by egpat 12 Apr 2024
What is this drug, Tamsulosin? The suffix -osin indicates it is an alpha blocker, and this tamsulosin is indicated for the treatment of benign prostatic hyperplasia or hypertrophy, commonly known as BPH. In this condition, we can observe enlargement of the prostate gland, resulting in decreased urinary output.
The prostate gland flanks the urethra, and with a normal size of the prostate gland, the urine output is normal, but in patients with an age greater than 60 years, we can observe some prostate enlargement, particularly this prostate enlargement, which is more common in patients with an age greater than 80 years. So in such conditions, because of prostate enlargement, the urethral pathway is somewhat constricted, so that even by constriction of the bladder, urine cannot be emptied, completely resulting in urinary retention. So in such patients, we can observe increased urinary frequency as well as urgency because the urine is not cleared from the bladder even by constriction of the bladder, and there is decreased urinary flow.
These two conditions result in the incomplete emptying of the bladder, so even though urinary frequency is increased, the bladder is not completely emptied, resulting in discomfort in the patients. So in such patients, we can observe increased urinary frequency as well as urgency, but urinary output is somewhat reduced. In those patients, tamsulosin can be used, which increases the urinary flow by relaxing the prostate tissue as well as the bladder neck muscles so that urinary flow can be increased.
When tamsulosin is used for BPH, a few important precautions should be considered. Here we will explore the precautions and important side effects of tamsulosin.
One of the important precautions of tamsulosin is that this drug can act on the vascular smooth muscle, which is expressed with alpha-1 receptors. These alpha receptors are responsible for vasoconstriction. Now tamsulosin acts as an alpha-1 blocker, so it blocks the alpha-1 receptors, resulting in vasodilation.
Now this vasodilation produces some hypotension and a decrease in blood pressure, which leads to so many side effects. Particularly, this hypotension changes with posture; that's why it's also called postural hypotension. So postural hypotension is one of the important side effects of tamsulosin. In this condition, the blood pressure is not changed with the gravitational pressure, and a change in posture leads to some hypotension. That's why this postural hypotension is also called orthostatic hypotension. So with the tamsulosin, we can observe a small decrease in both systolic and diastolic blood pressure. It can cause orthostatic hypotension, which changes with posture. So tamsulosin produces postural hypotension, resulting in the various symptoms in the patients. It can produce some lightheadedness because of postural hypotension and dizziness; some reeling sensations, even vertigo, can be produced.
The patient may be in a confused state, and all these conditions may result in syncope, the falling sensation within the patient. So care should be taken when this postural hypotension is significantly observed in the patients. This is more important for those patients who are driving the vehicles; otherwise, for those patients working with machinery, caution should be taken to monitor any symptoms of postural hypertension.
Similarly, this drug can produce one of the conditions, priapism, which is a very rare condition that is observed only in one patient out of 50 000 patients. Again, this is because of the vasodilation of the arteries supplying the corpus cavernosa. In this condition, there is a persistent erection of the penis for more than four hours without any relation to the time of intercourse or sexual interaction, and because of this prolonged erection, it may result in some painful erection in the patient. Even though this is a rare condition observed with tamsulosin, if it is observed, care should be taken because if it is left untreated, it may lead to some impotence in the patient.
Similarly, tamsulosin can be converted into metabolites by the cytochrome p450 system; one of the major metabolic pathways is the CYP3A4 enzyme. So many of the drugs are there that inhibit the CYP3A4 enzyme activity. For instance, ketoconazole is a strong inhibitor of the CYP3A4 enzyme, thereby inhibiting the metabolism of tamsulosin. When its metabolism is inhibited, its serum levels are increased, resulting in increased toxic reactions such as significant hypotension in the patients. That's why ketoconazole is contraindicated with tamsulosin.
Similarly, a few drugs, such as erythromycin, can also inhibit the CYP3A4 enzyme activity, but it is a moderate enzyme inhibitor. So when this tamsulosin is combined with erythromycin, caution should be taken to monitor any significant hypotension or toxic reactions to tamsulosin.
Another metabolic pathway for tamsulosin is mediated by the CYP2D6 enzyme. This is a minor metabolic pathway compared with the CYP3A4 enzyme. So few of the drugs, such as paroxetine and terbinafine, are going to inhibit this enzyme activity. So again, these drugs can increase the levels of tamsulosin. That's why these drugs should be carefully combined with tamsulosin. Particularly because of these interactions, when these drugs are co-prescribed with tamsulosin, a low dose of tamsulosin should be used, and it should be used at 0.4 mg in order to minimize these drug interactions.
Another important drug interaction is observed with phosphodiesterase type 5 inhibitors. We have drugs like sildenafil, tadalafil, vardenafil, and avanafil; all of these are phosphodiesterase type 5 inhibitors. They are used for the treatment of erectile dysfunction as well as pulmonary hypertension. These drugs mainly produce hypotension as an important side effect. So when these drugs are combined with tamsulosin, this hypotensive effect is more pronounced, resulting in severe hypotension, collapse, even coma, and death in the patients. So again, care should be taken when this tamsulosin is combined with phosphodiesterase type 5 inhibitors.
Similarly, this drug can produce intraoperative floppy iris syndrome (IFIS) during cataract surgery. This is not observed in all the patients. Those patients who are undergoing cataract surgery and who are administered tamsulosin before the surgery may have one of the syndromes, intraoperative floppy iris syndrome. Normally, during the cataract surgery, the lens is going to be incorporated by a micro-incision. So after the incision, the lens is going to be incorporated, and this method is known as phacoemulsification. But for this process, the pupil should be dilated. So proper dilatation of the eye is required. In the presence of tamsulosin, we can observe poor pupil dilatation and even miosis, pupillary constriction, and flaccid iris. All these conditions are collectively known as intraoperative floppy iris syndrome. So in such patients, tamsulosin should be carefully used because it interacts with cataract surgery.
The important side effects of tamsulosin are mainly related to its vasodilatory reactions. It can produce side effects related to the CNS, such as headaches because of cranial vasodilation, dizziness, lightheadedness, blurred vision, somnolence, and drowsiness, as well as some disturbance in sleep resulting in insomnia. All these side effects can be observed with tamsulosin.
Similarly, by acting on the urogenital system, it can produce some abnormal ejaculation. Prolonged erection can be observed, which may lead to some abnormal ejaculation in the patients.
It can also affect the respiratory system, resulting in rhinitis and pharyngitis, but apart from these side effects, one of the most important side effects of tamsulosin is hypotension, particularly postural hypotension. Because of this hypotension, it can produce some syncope in the patients, as well as increase cardiac activity, resulting in palpitations and less chest pain.
Here is a video on the precautions and side effects of tamsulosin, exploring all these key facts in detail.
Tamsulosin is indicated for the treatment of BPH at two doses: 0.4 mg and 0.8 mg. It is initially started at a low dose, such as 0.4 mg, but when this drug is given, it can produce some postural hypotension or orthostatic hypotension, resulting in syncope as well as fainting. So caution should be taken to monitor any symptoms of postural hypotension, and it should be carefully combined with CYP3A4 inhibitors as well as CYP2D6 inhibitors. When it is combined with phosphodiesterase type 5 inhibitors, it can produce some significant hypotension. During the cataract surgery, it can interact with the procedure and produce some intraoperative floppy iris syndrome, and very rarely, it can produce some prolonged erection of the penis, resulting in priapism. So with these precautions, tamsulosin can be used in the treatment of BPH.