2.1 Study Design and Patient Selection
This study is a single-centre, retrospective, PSM case‒control study. Eligible patients included those who developed DITP after treatment with drugs in our hospital from January 1, 2021, to December 31, 2021.
All patient data, including medical records and examination information, were obtained from the Hospital Information System (HIS). The ADE-ASAS-Ⅱ was based on trigger technology and text recognition technology, which can be connected to the HIS to extract patient information. Detailed descriptions of the ADE-ASAS-Ⅱ and its applications have been described in our previous study[16–18]. The monitoring plan of this study was conducted in the full-prescription mode, and the investigator preset the alarm index of the trigger without the monitoring drug, so once the monitoring index triggered the alarm index, the system could actively monitor all drugs that had a temporal relationship with TP as an early warning signal of DITP. Then, two clinical pharmacists blindly evaluated the alarm cases to confirm the results, and the cases with inconsistent evaluation results were submitted to the experts for final judgement to determine whether DITP occurred.
The inclusion criteria were as follows: 1) two consecutive platelet (PLT) counts that were < 100×109/L-1; 2) age ≥ 18 years old; and 3) a full prescription model (temporary and long-term prescriptions).
The exclusion criteria were as follows: 1) baseline PLT < 100×109/L-1; 2) patients with incomplete laboratory indexes before or after medication administration; 3) patients with incomplete clinical records; 4) patients of the haematology department; 5) involved drugs used in transarterial chemoembolization; and 5) a diagnosis that may cause TP, including primary immune thrombocytopenia, pseudothrombocytopenia purpura, haemophagocytic syndrome, thrombotic microvascular disease, disseminated intravascular coagulation, haemolUS syndrome, systemic lupus erythematosus, antiphospholipid syndrome, hyperplenism, myelodysplastic syndrome, leukaemia, aplastic anaemia, Gaucher disease (Gaucher disease), Evans syndrome, Fanconi anaemia, platelet angiohemophilia, hereditary thrombocytopenia (giant platelet syndrome, grey platelet syndrome, Berna And rd-Soulier syndrome, thrombocytopenia with radial deletion syndrome, Wiskott-Aldrich syndrome, MYH 9-associated disease), rheumatoid arthritis, lymphoma, HELLP syndrome, and cirrhosis.
The Naranjo Adverse Drug Reaction Probability Scale (Naranjo Scale) was used as a causality assessment tool[19].The diagnosis of an ADR was assigned to a probability category from the total score as follows: definite ≥ 9, probable 5 to 8, possible 1 to 4, and doubtful ≤ 0. Patients with scores ≥ 1 were defined as having DITP. Controls were defined as patients treated with similar drugs who did not develop DITP. To minimize confounding bias due to demographic characteristics, we performed 1:3 propensity core matching between the DITP and non-DITP groups to make the groups more comparable.
2.2 Data Collection and Definitions
Patient data were extracted from the HIS using the ADE-ASAS-Ⅱ. The patient characteristics included age, sex, weight, smoking history, drinking history, drug and food allergy history, history of autoimmune diseases, length of hospital days, suspected drug duration, and surgery before using suspected drugs. Concomitant drugs included antiplatelet drugs, anticoagulant drugs, antibiotics, antineoplastic drugs, immunosuppressant, and nonsteroidal anti-inflammatory drugs (NASIDs). Laboratory data included haemoglobin (HB), red blood cell (RBC) count, white blood cell (WBC) count, neutrophil (NEU) count, eosinophil (EOS) count, basophil (BASO) count, lymphocyte (LYM) count, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin (MCHC), red blood cell distribution width (RDW), PLT, mean platelet volume (MPV), direct bilirubin (DBIL), total bilirubin (TBIL), alanine transaminase (ALT), aspartate aminotransferase (AST), gamma glutamyl transferase (GGT), AST/ALT ratio, blood urea nitrogen (BUN), and estimated glomerular filtration rate (eGFR). Secondary data, such as eGFR, were calculated. We used the epidemiological collaborative creatinine equation (CKD-EPI) to calculate eGFR because it is more accuratethan the dietary modification (MDRD) formula recommended by clinical practice guidelines[20, 21]. Baseline PLT was defined as the last laboratory measurement between 7 days before and 2 hours after suspected drug administration. The other laboratory values were the most recent laboratory findings before the suspected drug was administered.
2.3 Statistical methods:
All statistical analyses and model development were performed with the statistical software packages R 4.0.2 (http://www.R-project.org, The R Foundation), STATA software (version 16.0) and Free Statistics software versions 1.7. For baseline characteristics, qualitative data were expressed by quantity and percentage using the χ2 test or Fisher's exact probability test. Quantitative data were presented as the mean ± standard deviation (standard deviation, SD) using the t test; those not meeting the normal distribution are presented as median and interquartile spacing (inter quartile range, IQR) using the Mann‒Whitney U test. All P values were flanked, and P < 0.05 was statistically significant.
To achieve similar baseline characteristics between the two groups, the patients with DITP and DITP and without DITP were matched using PSM. A 1:3 scale matching (calliper value of 0.05) was performed using the "psmatch2 package" of the STATA software. The propensity score was assessed according to age, sex, and BMI.
The cases and controls were matched with percentages of 70% and 30% to the development and validation groups, respectively. To identify the variables to build the DITP prediction model, we used the LASSO cross-validation algorithm to screen the variables [22]. We used logistic regression analysis for the development group. After the univariate analysis, the variables with significant differences (P < 0.05) were included in the LASSO regression algorithm to screen for predictors of DITP, the parameters with a parameter regression coefficient of 0 were deleted for dimension reduction, 5-fold cross validation was conducted, and two dotted lines were drawn at the selected values. Finally, the variables corresponding to the optimal λ were used to draw the nomogram.
The model was validated in terms of discrimination and calibration. Model discrimination was evaluated using the receiver operating characteristic (ROC) curve and the area under the curve (AUC). The calibration degree of the model was evaluated using a calibration curve.