Worldwide prescription drug sales fell 1.6% in 2012, but from this year they are set to start growing slowly and will then steadily increase, to reach a value of $895 billion by 2018, according to new research.

The worst of the patent cliff is now in the past, according to the study, the sixth annual World Preview report produced by life science sector analysis group  Evaluate. The study is forecasting a surge in drug approvals, R&D productivity and investor confidence which it says will drive expansion to 2018.

Out of the $227 billion-worth of global drug sales that are due to be at risk from generic erosion following patent expirations, only $110 billion will be lost over the next five years, the study estimates, and says that the main reason for this will be the growing contribution of biological products to global sales.

By 2018, 50% of sales of the top 100 products worldwide are predicted to come from biological products. Moreover, these products are expected to experience lower levels of sales erosion from biosimilar competition than traditional small molecules have from generic versions, the report forecasts.

The study's other current key findings include that:

- Pfizer was the world-leading pharmaceutical company last year in terms of worldwide prescription drug sales, with Novartis directly behind. However, by 2018, Novartis will have taken over as the biggest pharmaceutical company for worldwide prescription drug sales;

- worldwide pharmaceutical R&D spending is forecast to reach a total of $149 billion by 2018, having experienced an annual average growth rate of 1.4% between 2012 and 2018;

- Teva Pharmaceuticals continued to be the world's leading generic drugmaker last year;

- the market for anticoagulant therapies is set to increase 11.5% between 2012 and 2018, achieving the highest worldwide sales growth of major therapy categories during the period. Also, within the top 100 prescription products, biological drugs are expected to account for more than 50% of sales by 2018;

- orphan drugs are expected to account for sales worth $127 billion globally by 2018, when they will represent 16% of the entire worldwide prescription drug market;

- AbbVie's tumour necrosis factor (TNF) inhibitor Humira (adalimumab) is expected to be the world's biggest-selling drug product in 2018; and

- Gilead's hepatitis C polymerase inhibitor sofosbuvir, remains the industry's most valuable R&D product.