Herbal medicine for people with diabetic retinopathy

What was the aim of this review?
The aim of this Cochrane Review was to find out if herbal medicine is useful for people with diabetic retinopathy when compared with placebo, no treatment, non-herbal (conventional) medicine or surgical treatment. Cochrane researchers collected and analysed all relevant studies to answer this question and found 10 studies.

Key messages
It is not certain if herbal medicine is of benefit to people with diabetic retinopathy.

What did this review study?
Diabetes is a life-long condition that means that there is too much sugar in the blood. Usually, our bodies regulate the levels of sugar in the blood with a hormone called insulin. In diabetes, either there is not enough insulin to deal with the sugar, or the insulin does not work. People with diabetes can experience problems with their eyes. High blood sugar can affect the blood vessels at the back of the eye. This is known as diabetic retinopathy and can lead to problems with vision, including blindness in severe cases.

Worldwide, many medicinal herbs or herbal extracts are used to treat diabetic retinopathy. The Cochrane researchers looked at six different types of herbal medicines: Ruscus extract tablet, Sanqi Tongshu capsule, tetramethylpyrazine injection, Xueshuantong injection, Xuesaitong injection and Puerarin injection. These treatments lasted from two weeks to 12 months.

What were the main results of the review?
The Cochrane researchers found 10 relevant studies involving 754 participants; nine studies were from China and one was from Poland.

These studies compared herbal medicine combined with conventional treatment with conventional treatment alone for people with diabetic retinopathy. None of the studies reported where the funding for the study came from. The findings were as follows.

• None of the studies reported on the progression of diabetic retinopathy.
• The studies provided low-certainty evidence that herbal extracts may have increased the chances of visual improvement (being able to read 2 or more additional lines on an Eye chart, which is used to measure visual acuity).
• The Cochrane researchers judged the evidence on some of the signs of diabetic retinopathy (such as reduction in blood vessels bleeding at the back of the eye) as being very low-certainty.
• Similarly, there was low-certainty evidence as to the effect of herbal extracts on blood sugar levels but the available evidence suggested little effect.
• Most of the studies did not report on side effects. Two studies reported minor side effects such as uncomfortable stomach, itching, dizziness and headache.

How up-to-date is this review?
The Cochrane researchers searched for studies that had been published up to June 2018.

Authors' conclusions: 

No conclusions could be drawn about the effect of any single herb or herbal extract on diabetic retinopathy from the current available evidence. It was difficult to exclude the placebo effect as a possible explanation for observed differences due to the lack of placebo control in the included studies. Further adequately designed trials are needed to establish the evidence.

Read the full abstract...
Background: 

Diabetic retinopathy is one of the major causes of blindness and the number of cases has risen in recent years. Herbal medicine has been used to treat diabetes and its complications including diabetic retinopathy for thousands of years around the world. However, common practice is not always evidence-based. Evidence is needed to help people with diabetic retinopathy or doctors to make judicious judgements about using herbal medicine as treatment.

Objectives: 

To evaluate the effectiveness and harm of single herbal medicine for diabetic retinopathy.

Search strategy: 

We searched CENTRAL, which contains the Cochrane Eyes and Vision Trials Register, MEDLINE, Embase, OpenGrey, the ISRCTN registry, ClinicalTrials.gov and the ICTRP. The date of the search was 12 June 2018. We also searched the following Chinese databases in June 2013: Chinese BioMedical Literature Database (CBM), Traditional Chinese Medical Literature Analysis and Retrieval System (TCMLARS), Wanfang China Dissertation Database (CDDB), Wanfang China Conference Paper Database (CCPD) and the Index to Chinese Periodical Literature.

Selection criteria: 

We included randomised controlled trials (RCTs) and quasi-RCTs that investigated the effects of any single herb (or extracts from a single herb) as a treatment for people with diabetic retinopathy. We considered the following comparators: placebo, no treatment, non-herbal (conventional) medicine or surgical treatment.

Data collection and analysis: 

Two review authors independently extracted data and assessed the risk of bias in the studies. Our prespecified outcomes were: progression of diabetic retinopathy, visual acuity, microaneurysms and haemorrhages in the retina, blood glycated haemoglobin A1c (HbA1c) (%) and adverse effects. We performed meta-analyses using risk ratios (RR) for dichotomous outcomes and mean differences (MD) for continuous outcomes, with 95% confidence intervals (CI). We assessed the certainty of the evidence using GRADE.

Main results: 

We included 10 studies involving 754 participants, of which nine were conducted in China and one in Poland. In all studies, participants in both groups received conventional treatment for diabetic retinopathy which included maintaining blood glucose and lipids using medicines and keeping a stable diabetic diet. In three studies, the comparator group also received an additional potentially active comparator in the form of a vasoprotective drug. The single herbs or extracts included Ruscus extract tablet, Sanqi Tongshu capsule, tetramethylpyrazine injection, Xueshuantong injection, Puerarin injection and Xuesaitong injection. The Sanqi Tongshu capsule, Xueshuantong injection and Xuesaitong injection were all made from the extract of Radix Notoginseng (San qi) and the main ingredient was sanchinoside. The risk of bias was high in all included studies mainly due to lack of masking (blinding). None of the studies reported the primary outcome of this review, progression of retinopathy.

Combined analysis of herbal interventions suggested that people who took these herbs in combination with conventional treatment may have been more likely to gain 2 or more lines of visual acuity compared to people who did not take these herbs when compared to conventional intervention alone at the end of treatment (RR 1.26, 95% CI 1.08 to 1.48; 5 trials, 541 participants; low-certainty evidence). Subgroup analyses based on the different single herbs found no evidence for different effects of different herbs, but the power of this analysis was low. One study reported Sanqi Tongshu capsule might be associated with a greater reduction in microaneurysms and haemorrhages in the retina (very low-certainty evidence). The pooled analysis of two studies on tetramethylpyrazine or Xueshuantong injection showed such herbs may have had little effect on lowering HbA1c (MD 0.00, 95% CI -0.58 to 0.58; 215 participants; low-certainty evidence).

There was very low-certainty evidence on adverse events. Two studies reported minor adverse events such as uncomfortable stomach, urticaria, dizziness and headache. There was no report of observation on adverse events in the other studies.

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