Code T36.1X6AUnderdosing of cephalosporins and other beta-lactam antibiotics, initial encounter
T36.1X6A is a billable ICD-10-CM diagnosis code for underdosing of cephalosporins and other beta-lactam antibiotics, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). The code is not accepted as a principal diagnosis by the Medicare Code Editor. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Underdosing of drugs and medicaments, initial encounter.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T36.1X6A.
Coding GuidelinesGuidance
Underdosing refers to taking less of a medication than is prescribed by a provider or a manufacturer's instruction. Codes for underdosing should never be assigned as principal or first-listed codes. If a patient has a relapse or exacerbation of the medical condition for which the drug is prescribed because of the reduction in dose, then the medical condition itself should be coded.
The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of systemic antibiotics (T36). Use the following options for the applicable episode of care:
- A - initial encounter
- D - subsequent encounter
- S - sequela
Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Aztreonam
a monocyclic beta-lactam antibiotic originally isolated from chromobacterium violaceum. it is resistant to beta-lactamases and is used in gram-negative infections, especially of the meninges, bladder, and kidneys. it may cause a superinfection with gram-positive organisms.Cefaclor
semisynthetic, broad-spectrum antibiotic derivative of cephalexin.Cefadroxil
long-acting, broad-spectrum, water-soluble, cephalexin derivative.Cefamandole
semisynthetic wide-spectrum cephalosporin with prolonged action, probably due to beta-lactamase resistance. it is used also as the nafate.Cefatrizine
orally active semisynthetic cephalosporin antibiotic with broad-spectrum activity.Cefazolin
a semisynthetic cephalosporin analog with broad-spectrum antibiotic action due to inhibition of bacterial cell wall synthesis. it attains high serum levels and is excreted quickly via the urine.Cefixime
a third-generation cephalosporin antibiotic that is stable to hydrolysis by beta-lactamases.Cefmenoxime
a cephalosporin antibiotic that is administered intravenously or intramuscularly. it is active against most common gram-positive and gram-negative microorganisms, is a potent inhibitor of enterobacteriaceae, and is highly resistant to hydrolysis by beta-lactamases. the drug has a high rate of efficacy in many types of infection and to date no severe side effects have been noted.Cefmetazole
a semisynthetic cephamycin antibiotic with a broad spectrum of activity against both gram-positive and gram-negative microorganisms. it has a high rate of efficacy in many types of infection and to date no severe side effects have been noted.Cefonicid
a second-generation cephalosporin administered intravenously or intramuscularly. its bactericidal action results from inhibition of cell wall synthesis. it is used for urinary tract infections, lower respiratory tract infections, and soft tissue and bone infections.Cefoperazone
semisynthetic broad-spectrum cephalosporin with a tetrazolyl moiety that is resistant to beta-lactamase. it may be used to treat pseudomonas infections.Cefotaxime
semisynthetic broad-spectrum cephalosporin.Cefotetan
a semisynthetic cephamycin antibiotic that is administered intravenously or intramuscularly. the drug is highly resistant to a broad spectrum of beta-lactamases and is active against a wide range of both aerobic and anaerobic gram-positive and gram-negative microorganisms.Cefotiam
one of the cephalosporins that has a broad spectrum of activity against both gram-positive and gram-negative microorganisms.Cefoxitin
a semisynthetic cephamycin antibiotic resistant to beta-lactamase.Cefsulodin
a pyridinium-substituted semisynthetic, broad-spectrum antibacterial used especially for pseudomonas infections in debilitated patients.Ceftazidime
semisynthetic, broad-spectrum antibacterial derived from cephaloridine and used especially for pseudomonas and other gram-negative infections in debilitated patients.Ceftizoxime
a semisynthetic cephalosporin antibiotic which can be administered intravenously or by suppository. the drug is highly resistant to a broad spectrum of beta-lactamases and is active against a wide range of both aerobic and anaerobic gram-positive and gram-negative organisms. it has few side effects and is reported to be safe and effective in aged patients and in patients with hematologic disorders.Ceftriaxone
a broad-spectrum cephalosporin antibiotic and cefotaxime derivative with a very long half-life and high penetrability to meninges, eyes and inner ears.Cefuroxime
broad-spectrum cephalosporin antibiotic resistant to beta-lactamase. it has been proposed for infections with gram-negative and gram-positive organisms, gonorrhea, and haemophilus.Cephalexin
a semisynthetic cephalosporin antibiotic with antimicrobial activity similar to that of cephaloridine or cephalothin, but somewhat less potent. it is effective against both gram-positive and gram-negative organisms.Cephalosporinase
a cephalosporin antibiotic.Cephaloglycin
a cephalorsporin antibiotic.Cephaloridine
a cephalosporin antibiotic.Cephalosporins
a group of broad-spectrum antibiotics first isolated from the mediterranean fungus acremonium. they contain the beta-lactam moiety thia-azabicyclo-octenecarboxylic acid also called 7-aminocephalosporanic acid.First Generation Cephalosporins
cephalosporin agents with excellent coverage against gram-positive cocci, such as staphylococcus and streptococcus. they have some activity against the gram-negative bacteria, but in general, gram-negative activity is decreased compared to 2nd, 3rd, and 4th generation cephalosporins.Second Generation Cephalosporins
agents with less activity against gram-positive cocci than first generation cephalosporins but have increased activity against gram-negative bacilli.Third Generation Cephalosporins
agents that are structurally similar to other cephalosporins but have a broader spectrum of activity against bacteria than the first and second generation cephalosporins. these agents cover more resistant streptococcus, staphylococcus, gram-positive anaerobes, and more resistant strains of haemophilus, neisseria, proteus, escherichia coli, and klebsiella (hnpek).Cephalothin
a cephalosporin antibiotic.Cephradine
a semi-synthetic cephalosporin antibiotic.Clavulanic Acid
a beta-lactam antibiotic produced by the actinobacterium streptomyces clavuligerus. it is a suicide inhibitor of bacterial beta-lactamase enzymes. administered alone, it has only weak antibacterial activity against most organisms, but given in combination with other beta-lactam antibiotics it prevents antibiotic inactivation by microbial lactamase.Clavulanic Acids
acids, salts, and derivatives of clavulanic acid (c8h9o5n). they consist of those beta-lactam compounds that differ from penicillin in having the sulfur of the thiazolidine ring replaced by an oxygen. they have limited antibacterial action, but block bacterial beta-lactamase irreversibly, so that similar antibiotics are not broken down by the bacterial enzymes and therefore can exert their antibacterial effects.
Table of Drugs and ChemicalsClinical
Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.
Patient EducationClinical
Antibiotics
Antibiotics are medicines that fight bacterial infections in people and animals. They work by killing the bacteria or by making it hard for the bacteria to grow and multiply.
The full article covers:
- What are antibiotics?
- What do antibiotics treat?
- Do antibiotics treat viral infections?
- What are the side effects of antibiotics?
- Why is it important to take antibiotics only when they're needed?
- How do I use antibiotics correctly?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T36.1X6A to ICD-9-CMHistory
Code HistoryHistory
Questions About T36.1X6AOverview
Is T36.1X6A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of cephalosporins and other beta-lactam antibiotics, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T36.1X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of cephalosporins and other beta-lactam antibiotics, such as an emergency visit or first evaluation.
Can T36.1X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of cephalosporins and other beta-lactam antibiotics, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
Footnotes
[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.
