The golden run of India's prize shooter Gagan Narang ended at the Commonwealth Games on Tuesday when his sick partner struggled after refusing to take medication for fear of failing a doping test.

The 27-year-old Narang, who has won eight Commonwealth Games golds including four in Delhi, surprisingly finished outside the medals in the men's 50m Rifle Prone Pairs after a poor performance from partner Hariom Singh.

"It was very bad," Singh said. "I have not been well for four or five days, so I could not concentrate properly. I could not take medicine also because of the doping issue."

There have been two doping cases at the Games, Nigerian sprinters Samuel Olon and Osayemi Oludamola testing positive for the banned substance methylhexaneamine which is commonly used in nasal decongestants.

Narang, who won four Commonwealth golds in Melbourne four years ago, has one last chance to add to his medal haul in the 50m Rifle Prone singles on Wednesday.

India guaranteed their greatest Commonwealth Games gold medal haul on Tuesday when women's 10m air pistol pair Annu Raj Singh and Heena Sidhu secured the hosts' 31st title.

India equalled their previous best tally of 30 from the 2002 Manchester Games when Krishna Poonia won gold in the women's discus on Monday. Poonia's victory also ended India's 52-year wait for athletics gold.

While world champion Tejaswini Sawant or the pairing of Samresh Jung and Chandrasekhar Kumar Chaudhary looked the more likely to earn India's milestone gold medal, it was the women's pair that took the honour at Dr Karni Singh Shooting Range.

"The score is a little less than it should have been, but it's okay for today," Sidhu said.

Sawant lost out to Scotland's Jen McIntosh in the women's 50m rifle prone singles while Jung and Chaudhary came second best to Singapore's Bin Gai and Lip Meng Poh in the men's 25m standard pistol pairs.