Keep from freezing. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Unfortunately, counterfeit drugs are easy to distribute through online pharmacies, and many men are tempted to purchase online due to lower costs and embarrassment 7. Severe liver disease. The following information includes only the average doses of this medicine. It might work longer if you have mild to moderate erectile dysfunction.Manufacture and sale of sildenafil citrate drugs known as “generic Viagra” is common in India, where Pfizer’s patent claim does not apply. Trade names include Kamagra (Ajanta . Viagra is available in 3 doses of 25, 50, and mg doses or as single packet doses (5). Whereas, Kamagra comes in doses of 50 or mg for the tablet variant. Kamagra also has an oral jelly variant, which only comes in mg sachets. Typically, your first prescription would be for 50mg tablets and is changed See more. Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or .