How Do Beta3 Agonists Work?

Beta3 agonists are a relatively new class of medications prescribed to treat bladder overactivity which can cause urinary urgency and incontinence. Beta3 agonists ease the urination urge and increase bladder capacity by relaxing the bladder’s detrusor smooth muscle while the bladder is filling.

Beta3 agonists work by activating beta3 receptors, which are protein molecules on the detrusor muscle cell membranes. Beta3 receptors are adrenergic receptors that relax the detrusor muscle when activated by the hormones, epinephrine, and norepinephrine.

Beta3 agonists may be prescribed as monotherapy or in combination with a muscarinic antagonist. Muscarinic antagonists bind to muscarinic receptors and block the activity of acetylcholine, a chemical (neurotransmitter) that nerve endings secrete to make the detrusor muscle contract to release urine.

Beta3 agonists are administered as oral tablets or granules in suspensions, approved by the FDA for the treatment of the following conditions:

• Overactive bladder with symptoms of urge, incontinence, urgency, and frequency
• Pediatric neurogenic detrusor overactivity, a condition due to nerve damage or disease that causes overactivity of the bladder wall muscles, which normally relax to hold urine.

Side effects of beta3 agonists may include the following:

• Elevated blood pressure (BP) occurs predominantly in patients with preexisting hypertension
• Urinary tract infection
• Dry mouth
• Bronchitis (inflammation of the bronchial passage)
• Nasopharyngitis (inflammation of nose and throat)
• Sinusitis (inflammation of the sinuses)
• Rhinitis (inflammation of the nasal passage)
• Cystitis (bladder inflammation)
• Headache
• Back pain
• Arthralgia (joint pain)
• Diarrhea
• Nausea
• Constipation
• Dyspepsia (indigestion)
• Abdominal distention
• Gastritis
• Gastroenteritis
• Blurred vision
• Glaucoma (an eye condition that damages the optic nerve)
• Dizziness
• Fatigue
• Tachycardia (rapid heartbeat)
• Atrial fibrillation
• Palpitations
• Elevated BP
• Upper respiratory tract infection
• Cough
• Increase in residual urine volume
• Urinary retention
• Nephrolithiasis (kidney stones)
• Bladder pain
• Hot flush
• Skin and subcutaneous reactions such as:
  • Rash
  • Urticaria (hives)
  • Pruritus (itching)
  • Eczema
  • Drug eruption
  • Purpura (purple spots on the skin caused by small blood vessels bursting)
  • Lip edema
  • Angioedema (swelling in the tissue under the skin or mucous membranes including the face, lips, tongue, and larynx) with or without respiratory symptoms
  • Leukocytoclastic vasculitis (small vessel inflammation in the skin)
  • Stevens-Johnson syndrome (a rare medical emergency with flu-like symptoms and a painful rash) is associated with an increase in bilirubin and liver enzymes AST and ALT
• Reports of neoplasms (abnormal cell growth)
• Elevations in enzymes such as GGT, AST, ALT, and LDH
• Vulvovaginal pruritus
• Vaginal infection

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand names of beta3 agonist drugs include:

• Gemtesa
• mirabegron
• Myrbetriq
• vibegron