Drugmaker Schering-Plough yesterday reported a slight rise in third-quarter earnings as quality control problems at its US plants continue to disrupt production of respiratory and other drugs. The US firm, which employs about 1,000 people in Cork and Wicklow, said it earned $601 million, or 41 US cents per share, compared with $591 million, or 40 US cents per share, a year earlier and in line with analyst forecasts.