From d7c08565e0319dda7db17b864b63838eb3234e14 Mon Sep 17 00:00:00 2001
From: Gero1999 <gerardojoro@gmail.com>
Date: Mon, 12 Jan 2026 11:41:59 +0100
Subject: [PATCH 1/4] add exclude message in half.life.R

---
 R/half.life.R | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/R/half.life.R b/R/half.life.R
index 0dab3f1e..49306f3b 100644
--- a/R/half.life.R
+++ b/R/half.life.R
@@ -180,6 +180,10 @@ pk.calc.half.life <- function(conc, time, tmax, tlast,
     # as.numeric is for units handling
     dfK <- data[as.numeric(data$time) > as.numeric(ret$tmax), ]
   }
+  if (sd(data$log_conc, na.rm = TRUE) == 0) {
+    # All concentrations are the same (non-zero) value
+    attr(ret, "exclude") <- "No point variability in concentrations for half-life calculation"
+  }
   if (manually.selected.points) {
     if (nrow(data) > 0) {
       fit <- fit_half_life(data=data, tlast=ret$tlast, conc_units=conc_units)
@@ -266,6 +270,7 @@ pk.calc.half.life <- function(conc, time, tmax, tlast,
       class = "pknca_halflife_too_few_points"
     )
   }
+
   # Drop the inputs of tmax and tlast, if given.
   if (!missing(tmax))
     ret$tmax <- NULL

From 88812001107ccc9d0ce575df2ca405b4caa4d818 Mon Sep 17 00:00:00 2001
From: Gero1999 <gerardojoro@gmail.com>
Date: Mon, 12 Jan 2026 11:49:04 +0100
Subject: [PATCH 2/4] add direct return in flat line case

---
 R/half.life.R | 1 +
 1 file changed, 1 insertion(+)

diff --git a/R/half.life.R b/R/half.life.R
index 49306f3b..0ac21718 100644
--- a/R/half.life.R
+++ b/R/half.life.R
@@ -183,6 +183,7 @@ pk.calc.half.life <- function(conc, time, tmax, tlast,
   if (sd(data$log_conc, na.rm = TRUE) == 0) {
     # All concentrations are the same (non-zero) value
     attr(ret, "exclude") <- "No point variability in concentrations for half-life calculation"
+    return(ret)
   }
   if (manually.selected.points) {
     if (nrow(data) > 0) {

From 00c4d25afac3a3a173145df1380e77be51be1add Mon Sep 17 00:00:00 2001
From: Gero1999 <gerardojoro@gmail.com>
Date: Mon, 12 Jan 2026 11:49:24 +0100
Subject: [PATCH 3/4] test: add test case for half.life calculation of a flat
 line

---
 tests/testthat/test-half.life.R | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tests/testthat/test-half.life.R b/tests/testthat/test-half.life.R
index 202fa421..71efdd0a 100644
--- a/tests/testthat/test-half.life.R
+++ b/tests/testthat/test-half.life.R
@@ -506,3 +506,20 @@ test_that("get_halflife_points method (1: PKNCAdata, 2: PKNCAresults)", {
     info = "get_halflife_points uses lambda.z.time.last, not tlast"
   )
 })
+
+test_that("half-life has a exclude message when it cannot be calculated for flat data", {
+  result <- suppressMessages(
+    pk.calc.half.life(
+      conc = c(1, 1, 1, 1),
+      time = c(0, 1, 2, 3),
+      min.hl.points = 3,
+      allow.tmax.in.half.life = TRUE,
+      adj.r.squared.factor = 0.0001,
+      check = FALSE
+    )
+  )
+  expect_equal(
+    attr(result, "exclude"),
+    "No point variability in concentrations for half-life calculation"
+  )
+})

From a69150ce239f3398e9153676bd0973537091a6eb Mon Sep 17 00:00:00 2001
From: Gero1999 <gerardojoro@gmail.com>
Date: Mon, 12 Jan 2026 11:51:33 +0100
Subject: [PATCH 4/4] add issue references (#503)

---
 R/half.life.R                   | 2 +-
 tests/testthat/test-half.life.R | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/R/half.life.R b/R/half.life.R
index 0ac21718..0ab7aab6 100644
--- a/R/half.life.R
+++ b/R/half.life.R
@@ -180,8 +180,8 @@ pk.calc.half.life <- function(conc, time, tmax, tlast,
     # as.numeric is for units handling
     dfK <- data[as.numeric(data$time) > as.numeric(ret$tmax), ]
   }
+  # When all concentrations are the same (non-zero) value cannot compute half-life (#503)
   if (sd(data$log_conc, na.rm = TRUE) == 0) {
-    # All concentrations are the same (non-zero) value
     attr(ret, "exclude") <- "No point variability in concentrations for half-life calculation"
     return(ret)
   }
diff --git a/tests/testthat/test-half.life.R b/tests/testthat/test-half.life.R
index 71efdd0a..afd97d8b 100644
--- a/tests/testthat/test-half.life.R
+++ b/tests/testthat/test-half.life.R
@@ -507,7 +507,7 @@ test_that("get_halflife_points method (1: PKNCAdata, 2: PKNCAresults)", {
   )
 })
 
-test_that("half-life has a exclude message when it cannot be calculated for flat data", {
+test_that("half-life has a exclude message when it cannot be calculated for flat data (#503)", {
   result <- suppressMessages(
     pk.calc.half.life(
       conc = c(1, 1, 1, 1),