The cost of the three popular remedies for erectile dysfunction are all about the same, $9 per dose for sildenafil (Viagra), vardenafil (Levitra), or tadalafil (Cialis).  The largest size should always be bought, since all pills cost the same amount.  Some men will be able to cut the pills in half or in quarters and should do this on the first attempt in order to test how much is personally needed.  All work the same way, i.e., by blocking an enzyme called phosphodiesterase type 5.

The concentration of Viagra has been reported to be able to be increased by three methods: chewing the tablet and holding it under the tongue for a minute or two before swallowing the rest, consuming grapefruit juice 30-60 minutes earlier, and by taking the inexpensive over-the-counter cimetidine 800 mg. (Tagamet and others).  I have tried the first two so far and wasn't impressed.

Vardenafil (Levitra) Still Effective After Two Years: In a 12-month DB PC study with a 12-month extension of vardenafil 10 and 20 mg in 566 men with erectile dysfunction (ED), improvement was evident from week 4 and maintained through 2 years with both doses doing equally well. Penetration was achieved on 92-94% of attempts and erections that lasted long enough for successful intercourse were achieved on 87-89% of attempts. Side-effects were mild and transient with no cardiovascular safety concerns. Sustained efficacy and tolerability with vardenafil over 2 years of treatment in men with erectile dysfunction. Stief C, Porst H, Saenz De Tejada I, Ulbrich E, Beneke M; Vardenafil Study Group. Hannover, Germany. Int J Clin Pract. 2004 Mar;58(3):230-9

Bogus Research: Patients Preferred High Dose Tadalafil (Cialis) 2:1 Over Intermediate Dose Sildenafil (Viagra): In a DB Seattle crossover study, patients with ED were twice as likely to prefer tadalafil. A multicenter, randomized, double-blind, crossover study of patient preference for tadalafil 20 mg or sildenafil citrate 50 mg during initiation of treatment for erectile dysfunction. Govier F, Potempa AJ, Kaufman J, Denne J, Kovalenko P, Ahuja S. Clin Ther. 2003 Nov;25(11):2709-23. Ed: The dose of sildenafil used in this study was only half the maximum dose, whereas tadalafil was at its maximum dose.  This study was clearly rigged to favor Cialis.  The study was very likely funded by the manufacturers of Cialis. 

Erectile Dysfunction: Tadalafil (Cialis): Cialis is the third FDA approved ED drug, all of which are selective phosphodiesterase type 5 (PDE5) inhibitors. The others are sildenafil (Viagra) and vardenafil (Levitra). Cialis works in an average of 45 minutes compared to 30 minutes for the other two. Cialis lasts for 36 hours vs. 4 hours for the other two. A DB PC study of 348 men with ED found intercourse successful 24 hours after tadalafil 20 mg. in 53% vs. 29% with placebo and after 36 hours in 59% vs. 28% (H Porst et al, Urology 2003;62:121). Five trials involving 1112 men at 20 mg found 81% improved erections within the first 24 hours vs. 35% placebo. Intercourse was successful 75% of the time (GB Brock et al, J Urol 2002;168). 

    In a DB PC trial of 216 ED men with diabetes, 56% taking 10 mg. and 64% taking 20 mg reported improved erections vs. 25% placebo. (IS de Tejada, et al. Diabetes Care 2002;25:2159). In men with bilateral nerve-sparing radical prostatectomy, penetration with tadalafil was 54% vs. 32% with placebo (package insert; unpublished). 

    There are no adverse effects on spermatogenesis or reproductive hormones. Side-effects include headache, flushing, dyspepsia, rhinitis, back pain, and myalgia. All PDE5 drugs are contraindicated with nitroglycerin and nitrates. Tadalafil is contraindicated with doxazosin (Cardura) and similar drugs. Potent CYP3A4 inhibitors increase serum concentrations of tadalafil. This probably includes grapefruit juice. The Medical Letter recommends sticking with sildenafil (Viagra) until more information is available on safety. 

    Ed: Since all sizes of PDE5 pills cost the same amount, many men find they can buy the largest size, and cut it in half to get two doses for the price of one. By drinking grapefruit juice a little before the tadalafil, one quarter of a pill may be just as good as half a pill, thus getting four doses out of a single pill.

Cimetidine (Tagamet) Increases Viagra Blood Levels: In a study of giving sildenafil with or without cimetidine (800 mg) or 30-ml dose of a magnesium hydroxide/aluminium hydroxide antacid, the antacid had no impact on sildenafil blood levels.  The cimetidine did not affect how quickly the sildenafil blood level reached its peak, by did increase the general increased blood levels and the peak blood levels by 56% and 54%, respectively (P<0.01)(AUCt and Cmax). The effects of cimetidine and antacid on the pharmacokinetic profile of sildenafil citrate in healthy male volunteers. Wilner K, Laboy L, LeBel M. Pfizer Drugs. Br J Clin Pharmacol. 2002;53 Suppl 1:31S-36S.

Benign Prostatic Hypertrophy Increases Erectile Dysfunction: In the 4-year DB PC Proscar Long-Term Efficacy and Safety Study of 3,040 men with moderate to severe lower urinary tract symptoms and an enlarged prostate gland, at baseline every 1 point increase in benign prostatic hypertrophy urinary symptom score was associated with a 2% increased risk of erectile dysfunction (ED) even after controlling for age (p <0.001). At 48 months in placebo but not in finasteride treated men a 1-unit decrease in quasi-AUASS was associated with a slight but statistically significant decrease in ED. No association existed between increasing PSA and ED. The relationship among lower urinary tract symptoms, prostate specific antigen and erectile dysfunction in men with benign prostatic hyperplasia: results from the proscar long-term efficacy and safety study. Paick SH, Meehan A, et al. University of Washington, Seattle. Ed: Since finasteride seems to prevent both BPH and more ED, I expect that saw palmetto would, too.