Malegra FXT (generic name: sildenafil citrate and fluoxetine) is a combination of well-known sildenafil citrate (Viagra) and fluoxetine, a selective serotonin reuptake inhibitor (SSRI).
Antidepressants of the SSRI class including fluoxetine have long been used off-label to treat premature ejaculation. Delayed orgasm is a well known effect of such drugs.
Fluoxetine in combination with sildenafil citrate has been shown to be more effective than fluoxetine alone in delaying ejaculation and providing sexual satisfaction.
Usually a single dose before having sex is enough to achieve a satisfactory length of intercourse.