diff --git a/openhis-server-new/openhis-application/src/main/java/com/openhis/web/inpatient/service/DispensingServiceImpl.java b/openhis-server-new/openhis-application/src/main/java/com/openhis/web/inpatient/service/DispensingServiceImpl.java
new file mode 100644
index 000000000..e902d21ac
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+++ b/openhis-server-new/openhis-application/src/main/java/com/openhis/web/inpatient/service/DispensingServiceImpl.java
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+package com.openhis.web.inpatient.service;
+
+import com.openhis.web.inpatient.mapper.DispensingDetailMapper;
+import com.openhis.web.inpatient.mapper.DispensingSummaryMapper;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * 住院发退药业务实现
+ *
+ * 修复 Bug #503：发药明细与发药汇总单的触发时机不一致导致业务脱节风险。
+ *
+ * 解决思路：
+ * 1. 将发药明细的写入与发药汇总单的生成放在同一个事务中，确保两者要么同时成功，要么同时回滚。
+ * 2. 在写入明细后立即查询已写入的明细行数，只有在明细写入成功且行数大于 0 时才生成汇总单。
+ * 3. 将生成汇总单的 SQL 改为基于已写入的明细数据进行聚合，而不是基于旧的业务状态字段，避免因状态延迟导致汇总单提前生成。
+ * 4. 为防止并发冲突，在生成汇总单时使用行级锁 (FOR UPDATE) 锁定相关明细记录。
+ */
+@Service
+public class DispensingServiceImpl implements DispensingService {
+
+    private final DispensingDetailMapper dispensingDetailMapper;
+    private final DispensingSummaryMapper dispensingSummaryMapper;
+
+    public DispensingServiceImpl(DispensingDetailMapper dispensingDetailMapper,
+                                 DispensingSummaryMapper dispensingSummaryMapper) {
+        this.dispensingDetailMapper = dispensingDetailMapper;
+        this.dispensingSummaryMapper = dispensingSummaryMapper;
+    }
+
+    /**
+     * 发药操作，包含明细写入和汇总单生成，保持事务原子性。
+     *
+     * @param orderId   住院医嘱主键
+     * @param drugList  发药明细列表，每条包含 drugId、quantity 等信息
+     */
+    @Override
+    @Transactional(rollbackFor = Exception.class)
+    public void dispense(Long orderId, List<Map<String, Object>> drugList) {
+        if (orderId == null || drugList == null || drugList.isEmpty()) {
+            throw new IllegalArgumentException("发药参数缺失或明细为空");
+        }
+
+        // 1. 写入发药明细
+        for (Map<String, Object> drug : drugList) {
+            drug.put("orderId", orderId);
+            dispensingDetailMapper.insertDetail(drug);
+        }
+
+        // 2. 确认明细已写入（行锁防并发）
+        List<Map<String, Object>> writtenDetails = dispensingDetailMapper.selectDetailsForOrderForUpdate(orderId);
+        if (writtenDetails == null || writtenDetails.isEmpty()) {
+            throw new IllegalStateException("发药明细写入失败，无法生成汇总单");
+        }
+
+        // 3. 基于已写入的明细聚合生成汇总单
+        Map<String, Object> summary = dispensingSummaryMapper.calculateSummaryFromDetails(orderId);
+        if (summary == null || summary.isEmpty()) {
+            throw new IllegalStateException("汇总单计算失败");
+        }
+
+        // 4. 写入汇总单
+        dispensingSummaryMapper.insertSummary(summary);
+    }
+}