Tamsulosin induced diarrhea: a case report

Introduction

Tamsulosin is a uroselective α_1A adrenergic receptor blocker used for benign prostatic hyperplasia with lower urinary tract symptoms.¹ Other α₁ blockers (nonselective subtypes) include prazosin, terazosin, and doxazocin. As per one large-scale study, dizziness, abnormal ejaculation, headache, hypotension, gastrointestinal disorder, nausea, cardiovascular disorder, impotence, and dry mouth are frequent side effects associated with tamsulosin.² The reported frequency of diarrhea with tamsulosin is 0.1–1%³ is lower compared with prazosin (<4%),⁴ terazosin (4%)⁵ and doxazosin (1–3%).⁶ Clinicians favor tamsulosin in the treatment of benign prostatic hyperplasia due to its uroselective action as well as the reduced cardiovascular and gastrointestinal side effects. Herewith, we report a case of tamsulosin-induced diarrhea.

Case presentation

A 52-year-old male patient visited the surgical outpatient department of Sir Takhtsinhji General Hospital, Bhavnagar, India with complaints of pain during micturition and increased frequency of urine for 5 months. Ultrasonography findings showed right kidney size 88 × 46 mm (normal), left kidney size 107 × 55 mm, with tiny calculous in upper calyx, prostate size 34 × 39 × 35 mm, volume 26 ml and postvoidal residual volume (PURV) of 65 ml. Urine routine microscopy and routine blood investigations were within the normal values. The patient was diagnosed with benign prostatic hyperplasia with urinary tract infection and was prescribed a tablet of tamsulosin 0.4 mg daily, a tablet of norfloxacin 400 mg twice a day, omeprazole 20 mg twice a day, as well as ibuprofen 400 mg and dicyclomine 10 mg every 8 h for 7 days. On taking the first dose of prescribed medications, he developed watery diarrhea with a frequency of 5–6 times per day. The patient took oral rehydration solution (ORS) but diarrhea did not recover. Tamsulosin was withdrawn on the third day while the other medication was continued. The frequency of diarrhea decreased and he recovered within 2 days of stopping the drug. As the patient’s urinary symptoms did not improve, tamsulosin 0.4 mg was prescribed again after 7 days. Following re-administration of tamsulosin, the patient redeveloped watery diarrhea within 24 h. The patient was given ORS and tamsulosin was continued. Diarrhea gradually improved within 7 days and was not reported thereafter. Tamsulosin was continued for 2.5 months after which the patient underwent visual internal urethrotomy. The patient did not have hypertension, diabetes, allergies or similar events. Moreover, there was no change in his regular diet pattern during and before the course of the event.

The patient’s written informed consent was obtained during extensive history taking.

Discussion

Diarrhea is a common side effect of many drugs. In the present case, the patient received tamsulosin, norfloxacin, omeprazole and ibuprofen, which can commonly cause diarrhea. Culture and viral polymerase chain reaction investigations of stool were not performed to rule out the infective diarrhea; however, the temporal relationship and positive de-challenge and re-challenge confirmed tamsulosin as the culprit drug. As per the Naranjo causality assessment scale, diarrhea was probably related to tamsulosin (score 8) whereas according to the World Health Organization causality assessment scale, the relationship between diarrhea and tamsulosin was probable.

Sympathetic stimulation in the gastrointestinal system causes intestinal relaxation (α₁ and β₂ receptors effect) and constriction of the sphincter (α₁ receptor effect). The blockade of the α₁ receptor results in increased peristaltic movement with relaxation of the sphincter that causes diarrhea. Diarrhea is reported with selective α₁ blockers whereas, the nonselective α blocker phenoxybenzamine is found useful for nonresponsive diarrhea in animals.⁷ Among selective α₁ blockers, the incidence of diarrhea is found less with a uroselective α₁ blocker. The differences in incidence of diarrhea with different α receptor blockers can be due to differences in α subtype receptor specificity. The α₁ receptors have three different subtypes: α_1A, α_1B and α_1D. The internal anal sphincter has α_1A and α_1D receptors which cause its constriction.⁸ However, which α₁ subtype exists in intestinal smooth muscle is not clear. The lower incidence of diarrhea with tamsulosin as compared with a nonselective subtype α₁ blocker (prazosin) may be due to lack of its effect on intestinal smooth muscle. Moreover, the tone of the internal anal sphincter reduces with age that may also contribute to diarrhea.

In the present case, the patient developed diarrhea within 24 h of re-administration of tamsulosin and recovered within 7 days even though the course was continued. This suggests that the patient could have developed a tolerance to this side effect. Clinicians should keep this side effect in mind when prescribing tamsulosin and the patient should be informed about this side effect as well as the possibility of developing a tolerance to the drug.