The sublingual form of medication refers to lozenges that patients hold in the mouth under the tongue until it dissolves. Captopril is a medication that can make the heart and blood vessels work more efficiently, so it is suitable for people who have cardiovascular problems. The sublingual captopril form is typically used for emergency situations, where a patient suddenly develops very high blood pressure.
As of 2011, scientists do not know exactly how captopril works. It appears that the drug blocks one step in the sequence of reactions that can lead to the blood vessels constricting, which can halt rising blood pressure. This step involves the alteration of a substance called angiotensin I into a related substance called angiotensin II.
Angiotensin II is a molecule that tells the blood vessels to tighten up. When the blood vessels are tightened, the pressure of the blood inside the vessels increases. Blocking the production of angiotensin II therefore prevents the blood vessels from constricting, and reduces the pressure of the blood running through them. The drug falls into a category of medicines called angiotensin converting enzyme (ACE) inhibitors. ACE is the enzyme that turns angiotensin I into angiotensin II, and captopril acts directly on ACE to block it from working. As well as this action, the drug also affects other substances such as bradykinin and aldosterone, which partially control blood pressure.
Due to these useful characteristics of captopril, the drug is often prescribed as a tablet for the patient to take over the long term. When the drug is in the sublingual captopril form, however, it is suitable for emergency situations. If a person suddenly suffers a rapid increase in blood pressure but is not at risk of organ damage, a condition known as hypertensive urgency, then sublingual captopril can be administered. In its position under the tongue, the patient does not need to swallow it, and this reduces the risk of choking when the person is suffering the symptoms.
Sublingual captopril is not a cure for cardiovascular disease, but rather controls the rate of blood pressure down to safe levels when necessary. The effects last for an hour or more, after which more medication may be required. Possible side effects include feeling more tired than normal, bruising more easily, and irritation of the mouth or throat. A risk of allergy or chest pain is also sometimes associated with the drug.