Hyoscine-N-butylbromide (Buscopan)

Hyoscine-N-butylbromide, more commonly known by its brand name, Buscopan, is an antimuscarinic agent, widely used in radiology as an antispasmodic agent. It is employed to freeze bowel motion as part of many fluoroscopic, CT and MRI studies (its main use for many years was for barium GI studies). It is widely used in Europe but unlicensed in the USA; hence an alternative agent, glucagon is often employed.

Pharmacology

Biochemistry

Hyoscine-N-butylbromide is a chemical derivative of hyoscine, which is chemically an alkaloid and was originally plant-derived, from the Solanaceae (nightshade) family. Atropine, another well-known antimuscarinic agent was also originally derived from a plant from the same family. 

Hyoscine without side branch modification is unsuitable as an antimuscarinic agent as it crosses the blood-brain barrier and may give rise to some rather unpleasant side effects, e.g. delusions and hallucinations.

Administration

In adults, the standard dosage is 20 mg usually administered IV or IM. It can also be given orally, rectally or subcutaneously, but these routes are generally avoided in imaging ^ref.

In children, the IV dosage is 0.3 mg/kg up to a maximal 20 mg.

Contraindications

Buscopan may cause an elevation in the heart rate - an antimuscarinic effect - and this may exacerbate symptoms in those with unstable cardiac disease: namely acute coronary syndrome, recurrent cardiac pain at rest, uncontrolled left ventricular failure, and recent ventricular arrhythmias. There is no concern in other cardiac diseases, e.g. well-controlled ischemic heart disease, atrial fibrillation.

From 1963-2006 in the UK there were only 12 reported cases of cardiac side-effects, and only one fatality ¹. Even allowing for likely under-reporting of complications, this is still an impressive lack of serious adverse effects, when one considers that literally millions of safe doses were administered during this 43-year period.

A history of chronic open-angle glaucoma (COAG) is not a contraindication; despite this many departments continue to withhold its use in patients with a history of ‘glaucoma’. The misunderstanding derives from hyoscine-N-butylbromide’s propensity to rarely precipitate acute angle-closure glaucoma (AACG), an entirely different form of the disease (see complications below).

The other contraindications often quoted are generally of dubious concern with the low doses employed in radiological practice:

• myasthenia gravis

  • theoretical risk due to its anticholinergic mechanism, but most patients experience no problems as Buscopan’s main action is on receptors in the autonomic system, not those of skeletal muscle

• paralytic ileus

  • Buscopan might worsen this, however, this does not seem to be an issue, probably due to its short duration of action

• prostatism

  • Buscopan can inhibit the detrusor muscle, conceivably triggering acute retention; however, this does not seem to be an issue, probably due to its short duration of action

• porphyria

  • Buscopan now considered safe ²

Complications

Hyoscine-N-butylbromide is generally very well-tolerated. Its side effects generally relate to its antimuscarinic mechanism of action, the commonest being some blurring of the vision due to its inhibition of accommodation, mainly in those aged >40 years. This effect usually wears off rapidly, within 45 minutes. Patients are advised not to drive until vision returns to normal.

Rarely hyoscine butylbromide may trigger acute angle-closure glaucoma (AACG), one of the causes of an acute red eye. This is an ophthalmological emergency, as untreated it is sight-threatening, however, as long as patients attend an ED and are treated promptly their vision will not be at risk. Unfortunately, patients with this condition do not know they are at risk in advance of an attack and it has a completely different pathogenesis to the open-angle form. Therefore it is pointless asking about a history of glaucoma prior to giving the drug.

Allergy

A true immune-mediated allergy is very rare, with only a few reported cases ¹. Angioneurotic edema has rarely been reported ²; anaphylaxis is equally rare ³.

Pregnancy

There is almost no data on the safety of hyoscine or related agents during pregnancy, most published data is from its use at the time of labor. No research has examined whether there is an increased chance of miscarriage, stillbirth, premature delivery or intrauterine growth restriction. Official advice in the UK is that "the use of hyoscine during pregnancy may be justified where there is a clear clinical indication." ^7,8.

History and etymology

Scopolamine derives its name from one of the plants in the nightshade family, Scopolia carniolica. This itself was named after its presumptive discoverer, J A Scopoli ⁵. Hyoscine also takes its name from a member of the nightshade family, Hyoscyamus niger ⁶. Buscopan was first brought to the market in 1951 ⁴.