T42.5X6A Underdosing of mixed antiepileptics, initial encounter

Billable ICD-10-CM code, FY2026.

Built from T42.5X6 with 7th character A (initial encounter).

Applies from T42 Poisoning by, adverse effect of and underdosing of antiepileptic, sedative- hypnotic and antiparkinsonism drugs

Excludes2 (not included here)

• drug dependence and related mental and behavioral disorders due to psychoactive substance use (F10.--F19.-)

7th character note

• The appropriate 7th character is to be added to each code from category T42

7th character required

• A — initial encounter
• D — subsequent encounter
• S — sequela

Medicare Code Edits (MCE v43.1 (April 2026))

• Unacceptable principal diagnosis: These codes describe a circumstance which influences care but is not a current illness or injury, or capture only an underlying condition, and are unacceptable as principal diagnosis.

Code annotations containing back-references to T42.5X6A

Back-references to T42

• Use Additional: D46 Myelodysplastic syndromes ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: D52.1 Drug-induced folate deficiency anemia ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: D59.0 Drug-induced autoimmune hemolytic anemia ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: D59.2 Drug-induced nonautoimmune hemolytic anemia ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: D59.39 Other hemolytic-uremic syndrome ("code, if applicable, for adverse effect to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: D61.1 Drug-induced aplastic anemia ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: D64.2 Secondary sideroblastic anemia due to drugs and toxins ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: D64.2 Secondary sideroblastic anemia due to drugs and toxins ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: D70.2 Other drug-induced agranulocytosis ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: D72.12 Drug rash with eosinophilia and systemic symptoms syndrome ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: D84.821 Immunodeficiency due to drugs ("code for adverse effect if applicable, to identify adverse effect of drug (T36-T50 with fifth or six character 5)")
• Use Additional: D89.3 Immune reconstitution syndrome ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: E03.2 Hypothyroidism due to medicaments and other exogenous substances ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: E03.2 Hypothyroidism due to medicaments and other exogenous substances ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E06.4 Drug-induced thyroiditis ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: E09 Drug or chemical induced diabetes mellitus ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: E09 Drug or chemical induced diabetes mellitus ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E16.0 Drug-induced hypoglycemia without coma ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E22.1 Hyperprolactinemia ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E23.1 Drug-induced hypopituitarism ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E24.2 Drug-induced Cushing's syndrome ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E25.8 Other adrenogenital disorders ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E27.3 Drug-induced adrenocortical insufficiency ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E28.0 Estrogen excess ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E28.1 Androgen excess ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E29.1 Testicular hypofunction ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E61 Deficiency of other nutrient elements ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: E66.1 Drug-induced obesity ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: F02 Dementia in other diseases classified elsewhere ("intoxications (T36-T65)")
• Type 2 Excludes: F13.2 Sedative, hypnotic or anxiolytic-related dependence ("sedative, hypnotic, or anxiolytic poisoning (T42.-)")
• Use Additional: G21.19 Other drug induced secondary parkinsonism ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G24.0 Drug induced dystonia ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G25.1 Drug-induced tremor ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G25.3 Myoclonus ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G25.4 Drug-induced chorea ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G25.61 Drug induced tics ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G25.7 Other and unspecified drug induced movement disorders ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G40.5 Epileptic seizures related to external causes ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G43 Migraine ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G44.4 Drug-induced headache, not elsewhere classified ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G62.0 Drug-induced polyneuropathy ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G71.14 Drug induced myotonia ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: G72.0 Drug-induced myopathy ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: G92.8 Other toxic encephalopathy ("poisoning due to drug or toxin, if applicable, (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: G92.8 Other toxic encephalopathy ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: G92.9 Unspecified toxic encephalopathy ("poisoning due to drug or toxin, if applicable, (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: G92.9 Unspecified toxic encephalopathy ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: H21.81 Floppy iris syndrome ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: H26.3 Drug-induced cataract ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: H35.38 Toxic maculopathy ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: H35.38 Toxic maculopathy ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: H40.6 Glaucoma secondary to drugs ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: H91.0 Ototoxic hearing loss ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: H91.0 Ototoxic hearing loss ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: I42.7 Cardiomyopathy due to drug and external agent ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: I42.7 Cardiomyopathy due to drug and external agent ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: I47.21 Torsades de pointes ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: I95.2 Hypotension due to drugs ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: J70.2 Acute drug-induced interstitial lung disorders ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: J70.3 Chronic drug-induced interstitial lung disorders ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: J70.4 Drug-induced interstitial lung disorders, unspecified ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: J84.89 Other specified interstitial pulmonary diseases ("code, for adverse effect, to identify drug (T36-T50 with fifth or sixth character 5), if drug-induced")
• Use Additional: K12.32 Oral mucositis (ulcerative) due to other drugs ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: K22.1 Ulcer of esophagus ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: K22.1 Ulcer of esophagus ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: K52.1 Toxic gastroenteritis and colitis ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: K59.03 Drug induced constipation ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: K71 Toxic liver disease ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: K71 Toxic liver disease ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: K85.3 Drug induced acute pancreatitis ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L10.5 Drug-induced pemphigus ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L12.31 Epidermolysis bullosa due to drug ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L23.3 Allergic contact dermatitis due to drugs in contact with skin ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L24.4 Irritant contact dermatitis due to drugs in contact with skin ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L25.1 Unspecified contact dermatitis due to drugs in contact with skin ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L27.0 Generalized skin eruption due to drugs and medicaments taken internally ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L27.1 Localized skin eruption due to drugs and medicaments taken internally ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L29.81 Cholestatic pruritus ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L43.2 Lichenoid drug reaction ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L51 Erythema multiforme ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: L53.0 Toxic erythema ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: L53.0 Toxic erythema ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L56.0 Drug phototoxic response ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L56.1 Drug photoallergic response ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L64.0 Drug-induced androgenic alopecia ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L65 Other nonscarring hair loss ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L71 Rosacea ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: L93 Lupus erythematosus ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: M1A.2 Drug-induced chronic gout ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: M10.2 Drug-induced gout ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: M32.0 Drug-induced systemic lupus erythematosus ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: M34.2 Systemic sclerosis induced by drug and chemical ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: M34.2 Systemic sclerosis induced by drug and chemical ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: M80.8 Other osteoporosis with current pathological fracture ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: M81.8 Other osteoporosis without current pathological fracture ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: M83.5 Other drug-induced osteomalacia in adults ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Use Additional: M87.1 Osteonecrosis due to drugs ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: N14 Drug- and heavy-metal-induced tubulo-interstitial and tubular conditions ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")
• Use Additional: N14 Drug- and heavy-metal-induced tubulo-interstitial and tubular conditions ("code for adverse effect, if applicable, to identify drug (T36-T50 with fifth or sixth character 5)")
• Code First: P58.4 Neonatal jaundice due to drugs or toxins transmitted from mother or given to newborn ("poisoning due to drug or toxin, if applicable (T36-T65 with fifth or sixth character 1-4)")

Nearby codes

• T42.5X5 Adverse effect of mixed antiepileptics
• T42.5X5A Adverse effect of mixed antiepileptics, initial encounter
• T42.5X5D Adverse effect of mixed antiepileptics, subsequent encounter
• T42.5X5S Adverse effect of mixed antiepileptics, sequela
• T42.5X6 Underdosing of mixed antiepileptics
• T42.5X6A Underdosing of mixed antiepileptics, initial encounter (this code)
• T42.5X6D Underdosing of mixed antiepileptics, subsequent encounter
• T42.5X6S Underdosing of mixed antiepileptics, sequela
• T42.6 Poisoning by, adverse effect of and underdosing of other antiepileptic and sedative-hypnotic drugs
• T42.6X Poisoning by, adverse effect of and underdosing of other antiepileptic and sedative-hypnotic drugs
• T42.6X1 Poisoning by other antiepileptic and sedative-hypnotic drugs, accidental (unintentional)