Background Benzathine penicillin G is indicated for intramuscular (IM) administration. There have been reports of unintentional intravenous (IV) administration, which has been associated with cardiorespiratory arrest and death. This article reports on a case of inadvertent IV administration of benzathine penicillin G instead of IM injection. Clinical details A 29‐year‐old Saudi army male with no history of any chronic illness visited the Security Forces Hospital in Makkah because of injuries to his left hand and left ear as a result of a bomb blast. The patient underwent surgery, and was conscious, oriented and vitally stable after the operation. He was prescribed benzathine penicillin G to prevent wound infection, but the injection was incorrectly administered IV instead of IM. Outcomes The patient did not exhibit any visible clinical symptoms after receiving the drug via the wrong route. The patient's vital signs were fine and he did not have a fever. The full complete blood count was normal, except for a mild elevation in the neutrophil count (84%) and a mild decrease in lymphocytes (8.8%). Random blood glucose was 149 mg/dL and the activated partial thromboplastin time was 39.3 s. All other laboratory investigations were within the normal range. The creatinine concentration fluctuated between 0.8 and 1 mg/dL. Conclusion This was an obvious case of a drug‐related problem categorised as a ‘wrong route error’. The role of clinical pharmacists in preventing such errors is important to ensure patient safety.