Which one of the following medical emergency drugs must be administered by intramuscular injection rather than orally?

Adrenaline is indeed the drug that must be administered via intramuscular injection rather than orally because of its pharmacokinetic properties. When given intramuscularly, adrenaline is absorbed quickly into the bloodstream, allowing for rapid onset of action in emergency situations, such as anaphylaxis or severe asthma attacks. This method of administration bypasses the gastrointestinal tract, where the drug would be subject to degradation and a delayed effect if taken orally.

Other medications listed have different modes of administration. For example, aspirin is typically given orally for pain relief or to reduce inflammation, glyceryl trinitrate is often administered sublingually to treat angina, and salbutamol is commonly administered via inhalation to open airways in asthma management. These differences emphasize the importance of the route of administration in maximizing the effectiveness and speed of therapeutic interventions during medical emergencies.