The 1-Compartment Pharmacokinetic Fitter solves time–concentration data from IV / oral dosing for elimination rate constant (k), half-life (t½), volume of distribution (Vd), clearance (CL), AUC, and other key PK parameters using a one-compartment open model. The engine reuses BioPlayground's Phase 1 ELISA 4PL Levenberg-Marquardt nonlinear regression + analytic Jacobian + log-transform bounds + Gauss-Jordan linear solver, running entirely client-side with zero external dependencies. (D1: IV Bolus; D2–D5: Oral Bateman / Multi-dose / Diagnostics / Export)

(1) Alternative to PKSolver (Excel macro, dated / English-only) and Phoenix WinNonlin (annual six-figure license) — instant web + multilingual (2) Low barrier to entry for clinical pharmacology / drug-development newcomers (MS/PhD students) (3) Validated against gold-standard datasets (Vancomycin / Gentamicin / Theophylline) within ±2–5% (4) Reuses the Phase 1 ELISA 4PL LM core → extensible to IC50/EC50, qPCR Pfaffl, drug-stability fitting, etc.

① Choose route of administration (D1: IV Bolus; D2+: IV Infusion / Oral) ② Enter dose (mg) — defaults to 1000 mg (Vancomycin baseline) ③ Enter time–concentration pairs (drag handle to add/remove rows or "Load Vancomycin sample") ④ Pick weighting: • 1/y² (default, PK standard — Beal SL 1989, FDA Bioanalytical 2018) • Advanced toggle exposes Uniform / 1/y / 1/ŷ² ⑤ Click ▶ Fit — LM auto-converges (log-transform bounds + Jacobian chain-rule) ⑥ Output: k / t½ / Vd / CL / AUC / C₀ / R² / RSS / convergence + SVG concentration-time curve ⑦ D5 (planned): PNG / CSV / JSON export + full ko/en/ja i18n

Example 1) Vancomycin IV bolus (Bauer 3e Ch.16) → Dose = 1000 mg, t = [0.5, 1, 2, 4, 8, 12] h, C = [20, 16, 12, 7, 3, 1.3] mg/L → fit result: k ≈ 0.139 1/h, t½ ≈ 5.0 h, Vd ≈ 50 L, CL ≈ 6.9 L/h Example 2) Theophylline oral (SWY 7e Ch.7) — D2 planned → Dose = 300 mg, t = [0.25, 0.5, 1, 2, 4, 8, 12, 24] h, C = [3.3, 5.7, 7.1, 6.9, 5.0, 2.6, 1.4, 0.4] mg/L → expected: Ka ≈ 3.0 1/h, k ≈ 0.10 1/h Example 3) Gentamicin IV infusion (SWY 7e Ch.5) — D2 planned → R₀ = 100 mg/h, T_inf = 0.5 h, t = [0.5, 1, 2, 4, 8] h → expected: Vd ≈ 18 L, k ≈ 0.3 1/h