Effects in the Cardiovascular System (part 2)
There is another class of agents requiring special attention: α-blockers (e.g., doxazosin, terazosin, or tamsulosin) used as antihypertensive agents or in the treatment of benign prostate hyperplasia because of potential enhancement of blood pressure-lowering effects. For vardenafil, tadalfil, and sildenafil, the label precaution is used for a combination with α-blockers—especially with higher doses. No more than 25 mg of sildenafil should be taken within a 4-h window with an α-blocking agent.
In summary, the three available inhibitors of PDE-5 are well-tolerated by most of the cardiovascular patients, and blood pressure-lowering effects are mild. Generally, a base-line blood pressure of more than 90/60 mmHg should be a prerequisite for PDE-5 inhib-itors (or any vasodilator) to be applied. Various antihypertensive agents can safely be combined with sildenafil, vardenafil, or tadalafil; however, an NO donor cannot be com-bined, because hypotension can be life-threatening. Additionally, combination with α-blockers should be used with caution, as described earlier. It must again be emphasized that for PDE-5 inhibitors to be administered, a cardiovascular patient must achieve a stable cardiac condition without use of nitrates up to a level of 3 to 5 METs.
Save these important data, the effects of PDE-5 inhibitors on pulmonary arteries and pulmonary artery resistance are of special interest. There is increasing evidence that these agents may be useful in primary and some forms of secondary pulmonary hypertension. They appear to reduce pulmonary artery resistance and attenuate the effec-tive right-to-left shunting in some conditions. Most interestingly, there might be small, but relevant, differences between the three agents. Additional indications for these substances are conceivable in the near future.