Urine retention in a child treated with oral salbutamol.

It is known that voiding difficulties can be caused by some drugs, but little is known about the role about the route of administration, especially in children. We report here a case of a 3-year old Italian boy referred to the Pediatric Emergency Unit complaining of two episodes of acute urinary retention, both after therapy with oral salbutamol. In spite of recommendations to use inhaled salbutamol to treat acute wheezing, oral salbutamol is still sometimes used in some settings. Whereas other side effects of systemic salbutamol are described in children, to our knowledge this is the first description of acute urinary retention as an adverse drug reaction to oral salbutamol.

A 2-year, 8-month-old Italian child was referred to our Pediatric Emergency Unit with complaint of urinary retention. The patient was prescribed salbutamol therapy by the family pediatrician 4 days ago for an episode of wheezing. At this time, the route of salbutamol administration was not enquired. At the time of presentation, he had not gained continence of the sphincter muscles. The only abnormalities revealed on the physical examination were small eczematous eruptions on his face and a full bladder. This was found by palpation and percussion of the suprapubic area. The blood urea nitrogen and creatinine concentration were normal (blood creatinine = 0.51 mg/dL, blood urea nitrogen=25 mg/dL). A urine test strip resulted negative. Moreover, microscopic urinalysis and the urine culture were also negative. Catheterization was performed and 300 mL of clear urine was collected with rapid improvement of the symptoms. The child was then discharged with the diagnosis of idiopathic urinary retention.

The second episode occurred when the child was 3 years old. At that time also, he had not gained continence of the sphincter muscles. Again, physical examination revealed no abnormalities except for a full bladder. The parents, asked about the use of drugs, reported that the child was taking salbutamol again for wheezing. A detailed medical history revealed that the child was taking 1.5 mg of salbutamol orally three times a day, equivalent to the dosage of 0.1 mg/kg/dose (body weight 15 kg). This dose was the same used during the first episode. Both times, the child was given a bronchodilator orally by the family pediatrician because of the difficulty to coordinate the use of an inhaler expressed by parents. Catheterization was performed and 250 mL of clear urine was collected. The voiding difficulty disappeared when the oral salbutamol was stopped. A re-challenge was not performed.

A case of voiding difficulty in a child treated with inhaled ipratropium and salbutamol has been reported,[1] but to the best of our knowledge urinary retention as an adverse effect of systemic salbutamol has not yet been described in children so far. The urinary bladder of man and several animals has been studied in vitro with respect to the type of β-adrenergic receptors, and it is suggested that the β-adrenergic receptors in the human bladder are of a third type.[2] It is also known that the adrenergic stimulation of the human detrusor is mediated mainly through β3-adrenoreceptor activation.[3] This is supported by the observation that in human bladder there is a predominant expression of β3-adrenoreceptor (AR) messenger RNA. Concentration-dependant relaxing potential of salbutamol on the urinary bladder smooth muscle mediated by β-adrenoceptor activation has also been demonstrated in animals.[45] We hypothesize that voiding difficulty in this child was due to the sympathetic activity of salbutamol on the bladder. In our case, there was no concomitant drugs administration and oral salbutamol was not overdosed. We hypothesize that the relaxation of detrusor muscle in our patient may be due to the stimulation of both β3 and β2-adrenoreceptors, the latter being more sensitive because of a possible polymorphism that enhanced the action of salbutamol on detrusor muscle, even if the dose of salbutamol was appropriate.

In spite of the advantages of the inhaled form of salbutamol, oral salbutamol continues to be considered a treatment option in some settings, especially by community physicians. This case underlines the necessity to ask the parents about the use of inhaled bronchodilators and to enquire about the route of administration in the assessment of voiding problems in children.