Reaction

Therapeutic Response Unexpected With Drug Substitution reporting signals

Last recalculated 2026-09-14T18:28:35.993900+00:00 · 4,158 reports · 39 co-occurring drugs

As of the last recalculation, Therapeutic Response Unexpected With Drug Substitution appears in 4,158 FAERS reports alongside 39 co-occurring drug terms. The strongest observed disproportionality signal is EXTENDED PHENYTOIN SODIUM (PRR 25.6).

Important: FAERS is a spontaneous, voluntary, unverified reporting system. PRR and ROR identify reporting patterns for investigation; they are not incidence rates and do not establish causation.

Drug	Co-reports	PRR	ROR
Extended Phenytoin Sodium	84	25.6	25.8
Zonisamide	50	17.1	17.2
Lamotrigine Chewable Dispersible	159	11.5	11.5
Lamotirigine	158	11.4	11.5
Lamotrigine Extended-Release	158	11.4	11.5
Phenytoin	44	10.7	10.7
Primidone	21	10.4	10.4
Bupropion Hydrochloride	168	8.8	8.8
Lamotrigine	207	8.2	8.2
Oxcarbazepine	52	8.1	8.1
Quinapril Hydrochloride	11	7.0	7.0
Carbamazepine	89	6.8	6.8
Sertraline	138	6.1	6.1
Fentanyl	112	5.8	5.8
Divalproex Sodium	53	5.8	5.8
Fluoxetine	70	5.3	5.3
Lisinopril And Hydrochlorothiazide Tablets	8	5.1	5.1
Lisinopril And Hydrochlorothiazide	10	4.9	4.9
Lithium Carbonate	16	4.7	4.7
Oxycodone And Acetaminophen Tablets	11	4.6	4.6
Fluoxetine Hydrochloride	112	4.5	4.5
Enalapril Maleate	22	4.5	4.5
Amlodipine Besylate And Benazepril Hydrochloride	8	4.3	4.3
Methylphenidate Hydrochloride	49	4.2	4.2
Sertraline Hydrochloride	97	4.2	4.2
Warfarin Sodium	36	3.9	3.9
Metformin Hcl	42	3.8	3.8
Sumatriptan Succinate	19	3.8	3.8
Levetiracetam	95	3.6	3.6
Levetiracetam In Sodium Chloride	54	3.5	3.5
Levetiracetam Oral	54	3.5	3.5
Levetiracetam Injection	54	3.5	3.5
Metoprolol Succinate Er Tablets	43	3.5	3.5
Prednisolone Acetate	7	3.4	3.4
Fexofenadine	11	3.3	3.3
Oxycodone And Acetaminophen	12	2.6	2.6
Ziprasidone Mesylate	7	2.5	2.5
Oxycodone Hydrochloride	92	2.1	2.1
Methylphenidate	11	1.9	1.9

Related reactions

Data source: openFDA FAERS. See the OpenPV methodology and limitations.