Contraindications and warnings for use
The use of terazosin can cause a lowering of blood pressure due to its vasodilator effect, which in some cases, especially in subjects suffering from low blood pressure, can cause dizziness, weakness and even fainting; in these cases the patient should be laid down on a bed, lying down, until the symptoms disappear. The onset of dizziness and sudden syncope after the administration of terazosin is much greater in patients who use other antihypertensive drugs, in particular drugs of the class of ACE inhibitors or diuretics; therefore it is recommended to avoid co-administering terazosin with such drugs or at least to consider careful dose adjustment. These particular precautionary measures in avoiding the administration of antihypertensive drugs together with terazosin are very useful in avoiding the onset of severe hypotension.
Another class of drugs that it is not recommended to administer together with terazosin is that of phosphodiesterase type 5 inhibitors, such as sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra); therefore patients taking terazosin are advised to consult your doctor first if you are using any of the above medications for the treatment of erectile dysfunction.
From several clinical studies it has emerged that the occurrence of orthostatic hypotension after the administration of terazosin is greater in patients treated for symptoms of benign prostatic hyperplasia than in those treated for arterial hypertension, with a higher incidence in patients over 65 years of age; this is obviously due to the dose of terazosin used, which is very often higher in patients suffering from BPH.
Before starting the treatment of benign prostatic hyperplasia with terazosin it is recommended to undergo a careful check to exclude that the symptoms are actually attributable to prostate cancer, to be repeated even during treatment; in this regard, it is recommended to perform both digital rectal examination of the prostate and the determination of prostate specific antigen (PSA). In fact, the plasma concentration of prostate specific antigen is an important tool for detecting the presence or absence of prostate cancer. If the plasma concentration of the prostate specific antigen is greater than 4 ng / ml it is recommended to perform other checks and possibly a biopsy of the prostate, because these values may indicate the presence of prostate cancer.
Another drawback of treatment with terazosin can occur during cataract removal surgery; in some patients previously treated with terazosin the onset of the Intra-operative Floppy Iris Syndrome, which consists in the narrowing of the iris and in the shrinking of the pupil; in most cases patients had recently stopped terazosin treatment, 2 to 14 days before surgery, but in some very rare cases patients had stopped treatment more than 5 months before surgery. Therefore, in case the patient already knows that he must undergo surgery to remove the cataract, it is not advisable to start treatment with terazosin. It is also recommended that the ophthalmologist and the surgeon, during the pre-operative evaluation, to ascertain the possibility that the patient has been treated with terazosin, in order to have all the necessary information and means (such as for example the ring that it is used for the enlargement of the iris) to perform the surgery at its best.
Terazosin is metabolised, like most drugs, by the large family of CYP450 enzymes, particularly by the CYP3A4 isoenzyme. Therefore, all inhibitors of the CYP450 enzyme system, in particular inhibitors of the CYP3A4 isoenzyme, can cause changes in the plasma concentration of terazosin. In fact, the administration of terazosin together with ketoconazole, which is a strong inhibitor of CYP3A4, led to a significant increase in the plasma concentration of terazosin; therefore, concomitant administration of these two drugs is not recommended. Furthermore, as terazosin is metabolized almost entirely by the liver, administration of the drug to patients with moderately or severely impaired liver function is not recommended, although specific clinical studies on the effects of terazosin in patients with severely impaired liver function are not recommended. still exhaustive.
In the event of an overdose of terazosin, a drop in blood pressure may occur, leading to fainting, with vomiting and diarrhea; to lower the plasma levels of terazosin in case of over-dosage, it is recommended to undergo gastric lavages, in order to reduce the absorption of the drug, and to administer vasoconstrictors to counteract the lowering of blood pressure.
Pregnancy and breastfeeding
Before starting treatment with terazosin, the patient must inform her doctor about her pregnancy status or the planning of the same in the near future, in order to discuss with the doctor the risks and benefits deriving from the use of the drug during the pregnancy.
Until now, there are no appropriate clinical studies on the use of terazosin during pregnancy and the possible risks that may arise from it. Therefore recommendations and advice on the use of terazosin during pregnancy can be made based on clinical studies conducted on animals. For example, in a study conducted on rats it was noted that the administration of terazosin during pregnancy causes fetal resorption and a decrease in fetal weight; however it should be noted that the dose of terazosin administered was approximately 1300 times greater than the maximum therapeutic dose used in humans. In the same clinical study, this time in rabbits, it was noted that the administration of terazosin during pregnancy causes fetal resorption, a decrease in fetal weight and a greater than normal number of ribs (in this case the dose of terazosin administered was approximately 160 times higher than the maximum therapeutic dose used in humans). Finally, in postnatal studies conducted in rats given a dose of terazosin approximately 300 times higher than the maximum therapeutic dose used in humans, an increase in postpartum mortality was noted during the first three weeks of life of the newborn. Based on these clinical studies, due to insufficient human data, the use of terazosin during pregnancy is contraindicated.
Since there are not sufficient data even on the possibility of secretion of terazosin in breast milk, it is recommended to avoid the use of the drug during breastfeeding, especially in the first period of life of the newborn, or to seek another safer alternative drug.
Side and unwanted effects
Along with the desired therapeutic effects, a drug can also cause side or unwanted effects. Even though most patients using the drug do not experience any side effects, it is a professional obligation to mention all possible side effects that could occur following the administration of a given drug, ensuring that the patient is well informed and that can notify your doctor if any of these effects occur.
The most common undesirable effect that can occur following the administration of terazosin is dizziness, due to the hypotensive effect of the drug, which occurs in about 9% of treated patients. Another common undesirable effect of terazosin is sudden fainting, which affects about one percent of treated patients; to prevent this effect from occurring or to mitigate its extent, it is advisable not to get up suddenly, not to stay too long. stand for a long time and do not expose yourself in an excessive way to the hot climate; if you were to perceive the imminent fainting, it is recommended to lie down for a few minutes and then - before getting up - to sit another couple of minutes. Another side effect is the appearance of the flag iris syndrome (Intra-operative Floppy Iris Syndrome, which consists of the narrowing of the iris and the diminution of the pupil), which can occur during surgery for cataract removal, complicating the "surgery: if not managed properly, this complication can interfere with the positive outcome of the surgery itself.
Other less frequent side effects are those related to the gastrointestinal system, such as constipation, diarrhea, abdominal pain, dyspepsia and nausea; those related to the kidneys and urinary tract, such as increased urine production and the frequent need to urinate; those related to the respiratory system, such as nasal congestion and dyspnoea; those related to the cardiovascular system such as tachycardia, arrhythmia, edema, heart palpitations, orthostatic hypotension and peripheral ischaemia.
